Nouvelles Approches En Neurosciences Et Maladies Du Systeme Nerveux Central

Palais de l’Institut de France – Ancien Collège des Quatre-nations cl. G. Fessy - copyright Institut de France

FUNDAMENTAL RESEARCH NOUVELLES APPROCHES Programme etrésumés MALADIES DUSYSTEME THE FUTUREOFNEUROS ANDDISEASESOFTHE

EN NEUROSCIENCESET NERVEUX CENTRAL

Académie dessciencesdel’InstitutFrance CIENCES Académie nationaledemédecine 16 rueBonaparte 23 QuaideConti Paris, 10 Paris, 12mai2004 Amphit Salle Hugot - 11 mai2004

héâtre :

- - 75006Paris 75006Paris

BRAIN

NOUVELLES APPROCHES EN NEUROSCIENCES ET MALADIES DU SYSTEME NERVEUX CENTRAL

THE FUTURE OF NEUROSCIENCES : FUNDAMENTAL RESEARCH AND DISEASES OF THE BRAIN

Présidents

Nicole Le Douarin, Secrétaire perpétuelle de l’Académie des sciences Henri Korn, de l’Académie des sciences

Comité scientifique

Étienne-Émile Baulieu, Président de l’Académie des sciences, Jacques-Louis Binet, Secrétaire perpétuel de l’Académie nationale de médecine, Bertrand Fontaine, professeur CHU Pitié-Salpêtrière, Chris Frith, Academy of Medical Sciences of the United Kingdom, Marc Jeannerod, de l’Académie des sciences, Henri Korn, de l’Académie des sciences, Jean-Yves Lallemand, de l’Académie des sciences, Nicole Le Douarin, Secrétaire perpétuelle de l’Académie des sciences, Robert Naquet, de l’Académie des sciences, Jean Rosa, de l’Académie des sciences, André Syrota, directeur des sciences du vivant CEA, Antoine Triller, directeur de l’Unité Inserm U497, Jean-Didier Vincent, de l’Académie des sciences, de l’Académie nationale de médecine

Colloque organisé en collaboration avec

l’Académie nationale de médecine et l’Academy of Medical Sciences of the United Kingdom

Avec le soutien de

FIRAS Fondation internationale pour le rayonnement de l’Académie des sciences

Organisation

Fabienne Bonfils, assistée de Christine Martin et Noëlla Morand Service des colloques - Académie des sciences - Institut de France

Lundi 10 mai 2004 - Académie des sciences

9h00 Ouverture / Welcome address Étienne-Émile Baulieu, Nicole Le Douarin, Jacques-Louis Binet, Henri Korn

9h10 Conférence plénière / Plenary Lecture Intégration entre différentes échelles spatio-temporelles des signaux neuronaux Integrating Neuroscientific Data Across Spatiotemporal Scales Barry Horwitz, National Institutes of Health, Bethesda

Session 1 Moyens d'investigation des fonctions intégrées Investigation of Higher Functions Président / Chairman : André Syrota

10h00 Conférence introductive / Keynote Lecture Imagerie fonctionnelle : études de connectivité et d'électrophysiologie dans les actions neuronales de masse / Functional Imaging, Connectivity and Electrophysiology Investigations of Mass Neural Action Nikos K. Logothetis, Max Planck Institute for Biological Cybernetics, Tübingen

10h25 Activations et déactivations en imagerie fonctionnelle et leurs relations avec l'activité fonctionnelle de base / Activations and Deactivations in Functional Imaging and their Relationship to Baseline Functional Activity Marcus E. Raichle, Washington University School of Medicine, St. Louis

10h50 L'architecture fonctionnelle cérébrale révélée par l'IRM / The Functional Architecture of the Brain as Seen by MRI Denis Le Bihan, de l'Académie des sciences, Service Hospitalier F. Joliot, CEA Saclay

11h15 Discussion (15 min) + Pause

Session 2 Génétique et développement des pathologies du système nerveux Genetics, Development and Brain Diseases Président / Chairman : Antoine Triller

12h00 Contrôle génétique de l'anxiété et des états proches du stress / Genetic Control of Anxiety and Stress- Like Behaviour Wolfgang Wurst, GSF National Research Center for Environment and Health, Institute of Developmental Genetics, Munich

12h25 Mécanismes pathologiques du syndrome de retard mental avec X fragile et fonction de la protéine FMRP/ The Fragile X Mental Retardation Syndrome : Pathological Mechanisms and Function of the FMRP Protein Jean-Louis Mandel, de l'Académie des sciences, Institut de génétique et de biologie moléculaire et cellulaire, Strasbourg

12h50 Discussion (10 min)

Session 3 Neurosciences et maladies neurodégénératives Neuroscience and Neurodegenerative Diseases Président / Chairman : Jean-Jacques Hauw de l'Académie nationale de médecine

15h00 Conférence introductive / Keynote Lecture Maladies à prions : progrès récents et questions ouvertes / Prion Diseases : Recent Progress and Open Questions Adriano Aguzzi, Institute of Neuropathology, University Hospital of Zurich

15h40 Discussion

15h45 Biologie moléculaire et génétique de la maladie de Alzheimer / Molecular Biology and Genetics of Neurodegeneration in Alzheimer Disease Peter Saint George-Hyslop, Centre for Research in Neurodegenerative Diseases, University of Toronto

16h10 Action des neurostéroïdes au niveau des microtubules : une nouvelle approche de la neuroprotection et du traitement de la maladie de Alzheimer / Neurosteroids Acting at the Microtubule Level : Toward a Novel Approach of Neuroprotection and Treatment of Alzheimer Disease Étienne-Émile Baulieu, Président de l'Académie des sciences, membre de l'Académie nationale de médecine

16h35 Discussion (10 min) + Pause

Session 3 (suite) Président / Chairman : Bertrand Fontaine

17h05 La génétique de la maladie de Parkinson / Genetics of Parkinson's Disease Alexis Brice, CHU Pitié-Salpétrière, Paris

17h30 Rôle de l'imagerie fonctionnelle pour le diagnostic et le suivi de la maladie de Parkinson / Parkinson's Disease : Functional Imaging Studies on Diagnosis and Progression David J. Brooks, Hammersmith Hospital, Imperial College of Science, London

17h55 Discussion (5 min)

18h05 Maladie de Huntington et thérapie interventionnelle / Huntington Disease and Interventional Therapy Anne-Catherine Bachoud-Levi, CHU Henri Mondor, Créteil

18h30 Discussion (5 min)

Mardi 11 mai 2004 - Académie des sciences

Session 4 Epilepsies, Sclérose en plaques Epilepsies, Multiple Sclerosis Président / Chairman : Robert Naquet

9h30 Neurobiologie de l'épilepsie : trop d'informations, pas asse z de certitudes / The Neurobiology of Epilepsy : too much Information, not enough Knowledge Robert Sloviter, University of Arizona, Departments of Pharmacology and Neurology, Tucson

9h55 Développement cérébral et épilepsie de l'enfant / Developmental Abnormalities in Epileptic Children Olivier Dulac, CHU Saint Vincent de Paul, Paris

(Session 4 suite)

10h20 Discussion

10h30 Conséquences immunologiques et neurologiques de la sclérose en plaque / Multiple Sclerosis : Immunological Self Hatred and its Neurological Consequences Harmut Wekerle, Max Planck Institute for Neurobiology, Munich

10h55 Discussion (5 min) + Pause

Session 5 Physiopathologie sensorielle Sensory Functions Président / Chairman : Marc Jeannerod

11h30 Conférence introductive / Keynote Lecture Comment l'oreille fonctionne : transduction mécano-électrique et amplification de l'information par les cellules ciliées / How the Ear's Works Work : Mechanoelectrical Transduction and Amplification by Hair Cells A. Jim Hudspeth, Rockefeller University and Howard Hughes Medical Institute, New York

11h55 Surdité héréditaire humaine : contribution à la compréhension des bases moléculaires du développement et du fonctionnement des cellules sensorielles auditives / Human Hereditary Deafness : Unravelling the Developmental and Physiological Molecular Mechanisms of the Sensory Hair Cells Christine Petit, de l'Académie des sciences, Collège de France, Institut Pasteur, Paris

12h20 Discussion (10 min)

14h30 Allocution de Monsieur François d’Aubert, Ministre délégué à la Recherche

(suite de la session 5)

14h50 Rétinopathies pigmentaires : thérapeutiques potentielles au-delà des mutations Therapeutic Approaches in Retinal Dystrophies, Beyond the Discovery of Causative Genes José -Alain Sahel, CHU Saint-Antoine, Université Paris VI et Directeur de l'Unité INSERM 592

15h15 Discussion (5 min)

Session 6 Troubles du comportement Behavioral Dysfunction

Président / Chairman : Pierre Buser de l'Académie des sciences

15h20 Récepteurs nicotiniques et pathologies chez l'homme / Brain Nicotinic Receptors and Human Pathologies Jean-Pierre Changeux, de l'Académie des sciences, Collège de France, Institut Pasteur, Paris

15h45 Rôle de l'inhibition GABAergique dans le contrôle des fonctions cognitives et des émotions GABAergic Inhibition in the Regulation of Cognition and Emotion Hanns Möhler, Institute of Pharmacology, ETH and University of Zurich

16h10 Discussion (10 min) + Pause

16h40 Bases neurales des erreurs de perception et des hallucinations / The Neural Basis of Hallucinations and Delusions Chris Frith, Wellcome Department of Imaging Neuroscience, London

17h05 Imagerie cérébrale et autisme infantile / Brain Imaging and Childhood Autism Monica Zilbovicius, Service Hospitalier Frédéric Joliot, CEA, Orsay

17h30 Discussion (10 min)

17h40 Apport de l’imagerie dans la connaissance de l’addiction et des troubles compulsives The Addicted Brain Nora Volkow, Brookhaven National Laboratory, Upton, New York

Mercredi 12 mai 2004 - Académie nationale de médecine

Session 7 Nouvelles perspectives thérapeutiques Therapeutics : Future Perspectives Présidents / Chairmen : Jean-Didier Vincent et Yves Agid CHU Pitié-Salpêtrière, INSERM IFR70

9h00 Conférence introductive / Keynote Lecture Applications cliniques et biologiques des cellules souches dans le système nerveux central / Controlling Human ES Cells Ron McKay, NIH, Bethesda

9h40 Discussion

9h45 Stimulations électriques et thérapeutiques du système nerveux central / Therapeutic Electrical Stimulation of the Central Nervous System Alim Louis Benabid, de l’Académie des sciences, Inserm U318, CHU et Université J. Fourier, Grenoble

10h10 Prédiction des crises d'épilepsie / Can Epileptic Seizures be Predicted? Evidences from Non-Linear Analysis of Brain Electrical Activity Michel Le Van Quyen, CHU Pitié-Salpétrière, Paris

