[The modulation of septal influences on the hippocampal neurons by cholinergic substances].

To evaluate the functional significance of the cholinergic component of the septo-hippocampal input the effects of electrical stimulation of the medial septal area (MS--DB) on the hippocampal neurons were studied in chronic waking rabbits. Initial inhibitory effects 40-140 msec long were observed in 54% of neurons in intact rabbits. Other neurons usually responded by a diffuse excitation. Initial inhibitory effects absolutely dominated (90%) in the animals with the septum basally undercut. Increase of the endogenous acetylcholine level by physostigmine completely or partially blocked the effects of the stimulation in 78% of the hippocampal neurons at the background of increased theta-modulation. Scopolamine restored responsiveness of the neurons to the MS--DB stimulation. These effects were preserved in the animals with the septal undercutting. It is concluded that the general effect of the MS--DB on the hippocampal neurons consists in a non--cholinergic (GABA-ergic) primary suppression (reset) of their activity. The cholinergic component limits the efficacy of both extraseptal (brainstem) and septal inhibitory influences.