Responses of phasic and tonic hippocampal theta-on cells to cholinergics: differential effects of muscarinic and nicotinic activation.

The discharge patterns of tonic and phasic hippocampal formation theta-on cells were recorded in response to systemic administration of cholinergic agents, in urethane-anesthetized rats. Eserine and carbachol resulted in long trains of slow-wave theta and accompanying activation of tonic and phasic theta-on cells. Both slow-wave theta and the characteristic accompanying discharge patterns of theta-on cells were blocked by administration of atropine SO4, providing evidence that the effects of eserine and carbachol were mediated by muscarinic receptors. The systemic administration of nicotine resulted in 20-30 s of slow-wave theta and during this time, both tonic and phasic theta-on cell discharges were suppressed.