10h35 Stimulation magnétique transcranienne / Transcranial Magnetic Stimulation Alvaro Pascual-Leone, Beth Israel Deaconess Medical Center, Division of Behavioral Neurology, Boston

11h00 Discussion (15 min) + Pause

11h30 Cellules souches et perspectives thérapeutiques de la maladie de Parkinson / Toward a Stem Cell Therapy for Parkinson's Disease Anders Björklund, Wallenberg Neurosciences Center, Department of Physiological Sciences, University of Lunds, Suède

11h55 L'immunothérapie, une nouvelle chance de traitement de la maladie de Alzheimer / Abeta Immunotherapy as a Novel Treatment Opportunity for Alzheimer's Disease Dale B. Schenk, Elan Pharmaceuticals, Department of Neurobiology, San Francisco

12h20 Antagonistes de récepteurs cannabinoides centraux (CB1) et comportement alimentaire / Antagonists of Central (CB1) Cannabinoid Receptors and Ingestive Behavior Gérard Le Fur, de l’Académie des sciences, Sanofi-Synthélabo, Paris

12h45 Discussion (15 min)

13h00 Conclusion et synthèse / Conclusion : Henri Korn et Jean-Didier Vincent

Académie des sciences, 10 et 11 mai 2004 - Académie nationale de médecine, 12 mai 2004 Nouvelles approches en neurosciences et maladies du système nerveux central The Future of Neurosciences : Fundamental Research and Diseases of the Brain

INTEGRATING NEUROSCIENTIFIC DATA ACROSS SPATIOTEMPORAL SCALES

Barry Horwitz National Institutes of Health, Bethesda

One of the major challenges that will confront neuroscientists in their quest to understand the neural bases of normal and abnormal brain function is associated with the multiple spatial and temporal levels of investigation of neural structure and function. At each level vast quantities of data now can be acquired. However, it has been quite difficult to integrate across the different levels of study, since the data at each level have different spatiotemporal features. Adding to this complexity is the fact that neurons do not act in isolation, but rather are part of local and global networks. These interactions often are nonlinear in character, making it hard to determine how local interactions at one level result in the emergent phenomena seen at higher spatiotemporal scales. We and others have proposed that computational neural modeling and simulation provide a necessary way to attempt to deal with these issues.

We will illustrate this using functional neuroimaging, which has emerged as one of the most potent tools for investigating the neural bases of cognitive, sensorimotor, and emotional behavior, especially in human subjects. Moreover, neuroimaging has provided valuable information about the structural and functional features associated with many brain disorders. Prior to its introduction, most of what we knew about the neurobiological correlates of high-level brain function came from neuropsychological investigation of brain damaged patients, from electrical stimulation and recording of individuals undergoing neurosurgery, or from the examination of behavior following psychopharmacological intervention. Research using nonhuman primates and other mammals that examined their neuroanatomical connections, neurochemical architecture, performance changes produced by focal brain lesions, and electrophysiological microelectrode data obtained during specific behavioral tasks, was an additional source of important information. Human functional neuroimaging methods (PET, fMRI, EEG/MEG) have produced a wealth of new data that have added considerable information about the functional neuroanatomy of specific cognitive and other high-level functions. One feature makes these latter data so useful and yet, so difficult to deal with: unlike the more classical methods that investigate one neural region or element at a time (e.g., lesion analysis, electrophysiological recordings), functional neuroimaging data are essentially obtained simultaneously from much of the brain. Thus, they provide the capability to investigate not just what a single brain area does, but also how brain regions work together during the performance of individual cognitive tasks. Put simply, function brain imaging engenders the need for network analysis.

We will illustrate our use of computational neuroscience approach using neurobiologically realistic models of the visual and auditory object recognition pathways in human neocortex. Our models, based on neurophysiological and neuroanatomical data from primate and human studies, enable us to simultaneously simulate cellular electrophysiological and fMRI activities in multiple, interconnected brain regions (including primary and secondary sensory cortex, anterior temporal cortex, and prefrontal cortex), thus bridging these different levels of investigation. The electrical activities of the model neuronal units were constrained to agree with data from the neurophysiological literature. An fMRI experiment using stimuli and tasks similar to those used in our simulations was performed. The regional integrated synaptic activities of the model were used to determine simulated regional fMRI activities, and generally agreed with the experimentally observed fMRI data. Our results demonstrate that the models are capable of exhibiting the salient features of both electrophysiological neuronal activities and fMRI values that are in agreement with empirically observed data.

FUNCTIONAL IMAGING, CONNECTIVITY & ELECTROPHYSIOLOGY INVESTIGATIONS OF MASS NEURAL ACTION

Nikos K. Logothetis Max Planck Institute for Biological Cybernetics, Tübingen

Since its early development in the late 40’s nuclear magnetic resonance (NMR) has become a powerful analytical tool for the investigation of the atomic nucleus and its environment, lending itself to applications ranging from chemical analysis or the study of structures in solids to biomedical investigations. In the early 90’s the potential of this technique for functional brain mapping was demonstrated, causing a great deal of excitement in both basic and clinical neuroscience. It was shown that by using the appropriate pulse sequences the NMR (or simply MR) imaging technique can be actually made sensitive to local magnetic susceptibility alterations produced by changes in the concentration of deoxyhemoglobin in venous blood vessels. This blood oxygenation level dependent (BOLD) contrast mechanism was successfully implemented in awake human subjects as well as in small animals such as rats and cats.

In the first part of my talk I shall briefly describe some applications of spatially resolved fMRI in monkeys, including imaging with implanted RF coils. Such studies, in which voxels may contain as few as 600-800 cortical neurons, can help us understand how neural networks are organized, and how small cell assemblies contribute to the activation patterns revealed in fMRI.

In the second part, I’ll described experiments in which we simultaneously traced manganese chloride and wheat-germ-agglutinin conjugated to horseradish peroxidase (WGA-HRP) to evaluate the specificity of the former by tracing the neuronal connections of the basal ganglia of the monkey. By showing the sequential transport of Mn2+ from striatum to pallidum-substantia nigra and then to thalamus, we demonstrated MRI visualization of transport across at least two synapses in the CNS of the primate.

In the last part, I shall present the first results on the neural basis of the BOLD signal. We have recorded local field potentials (LFPs) as well as single- and multi-unit activity (SUA, MUA) in the visual cortex of anesthetized monkeys, and simultaneously collected T2*-weighted images. Our findings showed that visual stimulation causes a significantly stronger increase in the LFPs than in the MUA, and that the linear transform model predicts the measured fMRI responses well, often explaining more than 90% of the variance in the fMRI signal. LFPs were better predictors than MUA.

It is well established that LFPs represent slow waveforms, including synaptic potentials, afterpotentials of somato-dendritic spikes, and voltage-gated membrane oscillations. Such waveforms reflect both the input of a given cortical area and its local intracortical processing, including the activity of excitatory and inhibitory interneurons. For the most part, MUA represents the spiking of neurons, with single-unit recordings mainly reporting on the activity of the projection neurons that form the exclusive output of a cortical area. Thus, the fMRI signal is better correlated with the incoming input and the local processing in a given area than it is with the spiking activity.

This conclusion was supported by the additional observation that response adaptation - which may decouple the activity of projection neurons from that of interneurons - does not alter the BOLD response. Similarly, neurotransmitter injections during combined electrophysiology and fMRI experiments show unaltered BOLD signal with no spiking activity. Finally, experiments will be described that address the issue of whether BOLD can provide us with information on reductions in neural activity. Intracortical recordings in areas showing negative BOLD suggest that the latter follows a strong reduction of both spiking and LFP activity. Finally, on the basis of all recent fMRI and physiology results I will discuss the contribution of integrative approaches in our understanding of neural mass activity.

ACTIVATIONS AND DEACTIVATIONS IN FUNCTIONAL IMAGING AND THEIR RELATIONSHIP TO BASELINE FUNCTIONAL ACTIVITY

Marcus E. Raichle Washington University School of Medicine, St Louis

Functional brain imaging with positron emission tomography (PET) and magnetic resonance imaging (fMRI) has become the dominant tool in the investigation of the functional organization of the human brain in health and disease. The dominance is underscored by the emergence worldwide of brain imaging centers devoted exclusively to the study of the human and non-human primate brain in health and disease. The physiological basis for all imaging work with PET and fMRI is the remarkable relationship between local brain blood flow and its cellular function. When cell function changes in the normal vertebrate brain, blood flow follows in a very predictable manner making it possible for brain imaging to monitor local changes in cellular activity with great fidelity. Often overlooked in this work, however, is the fact that relative to the overall energy demands of the brain, these changes are exceedingly small. Thus, while the brain accounts for 20% of the energy consumption of the body, changes observed with PET and fMRI can be estimated to reflect less then a 1% change in the brain’s energy consumption. This raises a very important question: what is the energy consumed by the brain being used for? Recent evidence would strongly suggest that it is being used for cellular processes related to signaling and information processing rather than vegetative functions. While functional brain imaging signals represent small changes in brain energy consumption they do provide clues as to the nature of these underlying functions. This is especially the case for brain areas that decrease their activity during the performance of goal directed tasks. This presentation will explore these issues and emphasize the importance of exploring the baseline or so-called resting activity of the brain in seeking a true understanding of its function.

THE FUNCTIONAL ARCHITECTURE OF THE BRAIN AS SEEN BY MRI

Denis Le Bihan Membre de l’Académie des sciences, Service Hospitalier Frédéric Joliot, CEA, Orsay

Functional Magnetic Resonance Imaging (fMRI) has appeared as a powerful new tool which is very useful for cognitive neuroscience, as it offers the potential to look at the dynamics of cerebral processes underlying cognition, noninvasively and on an individual basis. Although work remains to be done to optimize the technique and to better understand its basic mechanisms, one may expect to build in a functional list of the brain cortical networks of regions implicated in sensory-motor or cognitive processes. Still, the real understanding of brain function requires direct access to the functional unit made of the neuron, so that one may look at the transient temporal relationships that exist between largely distributed groups of hundreds or thousands of neurons.

Furthermore, communication pathways between networks, which are carried by brain white matter, must be identified to establish connectivity maps at the individual scale, taking into account individual variability.

In this respect, MRI of molecular diffusion may play a significant role. The success of diffusion MRI, which was introduced in the mid 1980s is deeply rooted in the powerful concept that during their random, diffusion-driven displacements water molecules probe tissue structure at a microscopic scale well beyond the usual image resolution. The observation of these displacements thus provides valuable information on the structure and the geometric organization of tissues. The most successful application of diffusion MRI has been brain ischemia, following the discovery that water diffusion drops at a very early stage of the ischemic event. Diffusion MRI provides some patients with the opportunity to receive suitable treatment at a very acute stage when brain tissue might still be salvageable.

