Brain stem afferents to the rat medial septum.

Abstract

Activity of neurons in the medial septal nucleus and the diagonal band was recorded from urethane anesthetized rats. Responses of the cells to electrical stimulation of the raphe nuclei and nucleus locus coeruleus (LC) were measured. LC stimulation caused a long latency, 30-100 ms, and long duration, 100-300 ms, cessation of spontaneous activity of most recorded neurons. When bursting-type neurons were recorded, the stimulation occasionally caused a synchronized repetitive bursting firing pattern. Pre-treatment with drugs which interfere with catecholamine neurotransmission, i.e., reserpine and 6OHDA [6-hydroxydopamine], prevented the appearance of cellular responses to LC stimulation. Stimulation of the dorsal or the median raphe nuclei generated more complex and less clear-cut responses. These included several types of long (20-50 ms) and short (2-5 ms) latency responses. These responses were also accompanied in some cells by synchronized repetitive bursting. Interference with serotonin neurotransmission with PPCA [DL-p-chlorophenylalanine methyl ester hydrochloride] or reserpine reduced the detection of long latency responses. Short latency responses accompanied by evoked field potentials were recorded also after stimulation of dorsal tegmental nucleus. Rates of spontaneous firing cells were augmented after monoamine neurotransmission interruption; after fornix lesion, when there is supposedly an increased monoamine innervation of the septum, cells fire at lower rates than normal. Noradrenaline and serotonin may serve as neurotransmitters in the medial-septum-diagonal band areas.