Taste Buds and Neuromasts of Astyanax jordani: Distribution and Immunochemical Demonstration of Co-localized Substance P and Enkephalins.

The distribution and some immunohistochemical aspects of the taste buds and free neuromasts of the blind cave fish Astyanax jordani were investigated using serial sections of whole fish. Taste buds are restricted to the skin of the lips and the lower jaw. Neuromasts are widely distributed over the whole epidermis except the lips and are particularly numerous in the opercular region and the caudal fin; they are absent from all other fins. The histological structure of the taste buds and the free neuromasts is similar to that described in other fish. The former are composed of two types of cells. The free neuromast, as seen under the electron microscope, is also constituted by two types of cell: dark supporting cells and clear sensory cells whose basal cytoplasm contains presynaptic bodies. Immunohistochemical results obtained with the peroxidase antiperoxidase method revealed the presence of different peptides in the taste buds and the free neuromasts. The former contain substance P (SP) and enkephalins (leu- and metenkephalin); the latter contain SP and leuenkephalin, but no metenkephalin. These peptides are localized in the cytoplasm of the accessory and sensory cells but not in the nervous fibres. None of these peptides occur in the olfactory epithelium of A.jordani. These immunohistochemical results raise the question of whether SP, leuenkephalin or metenkephalin play a role in transmission between the sensory cells and the afferent fibre.