On the other hand, as diffusion is modulated by the spatial orientation of large bundles of myelinated axons running in parallel in brain white matter, an important potential application of diffusion MRI is the visualization of anatomical connections between different parts of the brain on an individual basis. Diffusion in the direction of the fibers is faster than in the perpendicular direction. This feature can be exploited to map out the orientation in space of the white matter tracks. With Diffusion Tensor Imaging, diffusion anisotropy effects in diffusion MRI data can be fully extracted, characterized and exploited, providing even more exquisite details on tissue microstructure. Furthermore, preliminary data suggest that diffusion MRI may also be used to visualize dynamic tissue changes associated with large neuronal activation.

CONTROLE GENETIQUE DE L´ANXIETE ET DES ETATS PROCHES DU STRESS GENETIC CONTROL OF ANXIETY AND STRESS-LIKE BEHAVIOUR

Wolfgang Wurst GSF National Research Center for Environment and Health, Institute of Developmental Genetics, München-Neuherberg

Pathological anxiety is a frequent concomitant of major depression and one of the key symptoms of human depressive disorder. Anxiety-like behaviour is associated with stress response and misregulation of the hypothalamic-pituitary-adrenocortical (HPA) system. In addition, dysfunction of the HPA system is one of the robust findings in patients with major depression including increased ACTH and cortisol levels and elevated levels of CRH in the cerebro-spinal fluid. The biological action of CRH are mediated via two G-protein-coupled seven-transmembrane domain receptors, CRH-R1 and CRH-R2. Based on the different neuroanatomical expression patterns of the two receptors, CRH-R1 was considered to play the key role in mediating CHR effects in depression and anxiety. To study CRH-R1 function in vivo, we have generated null mutants (Timpl et al., 1998). Homozygous CRH-R1 mutants display a severe impairment of stress-induced HPA system activation and marked glucocorticoid deficiency. In addition, these mutants exhibit increased exploratory activity and significantly reduced anxiety-like behaviour under basal and stress conditions.

Conventional knockout of CRHR1, therefore, affects both the neuroendocrine regulation and anxiety- related behavior. Therefore, the behavioral analyses of Crhr1 null mutants are hampered by the fact that Crhr1 knockout mice display severe glucocorticoid deficiency. As glucocorticoids play important roles in modulating fear and anxiety-related behaviour, the anxiolytic effect observed in conventional Crhr1 knockout mice may result from either Crhr1 deficiency itself or be influenced by a marked reduction in circulating glucocorticoid hormone levels in these animals. To address this question and to dissect CRH/Crhr1 central nervous system pathways modulating behavior from those regulating neuroendocrine function, we generated a conditional Crhr1 knockout mouse line using the Cre/loxP system driving Cre recombinase expression by a Calcium Calmodulin-kinase II a ?(CaMKII a) promoter (Müller et al., 2003). The CaMKII a gene is expressed with tissue- specificity predominantly in the mouse anterior forebrain during postnatal development with high expression levels in hippocampal neurons (pyramidal and granule cell layer), cortical layers and the amygdala. Disruption of CRH/Crhr1 signalling pathways in the aforementioned, behaviorally relevant neuronal circuitries significantly reduced anxiety-related behavior as demonstrated in different behavioral paradigms. In contrast to conventional Crhr1 mutants, basal plasma ACTH and corticosterone levels were 12 similar to wildtype levels in Crhr1loxP/loxPCaMKII a Cre conditional mutants. The behavioral phenotype of conditional Crhr1 mutants, therefore, is not likely to be influenced by central nervous system effects of circulating stress hormones. Moreover, conditional mutants showed a normal stress response to different durations of immobilization stress. However, hormone levels remained significantly elevated in Crhr1loxP/loxPCaMKII a Cre conditional mutants 30 and 90 min. following a short period of restraint stress, providing the first evidence that limbic Crhr1 is required for central control of HPA system feedback and hormonal adaptation to stress.

These data from Crhr1loxP/loxPCaMKII a Cre conditional mutants underline the importance of limbic Crhr1 in modulating anxiety-related behavior. Furthermore, our finding that specific forebrain circuits, but not the hypothalamic/pituitary CRH/CRHR1 system, are primarily responsible for the generation of anxiety-related behavior is consistent with the clinical observation that pathological anxiety can be observed in a wide range of stress-sensitive syndromes characterized by either hyperactivity (major depression) or hyporesponsiveness of the HPA system, such as post-traumatic stress disorder (post-traumatic stress disorder: Timpl et al., 1998; Müller et al., 2003).

Timpl, P., Spanagel, R., Sillaber, I., Kresse, A., Reul, J.M.H.M., Stalla, G.K., Blanquet, V., Steckler, T., Holsboer, F., and Wurst, W. (1998). Impaired stress response and reduced anxiety in mice lacking a functional corticotropin-releasing hormone receptor 1. Nat. Genet. 19,162-166. Müller, M.B., Zimmermann, S., Sillaber, I., Hagemeyer, T.P., Deussing, J.M., Timpl, P., Kormann, M.S.D., Droste, S.K., Kühn, R., Reul, J.M.H.M., Holsboer, F., and Wurst, W. (2003). Limbic corticotropin-releasing hormone receptor 1 mediates anxiety-related behaviour and hormonal adaptation to stress. Nat. Neurosci. 6, 1100-1107.

THE FRAGILE X MENTAL RETARDATION SYNDROME : PATHOLOGICAL MECHANISMS AND FUNCTION OF THE FMRP PROTEIN

Jean-Louis Mandel Membre de l’Académie des sciences IGBMC, CNRS/INSERM/Université Louis Pasteur, Illkirch, CU Strasbourg

Unstable expansions of triplet repeats have been found to cause a dozen of neurological diseases, by leading either to a gain of toxic properties at the level of the target proteins (Huntington and other polyglutamine diseases), or of the mutated mRNA (myotonic dystrophy), or to a loss of expression of the mutated gene (fragile X syndrome, Friedreich’s ataxia). The fragile X mental retardation syndrome, the most common cause of inherited (familial) mental retardation is caused by large methylated expansions of a CGG repeat in the FMR1 gene (full mutation), that lead to the loss of expression of FMRP, an RNA binding protein. Recently, an unexpected late onset neurodegenerative disease (FXTAS for Fragile X Tremor Ataxia syndrome) was observed in some patients with an unmethylated moderate expansion (premutation), that may be due to toxicity of the premutated mRNA.

In addition to moderate to severe cognitive impairment, male patients with the full mutation also often present with autistic like behavior, hypersensitivity to sensory stimuli, and hyperactivity. Discrete anomalies in dendritic spine morphology have been observed in brain of patients, and in an FMRP knock-out mouse model. FMRP, which has a well conserved homologue in drosophila, is proposed to act as a regulator of transport or translation of specific mRNAs, including synaptic activity-dependent translation. In particular, several studies indicate a role for FMRP in metabotropic glutamate receptor mediated synaptic plasticity. A major goal is to identify the mRNA targets of FMRP, and the protein interactors that may be involved in its function. We and others have shown that FMRP is able to bind specifically to mRNAs containing a G quartet structure. FMRP is also associated to microRNAs and the RISC complex (RNA induced silencing complex). Through analysis of protein interactors of FMRP, and of their genetic interactions in drosophila, we have uncovered a link with the Rac1 GTPase pathway. This pathway controls actin cytoskeleton remodeling and is notably involved in neurite growth and dendritic spine morphogenesis. Interestingly, several members of this pathway have been found mutated in other forms of mental retardation.

MALADIES A PRIONS : PROGRES RECENTS ET QUESTIONS OUVERTES PRION DISEASES : RECENT PROGRESS AND OPEN QUESTIONS

Adriano Aguzzi Institute of Neuropathology, University Hospital of Zürich Schmelzbergstr. 12, CH-8091 Zürich

Prions have been responsible for an entire century of tragic episodes. Fifty years ago, Kuru decimated the population of Papua New Guinea. Then, iatrogenic transmission of prions caused more than 250 cases of Creutzfeldt-Jakob disease. More recently, transmission of bovine spongiform encephalopathy to humans caused a widespread health scare. On the other hand, the biology of prions represents a fascinating and poorly understood phenomenon, which may account for more than just diseases, and may represent a fundamental mechanism of cross-talk between proteins. The two decades since Stanley Prusiner's formulation of the protein-only hypothesis have witnessed spectacular advances, and yet some of the most basic questions in prion science have remained unanswered.

MOLECULAR BIOLOGY AND GENETICS OF NEURODEGENERATION IN ALZHEIMER DISEASE

Peter St George-Hyslop Centre for Research in Neurodegenerative Diseases, University of Toronto Toronto Western Research Institute, Toronto Western Hospital

Alzheimer Disease (AD), like several other adult onset neurodegenerative diseases, is a multi-factorial illness with both genetic and non-genetic causes. Recent genetic studies have clearly identified four genes associated with inherited risk for AD (presenilin1 - PS1; presenilin 2 - PS2; amyloid precursor protein - APP; apolipoprotein E - APOE). These four genes account for about half of the total risk genetic risk for AD. Ongoing attempts to clone the remaining AD-susceptibility genes have to date provided tentative evidence for genes on chromosome 12, chromosome 10, and possibly on chromosomes 9 and 18. The identity of these genes remains unknown. Several other ‘candidate’ genes have been implicated on the basis of positive case:control allelic association studies, but the results of these association studies have not generally been widely replicated. Consequently, the true role for the majority of these other candidate genes currently remains unclear. Nevertheless, biological studies on the four validated AD-causing genes have helped depict a biochemical pathway that is activated by mutations in these genes. It seems that mutations in all of the four known AD-genes alter the production and/or clearance of Ab peptide – a proteolytic cleavage product of the APP protein. When taken together, these results imply that the accumulation of Ab within the brain is an important early and initiating event, at least in genetic cases, and probably also in sporadic cases. It remains unclear exactly how the accumulation of Ab is related to the accumulation of phosphorylated tau in neurofibrillary tangles (another neuropathological hallmark of AD). However, the discovery that polymorphisms/mutations in the tau gene are associated with inherited forms of frontotemporal dementia, as well as risk for progressive supranuclear palsy (PSP) and corticobasal degeneration (CBD) implies that misprocessing of the tau microtubule associated protein can also cause neurodegeneration. This convincingly argues that misprocessing of tau is itself a significantly deleterious biochemical event, and is not merely an innocent ‘secondary/bystander’ effect.

