| Objective:The pain experience includes sensory-discrimination as well as emotional-affective dimensions. A number of tests and studies have showed that, electroacupuncture can relieve the sensory-discrimination aspect of pain, which is through activating the opioid receptors in the ACC to play the role of pain relief. Clinical studies and animal experiments have showed that electroacupuncture treatment can alleviate the emotional-affective aspect of pain in human and animal, but the mechanism is unknown clearly so far.Human and animal studies have found that r ACC plays an important role in mediating emotional affective. Experiments have proved that the Conditioned Place Avoidance(CPA)caused by the emotional aspect of pain can disappear in the rats of removal of the bilateral r ACC. Therefore, we hypothesized that we can acticating the opiod receptors in the r ACC in order to alleviating the emotionl-discrimintion of pain which is caused by noxious stimulate. In the preliminary experiments, we gave mu-opioid receptor agonist DAMGO in the r ACC of rats, as a result,that could alleviate the conditioned place avoidance, but not affect the paw withdrawal latency(PWL). We came to the conclusion that the rat given DAMGO inside the r ACC could relive the emotional aspect of pain in rats and the process was not dependent on easing the sensory-discriminition of pain. Based on previous experimental results, we further speculated that electroacupuncture could relieve the pain emotional response through activating mu-opioid receptor. We will study if electroacupuncture can alleviate the CPA reaction in rats induced by CFA, and then give mu-opioid receptor antagonist CTOP within the r ACC rats before electroacupuncture to observe whether mu-opioid receptor antagonist within the r ACC will reverse this role of electroacupuncture, and try to discuss its mechanism.Methods:1. The CFA induced the model of persistent pain Male Sprague–Dawley rats weighting 250-270 g were divided into saline-injected group and CFA-injected group. CFA(0.08 ml) was injected into the left hind paw to set upinflammatory pain model. We give an injection of 0.08 ml saline(NS) as a control on the left hind paw of rats.2. CFA induced the conditioned place avoidance(C-CPA) response Male Sprague–Dawley rats weighting 250-270 g were divided into saline-injected group and CFA-injected group,(n = 5-8/group). By comparing the time rats spent in CFA matching room during the post-conditioning and pre-conditioning test, then counting the CPA Score, to determine whether rats made a CPA response.3. Electroacupuncture Male Sprague–Dawley rats weighting 250-270 g were divided into electroacupuncture group(EA) and sham electroacupuncture group(sham EA). After NS/CFA(0.08 ml) was injected into the left hind paw,insert the acupuncture needle into bilateral GB30. After connecting the acupuncture needle and electric acupuncture apparatus through the wires,gave the electroacupuncture stimulation.4. Paw Withdrawal Latency(PWL) test After the CPA training on first day and third day of, PWL was tested to observe the effect of CFA, electroacupuncture and CTOP of different doses injection in r ACC.5. Using the CFA-CPA modle to measure the emotional response Male Sprague–Dawley rats weighting 250-270 g were divided into eight groups,(n =5-9/group).(1)saline-injection into the left hind paw, the r ACC injected with NS, EA.(2)saline-injection into the left hind paw, the r ACC injected with NS, sham EA.(3)CFA-injection into the left hind paw, the r ACC injected with NS, EA.(4)CFA-injection into the left hind paw, the r ACC injected with NS,sham EA.(5)saline-injection into the left hind paw, the r ACC injected with 2/10/20(nmol/μl) CTOP, EA.(6)saline-injection into the left hind paw, r ACC injected with 2/10/20(nmol/μl) CTOP, sham EA.(7)CFA-injection into the left hind paw, r ACC injected with 2/10/20(nmol/μl) CTOP, EA.(8)CFA-injection into the left hind paw, the r ACC injected with 2/10/20(nmol/μl) CTOP, sham EA.Results:1. CFA could induce the CPA response.The PWL of CFA-injected group had a significant difference with the saline-injected group,(9.1±1.0 s vs 13.1±1.9 s, P<0.05,n=5), Injecting CFA into the left hind paw could set up the inflammatory pain model.Saline-injected group showed no aversion to either room(Pre 317.2±67.8 s vs Post352.1±113.8 s, P>0.05, n=5). In CFA-injected group, there was a significant difference that the time in CFA matching room between the post-conditioning test and the pre-conditioning test(Pre 323.5±105.5 s vs Post 151.4±58.38 s, P<0.05, n=6). There was a difference in CPA Score between CFA-injected group and saline-injected