大鼠脊髓后角浅层初级传入C纤维内μ阿片受体的免疫组织化学定位——光镜与电镜研究

IMMUNOHISTOCHEMICAL LOCALIZATION OF μ OPIOID RECEPTOR IN PRIMARY AFFERENT C FIBER WITHIN THE SUPERFICIAL LAYERS OF THE RAT SPINAL DORSAL HORN A LIGHT AND ELECTRON MICROCOPIC STUDY

目的在光镜及电镜下观察大鼠脊髓后角内μ阿片受体（ＭＯＲ）与Ｃ纤维的关系，为进一步揭示阿片镇痛的突触机制提供形态学证据。方法根据辣椒素对初级传入神经中Ｃ纤维的特异性神经毒性，在大鼠蛛网膜下腔注射辣椒素以毁损Ｃ纤维，用免疫组织化学ＡＢＣ法比较脊髓后角内ＭＯＲ免疫反应性的变化；根据西非单叶豆同工凝集素Ｉ－Ｂ４（ｇｒｉｆｏｎｉａｓｉｍｐｌｉｃｉｆｏｌｉａｉｓｏｌｅｃｔｉｎＩ－Ｂ４，Ｉ－Ｂ４）与初级传入Ｃ纤维选择性结合的特性，应用双标（免疫）组织化学电镜技术（ＡＢＣ－纳金法）分别标记脊髓后角内Ｉ－Ｂ４结合位点和ＭＯＲ。结果大鼠蛛网膜下腔注射辣椒素３～７ｄ后，其脊髓后角Ⅰ～Ⅱ层内的ＭＯＲ免疫反应性较对照动物明显减弱；电镜下在大鼠脊髓后角浅层内观察到，ＭＯＲ不仅定位于树突内，也分布在含Ｉ－Ｂ４结合位点的Ｃ纤维终末内。无论在树突内还是在轴突终末内，ＭＯＲ主要分布在非突触部位，仅少量ＭＯＲ与突触前膜和／或突触后膜有关。结论脊髓后角中部分ＭＯＲ来源于辣椒素敏感的Ｃ纤维，外源性吗啡或内源性吗啡样物质如内吗啡肽等ＭＯＲ激动剂在脊髓后角内既可通过突触后（树突内）的ＭＯＲ发挥作用，也可通过突触前（轴突终末内）的ＭＯＲ对Ｃ纤维产生突触前?

Objective\ To provide morphological evidences for further revealing synaptic mechanism of opioid analgesia,the relation of μ opioid receptor(MOR) to primary afferent C fiber in the spinal dorsal horn of the rat was light and electron microscopically observed.Methods\ According to the specific neurotoxicity of capsaicin to C fiber,capsaicin was injected subarachnoidally in the rat and the change of MOR immunoreactivity was detected in the rat spinal dorsal horn by using immunohistochemistry(ABC method);Based upon the selectivity of isolectin I B4 from griffonia simpliciflia binding to C fiber,the I B4 binding sites and MOR in the spinal dorsal horn were double labeled(immunohistochemical)histochemical electron microscopy(ABC Nanogold method).Results\ During 3～7 days after subarachnoidal injetion of capsaicin,the MOR immunorecativity in the laminae Ⅰ～Ⅱ of the spinal dorsal horn of the rat treated with capsaicin was markedly decreased as compared with that of the control rat.Under electron microscope,it was observed that in the superficial layers of the spinal cord,MOR was distributed in some axonal terminals including the terminals of C fibers containing I B4 binding sites as well as in the dendrites.In both the dendrites and the axonal terminals,MORs were mainly localized in the non synaptic membranes except for the minority associated with pre and/or post synaptic membranes.Conclusion\ A considerable amount of MOR in the spinal dorsal horn originates from the primary afferent C fibers and morphine or endogenous morphine like substances such as endomorphin may act not only on postsynaptic MOR in the dendrites but also on presynaptic MOR in the axonal terminal of C fiber to inhibit the input of C fiber,and in these processes,the nonsynaptic action of MOR agonists is likely essential.