Serotonin-, somatostatin- and chromogranin A-containing cells of the urethro-prostatic complex in the sheep. An immunocytochemical and immunofluorescent study.

The urethral and prostatic epithelial of the sheep contain a large number of amine- and/or peptide-producing neuroendocrine cells (NE), also called paraneurons. Four different cell types have been immunohistochemically recognised among them. The first contains the amine serotonin, the second the protein chromogranin A, the third the amine and the protein together and the fourth the hormone somatostatin. Serotonin-producing cells are elongated in shape and often show cytoplasmic dendrite-like processes directed towards the basal membrane and/or the lumen. Chromogranin A-containing cells are polymorphic and constitute the more numerous NE subpopulation. Cells containing both the bioactive substances seem to be less numerous than the chromogranin A cells and slightly more frequent than the serotonin cells. All these cell types are diffused along the whole urethro-prostatic complex and show their highest density in the collicular zone. Somatostatin-containing cells often show a unique cytoplasmic extension directed towards the basal membrane and are rare. It is supposed that the presence of serotonin in the urogenital tract is functionally correlated with the emission of urine and/or semen, while somatostatin is associated with the inhibition of local exocrine and/or endocrine secretions.