Thirst and salt appetite elicited by hypovolemia in rats with chronic lesions of the nucleus of the solitary tract

Cardiac vagal afferents terminating in the nucleus of the solitary tract (N TS) are believed to participate in stimulating neurohypophysial secretion o f vasopressin as well as increased ingestion of water and NaCl solution in response to decreased blood volume. However, we recently reported that chro nic lesions of NTS, which eliminate neural input from cardiac and arterial baroreceptors, do not impair hypovolemia-induced vasopressin secretion in r ats. In the present investigation we sought to determine whether those sens ory signals were necessary for hypovolemia-induced thirst and salt appetite . Rats with chronic lesions of the NTS increased consumption of water and N aCl solution normally when plasma volume was reduced isosmotically by subcu taneous injection of polyethylene glycol solution. These results were obtai ned whether rats were allowed to drink water or 0.15 M NaCl in one-bottle t ests or water and 0.5 NI NaCl in two-bottle tests. The induction of thirst and salt appetite by hypovolemia despite the apparent loss of neural input to the brain from cardiac volume-sensitive receptors indicates that other s ignals generated by plasma volume deficits can stimulate these behavioral r esponses in rats.