DISTRIBUTION OF PROENKEPHALIN mRNA IN THE RAT DISTAL COLON: AN IN SITU HYBRIDIZATION STUDY.

ABSTRACT

Since the discovery of the proenkephalin peptides, several immunohistochemical studies have demonstrated their localization in the gastrointestinal tract. A few reports have shown the presence of C-terminal extended forms of met-enkephalin without demonstrating the localization of their common precursor. To extend these immunohistochemical studies and to provide a more sensitive means of detecting enkephalinergic cell bodies, the present study examines the localization of proenkephalin mRNA in the colon of rat by in situ hybridization. Briefly, a 693b rat proenkephalin cRNA, corresponding to exon 3 was labelled with S^{3 5}UTP and hybridized to 4% paraformaldehyde post-fixed coronal, cryostat sections. The results demonstrate that cells expressing proenkephalin mRNA are localized between the two muscle layers, in the myenteric plexus. No labelling was found in submucous or mucosal layers. The cells expressing the proenkephalin mRNA are numerous, an average of 11 per coronal section. They are often grouped, with 5 to 15 other proenkephalin expressing cells and are sometimes scattered. Based on these results cells expressing proenkephalin mRNA are localised in myenteric plexus neurons and represent a large proportion of the total colonic neurons. In addition small diameter perikarya containing proenkephalin mRNA are localized around myenteric plexus and could represent interstitial cells. Studies are in progress to localize proenkephalin and prodynorphin mRNA throughout the gastrointestinal tract.