[Changes in the effect of acetylcholine on septo-hippocampal reactions after serotonin administration to rabbits].

Impulse activity and focal evoked potentials appearing in the hippocampus in response to testing stimuli applied to the septum medial nucleus were recorded in nonimmobilized and unanaesthetized rabbits. The efficiency of acetylcholine (ACh) action on septo-hippocampal reactions was tested before and after microiontophoretic administration of the serotonin (5-OT) or stimulation of the raphe nuclei. The 5-OT and raphe stimulation produced significant changes in the ACh action on septo-hippocampal reactions. In most cases, after microiontophoretic administration of 5-OT, the efficiency of ACh diminished, independently of excitatory or inhibitory effect of the 5-OT. Thus, the modulating action of 5-OT consists not only in protracted trace changes of the magnitude of septo-hippocampal reactions but also in trace reduction of septo-hippocampal responses to ACh.