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 pressure, which are sufficient to activate peripheral baroreceptors, produce a brief and selective cessation in the spontaneous activity of vasopressin-secreting cells in the hypothalamic supraoptic nucleus. This response appears to require the noradrenergic innervation of the diagonal band of Broca. The present study evaluated whether injections of norepinephrine into the diagonal band of Broca affect the spontaneous activity of supraoptic vasopressin-secreting neurons. Extracellular recordings were obtained from antidromically identified supraoptic neurons in pentobarbital anesthetized rats using a transpharyngeal approach. Injections of 200 nl of 10 muM norepinephrine into the diagonal band of Broca region arrested the spontaneous activity of 80% (12/15) of vasopressin-secreting neurons but only 7% (1/14) of oxytocin secreting-neurons demonstrated a comparable decrease in excitability. Vehicle injections did not influence the activity of any of the neurons tested. These results are consistent with the hypothesis that the baroreceptor-sensitivity of vasopressin neurons is mediated by a noradrenergic mechanism in the diagonal band of Broca.