HIPPOCAMPAL EEG RESPONSES INDUCED BY CARBACHOL AND ATROPINE INFUSIONSINTO THE SEPTUM AND THE HIPPOCAMPUS IN THE URETHANE-ANESTHETIZED RAT

Infusion of 1 mu g of carbachol, a potent cholinergic agonist, into th e lateral septum of the urethane-anaesthetized rat systematically caus ed the induction of clear-cut hippocampal theta (theta). However, infu sion of an equivalent amount of the drug into the hippocampus, close t o the recording electrode, failed to induce theta in 50% of the animal s and produced a mixture of theta waves and desynchronized activity, r esulting in atypical EEG patterns, in the remaining subjects. Both car bachol EEG effects were blocked by intraseptal infusion of the antimus carinic agent, atropine. Our data demontrate that muscarinic receptors in the septum are predominent sites for cholinergic agonist-antagonis t action capable of generating or suppressing hippocampal theta in the rat. They also indicate that intraseptal cholinergic mechanisms play an important role in the initiation and generation of this rhythm.