QUANTITATIVE-ANALYSIS OF MU-OPIOID AND DELTA-OPIOID RECEPTOR GENE-EXPRESSION IN RAT-BRAIN AND PERIPHERAL GANGLIA USING COMPETITIVE POLYMERASE CHAIN-REACTION

Competitive polymerase chain reaction assays following reverse transcr iption have been developed for quantitative analysis of delta and mu o pioid receptor gene expression. The assay was used to obtain quantitat ive measurements of mu and delta opioid receptor expression levels in different brain regions and sensory and sympathetic ganglia in the rat . The assays provide accurate estimates of the relative levels of rece ptor messenger RNAs by the inclusion in the assays of known amounts of internal standards with the same sequence, except for a small deletio n, as the target complementary DNA. The amplification products of targ et and competitor can be distinguished by size, and their amounts meas ured by densitometry. Expression of mu and delta opioid receptor messe nger RNAs in different regions of the rat brain, somatic and visceral sensory and sympathetic ganglia was investigated using this method. In the brain the highest density of delta receptor messenger RNA was det ected in the olfactory bulb, followed by the striatum. The mu receptor was expressed at highest levels in the midbrain-hypothalamic region. All the sensory ganglia studied expressed both mu and delta opioid rec eptor messenger RNAs. In the nodose ganglion we observed the highest l evel of mu receptor messenger RNA of any structure studied; in the tri geminal ganglion the level was about 10 times lower than that in the n odose ganglion. Among the dorsal root ganglia, mu receptor messenger R NA density was highest in the lumbar region, followed by the thoracic and cervical regions. The sympathetic superior cervical ganglion expre ssed a very low level of mu message. Delta receptor messenger RNA was detected only in the sensory ganglia, at levels that were considerably lower than in the striatum. The reverse transcription-polymerase chai n reaction assay is quantitatively reliable for comparison of messenge r RNA levels between different RNA extracts, and sensitive enough to p ermit the detection and assay of mu and delta opioid recetor gene expr ession in a single pair of sensory or autonomic ganglia from the rat.