Bursts of action potentials and intrinsic sensory neurons of the intestine

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The pattern of input to intestinal sensory neurons shapes their output and is, thus, fundamental to an understanding of the initiation and propagation of intestinal reflexes. Recent data suggests that this input consists largely of bursts of action potentials (APs). The origin of these bursts in 45 myenteric sensory neurons from guinea pig ileum was investigated. All neurons were near intact mucosa and intracellular electrophysiological recording techniques were used during selective electrical stimulation of the mucosal epithelium and of the cell body. Three types of bursts were seen: following an antidromic AP evoked by electrical stimulation of the mucosa; following an AP evoked at the soma; and spontaneously occurring. All bursts had an average intra-burst frequency of between 40-50 Hz and tended to occur in the same neurons. All APs in a burst persisted during somatic hyperpolarization and many had an inflection on their rising phase. They also persisted in low calcium solutions and a variety of ligand-gated ion channel receptor antagonists. TTX (300nM) abolished all bursts while TTX (30nM), tropisetron (30microM) or a high calcium, high magnesium solution selectively blocked the later APs in a burst. Results from collision experiments suggest that both the electrically and somatically evoked bursts originate near the sensory nerve terminals in the mucosa. These bursts of APs are widespread and have many characteristics in common suggesting similar mechanisms underlie generation of each. These data suggest that positive feedback between sensory nerve terminals and epithelial elements may be important in normal intestinal function.
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Bertrand, P. P
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UNSW Faculty