Sauvagine-like immunoreactivity in the bony fish urophysis and caudal neurosecretory system.

Immunoperoxidase methods were used to reveal Sauvagine-Like immunoreactivity (SVLI) in the urophysis and whole caudal neurosecretory system of fresh water fish Tinca tinca and Salmo gairdneri L. Both Dahlgren cell cytoplasm and axons, which reach the urophysis, were filled with SVLI granules. The urophysis shows: a) in the medullary zone, several SVLI Dahlgren cells and a thick network of SVLI axons; b) in the cortical zone, a series of complicated neurohemal knots where SVLI axonal endings surround and penetrate the capillary and glial cell networks. An individual variability and the possibility of a release of SVLI material into the cerebrospinal fluid were also demonstrated. These observations further suggest that, besides the biological effects, sauvagine and the urophysial substance urotensin I, may also have a similar structure.