Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC179
Calcium activity in submucosal neurons during the colonic migrating motor complex (CMMC) in the isolated murine large intestine
T. Okamoto1, P. O. Bayguinov1, M. J. Broadhead1, G. W. Hennig1, T. K. Smith1
1. Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada, United States.
Background: The CMMC is a spontaneous, rhythmic, neurally mediated motor pattern that is responsible for the propulsion of fecal pellets in mice (Heredia et al., 2010). The enteric nervous system consists of two ganglionated neural networks called the myenteric plexus, which lies between the longitudinal and circular muscle layers, and the submucosal plexus, which lies in the submucosa. The CMMC is generated by neurons within the myenteric plexus (Bayguinov et al., 2010), whereas neurons in the submucosal plexus regulate the secretion of water and electrolytes respectively. It is likely that these plexuses normally function as one system, since 3 of the 4 myenteric descending interneurons also project to the submucosal plexus, and sensory neurons in both plexuses communicate with one another (Furness, 2006). In this study, we have used Ca2+ imaging to examine whether submucosal neurons are activated during the CMMC. Methods: Mice (C57) were anaesthetized by inhalation of 5% isoflurane in 97% O2 + 3% CO2 and killed by cervical dislocation The whole murine colon was removed and opened along the mesenteric border and pinned with the mucosa uppermost in a recording chamber perfused with oxygenated Krebs’ solution at 34°C. A section of the mucosa was peeled away to expose the submucosal ganglia, which were loaded with Fluo-4 (Bayguinov et al., 2010). CMMCs either occurred spontaneously or were evoked by mechanically stimulating the mucosa with a brush or by colonic elongation, both applied at the anal end of the large bowel (Bayguinov et al., 2010; Heredia et al., 2010). Results: Values are means ± S.E.M. A spontaneous or an evoked CMMC was indicated by a contraction (duration: 25.0 ± 4.4 s; n=5) of the tissue. The majority of neurons (~80%) in submucosal ganglia (7.3 ± 1.4 neurons; n=5) exhibited spontaneous Ca2+ transients (frequency = 0.12 ± 0.03 Hz; n=15). During an evoked CMMC, submucosal neurons responded in 2 different ways: a series of fast Ca2+ transients superimposed on a prolonged rise in Ca2+ (frequency = 0.6 ± 0.1 Hz, duration =14.4 ± 1.5s; n=16) after a latency of 6.4 ± 1.4s (measured from onset of contraction), and/or an increase in Ca2+ transients which began during the latter part of the CMMC (frequency = 0.6 ± 0.1 Hz, duration =11.5 ± 2.7s, latency 19.5 ± 2.1s; n=9). Conclusion: Submucosal neurons are likely activated by myenteric neurons during the CMMC. Their different responses may represent their diverse functions (see Furness, 2006). However, it seems likely that there is an overall increase in secretion during fecal pellet propulsion.
Where applicable, experiments conform with Society ethical requirements