Semiquantitative distribution of galanin-receptor (GAL-R1) mRNA-containing cells in the male rat hypothalamus

The semiquantitative distribution of mRNA encoding for rat galanin receptor !GAL-RI was examined by in situ hybridization in the rat hypothalamus using a S-35-riboprobe. Most hypothalamic nuclei expressed GAL-R1 mRNA. In the anterior hypothalamus, high levels of expression were found in the medial preoptic area, paraventricular and supraoptic nuclei. Numerous cells also expressed the GAL-R1 mRNA with a moderate level of expression in the periventricular region. Very few GAL-R1-expressing cells were present in the suprachiasmatic nucleus. In the medial hypothalamus, numerous expressing cells were detected in the dorsomedial and ventromedial nuclei. The arcuate nucleus was moderately labeled throughout its rostrocaudal extent; labeled cell bodies were visible in the ventromedial and ventrolateral subdivisions as well. These results indicate that the GAL-R1 mRNA is not only expressed in anterior hypothalamic nuclei but also in the mediobasal hypothalamus and periventricular region. This hypothalamic distribution correlates well with that of I-125-GAL-binding sites and GAL-immunoreactive fibers. This distribution represents the morphological substrate for GAL roles in the hypothalamic regulation of neuroendocrine, behavioral and autonomic functions.