Opioid peptide mRNA expression in the colon of the rat

Since the discovery of opioid peptides, several immunohistochemical and rad ioimmunological studies have demonstrated their localization in the gastroi ntestinal tract without demonstrating the localization of their common prec ursor. The present study describes the distribution and the colocalization of proenkephalin and prodynorphin messenger RNAs (mRNAs) in the colon of ra t by in situ hybridization. Proenkephalin and prodynorphin mRNAs were found in myenteric plexus, but not in the submucous plexus or in the mucosa. In myenteric plexus, the number of neurons expressing proenkephalin is 2.5 tim es greater than that of the neurons expressing only prodynorphin. Furthermo re, double in situ hybridization histochemistry indicates that at least thr ee groups of opioid neurons can be distinguished, those containing proenkep halin and prodynorphin mRNAs together, and those containing only proenkepha lin mRNA or only prodynorphin mRNA. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.