NEUROPEPTIDE-Y - DISTRIBUTION OF IMMUNOREACTIVITY AND QUANTITATIVE-ANALYSIS IN DIENCEPHALIC STRUCTURES AND CEREBRAL-CORTEX OF DWARF HAMSTERS UNDER DIFFERENT PHOTOPERIODS

The distribution of neuropeptide Y-like immunoreactivity (NPY-LI) was investigated by immunohistochemistry and radioimmunoassay (RIA) in the brain of the Djungarian hamster (Phodopus sungorus) held under either long or short photoperiods. In the diencephalic and telencephalic str uctures studied, distinct patterns of NPY-LI were basically consistent in male and female animals of both groups. NPY levels detected by RIA from tissue samples taken at six time points throughout the 24-hour c ycle were in the range of 15-60 pmol/mg protein in the diencephalon or below 5 pmol/mg protein in cerebral cortex. In the diencephalon, immu noreactive structures were seen in the preoptic, peri- and paraventric ular, supraoptic, anterior, lateral, dorso- and ventromedial hypothala mic nuclei and in the median eminence. The suprachiasmatic nuclei exhi bited a dense innervation by NPY-LI terminals mainly in its ventrolate ral subdivision. NPY levels in the suprachiasmatic nucleus were noctur nally augmented under long-day, but not under short-day conditions. Th e quantification of NPY in the paraventricular nucleus revealed a decr ease at night in long-day animals and a small nocturnal augmentation i n short-day hamsters. In the pineal gland and habenular nuclei, varico se fibers were observed which appeared mainly perivascular in location (pineal) or formed a dense plexus (habenular nuclei). Pineal NPY cont ents fell during the night in long-day animals and were relatively con stant in short-day hamsters. NPY-LI structures were also observed in t he metathalamic intergeniculate leaflet and in a variety of telencepha lic structures including the cerebral. cortex, caudate nucleus putamen , lateral septal nucleus, bed nucleus of the stria terminalis and amyg dala.