DOCSLIB.ORG

Effects of Gabaa-Active Agents on Thermoregulataion in Rats

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Effects of Gabaa-Active Agents on Thermoregulataion in Rats Trakia Journal of Sciences, Vol. 8, Suppl. 2, pp 102-106, 2010 Copyright © 2009 Trakia University Available online at: http://www.uni-sz.bg ISSN 1313-7050 (print) ISSN 1313-3551 (online) EFFECTS OF GABAA-ACTIVE AGENTS ON THERMOREGULATAION IN RATS R. Nikolov*, K. Yakimova Department of Pharmacology and Toxicology, Medical Faculty, Medical University, Sofia ABSTRACT PURPOSE: Gamma-aminobutyric acid (GABA) is the principal inhibitory neurotransmitter, which is widely distributed throughout the mammalian brain including hypothalamus. Immunohistochemical research have reported GABA-ergic neurons and GABAA-receptors on the neurons of the preoptic area of anterior hypothalamus (PO/AH). The aim of this study was to investigate the influence of GABAA- ergic substances on thermoregulation in rats. METHODS: We have studied the effects of GABAA- active agents, muscimol and diazepam on core body temperature in rats after systemic administration (intraperitoneally, i.p.). Body temperature was measured with thermistor probes (TX8) and monitored on multichannel recorder THERMEX 16. RESULTS: Intraperitoneal injection of muscimol or diazepam has produced dose-dependent hypothermia. Hypothermic effect of muscimol was inhibited by pretreatment of bicuculline, a competitive antagonist of GABAA-receptors. Diazepam induced hypothermia was antagonized by pretreatment of animals with flumazenil, a competitive antagonist of benzodiazepine receptors. CONCLUSION: Hypothermia induced by muscimol or diazepam suggest involvement of GABAA receptors in the processes of thermoregulation. Key words: GABAA-active drugs, muscimol, diazepam, thermoregulation, rats. INTRODUCTION mushrooms Amanita muscaria, Amanita Thermoregulation is the complex physiologic pantherina, and Amanita gemmata, along with process involving both central and peripheral muscarine, muscazone,and ibotenic acid (7). autonomic mechanisms. The primary Muscimol is a potent GABAA agonist, thermoregulatory center resides in the preoptic activating the receptor for the brain's major area of the hypothalamus and controls the inhibitory neurotransmitter GABA. Muscimol balance between heat gain and heat loss. binds to the same binding site on the GABAA receptor complex as GABA itself, as opposed Many experimental studies suggest the to other GABAergic drugs such as barbiturates participation of GABA in the processes of and benzodiazepines which bind to separate thermoregulation. Immunohistochemical regulatory sites (8). research have reported GABA-ergic terminals and GABAA-receptors on the neurons of the Diazepam, a benzodiazepine derivative is preoptic area of the anterior hypothalamus mainly used to treat anxiety, insomnia, seizures (PO/AH) (1-2). Systemic or central including status epilepticus, and symptoms of administration of either GABA or GABAA and acute alcohol withdrawal. It is also used as a GABAB agonists usually produce hypothermia, premedication for inducing sedation, whereas antagonists of GABAA and GABAB anxiolysis or amnesia before certain medical receptors induce hyperthermia (3-6). procedures (e.g., endoscopy). Diazepam binds at benzodiazepine binding site that is located Muscimol is produced naturally in the on the postsynaptic GABAA receptors and ________________________________ enhances binding of GABA. Diazepam *Correspondence to: Dr. Rumen Nikolov, PhD, increases the frequency of GABA-mediated Department of Pharmacology, Faculty of Medicine, chloride ion channel opening (9). Medical University, 2 „Zdrave“ Str., 1431 Sofia Bulgaria, Tel.: +359 2 91 72 622 e-mail address: [email protected] 102 Trakia Journal of Sciences, Vol. 8, Suppl. 