Effects of stimulation of the hypothalamic paraventricular nucleus on blood pressure and renal sympathetic nerve activity.

Effects of electrical and chemical stimulation of the paraventricular nucleus (PVN) of the hypothalamus on blood pressure were examined in rats anesthetized with urethane-chloralose. Focal electrical stimulation (10-25 microA, 50 Hz, 0.5 msec) within the PVN consistently decreased blood pressure. Microinjection of L-glutamate (0.5 M, 80 n1) into the PVN led to a decrease in blood pressure, while the same amount of saline injection had no effect. The depressor response was not affected by cervical vagotomy. In order to obtain direct evidence for involvement of sympathetic nerve activity in the PVN-induced depressor response, effects of PVN stimulation on renal sympathetic nerve activity were examined. Low intensity electrical stimulation of the PVN inhibited renal sympathetic nerve activity, whereas the high intensity stimulation evoked a transient excitation followed by long lasting inhibition in renal sympathetic nerve activity. Latencies of the inhibitory and the excitatory responses were about 200 msec and 50-100 msec, respectively, judged by peristimulus time histograms. The result suggests that activation of PVN neurons produces a decrease in blood pressure due to inhibition of sympathetic outflows.