Action of anticholinergic drugs and their combinations with pentobarbital on theta burst neurons of the rabbit septum.

Abstract

1. Intravenous administration of scopolamine or atropine eliminates or decreases the stability of burst activity of cells of the medial nucleus and the nucleus of the diagonal band of the septum (MS-DB) with weak theta modulation and the theta rhythm on the hippocampal EEG. 2. Physostigmine, on the other hand, increases the stability of rhythmical bursts of many neurons, and in some cells the theta bursts reappear. 3. Neither scopolamine (atropine) nor physostigmine exert an action on the frequency of theta bursts or on the characteristics of theta cycles of MS-DB cells, irrespective of their initially low or high background frequency. 4. Sensory or reticular stimulation against a background of action by scopolamine or atropine may evoke theta activity in septal cells that have lost it, and also the theta rhythm on the hippocampal EEG. 5. Neurons with hyperstable theta bursts retain the stable rhythmical activity even under conditions of combined administration of maximum doses of choline-blockers and anesthetics. 6. The effect of choline-blockers is not selective as regards any frequency ranges of the rhythmical activity of the septal neurons. A proportion of septal hippocampal connections participating in the generation of the EEG theta rhythm are of a noncholinergic nature. 7. The concept of a single (septal) source of generation of the whole range of theta frequencies is proposed.