Involvement of septal muscarinic receptors in cholinergically mediated changes in rat rearing activity.

We tested the hypothesis that septal muscarinic receptors of the rat are involved in exploratory behavior control, at least as reflected in the measure of rearing activity. At a dose capable of inducing hippocampal theta rhythm, carbachol injection into the septum significantly increased the number of rearings from the 2nd to the 5th min postinjection. The increase was maximal in the 3rd min and gradually declined until the 9th min postinjection, when it was near the control level. This behavioral effect was blocked by prior injection of atropine. These data, when considered with other findings showing a similar motor response caused by the hippocampal injection of the cholinergic agonist, strongly suggest that the cholinoceptive cholinergic components of the septohippocampal system play a role in the release of exploratory behavior. This role might be mediated via muscarinic receptors at the septal level. Moreover, the time course of behavioral action of carbachol injected into the septum is of particular importance for studies on the effect of the drug on performance of the rat in learning and memory tests requiring contribution of exploratory behavior.