SUBTYPES Y1 AND Y2 OF THE NEUROPEPTIDE-Y RECEPTOR ARE RESPECTIVELY EXPRESSED IN PRO-OPIOMELANOCORTIN-CONTAINING AND NEUROPEPTIDE-Y-CONTAINING NEURONS OF THE RAT HYPOTHALAMIC ARCUATE NUCLEUS

The arcuate nucleus of the hypothalamus houses a number of neurochemic ally different cell populations. Among these, a dense cluster of small neuropeptide-Y (NPY)-expressing neurons is located in its ventromedia l subdivision and a pro-opiomelanocortin (POMC)-expressing neuron popu lation in its ventrolateral part. Furthermore, both neuropeptide Y Y1 and Y2 receptors (Y1-Rs and Y2-Rs) are expressed in the arcuate nucleu s. Here we analyse the co-expression of NPY and POMC/adrenocorticotrop ic hormone with the Y1-R and Y2-R in arcuate neurons using immunohisto chemistry and in situ hybridization. Many, but not all, POMC neurons e xpressed Y1-R mRNA and protein. Conversely, several Y1-R-positive, POM C-negative neurons were found. NPY-positive nerve terminals were found in close apposition to Y1-R-like immunoreactivity localized close to the dendritic and somatic cell membranes. Y2-R mRNA was found in almos t all NPY mRNA-expressing neurons, but also in a group of NPY mRNA-neg ative cells. These results show that the POMC neurons are targets for NPY, which is presumably present in, and released from, fibres origina ting in the ventromedial arcuate nucleus and which may play a role in NPY-induced feeding. Release of NPY, and possible coexisting messenger s, may be controlled by presynaptic Y2-R expressed in NPY neurons. Tak en together, the findings support the division of Y1-Rs and Y2-Rs into post- and presynaptic receptors, respectively.