2, 2010 NIKOLOV R., et al. The purpose of the present study was to assess thermistor probes (TX8) and monitored on the effects of GABAA-active agents, muscimol, multichannel recorder Iso-Thermex 16 a selective GABAA-agonist, and diazepam, a (Columbus Instruments, USA). The thermistor positive allosteric modulator of GABAA-ergic probes were lubricated and inserted rectally to receptors, on thermoregulation in rats. a depth of 6 cm. Before drug administration the initial temperature of the animals was MATHERIALS AND METHODS determined. Body temperatures were recorded Substances. The following substances were at 30, 60, 90, 120, 150 and 180 min following used: Muscimol (Sigma), Diazepam (Sigma), injection of the tested substances. The R(-)-Bicuculline methiodide (Sigma), and movements of the rats were slightly restricted, Flumazenil (Sigma). In the present study all as previously described (10). agents were administered intraperitoneally (i.p.) in a of volume 0.2 ml/100 g body weight. Data analysis. The results were calculated as Bicuculline was injected 10 min before delta (∆) values (mean ∆ values ± S.E.M.). GABAA-agonists (muscimol or diazepam) Transformed data were analyzed with two-way administrations. Flumazenil was injected analysis of variance (ANOVA). For statistical immediately before application of diazepam. significance a Student’s t-test was used. In all The rats from control group were treated with cases, values of P<0.05 were considered to be 0.9% sodium chloride (NaCl) in a volume of statistically significant. 0.2 ml/100 g body weight. RESULTS Experimental animals. The experiments were Effects of muscimol on core body temperature carried out on male Wistar rats (weight range in rats after systemic application 200-220 g), which were divided into groups of Intraperitoneal injection of muscimol (2 and 4 6-8 rats each. Rats were maintained on a mg/kg) caused dose-dependent decrease in the standard 12 h light/dark cycle and allowed core body temperature of the rats (Fig. 1). The food and water ad libitum. Individual rats were hypothermic effect was started soon after used in one experiment. The experiments were injection with a maximum observed at 90 min conducted in accordance with the International (P < 0.01) and attenuation until the 150 min. Guiding Principles for Biomedical Research The control group treated with saline showed Involving Animals. no change in body temperature of the rats. Pretreatment with bicuculline (2 mg/kg i.p.), a Body temperature measurements. All body selective GABAA antagonist inhibit muscimol- temperature experiments started at 10 a.m. and induced hypothermia in rats (Fig. 1). were conducted at ambient temperature of 22 ± 1°C. Body temperature was measured with 1 0.5 0 30' 60' 90' 120' 150' 180' time (min) -0.5 * * ** -1 * * tem C) perature (delta ** ** -1.5 ** -2 Fig. 1. Effects of intraperitoneal application (i.p.) of muscimol and bicuculline on body temperature in rats. Mean change (temperature delta °C) after i.p. administration of: S Muscimol 2 mg/kg, z Muscimol 4 mg/kg Bicuculline 2 mg/kg + Muscimol 4 mg/kg, ¡ 0,9% NaCl (control). Significant differences: *P < 0,05, **P < 0,01. Trakia Journal of Sciences, Vol. 8, Suppl. 2, 2010 103 NIKOLOV R., et al. Effects of diazepam on core body temperature dose of 2.5 or 5 mg/kg caused fall in core body in rats after systemic application temperature in rats at 30, and 60 min after drug Systemic administration of diazepam in dose 1 injection (P < 0.01), with a maximum observed mg/kg does not produce significantly changes at 30 min (Fig. 2). The control group treated in core body temperature in rats (Fig. 2). with saline showed no change in body Intraperitoneal administration of diazepam in temperature of the rats. 1.5 1 0.5 C) ° 0 30' 60' 90' 120' 150' 180' time (min) ** temperature (delta -0.5 ** ** -1 ** -1.5 Fig. 2. Effects of intraperitoneal application (i.p.). of diazepam on body temperature in rats. Mean change (temperature delta °C) after i.p. administration of: diazepam 1 mg/kg, z diazepam 2,5 mg/kg, S diazepam 5 mg/kg, and ¡ 0,9% NaCl (control). Significant differences: **P < 0,01. Hypothermia induced by diazepam (5 mg/kg i.p.) was antagonized with flumazenil (5 mg/kg i.p.) in pretreated rats (Fig. 3). 