Activation of μ-Opioid Pathway Is Associated with the Canceling Effect of Footshock Stimulus on the Restraint Stress-Induced Inhibition of Small Intestinal Motility in Rats

Abstract

We previously reported that small intestinal motility was significantly inhibited by restraint stress, but not by footshock stress. In the present study, we found that plasma β-endorphin levels were more significantly elevated by footshock stress than restraint stress, and that preloading of footshock stimulus canceled the inhibition of small intestinal motility by restraint stress. Pretreatment with the μ-opioid receptor antagonist naltrexone significantly attenuated this canceling effect of footshock stimulus. These results suggest that footshock stimulus may cancel the inhibition of small intestinal motility by restraint stress via activation of μ-opioid receptors.