KUOPION YLIOPISTON JULKAISUJA A. FARMASEUTTISET TIETEET 113 KUOPIO UNIVERSITY PUBLICATIONS A. PHARMACEUTICAL SCIENCES 113 TIINA KÄÄRIÄINEN Interaction of the Dopaminergic and Serotonergic Systems in Rat Brain Studies in Parkinsonian Models and Brain Microdialysis Doctoral dissertation To be presented by permission of the Faculty of Pharmacy of the University of Kuopio for public examination in Mediteknia Auditorium, Mediteknia building, University of Kuopio, on Saturday 13th December 2008, at 1 p.m. Department of Pharmacology and Toxicology Faculty of Pharmacy University of Kuopio JOKA KUOPIO 2008 Distributor: Kuopio University Library P.O. Box 1627 FI-70211 KUOPIO FINLAND Tel. +358 40 355 3430 Fax +358 17 163 410 http://www.uku.fi/kirjasto/julkaisutoiminta/julkmyyn.html Series Editor: Docent Pekka Jarho, Ph.D. Department of Pharmaceutical Chemistry Author’s address: Department of Pharmacology and Toxicology University of Kuopio P.O. Box 1627 FI-70211 KUOPIO Tel. +358 40 355 3776 Fax +358 17 162 424 E-mail: [email protected] Supervisors: Professor Pekka T. Männistö, M.D., Ph.D. Division of Pharmacology and Toxicology Faculty of Pharmacy University of Helsinki Senior assistant Anne Lecklin, Ph.D. Department of Pharmacology and Toxicology University of Kuopio Reviewers: Docent Pekka Rauhala, M.D., Ph.D. Institute of Biomedicine University of Helsinki Docent Seppo Kaakkola, M.D., Ph.D. Department of Neurology Helsinki University Central Hospital Opponent: Professor Raimo K. Tuominen, M.D., Ph.D. Division of Pharmacology and Toxicology Faculty of Pharmacy University of Helsinki ISBN 978-951-27-0851-2 ISBN 978-951-27-1144-4 (PDF) ISSN 1235-0478 Kopijyvä Kuopio 2008 Finland 3 Kääriäinen, Tiina. Interaction of the dopaminergic and serotonergic systems in rat brain: Studies in parkinsonian models and brain microdialysis. Kuopio University Publications A. Pharmaceutical Sciences 113. 2008. 125 p. ISBN 978-951-27-0851-2 ISBN 978-951-27-1144-4 (PDF) ISSN 1235-0478 ABSTRACT Dopamine and serotonin (5-hydroxytryptamine; 5-HT) are involved in several essential brain functions as well as in various neurological and mental disorders. Anatomical, electrophysiological and biochemical data point to an important interplay of the serotonergic and dopaminergic pathways. In particular, the serotonergic system has a modulatory role of on dopaminergic neurotransmission in the central nervous system (CNS). Various 5-HT receptor subtypes modulate dopamine release both directly by 5-HT receptors located on dopaminergic neurons, and indirectly via 5-HT heteroreceptors present on GABAergic neurons. Brain 5-HT/dopamine interactions are also putative targets for drug therapies in disorders related to alterations in dopaminergic or serotonergic neurotransmission, such as Parkinson’s disease (PD), schizophrenia and depression. However, the mechanisms to explain the interactions between 5-HT and dopamine in these brain dysfunctions are not well defined. The objectives of this study were 1) to explore the role of striatal 5-HT in the unilateral rat model of PD, and 2) to assess the ability of 5-HT2A/2C and 5-HT1A receptor ligands to modulate accumbal and striatal dopamine release and metabolism in normal rats. Also 3) the advantages and disadvantages of two types of 6-hydroxydopamine (6-OHDA)-lesion models were evaluated in neuroprotection studies with a flavonoid, quercetin. It was shown that acute intrastriatal L-dopa infusion decreased contralateral rotation of unilaterally 6-OHDA-lesioned rats, evidently by desensitization of ipsilateral dopamine D2 receptors. In an acute study, the decrease in the amount of rotations and imbalance of striatal 5-HT levels between intact and lesion side were abolished by inhibition of 5-HT synthesis. In a long-term study, continuous 2- week intrastriatal L-dopa infusion in 6-OHDA-rats also decreased the number of contralateral rotations induced by peripheral L-dopa and induced marked alterations in the ipsilateral serotonergic system (such as a long-term increase in 5-HT synthesizing enzyme tryptophan hydroxylase) as assessed on day 70 post- infusion. In normal rats, the anxiolytic 5-HT2A/2C antagonist, deramciclane, had an antidopaminergic effect similar to that of neuroleptics or the anxiolytic 5-HT1A agonist buspirone at a high dose. At least a 5-fold margin was found between the anxiolytic and neuroleptic doses of deramciclane in the rat. Striatal 5-HT content was differently affected by the two types of unilateral 6-OHDA-lesion models. Since it is known that striatal 5-HT is reduced in PD patients, it seems that the 6-OHDA medial forebrain bundle- lesioned rat models this situation unilaterally rather well. In these models, quercetin had no effect indicative of neuroprotection against nigrostriatal dopaminergic or serotonergic 6-OHDA-induced neuron damage in vivo. In conclusion, these results highlight the role of 5-HT neurons in the striatal dopaminergic imbalance that is responsible for the rotational behavior seen in the unilateral 6-OHDA rat. This study provides new information about the