The effects of chlormethiazole on single unit activity in rat brain; interactions with inhibitory and excitatory neurotransmitters

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Abstract
1 Extracellular recordings were made of single unit activity in the brainstem of urethane anaesthetized rats. Drugs were applied by microiontophoresis from multibarrelled micropipettes or administered intraperitoneally. 2 Chlormethiazole (CMZ) caused a decrease in spontaneous firing rate when applied with high currents (>40 nA). 3 When applied with lower currents CMZ did not cause changes in firing rate, but enhanced the inhibitory effects of γ-aminobutyric acid (GABA), muscimol and glycine in a dose-dependent manner. The inhibitory actions of acetylcholine were not affected. 4 Excitatory responses to glutamate and acetylcholine were unaffected by applications of CMZ which caused potentiation of GABA, muscimol and glycine. When applied at higher currents CMZ caused a decrease in the response to glutamate. 5 Intraperitoneal administration of CMZ (50–600 μmol kg−1) also enhanced responses to microiontophoretically applied GABA, muscimol and glycine. 6 These results are compared with those reported for other anticonvulsant drugs and possible mechanisms of action of CMZ are discussed.