CGRP as a transmitter in the sensory pathway mediating peristaltic reflex

The presence of calcitonin gene-related peptide (CGRP) in enteric and dorsal root ganglion neurons suggests that it might be involved as a transmitter in the sensory pathway that mediates the peristaltic reflex. This notion was examined in a three-compartment flat-sheet colonic preparation in which stimuli (muscle stretch or mucosal stimulation) were applied to the central compartment, while ascending contraction and descending relaxation were measured in the peripheral compartments. Both muscle stretch and mucosal stroking applied to the central compartment elicited CGRP release into the central, but not peripheral, compartments. The magnitude of release was proportional to the intensity of stimulation. Addition of the CGRP antagonists, human CGRP-(8-37) and Tyr0CGRP-(28-37), to the central compartment inhibited descending and ascending responses elicited by muscle stretch or mucosal stimulation. Addition of the sensory neurotoxin, capsaicin (0.01 to 1 microM), to the central compartment caused concentration-dependent release of CGRP; the resultant depletion of sensory transmitter resulted in a concentration-dependent decrease in ascending and descending responses elicited by muscle stretch and mucosal stimulation. Extrinsic denervation decreased basal CGRP release and abolished CGRP release and peristaltic responses normally elicited by muscle stretch but not CGRP release or peristaltic responses elicited by mucosal stimulation. The results indicate that extrinsic sensory pathways, which mediate the peristaltic response to muscle stretch, and intrinsic sensory pathways, which mediate the peristaltic response to mucosal stimulation, utilize CGRP as a sensory transmitter.