Ž . European Journal of Pharmacology 373 1999 153–161 www.elsevier.nlrlocaterejphar Effects of diazepam on extracellular brain neurotransmitters in pilocarpine-induced seizures in rats Ghous M. Khan a , Ilse Smolders a , Hilde Lindekens a , Jacqueline Manil b , Guy Ebinger c , Yvette Michotte a, ) a Department of Pharmaceutical Chemistry and Drug Analysis, Vrije UniÕersiteit Brussel, Laarbeeklaan 103, 1090 Brussels, Belgium b Department of Physiology and Physiopathology, Vrije UniÕersiteit Brussel, Laarbeeklaan 103, 1090 Brussels, Belgium c Department of Neurology, Vrije UniÕersiteit Brussel, Laarbeeklaan 103, 1090 Brussels, Belgium Received 16 July 1998; received in revised form 19 March 1999; accepted 23 March 1999 Abstract The present study was undertaken to gain insights into the mechanism of action of diazepam in focally-evoked pilocarpine-induced Ž . seizures by concomitantly assessing the changes produced in the extracellular levels of glutamate, GABA g-aminobutyric acid and Ž . dopamine. In vivo microdialysis, coupled to continuous monitoring of electrocorticographic ECoG recordings, was performed in freely Ž . moving rats. Intrahippocampal perfusion with 10 mM pilocarpine 40 min, 2 mlrmin produced limbic seizures. A single dose of Ž . intraperitoneal diazepam 5 mgrkg was administered 2 h after pilocarpine perfusion was started. Dialysates were sampled both from hippocampus and cerebellum and analysed by microbore liquid chromatography. Diazepam produced instant inhibition of behavioural and ECoG seizure activity. Pilocarpine-induced increases in the extracellular levels of glutamate and dopamine in hippocampus were promptly reduced by diazepam. No concurrent alterations in pilocarpine-induced increases in the extracellular levels of GABA in either hippocampus or cerebellum were seen. Pilocarpine enhanced cerebellar glutamate levels only transiently and levels returned to baseline before diazepam administration. No further changes in cerebellar glutamate levels were observed with diazepam. Our findings suggest that the anti-convulsant action of diazepam against pilocarpine-induced seizures is associated with a prompt attenuation of extracellular hippocampal glutamate overflow without concurrent alteration of pilocarpine-induced increases in endogenous GABA levels. Diazepam also significantly decreased pilocarpine-induced increases in extracellular dopamine levels within the hippocampus. No immediate alterations of the basal levels of the neurotransmitters monitored were observed with diazepam. q 1999 Elsevier Science B.V. All rights reserved. Ž . Keywords: Microdialysis; Electrocorticography; Glutamate; GABA g-aminobutyric acid ; Dopamine; Pilocarpine; Diazepam; Hippocampus; Cerebellum 1. Introduction Systemic diazepam is a well-established therapeutic approach to produce a prompt anti-convulsant effect when administered during an episode of seizures. Diazepam and other benzodiazepine mostly exert their pharmacological actions by allosterically modulating the GABA –benzodi- A azepine receptor complex to produce a facilitatory effect Ž . on the GABA g-aminobutyric acid -mediated inhibitory Ž . neurotransmission in the CNS central nervous system Ž Macdonald and Olsen, 1994; Costa and Guidotti, 1996; . Hoogerkamp et al., 1996 . At least part of the mechanism ) Corresponding author. Tel.: q32-2-4774744; Fax: q32-2-4774113 of action of benzodiazepines has been suggested to be mediated by an increase in the adenosine concentration Ž . Phillis and O’Regan, 1988 . Adenosine has a putative role in presynaptic inhibition of evoked release of glutamate and other neurotransmitters in the hippocampus. Although studies involving receptor binding and immunocytochemi- cal techniques have greatly illuminated the receptor mech- anism of action of benzodiazepines, the modulatory roles of the pertinent neurotransmitters in terms of their extracel- lular concentrations remain largely obscure. There is evidence that veratridine or K q -evoked in- creases in extracellular glutamate concentrations are de- Ž . creased by diazepam Baba et al., 1983 . The specific protective effect of diazepam against isoniazid-induced seizures was observed without any concomitant change in Ž . extracellular GABA levels Bernasconi et al., 1985 . Acute 0014-2999r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0014-2999 99 00209-5