GALANIN EXPRESSION IN CAROTID-BODY AFFERENT NEURONS

The present study examined expression and plasticity of the neuropepti de, galanin, in carotid body afferent neurons in the petrosal ganglion of the adult rat. The pattern of galanin expression was compared with that of tyrosine hydroxylase, a selective marker of dopaminergic caro tid body afferents in the petrosal ganglion. In normal animals, only 3 % of tyrosine hydroxylase-containing petrosal ganglion neurons co-expr essed galanin. Retrograde labeling studies, in which FluoroGold was in jected into the vascularly isolated carotid body, demonstrated that al l tyrosine hydroxylase-positive-galanin-positive cells in the petrosal ganglion project to this target. In addition, however, we unexpectedl y found that galanin expression was markedly increased in the petrosal ganglion following FluoroGold injection into the carotid body. On the other hand, tyrosine hydroxylase expression was unchanged, indicating that monoaminergic and peptidergic traits can be differentially regul ated in these cells. In summary, these data demonstrate that monoamine rgic chemoafferent neurons can co-express a peptidergic trait, similar to catecholaminergic neurons within the central and autonomic nervous systems, and that these cells retain the potential for phenotypic pla sticity in adulthood.