A direct hepatic osmoreceptive afferent projection from nucleus tractus solitarius to dorsal hypothalamus

Thirty units that responded antidromically to electrical stimulation of the zona incerta (ZI) or the dorsal portion of hypothalamus were recorded in the nucleus tractus solitarii (NTS). These units were analyzed in relation to hepatoportal afferent inputs. Electrical stimulation of the hepatic branch of the vagus nerve facilitated six units (facilitatory units) and suppressed 10 units (suppressed units). Effect of the portal infusion of hypertonic saline was examined on six facilitatory and eight suppressed units. One facilitatory unit and one suppressed unit increased their discharge rates in response to portal infusion. Four facilitatory units and one suppressed unit decreased their discharge rates in response to the same stimulation. Increased or decreased discharge rates in response to portal infusion of hypertonic saline were observed in units that responded antidromically to electrical stimulation of the paraventricular hypothalamic nucleus, the lateral hypothalamic area, or the ZI. It is concluded that hepatoportal osmoreceptive signals are conveyed to the hypothalamus or the ZI directly from the NTS.