Institution of a low-NaCl diet beginning at embryonic day 3 and continued throughout pre-and postnatal development has widespread effects on the neuroanatomical organization of the first gustatory relay in the nucleus of the solitary tract. To determine when these effects are expressed postnatally, the terminal field of the chorda tympani nerve was compared between sodiumrestricted and sodium-replete rats at postnatal days 15-17, postnatal days 25-27, postnatal days 35-37, and adults. Total terminal fields were significantly larger in postnatal days 35-37 and adult sodium-restricted rats compared with aged-matched controls. The group-related differences appear related more to a remodeling of the terminal field in the dorsal zone of the terminal field in controls. Specifically, the terminal field volume in the dorsal zone in controls decreased dramatically from postnatal days 25-27 to postnatal days 35-37 and then again from postnatal days 35-37 to adulthood. In contrast, the fields did not change during development in sodiumrestricted rats. These findings suggest that remodeling of the chorda tympani field occurs in controls at about the developmental period of taste response maturation. The lack of remodeling in sodium-restricted rats may be explained by a corresponding lack of functional response development to sodium salts. These results also illustrate the specificity and extent of how early dietary manipulations shape the developing brainstem.

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Taste thresholds for sucrose, NaCl, QHCl and citric acid were examined over the lifetime of seven rats. Significant yet subtle decreases in taste sensitivity were observed in the oldest subjects only.

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