Distribution of prolactin-releasing peptide mRNA in the rat brain.

In order to identify the distribution of prolactin-releasing peptide (PrRP) mRNA in the rat brain, we independently cloned cDNA of PrRP. Brains were removed from three adult males, and brains from three females each at 0200 and 1400 h on day 7 of pregnancy were obtained. By the nonradioactive in situ hybridization method, the location of PrRP mRNA was detected in very restricted brain areas. The distribution of PrRP mRNA signals was very similar in both sexes. In the hypothalamus, only the ventral part of the caudal dorsomedial nucleus had PrRP mRNA signals. Other forebrain areas did not show any positive signals. In the medulla oblongata, two discrete areas contained PrRP mRNA signals. No positive signal was found in the rostral part of the medulla oblongata extending to the anterior part of the area postrema. The caudal part of the nucleus of the solitary tract (NTS) had neurons with very strong signals of PrRP mRNA. The reticular nucleus showed a few PrRP mRNA positive neurons. The number of PrRP mRNA positive cells in the NTS was not different between experimental groups, although plasma prolactin levels in these animals were different. This anatomical information on the location of PrRP mRNA in the brain provides the framework to understand the physiological functions of PrRP in vivo.