Neuropeptide Y Y1 receptor mRNA in rodent brain: Distribution and colocalization with melanocortin-4 receptor

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Abstract
The central neuropeptide Y (NPY) Y1 receptor (Y1‐R) system has been implicated in feeding, endocrine, and autonomic regulation. In the present study, we systematically examined the brain distribution of Y1‐R mRNA in rodents by using radioisotopic in situ hybridization histochemistry (ISHH) with a novel sensitive cRNA probe. Within the rat hypothalamus, Y1‐R–specific hybridization was observed in the anteroventral periventricular, ventromedial preoptic, suprachiasmatic, paraventricular (PVH), dorsomedial, ventromedial, arcuate, and mamillary nuclei. In the rat, Y1‐R mRNA expression was also seen in the subfornical organ, anterior hypothalamic area, dorsal hypothalamic area, and in the lateral hypothalamic area. In addition, Y1‐R hybridization was evident in several extrahypothalamic forebrain and hindbrain sites involved in feeding and/or autonomic regulation in the rat. A similar distribution pattern of Y1‐R mRNA was observed in the mouse brain. Moreover, by using a transgenic mouse line expressing green fluorescent protein under the control of the melanocortin‐4 receptor (MC4‐R) promoter, we observed Y1‐R mRNA expression in MC4‐R–positive cells in several brain sites such as the PVH and central nucleus of the amygdala. Additionally, dual‐label ISHH demonstrated that hypophysiotropic PVH cells coexpress Y1‐R and pro–thyrotropin‐releasing hormone mRNAs in the rat. These observations are consistent with the proposed roles of the central NPY/Y1‐R system in energy homeostasis. J. Comp. Neurol. 482:217–243, 2005.