Neuropeptide Y Y1 receptors in the rat forebrain: autoradiographic demonstration of [125I][Leu31,Pro34]-NPY binding sites and neurons expressing Y1 receptor mRNA.

Using the specific monoiodinated NPY analog [Leu31,Pro34]-NPY we have localized NPY binding sites of the Y1 type in forebrain areas of the rat. The resulting receptor autoradiograms were compared with the regional distribution and cellular localization of the mRNA encoding Y1 receptor as demonstrated by in situ hybridization histochemistry. High densities of Y1 binding sites were present in the cerebral cortex, the claustrum, the thalamus and the medical mammillary nucleus, while moderate densities of Y1 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 Y1 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 Y1 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, Y1 mRNA and Y1 binding sites was compared, and possible implications of Y1 mediated actions within this nucleus are discussed. The present study further enlightens the anatomical distribution of NPY binding sites of the Y1 type within the central nervous system of the rat, and extends the understanding of central actions of NPY mediated via this type of receptor.