Differential occurrence and distribution of galanin in adrenal nerve fibres and medullary cells in rodent and avian species

The presence and distribution of galanin (GAL) in adrenal glands of rodent and avian species was investigated by light microscopic immunohistochemistry. GAL immunoreactivity was found in all medullary cells of guinea pig, duck and chicken adrenals. In contrast, only a subpopulation of medullary cells stained for GAL in Phodopus (Djungarian hamster) while the neuropeptide was completely missing in chromaffin cells of rat and pigeon. In rat, guinea pig and pigeon, GAL-immunoreactive nerve fibres were frequent in subcapsular regions and sparse in deeper cortical layers and in the chromaffin tissue. In contrast, only very few GAL fibres were found in Phodopus and no GAL fibres were observed in the adrenal glands of duck. In the chicken adrenal gland, fibres containing GAL were numerous throughout the organ and occurred in close vicinity to both steroidogenic as well as catecholaminogenic cells. The striking differences in the presence of GAL-positive cells and fibres are more pronounced between species within the rodent or avian group, respectively, than between the different vertebrate orders. The hitherto unknown and surprising variability of GAL expression and distribution in adrenal glands of various species suggests species-dependent functional (autocrine, paracrine and/or endocrine) roles of GAL in the neuroadrenal axis.