Ontogenetic changes in neuropeptide Y-immunoreactive cerebrospinal fluid-contacting neurons in the hypothalamus of the cloudy dogfish, Scyliorhinus torazame (Elasmobranchii).

Ontogenetic changes in neuropeptide Y-immunoreactive (NPY-ir) cerebrospinal fluid (CSF)-contacting neurons in the dogfish hypothalamus were studied immunohistochemically. NPY-ir CSF-contacting neurons first appeared in the median infundibular floor of the embryo at the 34 mm stage. At the 40 mm stage, similar neurons were found also in the saccus vasculosus (SV). The number of these neurons increased during the 54-80 mm stages, and the cells in the infundibular floor extended their basal processes to the neuropil of the median eminence, whereas the cells in the SV sent their axonal fibers to the tractus sacci vasculosi. After hatching, NPY immunoreactivity in the ventral hypothalamus became less dense, and the labeled CSF-contacting neurons tended to be confined to the nucleus lateralis tuberis, similarly as in the adults. The occurrence of NPY-ir CSF-contacting neurons in the SV was transient during the embryonic periods.