QUANTITATION OF MU-OPIOID RECEPTOR (MOR-1) MESSENGER-RNA IN SELECTED REGIONS OF THE RAT CNS

THE mu opioid receptor (MOR-1) mRNA was quantified in rat CNS by a sen sitive solution hybridization (SH) technique, employing a P-32-labeled riboprobe derived from the coding region of MOR-1 cDNA. In a Northern blot analysis this riboprobe hybridized to a 14 kb form of rat MOR-1 mRNA. The linear range of SH assay extends from 1 to 250 pg of MOR-1 s ense transcript (equivalent to 9.3-2325 pg of MOR-1 mRNA). A microdiss ection technique for reproducible sampling of selected CNS regions, fo llowed by the SH assay, allowed for a quantitative study of MOR-1 mRNA distribution. The highest levels of MOR-1 mRNA were present in medial thalamus (17.8 +/- 0.3 pg/mu g RNA), and the lowest in the cerebellum (0.4 +/- 0.1 pg/mu g RNA). Hypothalamus, dorsal spinal horn, nucleus raphe, periaqueductal gray, and sensorimotor cortex contained intermed iate levels. This distribution closely parallels the pattern of mu rec eptor binding, suggesting that both the mRNA and the receptor protein are colocalized within most of the regions studied.