Neuropeptide Y Y1 and Y5 receptors are co-expressed with GRP mRNA in the rat hypothalamic paraventricular nucleus

Abstract

A number of hypothalamic neuropeptide systems have been shown to participate in energy homeostasis. We have previously reported that food deprivation time-dependently decreased gastrin-releasing peptide (GRP) gene expression in the medial parvocellular portion of the hypothalamic paraventricular nucleus (PVN) in rats. This region of the hypothalamus receives a dense projection of neuropeptide Y (NPY) neurons from the arcuate nucleus and also expresses NPY receptors. Because this neuropeptide system is engaged during times of negative energy balance, we hypothesized that NPY may directly modulate GRP mRNA expression in the PVN during food deprivation. To address this question we examined whether GRP-containing neurons in the PVN expressed Y1 and Y5 receptors, two NPY receptor subtypes that have been implicated in food intake and energy balance. Double label in situ hybridization was accomplished by hybridization with a combination of radiolabeled probes for either Y1 and Y5 receptors and a digoxigenin-labeled probe for GRP. Emulsion autoradiography was used to detect NPY receptors and Cy3 was used for detection of GRP. Our results indicated that both GRP mRNA and Y1 and Y5 receptor mRNA's were co-localized in this hypothalamic region. This finding supports the possibility that the activity of GRP neurons in the PVN is directly linked to NPY signaling and may contribute to changes in GRP gene expression produced by food deprivation. Supported by NIH DK-046448.