Sensory responsiveness of single cells in the medial septal nucleus in intact and hypothalamic-deafferented rats

Abstract

The effects of sciatic, acoustic, and photic stimuli on spontaneous single cell activity were studied in the medial septal nucleus in intact rats and in animals with chronic bilateral lesions of the medial forebrain bundle, complete hypothalamic deafferentations, and small posterior hypothalamic deafferentations. The changes in the rate and pattern of unit firing were analyzed statistically and the responsiveness compared between the intact rats and those with lesions. The spontaneous activity of about one-half of the units was affected by the sensory stimulation and there was a convergence of more than one modality on the same neuron. Units which had a lower rate of firing were facilitated and those which had a higher rate of firing were inhibited by sensory stimulation. The marked changes in the rate of firing were not accompanied by alterations in pattern of discharge. In rats with hypothalamic islands the mean spontaneous firing rate was increased; however, the percentage of the responsive cells and the degree of convergence were significantly reduced. The present data demonstrate extensive sensory projections and convergence in the septum, the transmission of the responses by the mediobasal hypothalamus, and modulation by the latter of septal electrical activity.