Ca2+ transients in submucous neurons during the colonic migrating motor complex in the isolated murine large intestine

Background The colonic migrating motor complex (CMMC) is a spontaneous, rhythmic, and neurally mediated motor pattern generated by myenteric neurons, which can propel fecal pellets in mice. Our aim was to determine whether submucous neurons were also activated during the CMMC. Methods The isolated murine colon was opened and sections of mucosa were removed to expose the submucous ganglia, which were then loaded with Fluo‐4. Key Results Colonic migrating motor complexes, which occurred spontaneously or by mechanically stimulating the mucosa, were identified by displacement of the tissue (duration = 23.3 s). Between CMMCs, spontaneous Ca2+ transients (frequency = 0.9 Hz) were observed in 55% (n = 8) of submucous neurons. During the CMMC, 98% (seven ganglia, n = 7) of submucous neurons within the same ganglion exhibited rapid Ca2+ transients (1.6 Hz) superimposed on a sustained rise in Ca2+ (duration ∼23 s) that occurred 1.7 s following the mucosal stimulus; whereas other neurons exhibited a similar, but delayed response that occurred either at 7 or 13 s following the stimulus. The activity in submucous neurons was correlated with activity in adjacent nerve varicosities. Ondansetron (1 mm; 5‐HT3 antagonist) significantly reduced the frequency and duration of the Ca2+ transient responses. Conclusions & Inferences Activity in the submucous neurons appears to be secondary to that in the myenteric plexus and appears to be generated largely by activity in myenteric descending (serotonergic) interneurons. During the CMMC, there is likely to be an increase in secretion to lubricate and facilitate fecal pellet propulsion.