1.5 1 C) ° 0.5 0 30' 60' 90' 120' 150' 180' time (min) ** -0.5 temperature (delta temperature (delta ** -1 -1.5 Fig. 3. Effect of intraperitoneal application of diazepam and flumazenil on body temperature in rats. Mean change (temperature delta °C) after i.p. administration of: S diazepam 5 mg/kg, flumazenil 5 mg/kg + diazepam 5 mg/kg, and ¡ 0,9% NaCl (control). Significant differences: *P < 0,05, **P < 0,01. 104 Trakia Journal of Sciences, Vol. 8, Suppl. 2, 2010 NIKOLOV R., et al. DISCUSSION REFERENCES GABA is the principal inhibitory 1. Gritti, I., Mainville, L., Jones, B.E. Co- neurotransmitter, which is widely distributed distribution of GABA- with acetylcholine- throughout the mammalian brain including synthesizing neurons in the basal forebrain hypothalamus (11). GABA interacts with two of the rat. J Comp Neurol, 329: 438-457, major types of receptors, the ionotropic 1993. GABAA, and metabotropic GABAB receptors. 2. Fenelon, V.S., Herbison, A.E. In vivo (12). Probably, the hypothermic response regulation of specific GABA-A receptor induces by GABA-ergic agents which act as subunit messenger RNAs by increased direct GABA agonists is mediated by GABA concentration in rat brain. stimulation of GABAA and GABAB receptors Neurosci, 71: 661-670, 1996. (13). In mechanisms of GABA-mediated 3. Serrano, J.S., Minano, F.J., Sancibrian, M., hypothermia may be involved other central Duran, J.A. Involvement of bicuculline- neurotransmitters including serotonin, insensitive receptors in the hypothermic acetylcholine, dopamine (14-15). Experimental effect of GABA and its agonists. Gen studies reported interactions between GABA- Pharmacol, 16: 505-508, 1985. ergic
Load more

Recommended publications
  • Amnestic Concentrations of Sevoflurane Inhibit Synaptic
    Anesthesiology 2008; 108:447–56 Copyright © 2008, the American Society of Anesthesiologists, Inc. Lippincott Williams & Wilkins, Inc. Amnestic Concentrations of Sevoflurane Inhibit Synaptic Plasticity of Hippocampal CA1 Neurons through ␥-Aminobutyric Acid–mediated Mechanisms Junko Ishizeki, M.D.,* Koichi Nishikawa, M.D., Ph.D.,† Kazuhiro Kubo, M.D.,‡ Shigeru Saito, M.D., Ph.D.,§ Fumio Goto, M.D., Ph.D.࿣ Background: The cellular mechanisms of anesthetic-induced for surgical procedures do not have recollection of ac- amnesia are still poorly understood. The current study exam- tually being awake despite being awake and cooperative ined sevoflurane at various concentrations in the CA1 region of during the procedure.1 Galinkin et al.2 compared sub- rat hippocampal slices for effects on excitatory synaptic trans- Downloaded from http://pubs.asahq.org/anesthesiology/article-pdf/108/3/447/366512/0000542-200803000-00017.pdf by guest on 29 September 2021 mission and on long-term potentiation (LTP), as a possible jective, psychomotor, cognitive, and analgesic effects of mechanism contributing to anesthetic-induced loss of recall. sevoflurane (0.3% and 0.6%) with those of nitrous oxide Methods: Population spikes and field excitatory postsynaptic at equal minimum alveolar concentrations (MACs) in potentials were recorded using extracellular electrodes after healthy volunteers. They found that sevoflurane pro- electrical stimulation of Schaffer-collateral-commissural fiber inputs. Paired pulse facilitation was used as a measure of pre- duced a greater degree of amnesia and psychomotor synaptic effects of the anesthetic. LTP was induced using tetanic impairment than did an equal MAC of nitrous oxide but stimulation (100 Hz, 1 s). Sevoflurane at concentrations from had no analgesic actions.
