Susceptibility of the developing rat gustatory system to the physiological effects of dietary sodium deprivation

1. Multifibre responses were recorded from the chorda tympani nerve in rats fed either a NaCl-deficient diet or a NaCl-replete diet from 3 days post-conception to at least 28 days post-natal. Responses were also recorded in rats fed the NaCl-deficient diet during early development and then fed the NaCl-replete diet for 1-20 days beginning at 28 days post-natal, and in rats fed the NaCl-deficient diet only as adults. The epithelial sodium transport blocker, amiloride, was used to study the physiological effects of the diet on taste receptor membrane function and to characterize the events involved in recovery of function. 2. Responses to lingual application of sodium salts increased with increasing stimulus concentration; however, response magnitudes were reduced in rats fed the NaCl-deficient diet during early development compared to controls. Responses to non-sodium salts and non-salt stimuli were similar to controls. Amiloride was ineffective in suppressing taste responses to NaCl in deprived rats but effectively suppressed responses in controls by at least 50%. After early-deprived rats were fed a NaCl-replete diet, responses to sodium salts recovered to control levels within 15 days. There was a concomitant decrease in amiloride sensitivity during this period. 3. Rats fed the NaCl-deficient diet from early gestation through adulthood had responses similar to younger deprived rats in that sodium responses were lower than controls. However, rats deprived only as adults were similar to controls. 4. The peripheral gustatory system in developing rats is susceptible to the sodium content of the diet and is 'plastic' in that early effects can be reversed by restricting dietary sodium. Once dietary manipulations are instituted past a sensitive period, however, functional taste responses seem unaffected.