These results provide several important practical and theoretical advances. First, knowledge of the pathways generating Ab and causing accumulation of tau protein, now provide rational therapeutic targets (e.g. inhibitors of the enzymes producing Ab, antibodies and small molecules inhibiting Ab fibril assembly and toxicity, etc.). Secondly, these observations have also uncovered novel biological mechanisms such as g - secretase-mediated cleavage of Type 1 transmembrane proteins (termed regulated intramembranous proteolysis). This latter process appears to have an essential role in such diverse biological events as Notch signal transduction during development, and the production of Ab in adult-onset AD. During the next few years, further advances will occur that will clarify the functional relationships between the genesis of Ab and the accumulation of tau in neurofibrillary tangles. Additionally, it is likely that several of the therapeutic targets defined by the recent work described above will be brought to clinical trials, and will therefore allow us to directly test these hypotheses.

DES NEUROSTEROÏDES AG ISSENT DIRECTEMENT AU NIVEAU DES MICROTUBULES

VERS UNE NOUVELLE APPROCHE DE LA NEUROPROTECTION ET DU TRAITEMENT DE LA MALADIE D’ALZHEIMER

Étienne-Émile Baulieu*, Paul Robel, Arlette Fellous, Yann Duchossoy, Virginie Fontaine-Lenoir et Sébastien David (MAPREG et INSERM U. 488) * Président de l’Académie des sciences

Certains stéroïdes sont synthétisés dans le système nerveux et y agissent. Ce sont des « neurostéroïdes ». La pregnénolone (PREG) est un des plus abondants, mais son mécanisme d’action dans le Système Nerveux Central était inconnu jusqu’à ce que soit observée sa liaison spécifique à une « Microbutule Associated Protein » (MAP2), stimulant alors la polymérisation de la tubuline en microtubules et accroissant leur stabilité [1].

Au-delà de cette observation obtenue in vitro avec des protéines purifiées, on a démontré que le phénomène pouvait être observé dans des cellules nerveuses, impliquer aussi la protéine Tau, protéger plusieurs lignées cellulaires, y compris les cellules SY5Y de neuroblastomes humains surexprimant Tau, contre l’effet de composés dépolymérisant les microtubules, et diminuer les effets toxiques de l’acide okadaïque qui induit une phosphorylation anormale de Tau.

Deux modèles in vivo ont été étudiés : lésions de la moelle épinière chez le rat après traumatisme et ALZ17 modèle transgénique de maladie d’Alzheimer chez la souris. Dans les deux cas, un composé de synthèse analogue de la pregnénolone a nettement prévenu ou diminué les anomalies fonctionnelles nerveuses des animaux contrôle.

[1] Murakami K., Fellous A., Baulieu E.E., Robel P. Pregnenolone binds to microtubule-associated protein 2 and stimulates microtubule assembly. Proc Natl Acad Sci USA, 97:3579-84, 2000.

LA GENETIQUE DE LA MALADIE DE PARKINSON

Alexis Brice INSERM U289, Département de Génétique, Cytogénétique et Embryologie, et Fédération de Neurologie Hôpital Pitié-Salpêtrière, Paris

Alors que les facteurs de risque génétiques de la maladie de Parkinson ne sont pas encore connus, plusieurs gènes responsables de formes monogéniques de la maladie ont été identifiés. A ce jour, des mutations dans les gènes codant pour les protéines suivantes ont été impliquées : a-synucléine (PARK1), Parkine (PARK2), UCH-L1 (PARK5), DJ-1 (PARK7) et Nurr-1. Les mutations ponctuelles de l’a-synucléine sont rares mais très récemment, des réarrangements du gène à type de duplication et de triplication, toutes responsables de formes autosomiques dominantes, ont été mis en évidence. Des corrélations phénotype- génotype pour ces mutations montrent clairement un effet de dosage génique. Ces observations ont conduit à révéler que l’a-synucléine est un composant majeur des corps de Lewy, stigmate histopathologique de la maladie. La fonction de la synucléine reste inconnue mais un rôle dans le trafic vésiculaire est suspecté.

La situation de la Parkine est différente. Les mutations de ce gène très diverses, sont responsables d’environ 50% des cas familiaux et 15% des cas sporadiques de syndromes parkinsoniens de début précoce. Ces formes sont particulières par leur évolution lente et l’absence de corps de Lewy à l’examen neuropathologique. La Parkine est une E3 ubiquitine ligase dont les mutations entraînent une perte de fonction. Ce résultat établit un lien entre maladie de Parkinson et système ubiquitine-protéasome. En conséquence, il est postulé que l’accumulation des substrats de la Parkine pourrait être à l’origine de la dégénérescence sélective des neurones de la substantia nigra. Une dizaine de substrats ont déjà été identifiés dont certains suggèrent l’existence d’un lien fonctionnel entre Parkine et a-synucléine.

Il est possible de reproduire dans des systèmes cellulaires et chez l’animal l’agrégation de la synucléine avec parfois une toxicité que peut compenser la surexpression de la Parkine. En revanche, l’inactivation du gène de la Parkine chez la souris n’entraîne pas de dégénérescence des neurones dopaminergiques de la substantia nigra. La question est de savoir si les autres gènes impliqués dans les formes monogéniques de maladie de Parkinson impliquent les voies médiées par l’a-synucléine et la Parkine reste ouverte.

MALADIE DE HUNTINGTON ET THERAPIE INTERVENTIONNELLE

Anne-Catherine Bachoud- Lévi Equipe Avenir, INSERM U 421, Faculté de Médecine, Créteil Service de Neurologie, CHU Henri-Mondor, Créteil

La maladie de Huntington (MH) est une maladie rare neurodégénérative d’origine génétique, autosomique dominante à pénétrance complète, pour laquelle jusqu'à récemment aucune piste thérapeutique n'était envisagée. Elle débute aux environs de 35-45 ans par trois types d’atteintes diversement associées (cognitive, psychiatrique et motrice) pour conduire à la mort en environ 15-20 ans. Aucun traitement de cette maladie n’est validé actuellement.

A l'heure actuelle, on peut séparer les approches thérapeutiques en courants "déterministe" et "pragmatique". Le courant déterministe est basé sur le décryptage des mécanismes moléculaires qui conduisent à la mort neuronale (voir Brouillet et coll., 2001 pour une revue). Les thérapeutiques qui en découlent tentent d'interférer aussi bien sur les mécanismes généraux de mort neuronale que sur la chaîne spécifique d’événements moléculaires liée à la présence de la Huntingtine. Aucun des essais menés jusqu'ici sur l'une des voies de mort neuronale potentielles n'a été concluant chez les patients.

Le courant pragmatique repose sur le concept de neuroplasticité. Il tend à évaluer l’effet de traitements potentiels indépendamment de cibles physiopathologiques précises en considérant (1) l'atteinte primitive longtemps isolée des neurones GABAergiques moyens épineux du striatum dans la MH et (2) leur longue période de vie normale avant leur dégénérescence. Ces deux constats permettent d'envisager en effet, d'une part, de remplacer des neurones perdus (par greffe de cellules homologues) et, d'autre part, d'utiliser des molécules stimulatrices de la plasticité (comme des facteurs neurotrophiques) pour favoriser l'adaptation des neurones à des situations pathologiques. Ces deux voies de recherche thérapeutique, substitutive pour la première, protectrice pour la seconde, ont conduit récemment à des essais cliniques.

A l'heure actuelle, trois essais pilotes cliniques font des greffes intra-cérébrales une thérapeutique prometteuse en montrant des améliorations fonctionnelle et clinique (cognitive et motrice) à un voire deux ans (Bachoud-Lévi et al., 2000; Hauser et al., 2000, Rosser et al, 2002). Ces effets bénéfiques sont chaque fois couplés à la démonstration de greffons fonctionnels en tomographie à émission de positons. La portée de ces résultats est évidemment limitée par le petit nombre de patients impliqués dans chaque étude et c’est la raison pour laquelle nous avons débuté fin 2001 un essai multicentrique, randomisé, contrôlé, à large échelle (MIG- HD: Multicentric Intracerebral Grafting In Huntington's Disease), chez 60 patients répartis sur 6 centres en France et en Belgique. Ce programme s'étend progressivement aux autres pays européens (Allemagne, Suisse, Italie, Belgique flamande, Royaume Uni).

Si ces essais valident le caractère bénéfique de ces greffes, on ne pourra cependant attendre autre chose qu'un effet transitoire car l'implantation de neurones fœtaux n'a pas à priori d'effet protecteur au long cours sur les neurones de l'hôte qui restent affectés par la MH. C'est pourquoi, nous avons proposé en collaboration avec l'équipe de Patrick Aebischer (Lausanne) à 6 patients pendant deux ans une thérapie génique neuroprotectrice par implantation intra-cérébrale intraventiculaire de cellules BHK génétiquement modifiées pour produire du ciliary neurotrophic factor (CNTF) encapsulées dans une membrane semi- perméable. Les capsules étaient implantées et retirées tous les 6 mois. Cette étude a permis de conclure à l'innocuité de la procédure, et peut-être un effet positif sur l'évolution de la maladie mais comme seules la moitié des cellules BHK ont résisté à 6 mois d'implantation, (Bloch et al., soumis), il faut donc attendre la validation d'une nouvelle lignée cellulaire pouvant sécréter le CNTF pour reprendre un essai clinique de phase II.

Ainsi la dichotomie conceptuelle que nous avons introduite entre thérapie déterministe et pragmatique ou substitutive et protectrice n'a pas lieu d'être en pratique. Le traitement de la maladie de Huntington doit être envisagé comme leur complémentarité. Leurs conditions d'application, contraintes et limitations intrinsèques restent encore à approfondir mais l'on sait d'ores et déjà que si les greffes neuronales peuvent réparer un circuit neuronal elles ne peuvent prévenir la dégénérescence mais qu'à l'inverse les thérapeutiques neuroprotectrices et/ou déterministes peuvent sans doute limiter la dégénérescence neuronale mais en aucun cas réparer les circuits neuronaux détruits chez des patients symptomatiques. Le développement parallèle de traitements neuroprotecteurs et neuroréparateurs est donc une absolue nécessité.

THE NEUROBIOLOGY OF EPILEPSY : TOO MUCH INFORMATION, NOT ENOUGH KNOWLEDGE NEUROBIOLOGIE DE L'EPILEPSIE: TROP D'INFORMATIONS, PAS ASSEZ DE CERTITUDES

Robert S. Sloviter Departments of Pharmacology and Neurology, University of Arizona, Tucson

Temporal lobe epilepsy (TLE) is a common neurological disorder, and possibly unique in terms of the wealth of descriptive data that has been obtained from modern imaging techniques, electroencephalographic recording, depth recording before and during surgery, and studies of surgical and autopsy tissues. It may be useful conceptually to contrast TLE, a neurological disorder in which the nature of the network defect is largely unknown, with Parkinsons Disease, a disorder in which the loss of identified neurons disinhibits a known network, and results in the clinical signs of the disorder. Like patients with Parkinsons Disease, those with TLE exhibit a variety of pathological abnormalities, including neuronal loss and a network imbalance that presumably causes the clinical condition. However, unlike Parkinson’s Disease, the neuronal loss that presumably unbalances the network remains unidentified, and we do not have an effective drug treatment that both points to the identity of the defective component and corrects the network imbalance. Thus, in TLE, both the cause and the cure remain unknown, and we primarily utilize drugs that suppress the clinical signs, but do not correct the imbalance.

