NOREPINEPHRINE INJECTIONS IN DIAGONAL BAND OF BROCA SELECTIVELY REDUCE THE ACTIVITY OF VASOPRESSIN SUPRAOPTIC NEURONS IN THE RAT

In the rat, transient drug-induced elevations of arterial blood pressu re, which are sufficient to activate peripheral baroreceptors, produce a brief and selective cessation in the spontaneous activity of vasopr essin-secreting cells in the hypothalamic supraoptic nucleus. This res ponse appears to require the noradrenergic innervation of the diagonal band of Broca. The present study evaluated whether injections of nore pinephrine into the diagonal band of Broca affect the spontaneous acti vity of supraoptic vasopressin-secreting neurons. Extracellular record ings were obtained from antidromically identified supraoptic neurons i n pentobarbital anesthetized rats using a transpharyngeal approach. In jections of 200 nl of 10 muM norepinephrine into the diagonal band of Broca region arrested the spontaneous activity of 80% (12/15) of vasop ressin-secreting neurons but only 7% (1/14) of oxytocin secreting-neur ons demonstrated a comparable decrease in excitability. Vehicle inject ions did not influence the activity of any of the neurons tested. Thes e results are consistent with the hypothesis that the baroreceptor-sen sitivity of vasopressin neurons is mediated by a noradrenergic mechani sm in the diagonal band of Broca.