MOLECULAR-CLONING AND IN-SITU HYBRIDIZATION HISTOCHEMISTRY FOR RAT MU-OPIOID RECEPTOR

We cloned a cDNA for the rat mu-opioid receptor from a rat thalamus cD NA library. The deduced amino-acid sequence of rat mu-opioid receptor consists of 398 residues with the features shared by the members of th e G-protein coupled receptor family, and is 59% and 60% identical with those of rat kappa-opioid and mouse delta-opioid receptors, respectiv ely. Northern blot analysis showed that expression of mu-opioid recept or mRNA was intensive in the thalamus, striatum, hypothalamus and pons -medulla, moderate in the hippocampus and midbrain, and slight in the cerebral cortex and cerebellum. More detailed distribution of the mRNA in the rat brain was examined using the in situ hybridization techniq ue. Intense expression of mu-opioid receptor mRNA was observed in the internal granular and glomerular layers of the olfactory bulb, caudate putamen, nucleus accumbens, medial septum, diagonal band, medial preo ptic area, several nuclei of thalamus, amygdala, interpeduncular nucle us, medial raphe nucleus, inferior colliculus, parabrachial nucleus, l ocus coeruleus, nucleus solitary tract and ambiguus nucleus. Furthermo re, mu-opioid receptor mRNA was moderately expressed in the hippocampu s, globus pallidus, ventral pallidus, arcuate hypothalamic nucleus, su pramammillary nucleus, superior colliculus, periacqueductal gray, and several nuclei of lower brain stem, including raphe magnus nucleus, re ticular gigantocellular nucleus and lateral paragigantocellular nucleu s.