An obvious assumption that we can make about the etiology of temporal lobe epilepsy is that there is a derangement of excitatory and inhibitory mechanisms that, in some way, causes the occasional network discharges that define the clinical epileptic state. In my view, however, the extraordinary progress in our understanding of the neurophysiology of excitatory and inhibitory mechanisms has not yet been translated into an understanding of the pathophysiology of these systems as they may relate to epilepsy. Although one can imagine and propose a myriad of genetic, developmental, and acquired factors that might influence the excitatory/inhibitory balance, how do we determine which network malfunction actually occurs in patients, and how do we establish a causal relationship between any given mechanism and the clinical state, particularly for the vast majority of patients who do not have a strictly familial neurological disorder? For this answer, and to find a cure, we are largely dependent upon experimental animal models of acquired epilepsy.

The rate of progress in research on any neurological disorder is largely determined by the degree to which the animal models we use actually mirror the human condition. In this regard, it is my view that the most frequently used animal models of human temporal lobe epilepsy do not closely mirror the human condition, and that the popular belief to the contrary has delayed the development of better animal models. Several significant disparities between the features of the human disorder and those of the currently used animal models have been insufficiently considered, and include the following observations. Human temporal lobe epilepsy most commonly involves patients who have brief focal seizures, who exhibit usually limited, asymmetric brain damage, and who appear relatively normal on neurological examination. In contrast, animals subjected to prolonged and generalized status epilepticus to initiate the epileptogenic process exhibit frequent generalized seizures, severe and widespread bilateral brain damage, and severe behavioral abnormalities. In addition, although many TLE patients exhibit an atrophic hippocampus that is thought to be a common source of spontaneous seizures, hippocampal damage in animals subjected to status epilepticus is an inconsistent and possibly minor part of a much greater constellation of damage to other brain structures. Finally, many patients exhibit developmental structural abnormalities that presumably play a role in the clinical etiology, whereas most animal models involve insults in initially normal laboratory rats. Thus, the most widely used animal models do not involve pre-existing defects, which in humans, may render the brain more vulnerable to insults. Although much has been learned using the current animal models, the available information suggests the need for a critical reappraisal of the assumptions underlying the use of the current animal models, and the need for the development and study of experimental preparations that may more closely model the human epileptic state.

DEVELOPPEMENT CEREBRAL ET EPILEPSIES DE L’ENFANT

Olivier Dulac et Catherine Chiron CHU Saint Vincent de Paul, Paris

L’épilepsie désigne les symptômes liés à un fonctionnement hypersynchrone de populations de neurones, crises et/ou détérioration motrice, sensorielle ou cognitive. Chez l’enfant, comme chez l’adulte, elle peut résulter d’une prédisposition génétique ou d’une lésion cérébrale, celle-ci pouvant être prénatale. Elle peut en outre être la conséquence de crises longues ayant produit une lésion cérébrale, hippocampique, voire hémisphérique. La fréquence très élevée de l’épilepsie dans les premières années de vie traduit en outre l’implication possible de facteurs maturatifs. Cette fréquence élevée trouve son explication dans la présence d’un excès de synapses excitatrices au cours du développement, un phénomène transitoire nécessaire à l’établissement des réseaux fonctionnels du cerveau adulte. L’épilepsie partielle à paroxysmes centro- temporaux (EPCT) est l’essence même de l’implication de ce facteur propre à l’enfant.

Il est classique de dire chez l’adulte que l’épilepsie résulte d’un déséquilibre entre excitation et inhibition. Chez l’enfant, il y a physiologiquement une hyper-inhibition, qui s’accentue encore comme conséquence de l’hyper-excitation. Cette combinaison réalise les encéphalopathies épileptiques dans lesquelles la détérioration des fonctions cérébrales résulte de l’épilepsie elle-même. Le type même en est le syndrome des pointes-ondes continues du sommeil, forme extrême de l’EPCT. L’activité épileptique à un âge donné prédomine dans les parties du cerveau qui connaissent l’excès d’excitation le plus marqué à cet âge. Chez le nourrisson, il s’agit des régions postérieures : une lésion de cette partie du cerveau peut produire une épilepsie focale précoce. Lorsque le nourrisson dépasse 3-4 mois d’âge, il apparaît des anomalies paroxystiques diffuses associé à une modification du type de crises. Les anomalies intercritiques sont asynchrones en raison de l’absence de myéline qui permettrait une conduction rapide des activités paroxystiques. Les nouvelles crises sont des spasmes générés par des structures sous-corticales en conséquence de leur désinhibition liée au dysfonctionnement diffus du cortex. Cette combinaison constitue le syndrome de West. Un traitement assez précoce a non seulement un effet antiépileptique mais également antiépileptogène, prévenant la constitution d’une épilepsie chronique. Le contrôle des pointes et ondes lentes continues révèle des anomalies focales, montrant qu’ici l’épilepsie résulte de la combinaison de facteurs lésionnel et développemental. Chez l’enfant plus âgé, une association semblable prend le nom de syndrome de Lennox-Gastaut, qui associe crises toniques et pointes-ondes lentes tandis que l’association prédisposition génétique et facteurs maturatifs donne une épilepsie myoclonique, le syndrome de Doose.

Le lobe temporal est le siège de plusieurs types d’épilepsies. Une gliose temporale mésiale après état de mal fébrile chez le nourrisson donne une épilepsie à l’adolescence, le temps que maturent les voies mésio- néocorticales. Une dysplasie temporale néocorticale donne au contraire une épilepsie précoce. Des pointes- ondes continues du sommeil produisent une perte du langage, parfois sans crises. Ce syndrome de Landau- Kleffner est réversible s’il est identifié tôt. Un état de mal temporal et temporo-frontal bilatéral déclenché par la fièvre peut entraîner une perte des fonctions frontales, d’autant plus sévères qu’il persiste une épilepsie rebelle. Certains enfants peuvent avoir successivement plusieurs types d’épilepsie temporale.

Le retentissement cognitif de l’épilepsie est d’autant plus marqué que celle-ci a débuté précocement et que la lésion causale a été constituée tôt. Au cours de la maturation normale, les synapses qui reçoivent une activité asynchrone de leurs afférences sont préférentiellement éliminées. L’activité synchrone due à l’épilepsie prévient, au contraire, cette élimination et induit la persistance de réseaux épileptogènes qui auraient normalement du être éliminés au cours de la plasticité physiologique. Mais il persiste une possibilité de récupération, par les mêmes régions après disparition de l’épilepsie ou par les régions homologues contro- latérales (en particulier dans le cas du langage) tant que la période critique de maturation n’est pas terminée. Pour le langage, une récupération véritablement fonctionnelle par les aires contro-latérales n’est cependant possible que s’il y a eu destruction préalable de la région impliquée dans l’épilepsie.

En somme, la maturation est un facteur étiologique majeur de l’épilepsie pédiatrique, elle en accentue le retentissement sur les fonctions cérébrales et la pharmacorésistance, mais elle offre aussi des possibilités uniques de récupération.

MULTIPLE SCLEROSIS IMMUNOLOGICAL SELF HATRED AND ITS NEUROLOGICAL CONSEQUENCES

Hartmut Wekerle Department of Neuroimmunology, Max Planck Institute for Neurobiology, D-82152 Martinsried

Multiple sclerosis is the most important inflammatory affliction of the central nervous system in the Western world. It is characterized by a highly variable clinical picture with motor sensory and sensible disturbances, and by an unpredictable course. The active MS lesion displays inflammatory infiltrates, destruction of periaxonal myelin sheaths and, quite often, axonal degeneration. According to a currently prevailing pathogenic concept, MS is caused by an autoimmune attack against the body’s own CNS white matter, an example of immunological self hatred, as it could be termed. T cells, with receptors for myelin determinant are regular components of the healthy immune repertoire. Upon pathological activation, the autoimmune cross the endothelial blood-brain barrier, enter the CNS parenchyma and trigger a cascade of events that culminates in the fully developed MS plaque.

This concept is based on investigations using human CNS samples, mainly post-mortem material, as well as on experimental animal models. In this presentation new approaches along these two lines will be discussed. Novel molecular techniques allowing characterization of the T cell repertoire invading the human MS brain will be demonstrated as examples. Then, using Experimental Autoimmune Encephalomyelitis as model for aspects of MS, the behavior of autoimmune T cells before and during onset of disease will be visualized by molecular and imaging methodologies.

HOW THE EAR ’S WORKS WORK: MECHANOELECTRICAL TRANSDUCTION AND AMPLIFICATION BY HAIR CELLS

A. Jim Hudspeth Rockefeller University and Howard Hughes Medical Institute, New York

Uniquely among vertebrate sensory receptors, the hair cell amplifies its inputs. An active process in auditory organs increases responsiveness to sound by over one-hundredfold and simultaneously sharpens frequency selectivity. Two epiphenomena arise from the active process, compressive nonlinearity in responsiveness and spontaneous otoacoustic emissions (SOAEs). Although changes in the length of outer hair cells are thought to mediate amplification in the mammalian cochlea, the auditory receptor organs of non- mammalian tetrapods—which lack electromotile hair cells—display essentially identical sensitivity, tuning, nonlinearity, and SOAEs. The active process necessary to explain the properties of hearing in these animals may therefore constitute part or all of the mammalian cochlear amplifier as well.

When bathed in a low-Ca2+ saline solution resembling endolymph, a hair bundle from the sacculus of the bullfrog’s internal ear undergoes spontaneous oscillations of approximately ±20 nm. The frequency of oscillation increases with the load applied to the hair bundle by a flexible stimulus fiber; the range of 5-100 Hz corresponds well to the characteristic frequencies of afferent neurons innervating the sacculus. Application of the fluctuation-dissipation theorem, which relates a system’s mechanical responsiveness during stimulation to its reaction during thermal excitation, confirms that spontaneous oscillations involve energy expenditure by the hair bundle. These oscillations may therefore supply the energy requisite for the production of SOAEs.

When a sinusoidal mechanical input as small as ±1 nm is applied by a flexible stimulus fiber, the bundle’s movement is entrained if the frequency lies near that of unstimulated oscillation. As judged by the amplitude of the response, the bundle appreciably amplifies its input. Moreover, the bundle exhibits power gain: an active energy source in the bundle is required to counter the power dissipated by viscous drag and that withdrawn by the stimulus fiber. As the amplitude of stimulation is increased, the response grows as the one-third power of the input. This compressive nonlinearity, which resembles that for basilar-membrane motion in the mammalian cochlea, is anticipated for an amplificatory process poised near a Hopf bifurcation. Active hair-bundle motility therefore constitutes the active process of hair cells in the bullfrog’s sacculus.

