Distribution of nociceptin/orphanin FQ precursor protein and receptor in brain and spinal cord: A study using in situ hybridization and X-gal histochemistry in receptor-deficient mice

Nociceptin/orphanin FQ (N/OFQ) is an opioid-like heptadecapeptide agonist f or the opioid receptor homolog, N/OFQ receptor. To explore the precise dist ribution of the peptide-receptor system, the authors examined the brain and spinal cord from receptor-deficient mice bearing the targeted mutation (mo rc(m1)), a LacZ insertional mutation in the N/OFQ receptor gene. Precursor protein N/OFQ (preproN/OFQ) mRNA was detected by using in situ hybridizatio n, and the N/OFQ receptor was detected by using X-gal histochemistry. The N /OFQ receptor reflected by lacZ expression was observed at high levels in t he dentate gyrus, lateral septum, subparafascicular thalamic nucleus, media l preoptic area, median preoptic nucleus, ventromedial preoptic nucleus, an terior hypothalamic area, paraventricular hypothalamic nucleus, ventromedia l hypothalamic nucleus, auditory brainstem nuclei, pontine dorsal tegmentum , and nucleus of the solitary tract. In situ detection of the N/OFQ recepto r mRNA by digoxigenin-labeled riboprobes coupled with tyramide signal ampli fication in normal and wild-type mice resulted in the regional distribution paralleling the lacZ expression in these regions. PreproN/OFQ mRNA was exp ressed at high levels in the subparafascicular thalamic nucleus, central gr ay, central tegmental field, auditory brainstem nuclei, caudal spinal trige minal nucleus, and spinal dorsal hem. Furthermore, variable levels of expre ssion of the peptide and receptor were seen in distinct sites of the brain and spinal cord. These data indicate a correspondence of the peptide and th e receptor in local distribution at limbic, hypothalamic, and brainstem sit es. Together with concurrent physiologic and behavioral studies in mutant m ice, the results suggest functional roles for the N/OFQ system, including t he central regulation of learning and memory, hearing ability, water balanc e, food intake, and blood pressure. (C) 2000 Wiley-Liss, Inc.