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Involvement of Dopamine in Pilocarpine-Induced Limbic Motor

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Involvement of Dopamine in Pilocarpine-Induced Limbic Motor INVOLVEMENT OF DOPAMINE IN PILOCARPINE- INDUCED LIMBIC MOTOR SEIZURES IN THE RAT ABDUL MUNAF ALAM B.Pharm. (Hons) M.R.PharmS. The School of Pharmacy, University of London, 29-39 Brunswick Square, London WC1N 1AX A thesis submitted in partial fulfilment of the requirements of the University of London, Faculty of Medicine for the degree of Doctor of Philosophy. June 1995 ProQuest Number: 10105126 All rights reserved INFORMATION TO ALL USERS The quality of this reproduction is dependent upon the quality of the copy submitted. In the unlikely event that the author did not send a complete manuscript and there are missing pages, these will be noted. Also, if material had to be removed, a note will indicate the deletion. uest. ProQuest 10105126 Published by ProQuest LLC(2016). Copyright of the Dissertation is held by the Author. All rights reserved. This work is protected against unauthorized copying under Title 17, United States Code. Microform Edition © ProQuest LLC. ProQuest LLC 789 East Eisenhower Parkway P.O. Box 1346 Ann Arbor, Ml 48106-1346 To my family. A bstract ABSTRACT 1. The present study employed systemic administration of the cholinergic agonist, pilocarpine, to induce intractable limbic motor seizures in the rat. Stereotaxic microinjections of and Dg agonists and antagonists into the hippocampus, via implanted guide cannulae, were used to examine whether dopamine and Dg receptors modify this seizure activity. Pilocarpine-induced convulsions were attenuated by intrahippocampal injections of the Dg/Dg agonist LY 171555, and by the antagonist SCH 23390, whereas the Dg antagonist, raclopride, promoted seizures. Stimulating hippocampal receptors with SKF 38393 was without effect on seizure activity. These data suggest that dopamine exerts a dual effect on seizure activity in this area of the rat brain. 2. Stereotaxic studies were also performed to investigate the possibility that Dg receptors are capable of attenuating seizure propagation in the nucleus accumbens and Islands of Calleja. Intra-accumbens pretreatment with the Dg>Dg agonist RU 24213, protected animals against seizures, whilst the more selective Dg»Dg agonists LY 171555 and 7-OH-DPAT were less potent, and only attenuated seizures at non-Dg receptor selective doses. Apomorphine, a D/Dg/Dg agonist, delayed seizure onset, but not at higher doses. Similar results were obtained with these drugs when microinjected into the islands of Calleja. These findings provide evidence that dopamine systems limit seizure propagation through the limbic forebrain, but suggest this effect is mediated by Dg rather than Dg receptors. 3. The effects of pilocarpine-induced status epilepticus on the levels of dopamine, ant its metabolites DO PAC (4-hydroxy-3-methoxyphenylacetic acid) and HVA (3,4-dihydroxyphenylacetic acid) in eight brain regions were determined by high performance liquid chromatography. In seizing animals dopamine was found 1 1 1 A bstract to be raised in the striatum, and in both dorsal and ventral aspects of the hippocampus. Metabolite levels were elevated in striatum, substantia nigra, nucleus accumbens and cingulate cortex, and fell in the hippocampus, but remained unchanged in the olfactory tubercle and amygdala. These changes translated into an increase in dopamine turnover in the striatum, nigra, accumbens and cingulate cortex, and a fall in dopamine turnover in the hippocampus, with no change in the olfactory tubercle or amygdala. While these alterations do not permit a precise definition of dopamine's role in the pilocarpine-induced seizure process, it would seem that changes in some areas are likely to exacerbate (nigra, hippocampus) and in others to ameliorate (striatum, accumbens) seizure activity. It is most unlikely, therefore, that such alterations in dopaminergic activity represent a concerted effort by the brain to restore normality. 4. The effects of dopaminergic ligands on spontaneous zero Mg^^'-induced epileptiform activity were examined in the rat cingulate cortex slice. Dopamine either suppressed or facilitated paroxysmal discharges. The inhibitory effects were mediated by receptors since they were mimicked by a range of D^-selective ligands and blocked by the antagonist SCH 39166. Conversely, the facilitatory response was Dg receptor-mediated, since Dg receptor stimulation was found to augment epileptiform discharges in a Dg antagonist-sensitive manner. These findings lend further support to the proposition that dopamine is an important modulator of epileptiform activity in the intact brain, and that this involves both D^ and Dg receptors working in opposition to each other. IV A cknowledgements ACKNOWLEDGEMENTS Firstly, I would like to thank my