Displacement-clamp measurements reveal that a hair bundle displays negative slope stiffness over a range of positions subtending roughly ±10 nm. This phenomenon stems from the concerted gating of transduction channels: as each channel opens or closes, the change in gating-spring force encourages other channels to do likewise. Two processes power active hair-bundle motility, whether spontaneous or stimulus- evoked. First, the hair cell’s myosin Ic-based adaptation motor attempts to situate the hair bundle in the negative-stiffness region, causing the bundle to lunge across this unstable domain, thereby producing spontaneous oscillations. Stimuli trigger the bundle’s progression through the same trajectory, thereby entraining amplified bundle movements. Active bundle movements are also driven by rapid, Ca2+-dependent reclosure of transduction channels, a phenomenon capable of mediating oscillation even at kilohertz frequencies. Because the nonlinearity responsible for negative bundle stiffness, mechanical adaptation, and Ca2+-dependent channel reclosure appear to occur in all hair cells, the same mechanisms may power the active processes of hair cells in general, including those of the mammalian cochlea.

HUMAN HEREDITARY DEAFNESS : UNRAVELLING THE DEVELOPMENTAL AND PHYSIOLOGICAL MOLECULAR MECHANISMS OF THE SENSORY HAIR CELLS

SURDITE HEREDITAIRE HUMAINE : CONTRIBUTION A LA COMPREHENSION DES BASES MOLECULAIRES DU DEVELOPPEMENT ET DU FONCTIONNEMENT DES CELLULES SENSORIELLES AUDITIVES

Christine Petit Unité de Génétique des Déficits Sensoriels, INSERM U587 Institut Pasteur, 25 rue du Dr Roux - 75724 Paris cedex 15, France

The molecular mechanisms underlying the development and the functioning of the inner ear sensory hair cells, has escaped characterisation for a long time owing to the small number of these cells in the cochlea. Thus, the study of hereditary deafness provides a unique approach to gaining relevant insights into the understanding of these processes. Indeed, most early onset forms of hereditary deafness, whether in humans or in mice, are caused by monogenic defects affecting the cochlea, whilst (i) about a hundred genes are considered to be underlying the early onset forms of isolated deafness, and (ii) mutations in another 300 additional genes may also be accountable for syndromic forms of deafness in humans. The difficulties encountered in order to analyse isolated forms of deafness over the previous decade have now been settled and 37 genes involved in the isolated forms of deafness have been identified.

The analysis of the phenotypic abnormalities resulting from the inactivation of the corresponding genes, mostly in mice and for some of them in zebrafish too, have enabled us to identify genes likely to provide entry points into the understanding of the following aspects of the hair bundle development, i.e. the control of (i) the growth of the stereocilia composing the hair bundle, (ii) the cohesion of the hair bundle, (iii) the orientation of this structure and (iv) the neurotransmitter exocytosis. Notably, among their encoded hair bundle proteins, several unconventional myosins (myosin VIIa, VI, XV), cadherins (cadherin23 and protocadherin15) and PDZ domain-containing proteins (whirlin, harmonin) have been found. The analysis of the localisation of these proteins in wild-type and mutant mice combined with the characterisation of the interaction protein networks into which those proteins are integrated, has been performed. The role played by several of these molecules in the developing hair bundle or in the synapse will be discussed further.

BRAIN NICOTINIC RECEPTORS AND HUMAN PATHOLOGIES

Jean-Pierre Changeux Institut Pasteur, CNRS URA 2182 Récepteurs & Cognition, 25 rue du Dr Roux, Paris

Nicotinic receptors (nAChR) are important targets of the neuromodulator acetylcholine in the brain. At least ten neuronal nAChR subunits (a2-a10, b2-b4) have been identified in the vertebrate brain which form a variety of pentameric oligomers with different physiological and pharmacological properties and distribution. All of them behave as allosteric proteins which mediate the fast (msec) opening of the ion channel (activation) together with its short-term (100 msec to hrs) modulation (desensitization, potentiation, up-regulation). Moreover, nAChR intervene in both classical phasic transmission and neuromodulatory tonic regulation. To understand the role of a particular subunit (or group) of subunits in the various physiological, pharmacological and behavioral actions of acetylcholine and nicotinic agents, mice lacking the b2, the a4 and the a6 subunits were generated by homologous recombination.

-/- Adult b2 mice lack high affinity nicotine binding as the effects of nicotine on dopamine release and -/- electrical responses of mesencephalic dopaminergic neurons. Moreover, b2 mice show deficits in passive avoidance learning, taste discrimination and self-administration thus supporting the notion that b2-subunit containing nAChRs (nAChR*) mediate the reinforcing and addictive effects of nicotine. Furthermore, studies -/- -/- with a4 and a6 null mice reveal that a combination of a6/b2* and alpha4beta2* nAChRs mediate the endogenous cholinergic modulation of DA release at the terminal level, while somato-dendritic (non a6) a4b2* nAChRs most likely contribute to nicotine reinforcement. In addition, patch-clamp recordings, luorescencef imaging and single cell PCR in dopaminergic and gabaergic neurons from VTA and SN reveal a striking diversity in nAChR subunit composition between different cell types.

-/- -/- Nicotine antinociceptive effects are only partially lost in a4 and b2 mice indicating that nAChRs containing these subunits together with nAChRs of different subunit composition play a critical role in nicotine- elicited analgesia.

-/- Nicotine increases arousal and attention. Interestingly, b2 mice show an increased ventilatory response to a hypoxic challenge together with a reduction of transient movements (with H. Lagercrantz & G. Cohen) thus suggesting that b2 nAChR* play a role in sudden infant death syndrome (SIDS). EEG recordings further reveal a loss of the arousing properties of nicotine together with longer REM sleep episodes and reduced fragmentation of SWS episodes by microarousals (with J. Adrien and C. Lena). In addition, mutations in a4 and b2 nAChR* have been shown by various groups to be linked to nocturnal frontal lobe epilepsies occcuring during SWS. Thus the suggestion that a4 b2 high affinity nAChRs* regulate “states of consciousness”.

-/- An automated method to quantify mouse behavior reveals that, in the b2 mice, the high-order spatiotemporal organization of locomotion, conflict resolution and social interactions are selectively dissociated from low-level, more automatic motor behaviors (with S. Granon & P. Faure). Such deficits in executive functions resemble the rigid and asocial behavior found in autism and attention deficit hyperactivity disorders.

Finally, neuroanatomical, biochemical and electrophysiological parameters as well as spatial learning reveal region-specific alterations in b-/- mice during ageing suggesting a relationship with Alzheimer deficits.

The data are discussed in terms of neuronal models of cognitive learning by reward and access to consciousness (with S. Dehaene) which mobilize the prefrontal cortex.

GABAERGIC INHIBITION IN THE REGULATION OF COGNITION AND EMOTION

Hanns Möhler Institute of Pharmacology, University of Zurich and Department of Chemistry and Applied Biosciences, Swiss Federal Institute of Technology (ETH), Zurich

Following the example of Claude Bernard, nature is frequently investigated by the use of drugs. Benzodiazepines have been uniquely helpful in analyzing the role of GABAergic inhibitory neurotransmission in brain function.

By controlling spike timing and sculpting neuronal rhythms, inhibitory interneurons play a key role in regulating neuronal circuits. The pronounced diversity of GABAergic interneurons has provided selective targets for the modulation of distinct neuronal circuits via the GABA system. GABAA receptor subtypes can serve as tags for the analysis of behaviour and brain development.

By genetic manipulation of GABAA receptor subtypes, sedative and anxiolytic activity were attributed to distinct neuronal circuits characterized by the expression of a1- and a2GABAA receptors, respectively (1,2). In addition, temporal and spatial memory were selectively modulated by extrasynaptic a5GABAA receptors (3). Finally, specific GABAA circuits were discovered for visual cortical plasticity (4). Thus, the functional relevance of the diversity of inhibitory interneurons is increasingly being recognized and powerful new opportunities for CNS drug development have become apparent.

1) Nature 401, 796-800 (1999) 2) Science 290, 131-134 (2000) 3) Proc. Natl. Acad. Sci. USA 25, 8980-8985 (2002) 4) Science 303, 1681-1684 (2004)

THE NEURAL BASIS OF HALLUCINATIONS AND DELUSIONS

Chris Frith Wellcome Department of Imaging Neuroscience, University College, London

Hallucinations (false perceptions) and delusions (false beliefs) are abnormal subjective experiences that have their origins in disorders of the brain. These symptoms are typically associated with psychiatric disorders such as schizophrenia, but can also be observed in neurological patients. Comparisons with neurological patients with known and circumscribed brain damage can give clues to the neural basis of symptoms in psychiatric patients where no obvious brain damage can be identified. In order to link subjective experience with brain function it is necessary to develop cognitive models using terms that can be applied equally at a psychological and a physiological level of description. In addition it is desirable that our models will give us an idea of what it is like to experience psychotic symptoms. In this talk I shall consider a class of symptoms, known as passivity experiences, in which patients confuse their own actions with external events. These symptoms include hallucinations, such as hearing one's thoughts spoken aloud (thought broadcasting) and delusions, such as believing that one's actions are controlled by alien forces (delusions of control).

The basis of these symptoms seems to be a confusion between the patients' own actions and independent events happening in the outside world. The ability to make this distinction is of fundamental importance for any organism that acts upon the world in a voluntary manner. If I detect an image moving across my retina how do I know whether the movement is caused by an object moving in the outside world or by me moving my eyes? Likewise, if I hear a voice how do I know whether I am hearing my own voice as I speak or someone else's voice? There is nothing intrinsic to these signals that permits this distinction to be made.

It is now well established that the distinction is made through prediction. For example, on the basis of signals sent to the eye muscles the resulting movement of the imagine on the retina can be predicted. These re-efferent signals (more recently called forward models) can be used to discount self-generated changes and maintain the stability of the world. In the case of limb movements we can predict the future position of the limb in time and space and suppress awareness of the proprioceptive feedback the movement will generate. Some of these predictions are available to consciousness. As a result we are able to imagine how long an intended movement will take to perform. We can also anticipate errors when we become aware that the movement we have just initiated will not have the right consequences. In such cases we do not need to wait for sensory feedback to correct the error (central error correction). All these benefits of prediction are absent in patients with passivity experiences. They fail to make central error corrections. They do not produce the correct timing for imagined movements. They have difficulty detecting distorted visual feedback of their own actions. They fail to suppress proprioceptive feedback associated with voluntary movements. This failure is associated with over-activity in the parietal cortex. Similar results have been found in the domain of speech production for auditory hallucinations. Patients with schizophrenia show over-activity (as measured by EEG) in auditory cortex when speaking.