    [Show full text]
  • Picrotoxin-Like Channel Blockers of GABAA Receptors
    COMMENTARY Picrotoxin-like channel blockers of GABAA receptors Richard W. Olsen* Department of Molecular and Medical Pharmacology, Geffen School of Medicine, University of California, Los Angeles, CA 90095-1735 icrotoxin (PTX) is the prototypic vous system. Instead of an acetylcholine antagonist of GABAA receptors (ACh) target, the cage convulsants are (GABARs), the primary media- noncompetitive GABAR antagonists act- tors of inhibitory neurotransmis- ing at the PTX site: they inhibit GABAR Psion (rapid and tonic) in the nervous currents and synapses in mammalian neu- system. Picrotoxinin (Fig. 1A), the active rons and inhibit [3H]dihydropicrotoxinin ingredient in this plant convulsant, struc- binding to GABAR sites in brain mem- turally does not resemble GABA, a sim- branes (7, 9). A potent example, t-butyl ple, small amino acid, but it is a polycylic bicyclophosphorothionate, is a major re- compound with no nitrogen atom. The search tool used to assay GABARs by compound somehow prevents ion flow radio-ligand binding (10). through the chloride channel activated by This drug target appears to be the site GABA in the GABAR, a member of the of action of the experimental convulsant cys-loop, ligand-gated ion channel super- pentylenetetrazol (1, 4) and numerous family. Unlike the competitive GABAR polychlorinated hydrocarbon insecticides, antagonist bicuculline, PTX is clearly a including dieldrin, lindane, and fipronil, noncompetitive antagonist (NCA), acting compounds that have been applied in not at the GABA recognition site but per- huge amounts to the environment with haps within the ion channel. Thus PTX major agricultural economic impact (2). ͞ appears to be an excellent example of al- Some of the other potent toxicants insec- losteric modulation, which is extremely ticides were also radiolabeled and used to important in protein function in general characterize receptor action, allowing and especially for GABAR (1).
    [Show full text]
  • GABA Receptors
    D Reviews • BIOTREND Reviews • BIOTREND Reviews • BIOTREND Reviews • BIOTREND Reviews Review No.7 / 1-2011 GABA receptors Wolfgang Froestl , CNS & Chemistry Expert, AC Immune SA, PSE Building B - EPFL, CH-1015 Lausanne, Phone: +41 21 693 91 43, FAX: +41 21 693 91 20, E-mail: [email protected] GABA Activation of the GABA A receptor leads to an influx of chloride GABA ( -aminobutyric acid; Figure 1) is the most important and ions and to a hyperpolarization of the membrane. 16 subunits with γ most abundant inhibitory neurotransmitter in the mammalian molecular weights between 50 and 65 kD have been identified brain 1,2 , where it was first discovered in 1950 3-5 . It is a small achiral so far, 6 subunits, 3 subunits, 3 subunits, and the , , α β γ δ ε θ molecule with molecular weight of 103 g/mol and high water solu - and subunits 8,9 . π bility. At 25°C one gram of water can dissolve 1.3 grams of GABA. 2 Such a hydrophilic molecule (log P = -2.13, PSA = 63.3 Å ) cannot In the meantime all GABA A receptor binding sites have been eluci - cross the blood brain barrier. It is produced in the brain by decarb- dated in great detail. The GABA site is located at the interface oxylation of L-glutamic acid by the enzyme glutamic acid decarb- between and subunits. Benzodiazepines interact with subunit α β oxylase (GAD, EC 4.1.1.15). It is a neutral amino acid with pK = combinations ( ) ( ) , which is the most abundant combi - 1 α1 2 β2 2 γ2 4.23 and pK = 10.43.
    [Show full text]
  • Exploring the Activity of an Inhibitory Neurosteroid at GABAA Receptors
    1 Exploring the activity of an inhibitory neurosteroid at GABAA receptors Sandra Seljeset A thesis submitted to University College London for the Degree of Doctor of Philosophy November 2016 Department of Neuroscience, Physiology and Pharmacology University College London Gower Street WC1E 6BT 2 Declaration I, Sandra Seljeset, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I can confirm that this has been indicated in the thesis. 3 Abstract The GABAA receptor is the main mediator of inhibitory neurotransmission in the central nervous system. Its activity is regulated by various endogenous molecules that act either by directly modulating the receptor or by affecting the presynaptic release of GABA. Neurosteroids are an important class of endogenous modulators, and can either potentiate or inhibit GABAA receptor function. Whereas the binding site and physiological roles of the potentiating neurosteroids are well characterised, less is known about the role of inhibitory neurosteroids in modulating GABAA receptors. Using hippocampal cultures and recombinant GABAA receptors expressed in HEK cells, the binding and functional profile of the inhibitory neurosteroid pregnenolone sulphate (PS) were studied using whole-cell patch-clamp recordings. In HEK cells, PS inhibited steady-state GABA currents more than peak currents. Receptor subtype selectivity was minimal, except that the ρ1 receptor was largely insensitive. PS showed state-dependence but little voltage-sensitivity and did not compete with the open-channel blocker picrotoxinin for binding, suggesting that the channel pore is an unlikely binding site. By using ρ1-α1/β2/γ2L receptor chimeras and point mutations, the binding site for PS was probed.
