NEUROPEPTIDE-Y IN THE FOREBRAIN AND RETINA OF THE KILLIFISH, FUNDULUS-HETEROCLITUS

The organization of the neuropeptide Y (NPY)-immunoreactive system in the forebrain, pineal organ and retina of a biweekly spawning fish (Fu ndulus heteroclitus) was investigated. Immunoreactivity was encountere d in neurons of the nucleus olfactoretinalis, in the large population of neurons in the floor of the telencephalon, and in the nucleus entop eduncularis. Isolated somata were encountered in the hypophysiotropic hypothalamic nuclei, viz., the nucleus preopticus periventricularis, n ucleus preopticus, and nucleus lateralis tuberis. Immunoreactive somat a were also seen in the nucleus dorsomedialis thalami. The olfactory b ulb was abundantly innervated by NPY fibers. The telencephalon showed thick radiating processes basally and terminal fields with modest to h igh densities in the dorsal and lateral regions. NPY-immunoreactive fi bers were also conspicuous in the preoptic area, suprachiasmatic nucle us, tuberal hypothalamus, pituitary gland, and paraventricular thalami c regions; discrete CSF-contacting sites were also encountered. Of spe cial interest was the occurrence of NPY immunoreactivity in fibers of the pineal stalk and organ. In the retina, some amacrine cells display ed immunoreactivity, while the inner plexiform layer revealed a well-d eveloped pattern of NPY fibers different from that previously describe d for the goldfish.