Developmental Sodium Restriction and Gustatory Afferent Terminal Field Organization in the Parabrachial Nucleus

Dietary sodium restriction instituted early in prenatal development produces physiological, anatomical, and functional changes in the gustatory system. For example, a rearrangement of the chorda tympani nerve terminal field within the nucleus of the solitary tract (NST) is observed in rats sodium restricted during development. The altered pattern of the chorda tympani nerve innervation within the nucleus of the solitary tract remains even after dietary sodium is restored in the diet at adulthood. In light of these observations, the terminal fields of second-order projections from the nucleus of the solitary tract to the parabrachial nucleus (PBn) were examined. To determine the possible rearrangements of the second-order projections, the rostral pole of the NST in control, restricted, and repleted rats was injected with the fluorescent tracer Fluoro-Ruby and the terminal fields in the parabrachial nucleus were analyzed. Results show no differences in the size or topography of the parabrachial nucleus terminal field among control, restricted, and repleted rats. These results suggest that the terminal field of second-order gustatory neurons is resistant to dietary sodium restriction during development. The apparent target-dependent effects may relate to differences in the developmental processes along the gustatory pathway.