The visceromotor response is a whole body motor reflex to an acute visceral stimulus (Fig. 5). During distention of a hollow organ, muscles of the abdomen, trunk, and limbs contract. The magnitude of the electromyogram recorded from these muscles is positively correlated with the stimulus intensity providing a readily quantifiable measure of the response to dis-tention in an awake or lightly anesthetized animal. This visceromotor response is commonly used to study responses to distention or stimulation of hollow visceral organs including the colon (58-64), bladder (65), uterine-cervix/vagina (66-69), and ureter (70,71). Following inflammation, the magnitude of the visceromotor response increases: visceral hyperalgesia. Pharmacological (e.g., opioids or N-methyl-D-aspartate (NMDA) receptor antagonists) or surgical intervention that attenuates the perception of pain attenuates the magnitude of the visceromotor response, further supporting the validity of this end point as a measure of visceral pain and hyperalgesia.
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