AJP - Gastrointestinal and Liver Physiology, Vol 257, Issue 6 925-G929, Copyright © 1989 by American Physiological Society
Intramural neural control of opossum sphincter of Oddi
J. F. Helm, W. J. Dodds, J. Christensen and S. K. Sarna
Digestive System Research Center, Medical College of Wisconsin, Milwaukee 53226.
We evaluated the intramural neural control of the opossum sphincter of Oddi
(SO) in an in vitro preparation. Force transducers were used to record
contractions at four sites along the sphincter segment. To stimulate
intramural nerves, 10- to 120-s trains of pulses (4-10 V amplitude, 0.5 ms
duration, and 5 Hz frequency) were delivered to one of three electrode
pairs implanted along the SO. Electrical stimulation in the proximal, mid,
or distal SO elicited phasic contractions that invariably originated in the
proximal SO and propagated antegrade along the entire length of the
sphincter segment. Stimulus-evoked contractions resembled spontaneous
antegrade peristaltic contractions, but occurred at a higher rate
(12-20/min). Atropine completely blocked this excitatory response to nerve
stimulation. After atropine, nerve stimulation in the proximal, mid, or
distal SO abolished spontaneous contractions at and distal to the site of
stimulation for the duration of the stimulus. The inhibitory response to
nerve stimulation was completely blocked by tetrodotoxin but was unaffected
by phenoxybenzamine, tolazoline, or propranolol. We conclude that 1) the
opossum SO is innervated by intramural cholinergic excitatory nerves and
nonadrenergic noncholinergic inhibitory nerves; 2) cholinergic excitatory
nerves are organized in ascending neural pathways, whereas nonadrenergic
noncholinergic inhibitory nerves descend along the length of the SO; and 3)
these neural pathways may modulate SO peristalsis in vivo and participate
in ascending excitatory and descending inhibitory reflexes.