    [Show full text]
  • Toxicological and Pharmacological Profile of Amanita Muscaria (L.) Lam
    Pharmacia 67(4): 317–323 DOI 10.3897/pharmacia.67.e56112 Review Article Toxicological and pharmacological profile of Amanita muscaria (L.) Lam. – a new rising opportunity for biomedicine Maria Voynova1, Aleksandar Shkondrov2, Magdalena Kondeva-Burdina1, Ilina Krasteva2 1 Laboratory of Drug metabolism and drug toxicity, Department “Pharmacology, Pharmacotherapy and Toxicology”, Faculty of Pharmacy, Medical University of Sofia, Bulgaria 2 Department of Pharmacognosy, Faculty of Pharmacy, Medical University of Sofia, Bulgaria Corresponding author: Magdalena Kondeva-Burdina ([email protected]) Received 2 July 2020 ♦ Accepted 19 August 2020 ♦ Published 26 November 2020 Citation: Voynova M, Shkondrov A, Kondeva-Burdina M, Krasteva I (2020) Toxicological and pharmacological profile of Amanita muscaria (L.) Lam. – a new rising opportunity for biomedicine. Pharmacia 67(4): 317–323. https://doi.org/10.3897/pharmacia.67. e56112 Abstract Amanita muscaria, commonly known as fly agaric, is a basidiomycete. Its main psychoactive constituents are ibotenic acid and mus- cimol, both involved in ‘pantherina-muscaria’ poisoning syndrome. The rising pharmacological and toxicological interest based on lots of contradictive opinions concerning the use of Amanita muscaria extracts’ neuroprotective role against some neurodegenerative diseases such as Parkinson’s and Alzheimer’s, its potent role in the treatment of cerebral ischaemia and other socially significant health conditions gave the basis for this review. Facts about Amanita muscaria’s morphology, chemical content, toxicological and pharmacological characteristics and usage from ancient times to present-day’s opportunities in modern medicine are presented. Keywords Amanita muscaria, muscimol, ibotenic acid Introduction rica, the genus had an ancestral origin in the Siberian-Be- ringian region in the Tertiary period (Geml et al.
    [Show full text]
  • Bicuculline and Gabazine Are Allosteric Inhibitors of Channel Opening of the GABAA Receptor
    The Journal of Neuroscience, January 15, 1997, 17(2):625–634 Bicuculline and Gabazine Are Allosteric Inhibitors of Channel Opening of the GABAA Receptor Shinya Ueno,1 John Bracamontes,1 Chuck Zorumski,2 David S. Weiss,3 and Joe Henry Steinbach1 Departments of 1Anesthesiology and 2Psychiatry, Washington University School of Medicine, St. Louis, Missouri 63110, and 3University of Alabama at Birmingham, Neurobiology Research Center and Department of Physiology and Biophysics, Birmingham, Alabama 35294-0021 Anesthetic drugs are known to interact with GABAA receptors, bicuculline only partially blocked responses to pentobarbital. both to potentiate the effects of low concentrations of GABA and These observations indicate that the blockers do not compete to directly gate open the ion channel in the absence of GABA; with alphaxalone or pentobarbital for a single class of sites on the however, the site(s) involved in direct gating by these drugs is not GABAA receptor. Finally, at receptors containing a1b2(Y157S)g2L known. We have studied the ability of alphaxalone (an anesthetic subunits, both bicuculline and gabazine showed weak agonist steroid) and pentobarbital (an anesthetic barbiturate) to directly activity and actually potentiated responses to alphaxalone. These activate recombinant GABAA receptors containing the a1, b2, and observations indicate that the blocking drugs can produce allo- g2L subunits. Steroid gating was not affected when either of two steric changes in GABAA receptors, at least those containing this mutated b2 subunits [b2(Y157S) and b2(Y205S)] are incorporated mutated b2 subunit. We conclude that the sites for binding ste- into the receptors, although these subunits greatly reduce the roids and barbiturates do not overlap with the GABA-binding site.
