MUSCARINIC (M1) MEDIATION OF HIPPOCAMPAL SPONTANEOUS THETA RHYTHM IN FREELY MOVING CATS

THE effects of intrahippocampally applied different doses of muscarini c (atropine sulphate, pirenzepine, gallamine) and nicotinic (hexametho nium, mecamylamine) antagonists on the spontaneous theta rhythm in the cat hippocampal formation were investigated. The injections of atropi ne and pirenzepine abolished spontaneous theta but administration of g allamine did not affect the EEG pattern. The intrahippocampally admini stered nicotinic blockers, hexamethonium and mecamylamine, were comple tely ineffective in antagonizing theta waves. The data suggest that th e spontaneous theta rhythm in the cat is mediated by the M1 receptor s ubtype.