supervisor Dr. Mike Starr for his excellent guidance and enthusiasm during the course of this project. Thanks also to Prof. A. Florence for providing funding to support this work. I am grateful to Drs. Les Fowler and Chris Biggs for their expert help and advice in setting up the monoamine high performance liquid chromatography system. A special thanks to Nasir Hussain and Fazal Khan for their support and friendship throughout the project. I also wish to thank Shagufta A., Belinda K., Derek K, Doug R., Dave L., Jaqui M., Simi K., Chris C., Dave M., and Steve C. Finally, I would like to thank my family for their encouragement throughout. Table o f Contents TABLE OF CONTENTS Page Title I Dedication ii Abstract iii Acknowledgments v Table of Contents vi List of Figures xiii List of Tables xviii Ust of Abbreviations xviiii Publications xxii Chapter One General Introduction 1.1 Historical introduction to epilepsy 2 1.2 Classification of human epilepsy 3 1.2.1 Partial seizures 3 1.2.2 Generalised seizures 4 1.3 Neurochemical basis of epilepsy 5 1.4 GABA and epilepsy 5 1.5 Excitatory amino acids and epilepsy 8 1.5.1 In vitro studies 8 1.5.2 In vivo studies 10 1. 6 Catecholamines and epilepsy 12 1.6.1 The dopamine and Dg receptor subfamilies 13 1.6.2 Biochemical studies in humans 14 1.6.3 Biochemical studies in animals 16 1.6.4 Dopamine agonists in humans 19 1.6.5 Dopamine depleting drugs in humans 20 1.6.6 Dopamine antagonists in humans 20 VI Table o f Contents 1.6.7 Unselective dopamine agonists in animals 21 1.6.8 Unselective dopamine antagonists in animal studies 23 1.6.9 agonists in animal studies 23 1 .6 . 1 0 antagonists in animal studies 28 1 .6 . 1 1 Dg agonists in animal studies 28 1.6.12 Dg antagonists in animal studies 30 1.6.13 Dopamine and epilepsy: Current progress 30 1.7 Anatomical structures related to epilepsy 32 1.7.1 The hippocampus: Neurocircuitry 32 1.7.2 Hippocampal afferent connections 33 1.7.3 Hippocampal intrinsic pathways 33 1.7.4 Hippocampal efferent connections 35 1.7.5 The hippocampus and seizures 35 1.7.6 The basal ganglia 37 1.7.7 The basal ganglia and epilepsy 39 1.7.8 The Islands of Calleja 40 1.8 Pilocarpine seizure model 41 1.9 In vitro models of epileptiform activity 42 1.10 Aims of this work 44 Chapter Two Materials and Methods 2.1 Animals 47 2.2 Stereotaxic surgical procedures 47 2.2.1 Stereotaxic injections and seizure induction 47 2.2.2 Statistical analysis 48 2.2.3 Drugs 49 2.3 Histology 50 2.4 In vitro cingulate cortex slice electrophysiology 50 V l l Tcèle o f Contents 2.4.1 Preparation of cortical slices 50 2.4.2 Recording of epileptiform activity 52 2.4.3 Drug application 52 2.4.4 Data analysis 55 2.4.5 Drugs 55 2.5 Biochemical analysis of dopamine metabolism during pilocarpine-induced status epilepticus 56 2.5.1 Animals and tissue preparation 56 2.5.2 High performance liquid chromatography 57 2.5.3 Data analysis 57 2.5.4 Materials 57 Chapter Three Modulation of pilocarpine-induced limbic motor seizures by hippocampal and D. receptors. 3.1 Introduction 63 3.2 Results 64 3.2.1 Bilateral intrahippocampal injections of saline followed by systemic pilocarpine 64 3.2.2 Bilateral intrahippocampal injections of SKF 38393 followed by systemic pilocarpine 64 3.2.3 Bilateral intrahippocampal injections of SCH 23390 followed by systemic pilocarpine 70 3.2.4 Systemic injections of SKF 38393 versus seizures induced by intrahippocampal pilocarpine 70 3.2.5 Effect of bilateral intrahippocampal LY 171555 versus systemic pilocarpine 71 3.2.6 Effect of intrahippocampal LY 171555 on seizures induced by intrahippocampal carbachol 74 V l l l Table o f Contents 3.2.7 Bilateral intrahippocampal raclopride followed by a threshold dose of systemic pilocarpine 74 3.2.8 Combined intrahippocampal pretreatment with SKF 38393 and raclopride versus a threshold dose of systemic pilocarpine 77 3.3 Discussion 3.3.1 The role of hippocampal Dg receptors in limiting epileptogenesis 82 3.3.2 The role of hippocampal D^ receptors in epileptogenesis 85 3.3.3 Seizure modifying hippocampal D^ and Dg receptors: Possible mechanisms 8 8 3.3.4 The nucleus accumbens as a site for pilocarpine-induced epileptogenesis 90 3.3.5 Clinical implications 91 3.3.6 Conclusion 93 Chapter Four Effects of dopamine Dj receptor agonists on pilocarpine-induced limbic seizures. 4.1 Introduction 95 4.2 Results 98 4.2.1 Control seizures induced by pilocarpine 98 4.2.2 Bilateral intra-accumbens injection of saline versus systemic SKF 38393 and pilocarpine-induced seizures 98 4.2.3 Bilateral intra-accumbens injections of apomorphine versus systemic SKF 38393 and pilocarpine-induced seizures 99 4.2.4 Bilateral intra-accumbens injections of Dg agonists versus systemic SKF 38393 and pilocarpine-induced seizures 99 4.2.5 Bilateral intracallejal injection of saline versus systemic IX Table o f Contents SKF 38393 and pilocarpine-induced
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