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

Abstract

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 medial 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.