Abstract
Objective To investigate the effects of cannabinoid 1 receptor (CB1R) on regulating visceral sensitivity in rats with acute partial restraint stress. Methods Thirty Sprague-Dawley rats were divided into blank control (sham stress), acute stress and CB1R groups with 10 each. The frequency of discharge of electromyogram (EMG) was recorded at the 1st, 2nd, 5th and 8th day to evaluate the visceral sensitivity to colorectal distension (CRD) in rats. The expression of the CB1R mRNA was determined by means of RT-PCR at day 8. Results There was no significant difference in baseline discharge frequency among three groups at the 1st day. But the discharge frequencies corresponding to CRD at 40,60,80 mm Hg at the 2nd day were significantly lower in CB1R group [(22.37±1.49)/min, (42.24±3.03)/min and (69.09±5.54)/min, respectively] than in acute stress group [(39.71±1.84)/min, (84.45±8.85)/min and (112.56±11.66)/min, respectively, P<0.05)]. The discharge frequencies corresponding to CRD at 40, 60,80 mm Hg in acute stress group [(104.12±6.77)/min, (158.07±18.68)/min, (193.58±25.69)/min,respectively] showed a significant elevation at the 5th day in comparison with blank control group[(36.33±5.42)/min, (74.07±8.25)/min, (102.94±7.95)/min, respectively, P<0.05] or CB1R group [(74.66±6.44)/min,(140.10±4.68)/min and (160.39±5.60)/min,respectively, P<0.05]. However, at the 8th day after stress, there was no significant difference in discharge frequency among three groups. The expressions of CB1R mRNA in ileocecal junction, proximal colonic and distal colonic tissues were significantly higher in acute stress group (2.53±0.52, 2.29±0.42, 2.54±0.29 respectively) than in blank control group(0.56±0.15, 0. 73±0.12, 0.82±0.09, respectively, P<0.05). There was no effect of CB1R agonist on CB1R mRNA expression in rats. Conclusion The visceral sensitivity in rats induced by stress can trigger the accommodation of endogenous cannabinoid system that plays an important role in modulation of visceral sensitivity. Key words: Receptors, cannabinoid; Stress disorders, traumatic, acute; Hyperalgesia
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