DOUBLE IN-SITU HYBRIDIZATION STUDY ON COEXISTENCE OF MU-OPIOID, DELTA-OPIOID AND KAPPA-OPIOID RECEPTOR MESSENGER-RNAS WITH PREPROTACHYKININ-A MESSENGER-RNA IN THE RAT DORSAL-ROOT GANGLIA

Coexistence of the mRNA for each subtype of opioid receptor (OPR) with the mRNA for preprotachykinin A (PPTA), a precursor protein of substa nce P (SP), in the rat dorsal root ganglia was examined by double in s itu hybridization technique. About 90% and 30% of PPTA mRNA-positive n eurons expressed mu- and kappa-OPR mRNAs at high level, respectively. However, only about 3% of PPTA mRNA-positive neurons expressed delta-O PR mRNA at high level. These results suggest that mu- and kappa-OPRs e xist on most of and a part of the primary afferent terminals containin g SP, respectively. On the other hand, among the neurons which highly expressed mu-, delta- or kappa-OPR mRNA, PPTA mRNA was not expressed i n about 58%, 95% or 24% of those neurons, respectively. These findings suggest the possibility that OPRs co-exist with other neurotransmitte rs and/or neuromodulators than SP in the primary afferent neurons.