Patients with damage to parietal cortex (typically a result of stroke) show many of the same problems of making predictions about limb movements as do patients with passivity experiences. Furthermore patients with parietal lesions can have delusional beliefs. Some believe that their contra-lesional arm is not their own (somatoparaphrneia), while others deny that their arm is paralysed and claim to have moved it when this is not the case (anosognosia). These delusions are obviously very different from passivity experiences. Current speculation is that the symptoms associated with schizophrenia are not due to abnormalities restricted to parietal cortex, but rather to the failure of signals from frontal cortex to modify activity in parietal cortex appropriately. There is preliminary evidence for abnormal connectivity between frontal and posterior areas in patients during acute episodes of schizophrenia.

The difficulty patients with passivity experiences have in making predictions about the consequences of their movements would certainly explain why they do not feel properly in control of their movements. Indeed the failure to suppress proprioceptive feedback would make active movements feel like passive movements. But this is not sufficient to explain why these patients have the strong feeling that someone else is controlling their movements. There is an important contrast here with neurological patients experiencing an 'anarchic hand'. In these cases the contra-lesional hand makes movements that are unintended and unwanted by the patient. Yet the patient states that there is something wrong with the hand rather than that it is being controlled by someone else. Recent studies of action observation suggest a mechanism through which the psychotic patient might have a false experience of agency. When an act has an obvious consequence (for example, pressing a button to cause a sound) there is 'intentional binding' between the act and its consequence. The times of pressing the button and hearing the tome seem closer together in our subjective experience than they Académie des sciences, 10 et 11 mai 2004 - Académie nationale de médecine, 12 mai 2004 Nouvelles approches en neurosciences et maladies du système nerveux central The Future of Neurosciences : Fundamental Research and Diseases of the Brain really are. This intentional binding is equally strong when we observe someone else performing the act, but not if we watch a machine performing the act. This result shows that we have a strong perception of agency associated with acts whether these acts are our own or those of other people. Preliminary data suggests that patients with schizophrenia show stronger than normal intentional binding when observing their own acts. A strong sense of agency associated with a movement that felt as if it were passive would lead to the belief that one's actions were being controlled by an alien force. The neural basis of intentional binding remains to be explored, but there is likely to be a connection with the 'mirror' system identified in premotor cortex where neurones code for actions whether these are performed by the self or another.

BRAIN IMAGING AND CHILDHOOD AUTISM

Monica Zilbovicius Service Hospitalier Frédéric Joliot, CEA, Orsay

Childhood autism is an early, severe and global development disorder due to a brain dysfunction. Since its first description by Kanner (1943), autism has intrigued the medical and scientific world because autism associates severe cognitive-behavioral troubles with the absence of physical or cerebral dysmorphology. Therefore, a fundamental goal of the neurobiological study of autism is a description of brain regions that are dysfunctional. The advent of functional brain imaging techniques, such as positron emission tomography (PET), single photon emission tomography (SPECT) and functional MRI (fMRI), had opened a new and promising way to study brain dysfunction in autism. Both emission tomography techniques allow noninvasive and accurate measurements of cerebral glucose metabolism and/or cerebral blood flow. A large number of strategies can be used in the study of a specific brain disorder using functional brain imaging. Measurements can be performed at rest or during the performance of specific sensory, motor or cognitive task.

Two studies have reported a marked rest bilateral hypoperfusion located in the temporal lobes (superior temporal sulcus and gyrus) in autistic children (Zilbovicius et al., 2000; Ohnishi et al., 2000). In addition, the temporal hypoperfusion was detected individually in 77% of the autistic children. The temporal regions dysfunction may be implicated in almost most of the clinical symptoms (perceptive, emotional and cognitive deficit) observed in autism. These associative regions are highly connected with the frontal, parietal, limbic and associative sensory systems. For example, a dysfunction of the auditory cortex may explain why young autistic children are so often misdiagnosed as deaf and why they always have severe communication impairments. Dysfunction of the superior temporal sulcus may explain the emotional and cognitive components of autism, since this multimodal associative region is strongly connected with the fronto-parietal and limbic regions. In addition, the superior temporal region is increasingly recognized as a key component of the “social brain” and neuroimaging studies in normal subjects have emphasized the role of this structure in the processing of biological movements, including movements of the eyes, mouth, hands and body and in social perception (Allison et al., 2000). The finding of temporal hypoperfusion extends to primary autism recent results suggesting a link between temporal lobe dysfunction and autistic behavior in children with neurological disorder, such as epilepsy and herpes encephalitis.

The activation studies measure local changes of cerebral blood flow or blood oxygenation, reflecting the variation of synaptic activity during sensorial, cognitive or motor paradigms. Brain activation studies in autism using PET have showed an abnormal activation of frontal and temporal regions during « theory of mind » tasks (ability to recognize mental states of others) (Happé et al., 1996; Castelli et al., 2002). Using functional MRI (fMRI), several studies have showed an abnormal pattern of cerebral activation during face perception tasks in individuals with autism. Indeed, in controls, fMRI studies consistently show that several areas located in the fusiform gyrus and in the posterior superior temporal sulcus (STS) are specifically activated during face processing tasks. In contrast, recent fMRI studies in individuals with autism highlighted reduced or absent activation in the face fusiform area during face discrimination tasks (Schultz et al. 2000; Critchley et al. 2000; Pierce et al. 2001). Baron-Cohen et al. have tested the social intelligence of autistic adults and have showed that the autistic group activated less extensively the frontal area than the control group and did not activate the amygdale (Baron-Cohen et al., 1999). More recently, auditory activation PET and fMRI studies were performed in autistic adults and children during listening to speech-like sounds. Compared to controls, autistic patients showed lower activation of the left posterior STG (Boddaert et al., 2003, 2004). Finally, an fMRI study identified in normal adults voice-selective areas, located bilaterally along the superior temporal sulcus. We have recently observed an absence of activation of the “voice-selective area” in autistic adults (Gervais et al., submitted). These findings suggest that autism is associated with an abnormal pattern of activation of the temporal cortex.

In summary, two studies detected a localized rest bilateral hypoperfusion in the temporal lobes. These temporal regions are connected to the fronto-parietal multimodal associative systems which could explain the cognitive abnormalities found in autism, the limbic system which could explain the emotional abnormalities, as well as the auditory regions which could explain sensorial perception abnormalities found in autism. The functional brain studies during activation paradigms have detected abnormal activation cortical patterns in autistic subjects, either responding to auditory elementary stimuli or, to more complex cognitive paradigms.

THE ADDICTED BRAIN

Nora D. Volkow, M.D. Director, National Institute on Drug Abuse National Institutes of Health, Bethesda

Addiction is a disorder that involves complex interactions between a wide array of biological and environmental variables. Strategies for its prevention and treatment therefore, necessitate an integrated approach incorporating systems of analysis that span the molecular to the social. Pairing rapidly evolving technologies such as neuroimaging with sophisticated behavioral measurement paradigms has allowed extraordinary progress in elucidating many of the neurochemical and functional changes that occur in the brains of addicts. Although large and rapid increases in dopamine have been linked with the rewarding properties of drugs, the addicted state, in striking contrast, is marked by significant decreases in brain dopamine function. Such decreases are associated with dysfunction of prefrontal regions including orbitofrontal cortex (involved in salience attribution) and cingulate gyrus (involved in inhibitory control). In addiction, disturbances in salience attribution result in enhanced value given to drugs and drug-related stimuli at the expense of other reinforcers. Dysfunction in inhibitory control systems, by decreasing the addict’s ability to refrain from seeking and consuming drugs, ultimately results in the compulsive drug intake that characterizes the disease. Discovery of such disruptions in the fine balance that normally exists between brain circuits underling reward, motivation, memory and cognitive control have mportanti implications for designing multi-pronged therapies for treating addictive disorders.

CONTROLLING HUMAN ES CELLS

Ron McKay LMB/NINDS, National Institutes of Health, Bethesda

The frequent citation of diabetes, multiple sclerosis and Parkinson’s disease as targets of new stem cell based technologies is due in part to our work with mouse embryonic stem cells. Our group has now shown that human ES cells differentiate efficiently to the cell types of the early embryo including neurectoderm and different types of endodermal anlage. The human ES cells generate endodermal epithelia representing the initial step of endoderm differentiation. Highly differentiated liver cells can be derived from these structures and modifications of the approach will likely generate other terminal endodermal fates, including pancreatic cell types. Electro-physiological data shows that functional human dopamine neurons can be obtained in large numbers from human ES cells. These data confirm that cells of great clinical interest can be efficiently derived from human ES cells. This strategy has been most extensively discussed in the context of degenerative diseases but improved understanding of the mechanisms of self-renewal and fate choice will have implications in many areas of medicine. These arguments suggest that the derivation and manipulation of human embryonic stem cells will rapidly become central to bio-medical research.

THERAPEUTIC ELECTRICAL STIMULATION OF THE CENTRAL NERVOUS SYSTEM

Alim Louis Benabid Membre de l’Académie des sciences, INSERM U318, Grenoble

Surgery and pharmacology have always been the only therapeutic tools available to treat diseases of the human central nervous system. Surgery is mostly ablative, by section of pathways or destruction of cellular centres. The excitable nature of the nervous tissue has led early to methods designed to enhance the normal functions of the brain by deep electrical stimulation. The discovery that the effects of stimulation were dependent on the frequency, enhancing the neural activity at low frequency, and surprisingly inhibitory at high frequency. This empirical observation has been the source of a new surgical tool, featuring original properties, such as reversibility, adaptability and reduced invasiveness. Such a delicate method, delivered through electrodes which can be placed in all strategic places, and have provided a powerful alternative to ablative surgery, in the targets which were previously destroyed to treat tremor, such as in the thalamus Vim, or to treat dyskinesias such as in the internal pallidum GPi. The reduced morbidity of the method has permitted bilateral surgery in one session, which was avoided with lesioning techniques. The stability and the amplitude of the clinical benefit have progressively led deep brain stimulation(DBS) at high frequency (HF) to replace the classical ablative stereotactic methods. Large series with long follow-up and stable benefit are being published, and the spreading of this practice all over the world has proven that HF-DBS is a robust method, not limited to hyper trained teams and centres. In addition to the previous targets of ablative surgery, new structures of the brain, have become targets on the basis of their functional properties as revealed by neurophysiological data provided by basic research: this was the case of the subthalamic nucleus, which not only has not expressed its bad reputation of inducer of hemiballism but on the contrary appears to be the surgical counterfeit of dopamine, whose benefits as well as side effects to certain extent, are mimicked by bilateral HF-DBS of STN. The cost of the equipments, and the persistence of a surgical, although mild, potential morbidity are the limiting factors to a wider and earlier application of this treatment to Parkinsonian patients. However, this has made possible, as in STN, to extend the method to targets on the unique basis of a theoretically predicted efficiency in a given pathological situation. This is the case for the posterior hypothalamus in severe cluster headaches with convincing and stable results, and for the STN in epilepsy, as well a several targets for obsessive compulsive disorders, which could be reconsidered for surgery, after the long period where ablative psychosurgery was in dismay. Several deep brain structures are currently being investigated in various diseases or syndromes, all of them confirming the reduced invasiveness, the reversibility , but moreover the key importance of the high frequency. Besides these extending applications and field of interest as a functional neurosurgical tool, HF-DBS has triggered a large movement of research to understand its mechanism and investigate its effects, not only acute and local but also at middle and long term as well as at distance from the target. It is difficult to understand under the light of the current knowledge of neurophysiology how could electrical stimulation induce an effect mimicking the destruction of the same target. Excitation of an inhibitory network originating and ending in the stimulated area cannot explain the fact that this effect is observed so far in all tested targets. Inhibition of firing after the stimulation period has been often observed, but what happens during stimulation is technically difficult due to the artefacts. Artefact suppression is making progresses and some recent report would tend to support the theory of inhibition of firing .in Vim, GPi and STN, although other report provide conflicting data.

