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Departments of Physiology and Medicine, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia 23298-0551
The circuit of myenteric interneurons that
regulate excitatory input to longitudinal colonic muscle was identified
using dispersed ganglia and longitudinal muscle strips with adherent
myenteric plexus from rat distal colon. The preparations enabled
measurement of neurotransmitter release from interneurons
and/or excitatory motoneurons innervating longitudinal muscle.
1,1-Dimethyl-4-phenylpiperizinium (DMPP) and somatostatin were used to
activate myenteric neurons in dispersed ganglia and muscle strips,
respectively. DMPP-stimulated vasoactive intestinal peptide (VIP)
release in dispersed ganglia was inhibited by
[Met]enkephalin and bicuculline and augmented by naloxone
and GABA, implying that inhibitory opioid and stimulatory GABA neurons
regulate the activity of VIP interneurons. In muscle strips, VIP
stimulated basal and augmented somatostatin-induced substance P (SP)
release; the somatostatin-induced increase in SP release was inhibited
by VIP-(10
28) and
NG-nitro-L-arginine, implying that
excitatory VIP neurons regulate tachykinin motoneurons innervating
longitudinal muscle. Somatostatin inhibited [Met]enkephalin
and stimulated VIP release; basal and somatostatin-stimulated VIP
release were inhibited by [Met]enkephalin and bicuculline
and augmented by naloxone and GABA, implying that inhibitory pathways
linking somatostatin, opioid, and GABA neurons regulate VIP
interneurons, which in turn regulate tachykinin and probably
cholinergic motoneurons.
peristaltic reflex; myenteric plexus; neurotransmitter release; enteric nervous system; neuropeptides
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