Cholinergically-induced theta-like oscillations in the hippocampal formation of freely moving cats

The present investigation was undertaken to assess the role of the cholinergics in the production of theta (theta) rhythm in the cat hippocampal formation. Intrahippocampal injections of carbachol, muscarine or eserine produced a well synchronized high frequency cholinergic theta activity (HFC) in a range of 5-12 Hz. Subsequent intrahippocampal injection of muscarinic antagonist, atropine sulphate, completely blocked this cholinergic-induced EEG pattern. The nicotinic antagonist, hexamethonium, was without any effect on the cholinergic-induced rhythmical waves. We suggest that HFC may result from the activation of the oscillatory mechanism intrinsic to the cat hippocampal formation.