QUANTITATIVE DISTRIBUTION OF THE DELTA-OPIOID RECEPTOR MESSENGER-RNA IN THE MOUSE AND RAT CNS

We have used a sensitive solution hybridization assay that employs a riboprobe obtained from the mouse delta opioid receptor (DOR) coding sequence to quantitate the relative abundance of DOR mRNA in the central nervous system (CNS) of the adult mouse and rat. In brain Poly A+ RNA extracts this riboprobe hybridized to a single 10 kb transcript from mouse and two transcripts, one of 12 and the other of 4.5 kb in size from rat. In mouse CNS the highest levels of DOR mRNA were found in the caudate-putamen at 3.3 +/- 0.1 (SEM) pg/ug RNA. DOR mRNA levels in the range from 2.6 to 2.1 pg/ug RNA were measured in frontal cortex, nucleus accumbens, whole brain and olfactory tubercle. Spinal cord, periaqueductal gray and hippocampus had DOR mRNA levels in the range from 1.8 to 1.5 pg/ug RNA, while medial thalamus and cerebellum had the lowest levels (0.5 pg/ug RNA). These results correlate with the reported relative distribution of DOR mRNA in mouse using an in situ hybridization technique. In rat CNS, the highest levels of DOR mRNA were measured in caudate-putamen at 2.3 +/- 0.1 pg equivalents/ug RNA. Whole brain, cerebral cortex, olfactory bulb and brain stem had levels in the range from 1.5 to 0.9 pg equivalents/ug RNA while the lowest DOR mRNA levels were measured at 0.5 pg equivalents/ug RNA or less in thalamus, hippocampus, substantia nigra and cerebellum. This study demonstrates the ability of solution hybridization assays to quantitate homologous (mouse) as well as similar but heterologous (rat) DOR mRNA levels.