Solitary nucleus excitation of supraoptic vasopressin cells via adrenergic afferents

Recent studies confirm that the supraoptic nucleus (SON) receives a direct projection from the nucleus of the solitary tract (NTS). We have examined the effect of NTS stimulation on antidromically identified SON neurosecretory cells that were classified as arginine vasopressin (AVP) or oxytocin (OXY) secreting in accord with basal activity patterns and responsiveness to arterial baroreceptor activation. Medial NTS stimulation at the level of the obex or area postrema excited 78% (59 of 76) of putative AVP cells (onset latency 52 +/- 1 ms) but only 20% (3 of 15) of putative OXY cells. Commissural NTS stimulation did not excite AVP cells (n = 13). After complete SON catecholamine afferent disruption, achieved by local injection of 6-hydroxydopamine, AVP cells tested were unresponsive to medial NTS stimulation (12 of 13), although arterial baroreceptor activation inhibited four of four cells. These data indicate that medial NTS stimulation preferentially excites SON AVP cells and that this effect involves an adrenergic input to SON. A direct projection from the A2 catecholamine cell group of the NTS may be involved, although the long latency to excitation and the poor correspondence between effective NTS stimulation sites and the location of the A2 group within NTS raise the possibility that a relay projection, possibly through the A1 catecholamine cell group of the ventrolateral medulla, may be involved.