A302 LUMINAL SHORT-CHAIN FATTY ACIDS RESTORE MOTILITY IN GERM-FREE MICE

The bidirectional relationship between colon motility and microbiota needs further study. Germ free (GF) mice are unable to ferment resistant starch into short-chain fatty acids (SCFA). Previous studies have shown that these mice have a significantly longer transit time than controls. We investigated motility patterns in isolated GF mouse colons in an attempt to elucidate the role microbiota-derived metabolites play in governing motility. The mouse colon was luminally-perfused inside an organ bath. After equilibration of 30min, a phosphate buffer (PBS) was perfused into the lumen, followed by a cocktail of SCFA (1mM butyrate & propionate, 5mM acetate) dissolved in PBS. Motility was video recorded and spatiotemporal maps were produced by plotting diameter changes along the colon over time. The outflow from the colon was connected to a pressure transducer that recorded the volume of outflow produced by each contraction. ICC were identified by immunohistochemistry using cKit antibodies. GF mice had abnormal motility patterns. GF baseline conditions were either dominated by slowly propagating contractions that did not produce outflow (Figure1B) and long distance contractions (LDCs) that were interrupted by relaxation in the mid colon. The 20 cpm ICC slow wave driven background contractions appeared normal. The GF baseline condition had a significantly higher number of contractions than the control baseline condition (P<0.001). Under the same conditions, control activity was dominated by normal propulsive LDCs. The average volume of output per contraction was significantly higher in the control baseline than the GF baseline condition (P<0.05). After adding SCFA, motor patterns from the GF mouse closely resembled that of the control, characterised by rhythmic LDCs that were not interrupted (Figure1B). The percentage of contractions that were LDCs increased significantly following SCFA administration to the GF colon (P<0.001). c-Kit staining of the ICC networks in both strains of mice showed no difference in the structural integrity of these networks. The results indicate that in the absence of SCFA, the GF colon had normal myogenic ICC directed motility but the stimulus dependent motor activity was abnormal. Our hypothesis is that distention-induced motor patterns do not develop in a typical manner when the inner mucus layer does not contain microbiota-derived metabolites, in particular SCFA. Administering SCFA provided the correct mucosal stimulation environment required to generate normal rhythmic propulsive contractions. We hypothesize that SCFA indirectly activate 5-HT release from enterochromaffin cells thereby lowering the threshold for distention-induced LDCs. The reduced transit time observed in GF mice is due to reduced ability to generate distension-induced propulsive LDCs although the neural machinery to produce LDCs is fully present. Figure1: Spatiotemporal maps of the germ free mouse colon. Above, Image A shows the germ free baseline condition and below, Image B shows the same mouse with intraluminal perfusion of SCFA. Both images are 20 minutes in length. CIHR