ABSTRACT
Unit discharges of neurons of the hypothalamic ventromedial nucleus region (HVM) and its surrounding structures including paraventricular nucleus, anterior hypothalamic area,and hypolhalamic dorsomcdial nucleus, were recorded in the ureth-ane-anesthetized and flaxidel-immobilized rats. In HVM,8 of 82 units showed periodical fluctuations in discharge rate, which could be categorized into two types: (1) With alternating active and silent phases 5 (2) with gradually waxing and waning phases. The duration of cach cycle varied from 1 to 5 minutes in different neurons. The periodicity disappeared after intraperitoneal injection of nembutal, while the average discharge rate was raised somewhat. This result suggested that the depressing pha-s of periodical activity of the HVM neuron might probably result from the inhibitory action in certain neuronal circuit, rather than from the intrinsic property of the recorded neurons. The effect of picrotoxin was contradictory. No periodical activity was noted in the 47 recorded neurons outside of the HVM.