Septal cholinergic mediation of hippocampal theta in the cat

The effects of intraseptally microinjected muscarinic (atropine sulfate, pirenzepine and gallamine) and nicotinic (hexamethonium) antagonists on spontaneous, sensory and electrically-induced hippocampal (HPC) theta EEG activity were investigated in the freely behaving cat. Administration of hexamethonium failed to elicit a detectable effect on H PC theta. Injections of atropine and pirenzepine abolished, whereas the injection of gallamine only reduced hippocampal theta. Moreover, a gradual recovery of theta amplitude and power was observed, while frequency recovered rapidly. Our data provide further evidence that the septal M1 and M2 muscarinic receptor subtypes mediate the HPC theta in this species. Intraseptal microinjection of cholinergic agonist (carbachol) produced almost a continuous HPC theta with increased amplitude and power. The contribution of the medial septal cholinergic projections to HPC theta frequency and amplitude was also discussed. (C) 2002 Elsevier Science Inc. All rights reserved.