MUSCARINIC (M1)-MEDIATION OF CARBACHOL-INDUCED THETA IN THE CAT ENTORHINAL CORTEX IN-VITRO

ENTORHINAL cortex slice preparations obtained from the cat exhibited t heta rhythm during perfusion with 50 mu M carbachol. The effect of car bachol was antagonized by the muscarinic blocker atropine sulphate, bu t not by hexamethonium and mecamylamine, which are antagonists of the nicotinic receptor. Further analysis of the pharmacological profile of these carbachol-induced theta oscillations showed the M1 receptor sub type to be involved in mediation of this EEG activity: the theta rhyth m was antagonized by the M1 receptor blocker pirenzepine, but was unaf fected by gallamine, an antagonist of the M2 receptor subtype.