NEUROENDOCRINE CELLS IN THE GILLS OF THE BOWFIN AMIA-CALVA - AN ULTRASTRUCTURAL AND IMMUNOCYTOCHEMICAL STUDY

Neuroendocrine (NE) cells were localized by electron microscopy and immunocytochemistry in the gill epithelium of bowfin Amia calva. The NE cells are dispersed in whole epithelium of the gill as solitary cells without intraepithelial innervation. All the observed NE cells do not reach the surface of the epithelium. The NE cells are characterized by a large nucleus with patches of condensed chromatin, numerous mitochondria, a well developed Golgi apparatus and a few dense core vesicles of various size scattered in the cytoplasm. Dense core vesicles range from 100 to 560 nm in diameter, while a clear space between the electron dense core and the limiting membrane ranges from 20 to 240 nm. Immunocytochemical observations reveal the presence of general neuroendocrine markers such as neuron-specific enolase and bioactive substances: serotonin, leu-enkephalin and met-enkephalin. We demonstrate the presence of endothelin - for the first time in fish - and suggest a local paracrine role for the NE cells. Some ultrastructural aspects and the immunocytochemical characteristics of NE cells of bowfin gills are common with those encountered in such cells of other lower vertebrate species.