    [Show full text]
  • The Protective Effect of Nicardipine on Iron-Induced Purkinje
    Fırat Tıp Dergisi 2008;13(3): 167-170 Experimental Research www.firattipdergisi.com The Protective Effect of Nicardipine on Iron-Induced Purkinje Cell Loss in Rat Cerebellum: A Stereological Study Ramazan KOZAN a1 , M. Ömer BOSTANCI 2, Fatih SEFĐL 2, Faruk BAĞIRICI 2 1 Mustafa Kemal University, Faculty of Medicine, Department of Physiology, HATAY 2 Ondokuz Mayis University, Faculty of Medicine, Department of Physiology, SAMSUN ABSTRACT Objective: The aim of the present study is to investigate the effect of nicardipine, a calcium channel blocker, on the neurotoxicity induced by intracerebroventricular (i.c.v.) iron injection in rats. Materials and Methods: Animals were divided into three groups; control, iron and iron+nicardipine groups. Rats in iron and iron+nicardipine groups received i.c.v. FeCl 3, while rats in control group received the same volume of saline. All animals were kept alive for ten days following the operation and animals in iron+nicardipine group were injected intraperitoneally nicardipine (10 mg/kg/day) once a day during this period. After ten days, all rats were perfused intracardially and cerebellar tissues were stained with Cresyl violet. Means of total Purkinje cells numbers in the cerebellum were estimated using the optical fractionator counting method. Results: Means of total Purkinje cells numbers in the cerebellum as follows: 317182±9667, 209002±7836 and 265659±8291 in the control, iron and iron+nicardipine groups, respectively. Total number of Purkinje cells in iron and iron+nicardipine groups were significantly lower than control animals (p< 0.05). However, comparison between iron and iron+nicardipine groups revealed that nicardipine significantly attenuates the iron-induced Purkinje cell loss (p<0.05).
    [Show full text]
  • Molecular Changes in Opioid Addiction: the Role of Adenylyl Cyclase and Camp/PKA System 205
    CHAPTER SEVEN Molecular Changes in Opioid Addiction: The Role of Adenylyl Cyclase and cAMP/PKA System ,1 † Patrick Chan* , Kabirullah Lutfy * Department of Pharmacy and Pharmacy Administration, Western University of Health Sciences, College of Pharmacy, Pomona, California, USA † Department of Pharmaceutical Sciences, College of Pharmacy, Western University of Health Sciences, Pomona, California, USA 1 Corresponding author: e-mail address: [email protected]. Contents 1. Introduction 204 2. The Adenylyl Cyclase Pathway 205 2.1 Adenylyl Cyclase 205 2.2 Protein Kinase A 207 3. Opioid Effect on cAMP-Responsive Element-Binding Protein 209 4. Molecular Changes in Brain Regions That May Underlie Opiate Dependence 211 4.1 Molecular Changes in the Locus Coeruleus 211 4.2 Molecular Changes in the Amygdala 214 4.3 Molecular Changes in the Periaqueductal Gray 216 5. Molecular Changes in the Ventral Tegmental Area 217 6. Molecular Changes in Other CNS Regions 218 7. Conclusions 219 References 219 Abstract For centuries, opiate analgesics have had a considerable presence in the treatment of moderate to severe pain. While effective in providing analgesia, opiates are notorious in exerting many undesirable adverse reactions. The receptor targets and the intra- cellular effectors of opioids have largely been identified. Furthermore, much of the mechanisms underlying the development of tolerance, dependence, and withdrawal have been delineated. Thus, there is a focus on developing novel compounds or strategies in mitigating or avoiding the development of tolerance, dependence, and withdrawal. This review focuses on the adenylyl cyclase and cyclic adenosine 3,5-monophosphate (cAMP)/protein kinase A (AC/cAMP/PKA) system as the central player in mediating the acute and chronic effects of opioids.
