Neurophysiology of a central baroreceptor pathway projecting to hypothalamic vasopressin neurons

Controversy exists as to the neural network whereby peripheral arterial baroreceptor information is transmitted to vasopressin (VP)-secreting neurons of the hypothalamic supraoptic nucleus (s.o.n.). In vivo electrophysiological studies in the rat were undertaken to characterize the selective depression of VP cell activity consequent to activation of peripheral baroreceptors. Electrical stimulation of the diagonal band of Broca (DB) in the rat evoked a similar selective inhibition of vasopressinergic neurons of the s.o.n. Local application of bicuculline, a GABA antagonist, abolished both the DB-evoked and baroreceptor-induced inhibition of VP-secreting neurons. In addition, recordings from DB neurons antidromically activated from the s.o.n. displayed an increase in firing consequent to baroreceptor activation, coinciding with the suppression of firing in s.o.n. VP neurons. These observations collectively indicate that an intrinsic GABA projection arising in the DB cell group selectively inhibits vasopressinergic neurons of the s.o.n. and that this pathway mediates peripheral arterial baroreceptor activity that influences the release of VP in the neurohypophysis. These data may be of critical importance in our understanding the etiology of those forms of experimental hypertension where abnormalities in central baroreceptor pathways have been implicated but not proven.