| Objective:The pain can be divided into two basic parts: sensory-discrimination and emotional-affective dimensions. A large number of research data shows that these two different components are made up of different central mechanisms and mediated by separate neural pathways. Behavioral, electrophysiological and brain imaging studies of human and animals found that anterior cingulate cortex(ACC), it involved in the formation of the pain-induced aversion and behaviour which caused by disgusted emotion which associate with pain,especially rostral ACC(r ACC). Using surgical or other methods to damage the bilateral r ACC and surrounding tissues can inhibit the behavior produces of pain-related negative emotions induced conditioned place avoidance(CPA). Electroacupuncture(EA) has been widely used in clinical chronic pain. Recently, some studies and our animal experiments results strongly suggest that, The activation of NMDA receptors in the r ACC involved in the formation of the pain associated with bad mood.In this experiment, we used complete Freund’s adjuvant induced conditioned place avoidance model and Pain related behavior detection, combined with respectively injected different concentration of APⅤ,a glutamate binding site(gin site) antagonist of NMDA receptors, or DNQX, an antagonist of AMPA receptors. Whether the antagonism of NMDA receptor within the r ACC have relief of emotional response which caused by chronic inflammatory CFA-induced pain stimulation, and NMDA receptor in the mechanism of this effect may be involved in analysis.Methods:1. To set up CFA-induced chronic persistent pain model。In our experiment, we use male Sprague–Dawley rats(weight 250-270g), which were given subcutaneous injection of CFA in the left hind paw. The rats in control group were given subcutaneous injection of the same dose of NS.2.To establish the CFA-induced conditioned place avoidance(C-CPA) model.(1) uninjected control group,(2)saline-injected control group,(3) CFA-injected group, n = 6-12/group. The dose of saline or CFA is 0.08 ml per rat. We determined the chronic inflammatory pain caused by the injection of CFA as a specific factor, and coupled with the environmental conditions which can be distinguished, so we can established the C-CPA model. We compared the. time spent on pain-paired room during the Day 3 CPA test and the time spent on Day 1 CPA test.3. The C-CPA model is used to inspect the function of AP or DNQX on pain Ⅴemotional affect.hind paw, NS was administrated into r ACC,(2) NS was injected in the left hind paw, NS was administrated into r ACC(3) CFA was injected in the left hind paw, administrated 0.5/ 2/ 8/ 12/ 16nmol/μl AP or DNQX into r ACC severally,Ⅴ(4) NS was injected in the left hind paw, administrated 0.5/ 2/ 8/ 12/ 16nmol/μl AP or DNQX into r ACC severally. Ⅴ4. Testing the Paw Withdrawal Thermal latency(PWL)PWL will be test after the training of C-CPA behavior at Day 1 and Day 3.Results:1. The injection of CFA in rats hind paw could induce reaaction of CPA.Uninjected and NS-injectedshowed us that there is no difference aversion to either room. CFA-injected showed it is significant that the measurement value of Day 3 CPA is less than the basic value of Day 1 CPA, CPA score value is bigger, so CFA-induced pain produced a version of pain-paired enviroment.2. APⅤ was administrated into rACC, this could inhibit C-CPA behavior.The group of injected CFA in left hind paw and NS in rACCshowed significant C-CPA response. When we injected different dose of APⅤ into r ACC, it showed in 0.5( nmol/μl) APⅤ group, there are no difference of time spent on CFA-paired chamber between Day 3 and Day 1.As the dose was increased into 2/ 8nmol/μl, magnitude of CPA between these two groups was no statistically significant, but have statistically significant with CFA-NS group. This means at a appropriate dose of AP, ⅤC-CPA response could be inhibited by APⅤ. As the dose increased into 12/ 16nmol/μl magnitude of CPA was statistically significant. When injected NS in left hind paw, and injected 5 dose of AP Ⅴinto r ACC respectively, it is showed that no place avoidance or place preference did not appeared, the same as the reported results. The score of CPA and CPP among groups were no statistically significant.3. When DNQX was injected into rACC, there is no effect could inhibit C-CPA response.CFA-injected, different dose of DNQX( 0.5/ 2/ 8/ 12/ 16nmol/μl)was injected into r ACC, there are no difference of CPA score among groups, NS-injected, and injected different dose of DNQX( 0.5/ 2/ 8/ 12/ 16nmol/μl)into r ACC, compared the CPA scores of this 5 groups, there were no statistical significant between them. This meant that DNQX couldn’t inhibit C-CPA response and there were still no place avoidance or place preference.4. Injection of CFA in rats’ left hind paw will change the value of PWL.We choosed PWL as the observed value of response to thermal stimuli, and detection followed Day 1 and Day 3 CPA in quick succession, in CFA-injected group, PWL was decreased in Day 3 test, but in NS-injected group, PWL in Day 3 test has no difference with result in Day 1 test.5. AP Ⅴcan relief C-CPA response but will not change the sensory-discriminative of pain caused by CFA.In CFA-injected into left hind paw and different dose of APⅤ or DNQX injected into r ACC groups, PWL in Day 3 test has significantly decrease compared with Day 1. As control group, injected NS into left hind paw of rats, the changes of PWL were not so obvious.6.The results of immunofluorescence staining and western-blot were to follow-up perfect.Conclusion:1. APⅤ, as a NMDA receptor antagonists can relief the affective dimensions which induced by CFA at low doses(2/ 8nmol/μl). High doses(12/ 16nmol/μl) may not ease the affective dimensions caused by complete Freund’s adjuvant.2. DNQX, as a AMPA receptor antagonists may have no effect on the affective dimensions.Ⅴdimensions of pain caused by injection of complete Freund’s adjuvant is not by inhibiting sensory-discriminative of pain. |
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