serotonergic effects after local exogenous L-dopa in acute and long-term administrations into the striatum of dopamine depleted rat. The results may help to further clarify the role of the serotonergic system in the action of L-dopa under dopamine deficiency. Additionally, the clear unilateral 5-HT damage in this widely used rat model should be taken into account in further studies. This study also confirms earlier reports of dopamine modulating properties of 5-HT1A and 5-HT2A/2C ligands, particularly in the mesolimbic system, and provides further evidence that combined affinity of 5-HT/ dopamine D2 receptors may be beneficial in drug actions modulating dopaminergic tone in the CNS. The lack of effect of quercetin in 6-OHDA-rats casts serious doubt on the neuroprotective effects of this bioflavonoid in experimental PD in vivo. National Library of Medicine Classification: WL 359, WL 307, QY 58, QV 126, WK 725 Medical Subject Headings: Parkinson Disease; Disease Models, Animal; Brain; Corpus Striatum; Neurotransmitter Agents; Serotonin; Receptors, Serotonin; Dopamine; Receptors, Dopamine; Ligands; Levodopa; Behavior, Animal; Rotation; Tryptophan Hydroxylase; Flavonoids; Quercetin; Oxidopamine; Microdialysis; Rats 4 5 “If the human brain were so simple that we could understand it, we would be so simple that we couldn’t.” Emerson Pugh, English philosopher, 1997 6 ACKNOWLEDGEMENTS The present study was carried out in the Department of Pharmacology and Toxicology, University of Kuopio, during the years 2003 – 2008. I want to express my deepest gratitude to my principal supervisor Professor Pekka T. Männistö, who made this thesis possible. His encouragement, support and vast expertise have guided me throughout this project. Furthermore, even though he left to work in the University of Helsinki in 2004, he has always been able to find time for me. It has been a great privilege to work with Pekka. I wish also to thank my second supervisor, Anne Lecklin, Ph.D. for being my local adviser here in Kuopio. I express my gratitude to the official reviewers Docent Pekka Rauhala and Docent Seppo Kaakkola for their valuable comments and constructive criticism for improving the manuscript of this thesis. Furthermore, I am very grateful to Ewen MacDonald, Ph.D. for revising the language. I am honored to have Professor Raimo K. Tuominen as my opponent. I am indebted to my all co-authors for their significant contributions to this work. Especially, I wish to thank my collaborators in PTM’s team in Viikki, University of Helsinki; J. Arturo García-Horsman, Ph.D., Mikko Käenmäki, M.Sc., Bernardino Ossola, M.Sc. and Marjo Piltonen, M.Sc. I want to express my special thanks to Marjo Piltonen for her help and friendship during these studies and for her kind hospitality during my several visits to Helsinki. I also wish to thank Marko Huotari, Ph.D., for introducing me the world of the stereotaxis during my early days in the Department. I sincerely thank all of the present and former personnel of Department of Pharmacology and Toxicology. I wish to thank my colleagues, particularly Markus Forsberg, Ph.D., Aaro Jalkanen, M.Sc., Pasi Lampela, Ph.D., Šárka Lehtonen, Ph.D., Timo Myöhänen, Ph.D., Katja Puttonen, M.Sc., Minna Rahnasto, M.Sc., Kaisa Salminen, M.Sc., Timo Sarajärvi, M.Sc., Marjo Tampio, M.Sc., and Jarkko Venäläinen, Ph.D., for their support and friendship. I wish to express my special and sincere thanks to Markus Forsberg for being a mentor particularly during the time when I was completing this thesis, and for many discussions regarding scientific and not-so- scientific matters. I am grateful for Pirjo Hänninen and Jaana Leskinen for their excellent technical assistance and advice, and I wish to thank Leena Oksanen for all the help during these years. I owe special thanks to the personnel of National Laboratory Animal Center for their seamless collaboration. I also wish to thank all of those who may not find their names here, but who contributed in some way during these years. I warmly thank all my dear friends outside the university, especially Merja Rytkönen, Kristiina “Krisu” Saarelainen, Leena Tähtivaara and Anu von Delvig with their families, for sharing the joys and sorrows for many years. In addition, you all have supported me through this long process – I am so fortunate to have friends like you! I express my warmest gratitude to my family; my parents, Irma and Seppo, and my little brothers, Mikko, Antti and Olli for their endless encouragement, care, support and understanding – you have always had confidence in me. Special thanks to Antti for many joyful moments and for your curiosity about scientific issues – there really is a bit of art in everything, even in science! Per aspera ad astra. Finally, I am ready for the new and fascinating challenges which lay ahead of me in the brighter future. This work was supported in part by grants from the Finnish Cultural Foundation of Northern Savo, the Finnish Parkinson Foundation, University of Kuopio and the Foundation of Aleksanteri Mikkonen, which are greatly appreciated.