DISTRIBUTION OF PREPRO-NOCICEPTIN ORPHANIN FQ MESSENGER-RNA AND ITS RECEPTOR MESSENGER-RNA IN DEVELOPING AND ADULT-MOUSE CENTRAL NERVOUS SYSTEMS/

Nociceptin/orphanin FQ (N/OFQ) and its receptor share similarities to opioids and their receptors in terms of the molecular structure and si gnaling pathway, but the two systems exhibit different actions in vivo . To understand the mechanism of N/OFQ-system actions, we examined, by in situ hybridization analysis, the distribution of preproN/OFQ and N /OFQ receptor mRNAs in the developing and adult mouse central nervous systems (CNS). In most neural regions, preproN/OFQ mRNA was mainly exp ressed in a small population of middle-sized neurons. These neurons we re scattered between large projection-type neurons or within the neuro pil, suggestive of interneurons. In some other nuclei (lateral septum, bed nucleus of the stria terminalis, reticular thalamic nucleus, infe rior colliculus, and rostral periolivery nucleus), preproN/OFQ mRNA wa s expressed in a number of large projection-type neurons. By contrast, N/OFQ receptor mRNA was evenly expressed in most neurons of the adult CNS. Considering the inhibitory actions of N/OFQ, the distinct cellul ar expression pattern of the N/OFQ system suggests that the release of N/OFQ from interneurons may lower neuronal and synaptic activities of neighboring neurons, leading to integration or modulation of local ci rcuits. Furthermore, the cellular expression pattern, distinct from th at of the opioid system, may provide a possible molecular/cellular bas is for the different in vivo actions of N/OFQ and opioids. In embryoni c stages, both preproN/OFQ and N/OFQ receptor mRNAs were highly and wi dely expressed in the mantle zone, suggesting the possible importance of N/OFQ signaling in CNS development. J. Comp. Neurol. 399:139-151, 1 998. (C) 1998 Wiley-Liss, Inc.