    [Show full text]
  • Opposing Actions of Sevoflurane on Gabaergic and Glycinergic Synaptic Inhibition in the Spinal Ventral Horn
    Opposing Actions of Sevoflurane on GABAergic and Glycinergic Synaptic Inhibition in the Spinal Ventral Horn Veit-Simon Eckle, Sabrina Hauser, Berthold Drexler*, Bernd Antkowiak, Christian Grasshoff Experimental Anesthesiology Section, Department of Anesthesiology & Intensive Care, Tu¨bingen University Hospital, Eberhard-Karls-University, Tu¨bingen, Germany Abstract Background: The ventral horn is a major substrate in mediating the immobilizing properties of the volatile anesthetic sevoflurane in the spinal cord. In this neuronal network, action potential firing is controlled by GABAA and glycine receptors. Both types of ion channels are sensitive to volatile anesthetics, but their role in mediating anesthetic-induced inhibition of spinal locomotor networks is not fully understood. Methodology/Principal Findings: To compare the effects of sevoflurane on GABAergic and glycinergic inhibitory postsynaptic currents (IPSCs) whole-cell voltage-clamp recordings from ventral horn interneurons were carried out in organotypic spinal cultures. At concentrations close to MAC (minimum alveolar concentration), decay times of both types of IPSCs were significantly prolonged. However, at 1.5 MAC equivalents, GABAergic IPSCs were decreased in amplitude and reduced in frequency. These effects counteracted the prolongation of the decay time, thereby decreasing the time- averaged GABAergic inhibition. In contrast, amplitudes and frequency of glycinergic IPSCs were not significantly altered by sevoflurane. Furthermore, selective GABAA and glycine receptor antagonists were tested for their potency to reverse sevoflurane-induced inhibition of spontaneous action potential firing in the ventral horn. These experiments confirmed a weak impact of GABAA receptors and a prominent role of glycine receptors at a high sevoflurane concentration. Conclusions: At high concentrations, sevoflurane mediates neuronal inhibition in the spinal ventral horn primarily via glycine receptors, and less via GABAA receptors.
    [Show full text]
  • Benzamil Inhibits Neuronal and Heterologously Expressed Small
    *Manuscript Click here to view linked References Benzamil inhibits neuronal and heterologously expressed small conductance Ca2+-activated K+ channels Marisol Sampedro Castañeda1,3, Raffaella Tonini1,2 , Christopher D. Richards1, Martin Stocker1* and Paola Pedarzani1* 1Research Department of Neuroscience, Physiology and Pharmacology, University College London, London, UK. 2Neuromodulation of Cortical and Subcortical Circuits Laboratory, Fondazione Istituto Italiano di Tecnologia, Genova, Italy. 3Kinases and Brain Development Laboratory, The Francis Crick Institute, London, UK ORCID: Paola Pedarzani - https://orcid.org/0000-0002-2665-7911 Martin Stocker - https://orcid.org/0000-0003-3993-5666 *To whom correspondence should be addressed at: Research Department of Neuroscience, Physiology and Pharmacology University College London, Gower Street, London WC1E 6BT, United Kingdom Tel.: +44-(0)20-7679-7744 (PP) or +44-(0)20-3549-5671(MS) E-mail: [email protected] or [email protected] 1 Abstract Small conductance Ca2+-activated K+ (SK) channels are expressed throughout the soma and dendrites of pyramidal neurons in the neocortex and hippocampal formation, where they participate in the local regulation of membrane excitability and synaptic signals. Through their inter-play with Ca2+ channels, SK channels regulate Ca2+ influx triggered by back-propagating action potentials in dendrites. Inhibition of SK channels affects both the amplitude and duration of Ca2+ transients, but the role of Ca2+ clearance mechanisms and their link to SK channel activity has not been established. Here we report the effect of the Na+/Ca2+ exchanger (NCX) inhibitor benzamil on Ca2+ extrusion and SK channels in the regulation of dendritic Ca2+ signals. Benzamil increased the duration and amplitude of dendritic Ca2+ transients elicited by back- propagating action potentials in hippocampal pyramidal neurons.
