NEUROPEPTIDE-Y Y-1 RECEPTORS IN THE RAT FOREBRAIN - AUTORADIOGRAPHIC DEMONSTRATION OF [I-125] [LEU(31),PRO(34)]-NPY BINDING-SITES AND NEURONS EXPRESSING Y-1 RECEPTOR MESSENGER-RNA

Using the specific monoiodinated NPY analog [Leu(31),Pro(34)]-NPY we have localized NPY binding sites of the Y-1 type in forebrain areas of the rat. The resulting receptor autoradiograms were compared with the regional distribution and cellular localization of the mRNA encoding Y-1 receptor as demonstrated by in situ hybridization histochemistry. High densities of Y-1 binding sites were present in the cerebral cortex, the claustrum, the thalamus and the medial mammillary nucleus, while moderate densities of Y-1 binding sites were observed in the amygdalahippocampal complex. Lower binding densities were observed in septal nuclei, most hypothalamic nuclei and the circumventricular organs. High levels of Y-1 mRNA were observed in the granula cell layer of the hippocampal dentate gyrus, several thalamic nuclei and the hypothalamic arcuate nucleus, while moderate levels of Y-1 mRNA were seen in the frontoparietal cortex, several thalamic nuclei, the hippocampal pyramidal layers, the subiculum, the olfactory tubercle, the claustrum and a number of hypothalamic nuclei. Using the hypothalamic arcuate nucleus as an example, the distribution of immunoreactive NPY, Y-1 mRNA and Y-1 binding sites was compared, and possible implications of Y-1 mediated actions within this nucleus are discussed. The present study further enlightens the anatomical distribution of NPY binding sites of the Y-1 type within the central nervous system of the rat, and extends the understanding of central actions of NPY mediated via this type of receptor.