Non-neuronal, but atropine-sensitive ileal contractile responses to short-chain fatty acids: age-dependent desensitization and restoration under inflammatory conditions in mice.

Intestinal epithelial cells sense short-chain fatty acids (SCFAs) to secrete non-neuronal acetylcholine (ACh). However, the roles of luminalSCFAs and epithelialACh under normal and pathological conditions remain unknown. We examined ileal contractile responses toSCFAs at different ages and their mucosal cholinergic alterations under inflammatory conditions. Ileal contractile responses toSCFAs in 1-day-old pups to 7-week-old mice were compared using an isotonic transducer, and responses to an intraperitoneal injection of lipopolysaccharide (LPS) were analyzed in 7-week-old mice. ThemRNAexpression levels of aSCFAactivate free fatty acid receptor, acetylcholinesterase (AChE), choline acetyltransferase (Chat), and choline transporter-like protein 4 (CTL4) were measured using real-time quantitativeRT-PCRAChE was analyzed by histochemical and optical enzymatic assays. Atropine-sensitive ileal contractile responses toSCFAs occurred in all 1-day-old pups, but were frequently desensitized after the weaning period. These contractile responses were not inhibited by tetrodotoxin and did not appear when the mucosal layer had been scraped off. Contractile desensitization in 7-week-old mice was abolished in the presence of theAChE inhibitor, eserine, which was consistent with increasedAChE activity after weaning. Ileal contractions toSCFAs in adult mice were restored byLPS, which significantly increased the epithelialmRNAexpression of Chat andCTL4. Atropine-sensitive ileal contractile responses toSCFAs constitutively occur in the newborn period, and are desensitized during developmental stages following the up-regulated expression ofAChE in the villous mucosa, but are restored under inflammatory conditions possibly via the release of epithelialACh.