海马参与雌激素加重咬合干扰致去卵巢大鼠慢性咬肌痛敏

Hippocampus is involved in 17β-estradiol exacerbating experimental occlusal inter-ference-induced chronic masseter hyperalgesia in ovariectomized rats

目的:探究海马参与雌激素(主要为17β-雌二醇,17β-estradiol,E2)和实验性咬合干扰(experimental occlusal interference,EOI)对双侧卵巢摘除(ovariectomy,OVX)大鼠慢性咬肌痛敏影响的分子机制。方法:将32只OVX大鼠随机分为4组(8只/组),对照组:OVX组,于OVX术后7 d开始0μg/d E2(即用溶剂vehicle替代),不施加EOI;实验组:(1)OVX+E2组,于OVX术后7 d开始80μg/d E2替代,不施加EOI;(2)OVX+EOI组,于OVX术后7 d开始0μg/d E2替代,术后17 d施加EOI;(3)OVX+E2+EOI组,于OVX术后7 d开始80μg/d E2替代,术后17 d施加EOI。于OVX术前、术后7 d(E2替代开始)、术后17 d(E2替代10 d,即EOI开始)、术后24 d(EOI 7 d)分别测试机械刺激反应阈值,建模完成后取大鼠双侧海马进行免疫荧光染色,观察海马CA3区神经元磷酸化细胞外信号调节激酶(phospho-extracellular signal regulated kinase 1/2,p-ERK1/2)表达情况,以及取大鼠双侧海马进行Western Blot定量检测p-ERK1/2表达量。结果:与对照组[左侧:(135.3±8.5)g,右侧:(135.4±10.8)g]相比,OVX+E2组[左侧:(113.3±5.6)g,右侧:(112.5±5.6)g]和OVX+EOI组[左侧:(93.3±5.4)g,右侧:(90.8±5.5)g]大鼠双侧咬肌机械刺激反应阈值显著降低(P<0.01);OVX+E2+EOI组[左侧:(81.2±6.2)g,右侧:(79.8±7.7)g]阈值降低较对照组、OVX+E2组和OVX+EOI组显著(P<0.05);对照组、OVX+E2组、OVX+EOI组和OVX+E2+EOI组大鼠双侧海马CA3区p-ERK1/2阳性神经元比例依次增高,且组间差异有统计学意义(P<0.05);p-ERK1/2蛋白表达量在对照组、OVX+E2组、OVX+EOI组依次增高,组间差异无统计学意义(P>0.05),OVX+E2+EOI组p-ERK1/2表达量显著高于其他3组(P<0.05)。结论:高浓度E2可加重EOI导致的OVX大鼠慢性咬肌痛敏,其中枢机制可能与海马内ERK1/2信号通路有关。

Objective:To investigate the influence of chronic masseter hyperalgesia induced by 17β-estradiol(E2)and experimental occlusal interference(EOI)on underlying mechanism in hippocampus of ovariectomized(OVX)rats.Methods:In the study,32 OVX rats were randomly divided into 4 groups(8 rats/group):The control group was OVX group,and 0μg/d E2(vehicle)injection was started 7 d after OVX without EOI;in the experimental group(1)OVX+E2 group,80μg/d E2 injection was started 7 d after OVX without EOI;in the experimental group(2)OVX+EOI group,vehicle injection was started 7 d after OVX and EOI was applied 17 d after OVX;in the experimental group(3)OVX+E2+EOI group,80μg/d E2 injection was started 7 d after OVX and EOI was applied 17 d after OVX.Bilateral masseter muscle mechanical withdrawal thresholds were measured before OVX,7 days after OVX(before E2 injection),17 days after OVX(10 days after E2 injection and before EOI)and 24 days after OVX(7 days after EOI).Immunofluorescence staining was used to reveal phospho-extracellular signal regulated kinase 1/2(p-ERK1/2)-positive neurons in CA3 of hippocampus.The protein expression of p-ERK1/2 in hippocampus was detected using Western Blot.Results:Compared with the control group[left side:(135.3±8.5)g,right side:(135.4±10.8)g],bilateral masseter muscle mechanical withdrawal thresholds of OVX+E2 group[left side:(113.3±5.6)g,right side:(112.5±5.6)g]and OVX+EOI group[left side:(93.3±5.4)g,right side:(90.8±5.5)g]were decreased(P<0.01).Bilateral masseter muscle mechanical withdrawal thresholds were significantly lower in OVX+E2+EOI group[left side:(81.2±6.2)g,right side:(79.8±7.7)g]than in the control,OVX+E2 and OVX+EOI groups(P<0.05).The proportion of p-ERK1/2 positive neurons in the CA3 region of the hippocampus was increased in the control,OVX+E2,OVX+EOI and OVX+E2+EOI groups in turn,and the difference between the groups was statistically significant(P<0.05).p-ERK1/2 protein expression was increased in the control,OVX+E2 and OVX+EOI groups in turn,but the difference was not statistically significant(P>0.05).p-ERK1/2 expression was significantly higher in OVX+E2+EOI group than in the other three groups(P<0.05).Conclusion:High concentration of E2 could exacerbated EOI-induced chronic masseter hyperalgesia in ovariectomized rats,and its central mechanism may be related to the upregulation of the phosphorylation of ERK1/2 in hippocampus.