Behavioral and electrophysiological taste responses change after brief or prolonged dietary sodium deprivation

Dietary Na⁺ deprivation elicits a hormonal response to promote sodium conservation and a behavioral response to increase sodium ingestion. It has generally been accepted that the former occurs within 24 h after sodium deprivation, while the latter is delayed and may not appear until as much as 10 days later. Na⁺ deprivation of similar duration also decreases the sensitivity of the chorda tympani nerve (CT) to NaCl, suggesting that changes in CT responses are necessary for increased NaCl intake. However, previous work from our laboratory showed that licking responses to NaCl solutions increase after only 2 days of Na⁺ deprivation, suggesting rapidly occurring changes in response to NaCl taste. The present experiments examined the effects of 2 days of dietary Na⁺ deprivation on CT responses to NaCl and patterns of NaCl consumption and found that Na⁺-deficient rats licked significantly more during the first NaCl intake bout compared with control rats. CT responses to NaCl were reduced at all concentrations after brief Na⁺ deprivation compared with Na⁺-replete control rats and did not decrease further with prolonged (10 days) dietary Na⁺ deficiency. Moreover, amiloride, which suppressed CT responses to NaCl by ∼30% in control rats, had virtually no effect on CT responses in Na ⁺-deprived rats. Thus, 2 days of Na⁺ deprivation is sufficient to alter patterns of ingestion of concentrated NaCl and to reduce gustatory responses to NaCl. Furthermore, changes in gustatory responses to NaCl during dietary Na⁺ deprivation may involve the amiloride-sensitive component of the CT.