An enteric occult reflex underlies accommodation and slow transit in the distal large bowel.
OBJECTIVE
Transit of fecal material through the human colon takes > or =30 hours, whereas transit through the small intestine takes 24 hours. The mechanisms underlying colonic storage and slow transit have yet to be elucidated. Our aim was to determine whether an intrinsic neural mechanism underlies these phenomena.


METHODS
Recordings were made from circular muscle (CM) cells and myenteric neurons in the isolated guinea pig distal colon using intracellular recordings and Ca(2+) imaging techniques. Video imaging was used to determine the effects of colonic filling and pellet transit.


RESULTS
Circumferential stretch generated ongoing oral excitatory and anal inhibitory junction potentials in the CM. The application of longitudinal stretch inhibited all junction potentials. N-omega-nitro-L-arginine (100 micromol/L) completely reversed the inhibitory effects of longitudinal stretch suggesting that nitric oxide (NO) inhibited interneurons controlling peristaltic circuits. Ca(2+) imaging in preparations that were stretched in both axes revealed ongoing firing in nNOS +ve descending neurons, even when synaptic transmission was blocked. Inhibitory postsynaptic potentials were evoked in mechanosensitive interneurons that were blocked by N-omega-nitro-L-arginine (100 micromol/L). Pellet transit was inhibited by longitudinal stretch. Filling the colon with fluid led to colonic elongation and an inhibition of motility.


CONCLUSIONS
Our data support the novel hypothesis that slow transit and accommodation are generated by release of NO from descending (nNOS +ve) interneurons triggered by colonic elongation. We refer to this powerful inhibitory reflex as the intrinsic occult reflex (hidden from observation) because it withdraws motor activity from the muscle.
Dickson
Eamonn J
EJ
Department of Physiology & Cell Biology, University of Nevada School of Medicine, Reno, Nevada 89557, USA.
Spencer
Nick J
NJ
Hennig
Grant W
GW
Bayguinov
Peter O
PO
Ren
Jim
J
Heredia
Dante J
DJ
Smith
Terence K
TK
D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D003106:Colon / Q000166:cytology / Q000294:innervation* / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005769:Gastrointestinal Motility / Q000502:physiology*; D006168:Guinea Pigs; D007395:Interneurons / Q000502:physiology; D008297:Male; D008465:Mechanoreceptors / Q000502:physiology; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009130:Muscle, Smooth / Q000166:cytology / Q000294:innervation / Q000502:physiology; D009197:Myenteric Plexus / Q000502:physiology; D009569:Nitric Oxide / Q000378:metabolism*; D019335:Nitroarginine / Q000494:pharmacology; D010528:Peristalsis / Q000502:physiology*; D012018:Reflex; D009435:Synaptic Transmission / Q000502:physiology
D004791:Enzyme Inhibitors; D019335:Nitroarginine; D009569:Nitric Oxide