Muscarinic (M1) mediation of hippocampal spontaneous theta rhythm in freely moving cats.

The effects of intrahippocampally applied different doses of muscarinic (atropine sulphate, pirenzepine, gallamine) and nicotinic (hexamethonium, mecamylamine) antagonists on the spontaneous theta rhythm in the cat hippocampal formation were investigated. The injections of atropine and pirenzepine abolished spontaneous theta but administration of gallamine did not affect the EEG pattern. The intrahippocampally administered nicotinic blockers, hexamethonium and mecamylamine, were completely ineffective in antagonizing theta waves. The data suggest that the spontaneous theta rhythm in the cat is mediated by the M1 receptor subtype.