RESPONSES OF SEPTAL THETA-ON AND THETA-OFF CELLS TO ACTIVATION OF THE DORSOMEDIAL-POSTERIOR HYPOTHALAMIC REGION

The effect of different levels of electrical stimulation of the dorsomedial-posterior hypothalamic region, on the discharge properties of septal θ-on and θ-off cells, was investigated in urethane-anesthetized rats. In the present sample of 45 cells recorded in the medial septum/ventral limb of the diagonal band of Broca, 43 of the 45 (96%) were affected by the stimulation. The majority of θ-on cells were intensely activated by this stimulation (two were inhibited) and all θ-off cells were inhibited (ranging from partial to complete inhibition). Stimulation did not change a cell's classification as "on" or "off", nor did it alter its discharge pattern (phasic or tonic). Stimulation did have a profound effect on phasic nonlinear θ-on cells. Phasic nonlinear θ-on cells, by definition, did not alter their discharge rate in relation to the increasing frequency of spontaneously occurring or tail-pinch-induced θ. However, stimulation of the dorsomedial-posterior hypothalamus resulted in 11 out of 13 (85%) of the phasic nonlinear cells increasing their discharge rates in relation to the increasing frequency of the hypothalamically induced θ (i.e., became linear). Stimulation had no effect on two cells classified as unrelated to θ. © 1990.