LOCALIZATION OF NEUROPEPTIDE Y-LIKE IMMUNOREACTIVITY IN THE SACCUS VASCULOSUS OF CARTILAGINOUS AND BONY FISHES

The distribution of perikarya and fibers containing neuropeptide Y (NP Y)-like immunoreactant was studied in the saccus vasculosus of cartila ginous and bony fishes by immunohistochemistry using streptavidin-biot in technique. NPY-positive fibers were demonstrated in most of the 20 species examined, although the density of the fibers varied among the species. In the white sturgeon, Acipenser transmontanus, NPY-positive varicose fibers formed a supraependymal plexus. On the other hand, NPY -positive perikarya could be demonstrated in the ayu, Plecoglossus alt ivelis, in which an NPY-positive, presumed afferent fiber fascicle was encountered. These results suggest an involvement of NPY or related s ubstance in the saccus vasculosus function and its regulation.