A study of the rat neuropeptide B/neuropeptide W system using in situ techniques

In the rat, the neuropeptide B/neuropeptide W (NPB/NPW) system is composed of two ligands, neuropeptide B (NPB) and neuropeptide W (NPW), and one receptor, GPR7. Although preliminary analyses show roles in feeding, hormone secretion, and analgesia, the lack of a detailed anatomical map impairs our understanding of the NPB/NPW system. We demonstrate in this report the expression patterns of GPR7, NPB, and NPW precursor messenger ribonucleic acid (mRNA) in the rat brain by using in situ hybridization and in situ binding experiments. The amygdala expresses the highest levels of GPR7 mRNA and binding signals. Other nuclei with high levels of expression and binding are the suprachiasmatic and the ventral tuberomamillary nuclei. Moderate levels are seen in the dorsal endopiriform, dorsal tenia tecta, bed nucleus, and the red nucleus. Low levels are in the olfactory bulb, parastrial nucleus, hypothalamus, laterodorsal tegmentum, superior colliculus, locus coeruleus, and the nucleus of the solitary tract. Although the NPB precursor is mostly expressed at low levels in the brain, moderate expression is seen in anterior olfactory nucleus, piriform cortex, median preoptic nucleus, basolateral amygdala, hippocampus, medial tuberal nucleus, substantia nigra, dorsal raphe nucleus, Edinger-Westphal nucleus, and the locus coeruleus. To our surprise, the expression of NPW precursor was not detected. Our study greatly expands the preliminary in situ data previously reported. With this map of the NPB/NPW system in the rat brain, a better understanding of the functional implications of the system in various behavioral paradigms is now possible.