group(-172.1±97.3 s vs 12.6±81.2 s, P<0.05, n1=5, n2=6). CFA induced conditioned place avoidance(C-CPA).2. Electroacupuncture could alleviate the C-CPA.After injecting 0.08 ml CFA into rats, left hind paw, EA/sham EA would be gave at bilateral GB30. The sham EA group spent less time in CFA matching room during the post-conditioning test than the pre-conditioning test(Post 151.4±23.8 s vs Pre 323.5±43.1 s,P<0.05, n=6). The EA group showed no aversion to either room(Post 248.9±144.1 s vs Pre234.9±54.57 s, P<0.05, n=5). There was a significant difference in CPA Score between EA group and sham EA group(13.9±47.2 s vs- 172.1±39.7 s, P<0.05, EA group n=5, sham EA group n=6).After 0.08 ml NS was injected into the left hind paw, gave EA/sham EA at bilateral GB30. The sham EA group showed no aversion to either room(Post 352.1±50.9 s vs Pre317.2±30.3 s, P>0.05, n=5). The EA group also showed no aversion to either room(Post250.2±112.4 s vs Pre 305.6±45.9 s, P>0.05, n=5). There was no significant difference in CPA Score between EA group and sham EA group(-64.49±52.9 s vs 12.6±36.3 s, P>0.05,sham EA group n=5, EA group n=9). Electroacupuncture itself did not make an effect on the emotion of rats.The day after injecting 0.08 ml CFA into rats, left hind paw and giving EA/sham EA at bilateral GB30, tested the PWL of both groups. There was no significant difference in PWL between EA group and sham EA group(12.0±1.4 s vs 9.1±0.4 s, P>0.05, n=5).Electroacupuncture has not allivated the PWL of rats on the second day.3. CTOP injected into r ACC could reverse the effect of electroacupuncture’s alleviation of the C-CPA.CTOP/NS were injected into r ACC of CFA-injected group before the electroacupuncture. The rats of CTOP group spent less time in CFA matching room during the post-conditioning test than pre-conditioning test(Post 210.5±59.8 s vs Pre 307.8±47.0s, P<0.05, n=5). The NS group showed no aversion to either room(Post 248.9±64.5 s vs Pre 234.9±24.4 s, P>0.05, n=5). There was a significant difference in CPA score between CTOP group and NS group(-127.5±24.1 s vs 13.9±47.2 s, P<0.05,n=5). CTOP injectedinto rACC can reverse the effect of electroacupuncture’s alleviation of the C-CPA.CTOP/NS were injected into r ACC of CFA-injected group without electroacupuncture.The CTOP group showed no aversion to either room(Post 255.1±71.8 s vs Pre 403.5±46.2s, P<0.05, n=5). The NS group also showed no aversion to either room(Post 151.4±23.8 s vs Pre 323.5±43.1 s, P<0.05, n=6). There was no significant difference in CPA score between CTOP group and NS group(-148.4±50.5 s vs-172.1±39.7 s, P>0.05, n=5). CTOP injected into r ACC itself did not make an effect on the emotion of rats.Different doses of CTOP injected into r ACC of CFA-injected groups respectively could make significant different effects. There was no difference in CPA score between 2nmol/μl CTOP group and NS group(-2.0±18.8 s vs 13.9±47.2 s, P>0.05, n=7). There was a significant difference in CPA score between 10 nmol/μl CTOP group and NS group(-97.3±30.3 s vs 13.9±47.2 s, P<0.05, n=7). There was a significant difference in CPA score between 20 nmol/μl CTOP group and NS group(-127.5±24.1 s vs 13.9±47.2 s,P<0.05, n=7). There was a significant difference in CPA score between 10 nmol/μl CTOP group and 2 nmol/μl CTOP group(-97.3±30.3 s vs-2.0±18.8 s, P<0.05, n=7). There was a significant difference in CPA score between 20 nmol/μl CTOP group and 2 nmol/μl CTOP group(-127.5±24.1 s vs-2.0±18.8 s, P<0.05, n=7). There was no significant difference in CPA score between 10 nmol/μl CTOP group and 20 nmol/μl CTOP group(-97.3±30.3 s vs-127.5±24.1 s, P>0.05, n=7). 2 nmol/μl CTOP injected into r ACC can,t reverse the effect of electroacupuncture,s alleviation of the C-CPA. While 10 nmol/μl CTOP and 20 nmol/μl CTOP injected into r ACC both can reverse the effect of electroacupuncture,s alleviation of the C-CPA.The day after giving different doses of CTOP(2 /10 /20 nmol/μl) or NS into r ACC of CFA-injected group, tested the PWL of groups. There was no significant difference in PWL between groups(P>0.05). The PWL of naive group was 10.9±0.9 s, n=6; the PWL of2nmol/μl CTOP group was 7.2±0.6 s, n=5; the PWL of 10nmol/μl CTOP group was 11.0 ±1.3 s, n=5; the PWL of 20nmol/μl CTOP group was 8.1±2.1 s, n=5. Giving different dose of CTOP into r ACC of CFA-injected group has not affected the PWL of rats.Conclusion:1. Electroacupuncture could alleviate pain affective reaction induced by CFA.2. The effect of electroacupuncture,s alleviating CFA induced pain affective was mediated by activating the r ACC mu-opioid receptor. |
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