<b>Diversity of the intestinal microbiota differently affects non-neuronal and atropine-sensitive ileal contractile responses to short-chain fatty acids in mic</b><b>e </b>

Non-neuronal and atropine-sensitive ileal contractile responses to short chain fatty acids (SCFAs) are detected in the neonatal stage, and change with age or inflammatory conditions. However, the roles of luminal SCFAs in developmental changes have not yet been elucidated. We examined ileal contractile responses to SCFAs in mice colonized with different SCFA-producing intestinal microbiota under normal and inflammatory conditions. Using conventional (Conv), germ-free (GF), and gnotobiotic mice infected with Bifidobacterium (GB-bif), Propionibacterium (GB-prop), or Lactobacillus (GB-lact), ileal contractions were measured in 1-day-old neonates and 7-week-old mice using an isotonic transducer. Contractions occurred in all 1-day-old neonates, and were significantly desensitized in the adult stage in the Conv, GB-bif, and GB-prop groups, but not in the GF and GB-lact groups. An injection of lipopolysaccharide frequently restored desensitized contractions; however, the contraction rate did not change in the GF and GB-lact groups. The relative mRNA expression of a SCFA receptor (GPR43) or nicotinic acetylcholine receptor α7 was weaker in the GF group (0.3-fold or 0.4-fold expression level, respectively) than in the Conv group. In conclusion, the luminal inhabitation of SCFA-producing bacteria may potentiate the regulation of non-neuronal and atropine-sensitive ileal contractile responses to SCFAs under healthy and inflammatory conditions.