Distinct populations of sensory neurons mediate the peristaltic reflex elicited by muscle stretch and mucosal stimulation

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Abstract
Recent studies suggest that muscle stretch and mucosal stimulation elicit intestinal peristalsis by activating distinct populations of sensory neurons that converge on the same population of enteric motor neurons. The present study sought to characterize the origin and projections of these sensory neurons. The reflex was elicited by applying muscle stretch and mucosal stroking to the central compartment of a three-compartment flat-sheet preparation of rat colon while ascending contraction and descending relaxation were measured in the orad and caudad compartments, respectively. Identical graded responses were elicited by muscle stretch and mucosal stimulation: atropine (1 microM) and the tachykinin antagonist spantide (10 microM) inhibited ascending contraction when added to the orad compartment only, while the vasoactive intestinal peptide antagonist VIP10–28 (10 microM) and the NO synthase inhibitor NG-nitro-L-arginine (100 microM) inhibited descending relaxation when added to the caudad compartment only. Addition of capsaicin (1 microM) to the central compartment for 30 min abolished ascending contraction and descending relaxation elicited by muscle stretch and mucosal stimulation. Recovery of response was complete when capsaicin was applied to the mucosa of the colon in situ and measurements made 1 d after, implying that at this low concentration capsaicin depleted sensory nerve terminals of their transmitter content.(ABSTRACT TRUNCATED AT 250 WORDS)

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