Based on the hypothesis that HF inhibits neural firing and that hyperactivity of STN might induce an elevated glutamate release which could participate to the pathogenic process of Parkinson’s disease, we have investigated the putative neuroprotective effect of HF-DBS of STN in 6OHDA rats and recently in MPTP monkeys. Both experiments strongly support this hypothesis, which would suggest to apply it at earlier stages in Parkinsonian patients and call for controlled human clinical trials. If the inhibitory effect of HF on the soma of neurons is still debated and challenged, there is a clear consensus that both high (HF) and low (LF) frequencies excite axons and fibers in general, raising the question of what happens along the projection axons and at the level of synapses. We performed in vitro experiments on glandular cells which have clearly shown that protein synthesis and neurotransmitter release are significantly decreased by HF and not by LF. Evidence is being gathered that this happens at the level of gene expression, which seems to be locally and acutely inhibited, but also influenced at distance and at middle term. If confirmed, these preliminary data would have considerable impact not only on acute reversal of symptoms in various diseases, but also as a new method to induce long term changes in the brain and modulate or even drive plastic changes or developmental events. The physiology of electrical stimulation in general, or even at a larger scale, the biological effects of electricity might be further investigated, as for instance the enhancement of gene permeation of the cell nuclei, in the process of electropermeation or electroporation.

CAN EPILEPTIC SEIZURES BE PREDICTED? E VIDENCES FROM NON-LINEAR ANALYSIS OF BRAIN ELECTRICAL ACTIVITY

Michel Le Van Quyen Laboratoire de Neurosciences Cognitives et Imagerie Cérébrale, LENA CNRS UPR 640, Hôpital de la Pitié-Salpêtrière, Paris

The growing need for a better understanding of large-scale brain dynamics has stimulated in the last decade the development of new data analysis techniques. Progress in this domain has greatly benefited from developments in nonlinear time series analysis. In the recent years, the application of these tools showed that it is possible of extracting information from the EEG that allows an anticipation of epileptic seizures several minutes in advance (1). More recently, applications of phase synchronization measure have been shown to be useful in gathering spatio-temporal information about the epileptogenic process. The method is based on a direct estimation of the instantaneous phase of a signal and, hence, are ideal for analyzing nonstationary EEG recordings whose synchronization properties evolve over time. In my presentation, I will demonstrate the capacity of this measure for seizure anticipation in continuous recordings of long periods of time. In particular, I will propose a general statistical approach for detecting quantifiable spatial or temporal shifts in EEG synchronization, including a systematic study of false positives. The results open new perspectives for the anticipation of epileptic seizure, as well as for the modeling of the underlying neurophysiology.

[1] Le Van Quyen M et al. The Lancet 2001; 357: 183-188

TRANSCRANIAL MAGNETIC STIMULATION

Alvaro Pascual-Leone Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA

Repetitive transcranial magnetic stimulation (rTMS) allows the non-invasive modulation of activity in a specified cortical target in the brain convexity and its functionally connected cortico-subcortical neural network. Cortical excitability of the directly targeted brain region can be increased or decreased beyond the duration of the rTMS train by the induction of phenomena similar to long-term depression (LTD) or long-term potentiation (LTP) respectively. Network effects can result in behavioral benefits through paradoxical functional facilitation, induction of desirable plastic changes, or release of specific neurotransmitters. Repetitive TMS can serve as proof-of-principle prior to more invasive neuromodulatory approaches and can, in itself, lead clinically relevant therapeutic effects in a variety of neuropsychiatric conditions, including depression, pain, bradykinesia in Parkinson’s disease, and neurorehabilitation from aphasia and hemiparesis. TMS provides a non-invasive method for controlled interventions aimed at enhancing recovery of function and minimizing the impact of disease, but also at enhancing skill acquisition and optimizing a given cognitive function in normal subjects under certain circumstances.

TOWARD A STEM CELL THERAPY FOR PARKINSON´S DISEASE

Anders Björklund Wallenberg Neuroscience Center, Department of Physiological Sciences, Lund University, BMC A11, S-221 84 Lund

Cell replacement therapy for Parkinson´s disease is based on the idea that implanted dopamine neurons may be able to substitute for the lost nigrostriatal neurons. In rodent and primate models of Parkinson’s disease it has been shown that transplanted dopamine neuroblasts can re-establish a functional innervation and restore dopaminergic neurotransmission in the area of the striatum reached by the outgrowing axons; that the grafted neurons are spontaneously active and release dopamine in an impulse-dependent manner, at both synaptic and non-synaptic sites; and that they can reverse or ameliorate some of the Parkinson-like motor impairments induced by damage to the nigrostriatal system. Clinical trials in patients with advanced Parkinson´s disease have shown that dopamine neuroblasts obtained from fetal human mesencephalic tissue can survive and function also in the brains of PD patients, restore striatal dopamine release, and ameliorate impairments in motor behavior.

The principal limitation of this approach is the problems associated with the use of tissue derived from aborted human fetuses, and the large numbers of donors needed to obtain good therapeutic effects. Until now, transplantation of dopamine neurons has focused primarily on differentiated neuroblasts and young postmitotic neurons, at the stage of neuronal development that is optimal for survival and growth of the grafted cells. However, progenitors taken at earlier stages of development might prove more effective. Efforts are now made to expand multipotent neural stem- or progenitor cells in vitro, and control their phenotypic differentiation into a dopaminergic neuronal fate. Initial results suggest that in vitro expanded cells can survive and function after transplantation to the striatum in the rat PD model, but the overall yield of surviving dopamine neurons has been very low. With further development, expanded progenitors or dopamine neuron precursors, possibly in combination with cell engineering techniques, may offer new sources of cells for replacement therapy in PD.

ABETA IMMUNOTHERAPY AS A NOVEL TREATMENT OPPORTUNITY FOR ALZHEIMER’S DISEASE

Dale Schenk Elan Pharmaceuticals, 800 Gateway Blvd, South San Francisco CA 94080

Alzheimer’s disease (AD) is a neurodegenerative disease affecting millions of individuals in the U.S. population alone. Although a number of therapeutic treatments are now available to treat AD, they do not affect the underlying cause and are unlikely to fundamentally change the course of the disease in affected individuals. In the absence of such agents in the relatively near future, the devastation the AD will impart on our society will be profound. Attempts to develop treatments for AD that have a hope of altering disease progression are currently aimed at the primary pathologies of the disease, beta amyloid plaques and tau containing neurofibrillary tangles. To aid in the development of targeted therapeutic agents, animal models that are transgenic for both the amyloid precursor protein (APP) and tau have been developed. If beta amyloid peptide is indeed the cause of these changes, then either reductions in the production of the peptide or increased clearance should reduce both the plaque lesions as well as secondary responses to the insult. In this regard, Abeta immunotherapy, which facilitates beta amyloid peptide and plaque clearance-reduces plaque burden and improves behavioral outcomes in APP transgenic mice. Based upon these findings, significant clinical effort is underway to identify a form of Abeta immunotherapy for treatment of AD. Surprisingly, analysis of autopsy material from treated patients suggests plaque clearance is likely occurring. Side effects involving encephalitis were seen in a phase 2 study using Abeta 42 as the immunogen (i.e. AN 1792), nevertheless, preliminary analysis on a variety of clinical outcome measures is more optimistic and warrants a continued effort in this area with second generation approaches, such as monoclonal antibodies and immunoconjugates, to more fully test the beta amyloid hypothesis. A passive antibody approach is currently in phase 1 clinical trial.

ANTAGONISTES DE RECEPTEURS CANNABINOIDES CENTRAUX (CB1) ET COMPORTEMENT ALIMENTAIRE

Gérard Le Fur Membre de l’Académie des sciences, Sanofi-Synthélabo, Paris

Les récepteurs cannabinoides de type 1 (CB1) et ses ligands endogènes, anandamide et autres endocannabinoides sont impliqués dans la régulation du comportement alimentaire. Les propriétés stimulantes de l'appétit chez l'homme de la marijuana sont décrites depuis de nombreuses années. L'administration d'endocannabinoides centralement ou à la périphérie stimule la prise alimentaire chez les rongeurs. L'utilisation de souris "knock out" des récepteurs CB1 a montré leur importance au niveau central dans le nucléus accumbens (circuits de récompense) ou dans l'hypothalamus (centre de la faim) mais aussi au niveau périphérique dans le tissu adipeux (régulation de la masse graisseuse).

Rimonabant (SR 141716) est le premier antagoniste spécifique des récepteurs CB1. Il s'oppose donc aux actions des endocannabionoides libérés tant au niveau du système nerveux central qu'à la périphérie. Il diminue la prise alimentaire chez les rongeurs et s'oppose à l'hyperphagie induite par divers neuropeptides (NPY, Orexin, MCH). De plus, il diminue la prise de poids des rongeurs dans des modèles d'obésité comme les rats Zucker (fafa) ou les souris "DIO". Ces effets sont probablement liés à une action directe au niveau des centres de la faim, au niveau hypothalamique, des circuits de récompense localisés dans le nucleus accumbens ainsi qu'un effet au niveau du tissu adipeux car le rimonabant augmente l'adiponectine. Cette adipokine pourrait expliquer les effets du rimonabant tant au niveau lipidique que glucidique.

Chez l'homme, le rimonabant dans deux études de phase III a démontré une réduction du poids chez des obèses présentant une dyslipidémie tout en améliorant leur profil lipidique et glucidique ainsi qu'une aide au sevrage tabagique chez des patients qui désiraient cesser de fumer sans pour autant prendre du poids.

Ces résultats démontrent le rôle du système endocannabinoide dans le comportement alimentaire.