Electroacupuncture alleviates stress-induced visceral hypersensitivity through an opioid system in rats

AIM:To investigate whether stress-induced visceral hypersensitivity could be alleviated by electroacupuncture(EA) and whether EA effect was mediated by endogenous opiates.METHODS:Six to nine week-old male SpragueDawley rats were used in this study.Visceral hypersensitivity was induced by a 9-d heterotypic intermittent stress(HIS) protocol composed of 3 randomly stressors,which included cold restraint stress at 4?℃ for 45 min,water avoidance stress for 60 min,and forced swimming stress for 20 min,in adult male rats.The extent of visceral hypersensitivity was quantified by electromyography or by abdominal withdrawal reflex(AWR) scores of colorectal distension at different distention pressures(20 mmHg,40 mmHg,60 mmHg and 80 mmHg).AWR scores either 0,1,2,3 or 4 were obtained by a blinded observer.EA or sham EA was performed at classical acupoint ST-36(Zu-San-Li) or BL-43(Gao-Huang) in both hindlimbs of rats for 30 min.Naloxone(NLX) or NLX methiodide(m-NLX) was administered intraperitoneally to HIS rats in some experiments.RESULTS:HIS rats displayed an increased sensitivity to colorectal distention,which started from 6 h(the first measurement),maintained for 24 h,and AWR scores returned to basal levels at 48 h and 7 d after HIS compared to pre-HIS baseline at different distention pressures.The AWR scores before HIS were 0.6 ± 0.2,1.3 ± 0.2,1.9 ± 0.2 and 2.3 ± 0.2 for 20 mmHg,40 mmHg,60 mmHg and 80 mmHg distention pressures,respectively.Six hours after termination of the last stressor,the AWR scores were 2.0 ± 0.1,2.5 ± 0.1,2.8 ± 0.2 and 3.5 ± 0.2 for 20 mmHg,40 mmHg,60 mmHg and 80 mmHg distention pressures,respectively.EA given at classical acupoint ST-36 in both hindlimbs for 30 min significantly attenuated the hypersensitive responses to colorectal distention in HIS rats compared with sham EA treatment [AWRs at 20 mmHg:2.0 ± 0.2 vs 0.7 ± 0.1,P = 4.23 711 E-4;AWRs at 40 mmHg:2.6 ± 0.2 vs 1.5 ± 0.2,P = 0.00 163;AWRs at 60 mmHg:3.1 ± 0.2 vs 1.9 ± 0.1,P = 0.003;AWRs at 80 mmHg:3.6 ± 0.1 vs 2.4 ± 0.2,P = 0.0023;electromyographic(EMG) at 20 mmHg:24 ± 4.7 vs 13.8 ± 3.5;EMG at 40 mmHg:60.2 ± 6.6 vs 30 ± 4.9,P = 0.00 523;EMG at 60 mmHg:83 ± 10 vs 39.8 ± 5.9,P = 0.00 029;EMG at 80 mmHg:94.3 ± 10.8 vs 49.6 ± 5.9,P = 0.00 021].In addition,EA at the acupuncture point BL-43 with same parameters did not alleviate visceral hypersensitivity in HIS rats.EA in healthy rats also did not have any effect on AWR scores to colorectal distention at distention pressuresof 20 and 40 mmHg.The EA-mediated analgesic effect was blocked by pretreatment with NLX in HIS rats [AWR scores pretreated with NLX vs normal saline(NS) were 2.0 vs 0.70 ± 0.20,2.80 ± 0.12 vs 1.50 ± 0.27,3 vs 2.00 ± 0.15 and 3.60 ± 0.18 vs 2.60 ± 0.18 for 20 mmHg,40 mmHg,60 mmHg and 80 mmHg;P = 0.0087,0.0104,0.0117 and 0.0188 for 20,40,60 and 80 mmHg,respectively].Furthermore,EA-mediated analgesic effect was completely reversed by administration of m-NLX,a peripherally restricted opioid antagonist(EMG pretreated with m-NLX vs NS were 30.84 ± 4.39 vs 13.33 ± 3.88,74.16 ± 9.04 vs 36.28 ± 8.01,96.45 ± 11.80 vs 50.19 ± 8.28,and 111.59 ± 13.79 vs 56.42 ± 8.43 for 20 mmHg,40 mmHg,60 mmHg and 80 mmHg;P = 0.05 026,0.00 034,0.00 005,0.000 007 for 20 mmHg,40 mmHg,60 mmHg and 80 mmHg,respectively).CONCLUSION:EA given at classical acupoint ST-36 alleviates stress-induced visceral pain,which is most likely mediated by opioid pathways in the periphery.

Oxytocin decreases colonic motility of cold water stressed rats via oxytocin receptors

AIM: To investigate whether cold water intake into the stomach affects colonic motility and the involvement of the oxytocin-oxytocin receptor pathway in rats.METHODS: Female Sprague Dawley rats were used and some of them were ovariectomized. The rats were subjected to gastric instillation with cold(0-4℃, cold group) or room temperature(20-25℃, control group) saline for 14 consecutive days. Colon transit was determined with a bead inserted into the colon. Colonic longitudinal muscle strips were prepared to investigate the response to oxytocin in vitro. Plasma concentration of oxytocin was detected by ELISA. Oxytocin receptorexpression was investigated by Western blot analysis. Immunohistochemistry was used to locate oxytocin receptors.RESULTS: Colon transit was slower in the cold group than in the control group(P < 0.05). Colonic smooth muscle contractile response to oxytocin decreased, and the inhibitory effect of oxytocin on muscle contractility was enhanced by cold water intake(0.69 ± 0.08 vs 0.88 ± 0.16, P < 0.05). Atosiban and tetrodotoxin inhibited the effect of oxytocin on colonic motility. Oxytocin receptors were located in the myenteric plexus, and their expression was up-regulated in the cold group(P < 0.05). Cold water intake increased blood concentration of oxytocin, but this effect was attenuated in ovariectomized rats(286.99 ± 83.72 pg/mL vs 100.56 ± 92.71 pg/mL, P < 0.05). However, in ovariectomized rats, estradiol treatment increased blood oxytocin, and the response of colonic muscle strips to oxytocin was attenuated.CONCLUSION: Cold water intake inhibits colonic motility partially through oxytocin-oxytocin receptor signaling in the myenteric nervous system pathway, which is estrogen dependent.