Localized release of serotonin (5-hydroxytryptamine) by a fecal pellet regulates migrating motor complexes in murine colon.
OBJECTIVE
The colonic migrating motor complex (CMMC) is a motor pattern that regulates the movement of fecal matter through a rhythmic sequence of electrical activity and/or contractions along the large bowel. CMMCs have largely been studied in empty preparations; we investigated whether local reflexes generated by a fecal pellet modify the CMMC to initiate propulsive activity.


METHODS
Recordings of CMMCs were made from the isolated murine large bowel, with or without a fecal pellet. Transducers were placed along the colon to record muscle tension and propulsive force on the pellet and microelectrodes were used to record electrical activity from either side of a fecal pellet, circular muscle cells oral and anal of a pellet, and in colons without the mucosa.


RESULTS
Spontaneous CMMCs propagated in both an oral or anal direction. When a pellet was inserted, CMMCs increased in frequency and propagated anally, exerting propulsive force on the pellet. The amplitude of slow waves increased during the CMMC. Localized mucosal stimulation/circumferential stretch evoked a CMMC, regardless of stimulus strength. The serotonin (5-hydroxytryptamine-3) receptor antagonist ondansetron reduced the amplitude of the CMMC, the propulsive force on the pellet, and the response to mucosal stroking, but increased the apparent conduction velocity of the CMMC. Removing the mucosa abolished spontaneous CMMCs, which still could be evoked by electrical stimulation.


CONCLUSIONS
The fecal pellet activates local mucosal reflexes, which release serotonin (5-hydroxytryptamine) from enterochromaffin cells, and stretch reflexes that determine the site of origin and propagation of the CMMC, facilitating propulsion.
Heredia
Dante J
DJ
Department of Physiology & Cell Biology, University of Nevada School of Medicine, Reno, Nevada, USA.
Dickson
Eamonn J
EJ
Bayguinov
Peter O
PO
Hennig
Grant W
GW
Smith
Terence K
TK
D000818:Animals; D003106:Colon / Q000294:innervation* / Q000502:physiology*; D005071:Evoked Potentials / Q000502:physiology; D005243:Feces; D005260:Female; D005769:Gastrointestinal Motility / Q000187:drug effects / Q000502:physiology*; D007413:Intestinal Mucosa / Q000294:innervation / Q000502:physiology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008839:Microelectrodes; D009046:Motor Neurons / Q000502:physiology*; D009119:Muscle Contraction / Q000502:physiology; D009130:Muscle, Smooth / Q000294:innervation / Q000502:physiology; D017294:Ondansetron / Q000494:pharmacology; D012701:Serotonin / Q000378:metabolism*; D012702:Serotonin Antagonists / Q000494:pharmacology
D012702:Serotonin Antagonists; D012701:Serotonin; D017294:Ondansetron