Neuroanatomical alterations in the rat nucleus of the solitary tract following early maternal NaCl deprivation and subsequent NaCl repletion

Abstract

Restricting the NaCl content in the rat maternal and preweaning diet results in a significant and specific reduction (60%) of chorda tympani nerve responsiveness to sodium stimuli in the offspring. Repletion of dietary sodium at any time during postnatal development results in a complete and persistent recovery of chorda tympani nerve function. To learn whether the maturation of postsynaptic cells are also affected by the early dietary manipulation, dendritic morphology, neuronal and glial densities and numbers were studied within the area of the nucleus of the solitary tract (NTS). Examination of dendritic morphologies in Golgi-Cox stained neurons revealed that cells with multipolar and fusiform somata in the rostral NTS exhibited longer dendrites following dietary NaCl deprivation during development (deprived rats) than in controls. These changes were generally maintained in rats initially deprived of NaCl and then fed a NaCl-replete diet postweaning ("recovered" rats). In contrast, ovoid neurons were not affected by NaCl deprivation but had increases in the lengths of their dendrites following "recovery." Along with dendritic alterations, the packing density of neurons in the rostral NTS was greater in NaCl-deprived rats than in controls, but was similar to controls following "recovery." Glial packing density also increased following deprivation and remained high in "recovered" rats. These results indicate that activity-dependent events as well as events not related to afferent activity (e.g., hormonal changes) may influence the morphological development of NTS neurons. In addition, significant interactions among primary afferent fibers, central neurons, and glia may direct development within the central gustatory system.

Age-related decrease of the chorda tympani nerve terminal field in the nucleus of the solitary tract is prevented by dietary sodium restriction during development

“…Further morphological alterations occur in the structure of neurons located within the NTS. The dendritic organization of NTS neurons in developmentally sodium restricted rats and in restricted rats fed the sodium replete diet after weaning are much different than that in control rats (King and Hill, 1993). The dendrites of putative relay neurons, multipolar and fusiform neurons, are longer and/or have more dendritic processes in sodium restricted rats compared with controls.…”

Maturation of neuron types in nucleus of solitary tract associated with functional convergence during development of taste circuits

“…In contrast to elongate and multipolar neurons, the primary dendrites of ovoid cells extended over a long distance and exhibited little or no branching. Other investigators described these basic neuron categories in the NST of rat (Lasiter, Wong and Kachele, 1989;King and Hill, 1993) and hamster (Whitehead, 1988 sionally identified neurons with characteristics similar to those categorized as "tufted" by Whitehead (1988) in adult hamster NST. However, tufted neurons were seen so infrequently in our sections of rostra1 NST that they are not included for data quantification.…”

Neural Plasticity in the Gustatory System

“…Specific cell types in the rostral pole of the adult rat NTS restricted of dietary sodium from E3 show pronounced and permanent increases in dendritic length and number, whereas other cell types are spared. 57 Neurons affected by dietary restriction are putative relay neurons. 58 These data strongly suggest that the morphological effects of early dietary manipulations are specific to certain cell types and may relate to their function.…”

“…58 These data strongly suggest that the morphological effects of early dietary manipulations are specific to certain cell types and may relate to their function. 57 It is unclear, however, whether changes in terminal field organization affect the dendritic organization of the NTS or vise versa. Specificially, do the postsynaptic changes in dendrites govern the abnormally enlarged terminal fields or do the enlarged terminal fields govern the abnormally large dendrites on putative relay neurons?…”

“…Restoration of a sodium-replete diet exaggerates instead of restores normal morphology. 52,57 This has important implications for brain stem development of non-gustatory structures as well as permanently affecting taste-elicited behaviors.…”