Role of cannabinoid receptor-2 in small intestinal fasted myoelectric activity of rats

Abstract

Cannabinoid receptor-1 (CB1R) and cannabinoid receptor-2 (CB2R) have significant roles in the esophagus, small intestine, and colon motility in the postprandial period besides gastric emptying, secretion, and defecation in the gastrointestinal system. Furthermore, our previous study showed that activation of peripheral CB1R inhibited migrating myoelectric complex (MMC), forming the source of fasted small intestinal motility. However, the role of the central/peripheral CB2Rs on the MMC pattern is still unknown. The present study aimed to investigate the roles of peripheral and central CB2Rs in forming and regulating small intestine MMC patterns in rats. In this study, we used 42 adult male Sprague-Dawley rats (n:7). We implanted bipolar electrodes in three different jejunum sites of rats (J1, J2, J3) to record the MMC pattern. We placed a cannula in the right lateral ventricle to perform drug intracerebroventricularly (i.c.v.) and implanted a catheter in the right jugular vein to inject the drug intravenously (i.v). After the amelioration period, we conducted experiments following an 18-hour fasting period and later took at least a one-hour baseline recording of the MMC pattern. Then, we injected JWH 133, a CB2R agonist i.v. (1.25-10 mg/kg) or i.c.v. (2.5- 20 μg/rat) and also administered AM 630, a CB2R antagonist, i.v. (0.25-2 mg/kg) or i.c.v. (2.5-20 μg/rat). We compared the effects of JWH 133 or AM 630 on the MMC pattern to the vehicle group (10% dimethyl sulfoxide). Centrally or peripherally injected JWH 133 and AM 630 did not cause any change in the spike frequency and the number of the MMC cycle. The results of the present study propose that CB2Rs are involved in neither endogenous formation nor exogenous regulation of the fasting myoelectric activity in healthy fasted rats.