    [Show full text]
  • A Molecular Mechanism for Choosing Alcohol Over an Alternative Reward Eric Augier, Estelle Barbier, Russell S
    Corrected 9 July 2018. See full text. RESEARCH ALCOHOL DEPENDENCY ward 26.2% of the time (Fig. 1C). However, al- though the vast majority of rats strongly preferred saccharin,aminority,4ratsoutof32inthefirst A molecular mechanism for choosing experiment (12.5% of the population, Fig. 1D, left) continued to choose alcohol despite having access to a high-value alternative (alcohol-preferring, alcohol over an alternative reward AP). Although this was a small number, it aligns well with human addiction rates (7, 8) and promp- Eric Augier1*, Estelle Barbier1, Russell S. Dulman2, Valentina Licheri3, Gaëlle Augier1, ted us to expand the study of individual differences Esi Domi1, Riccardo Barchiesi1, Sean Farris4, Daniel Nätt1, R. Dayne Mayfield4, in choice behavior. Ultimately, this percentage Louise Adermark3, Markus Heilig1 was stable across a large number of rats from successive batches (see below; Fig. 1D, right). Alcohol addiction leads to increased choice of alcohol over healthy rewards. We established Alcohol preference was not influenced by hold- an exclusive choice procedure in which ~15% of outbred rats chose alcohol over a ing prior history of alcohol and saccharin self- high-value reward. These animals displayed addiction-like traits, including high motivation administration identical (fig. S3). to obtain alcohol and pursuit of this drug despite adverse consequences. Expression of the g-aminobutyric acid (GABA) transporter GAT-3 was selectively decreased within the Extensive pre-exposure to saccharin amygdala of alcohol-choosing rats, whereas a knockdown of this transcript reversed choice does not affect subsequent preference of rats that originally chose a sweet solution over alcohol. GAT-3 expression alcohol choice was selectively decreased in the central amygdala of alcohol-dependent people compared People who go on to develop addictive disorders to those who died of unrelated causes.
    [Show full text]
  • Assessment of Neuronal Activity Using Microelectrode Array
    In vitro Toxicology eCiphr®Neuro: Assessment of Neuronal Activity Using Microelectrode Array Background Information Protocol • The eCiphr®Neuro assay uses primary Cell Type cultures of rat cortical neurons. Primary rat cortical neurons • Cyprotex’s neuronal assay uses Analysis Platform high throughput microelectrode Maestro 48-well MEA system (Axion BioSystems) array (MEA) technology to monitor electrophysiological activity. Test Article Concentrations 4 concentrations in triplicate (dependent on customer requirements) • Neurons grown on microelectrode arrays recapitulate many features of Quality Controls neurons in vivo, including spontaneous Negative control: 0.2% DMSO (vehicle) activity (spiking and bursting), plasticity, ‘The unique capabilities of Positive controls: picrotoxin and domoic organisation and responsiveness to a MEAs to provide functional acid (at single concentration) wide range of neurotransmitters and measurements of network pharmacological agonists/antagonists1. activity, including spontaneous Data Delivery Firing rate (spikes/second) activity, evoked activity, and • This technology provides a unique Burst rate (spikes/second) responses to pharmacological in vitro system for preclinical drug Number of spikes in burst challenges, therefore offers an discovery, neurotoxicity assessment and Percent of isolated spikes advantage over other potential disease modelling. Coefficient of variation (CV) of the inter-spike screening approaches that rely intervals (ISI) on biochemical or structural Burst duration endpoints.’ Normalised IQR (inter-quartile range) burst duration 1Robinette BL et al., (2011) Front Interburst interval Neuroeng 4; 1-9 Mean ISI-distance (measure of synchrony) Normalised Median Absolute Deviation (MAD) burst spike number Median ISI/Mean ISI To find out more [email protected] In vitro networks of neurons are spontaneously active and express patterns of electrical activity as part of their normal function2.
    [Show full text]