A hepatoportal osmoreceptive afferent projection from nucleus tractus solitarius to caudal ventrolateral medulla.

This study was performed to examine projection of nucleus tractus solitarii (NTS) neurons to the caudal ventrolateral medulla (cVLM) in rats. One hundred and seven neurons that responded antidromically to electrical stimulation of the cVLM were recorded within the NTS. Electrical stimulation of the hepatic branch of the vagus nerve (hepatic vagus) elicited facilitation on 62 neurons (facilitatory neurons) and suppression on 6 neurons (suppressed neurons). Effect of portal infusion of hypertonic saline was examined on 44 facilitatory and 4 suppressed neurons. Twelve facilitatory and 2 suppressed neurons showed a decrease in the discharge rate. One suppressed neuron showed an increase in the discharge rate. It is concluded that hepatoportal osmoreceptive signals are conveyed from the NTS to the cVLM. The responses are mostly characterized by the decrease in the discharge rate by portal infusion of hypertonic saline.