Zou X, Lin Q, Willis W D
Department of Anatomy and Neuroscience, Marine Biomedical Institute, The University of Texas Medical Branch, Galveston, TX 77555-1069, USA.
Neuroscience. 2001;106(1):171-82. doi: 10.1016/s0306-4522(01)00175-0.
GABAergic neurons play an important role in the generation of primary afferent depolarization, which results in presynaptic inhibition and, if large enough, triggers dorsal root reflexes. Recent electrophysiological studies by our group have suggested that increased excitation of spinal GABAergic neurons by activation of N-methyl-D-aspartate (NMDA) and non-NMDA receptors following intradermal injection of capsaicin results in the generation of DRRs that contribute to neurogenic inflammation. The present study was to determine if changes in the expression of Fos protein occur in GABAergic neurons in the lumbosacral spinal cord following injection of capsaicin into the glabrous skin of one hind paw of anesthetized rats and if pretreatment with an NMDA receptor antagonist, D-(-)-2-amino-7-phosphonoheptanoic acid (AP7) or a non-NMDA receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) blocks Fos expression in these neurons. The experiments used western blots and immunofluorescence double labeling staining following capsaicin or vehicle injection. Western blots showed that Fos protein was increased on the ipsilateral side in spinal cord tissue 0.5 h after capsaicin injection. Pretreatment with AP7 or CNQX caused a decrease in capsaicin-induced Fos expression. Immunofluorescence double labeling showed that the proportion of Fos-positive GABAergic neuronal profiles was significantly increased following capsaicin injection (48.8+/-4.8%) compared to the vehicle injection (23.8+/-5.1%) in superficial laminae on the ipsilateral side in lumbosacral spinal cord (P<0.05). However, when the spinal cord was pretreated with AP7 (5 microg) or CNQX (0.2 microg), only 9.1+/-0.6% or 7.1+/-0.8% of GABA-immunoreactive neuronal profiles were stained for Fos following capsaicin injection. The blockade of the capsaicin-evoked Fos staining was dose-dependent. These findings suggest that GABAergic neurons take part in dorsal horn circuits that modulate nociceptive information and that the function of GABAergic neurons following capsaicin injection is partially mediated by NMDA and non-NMDA receptors.
γ-氨基丁酸能神经元在初级传入去极化的产生中起重要作用，初级传入去极化会导致突触前抑制，并且如果去极化程度足够大，会触发背根反射。我们小组最近的电生理研究表明，在皮内注射辣椒素后，通过N-甲基-D-天冬氨酸（NMDA）和非NMDA受体的激活增强脊髓γ-氨基丁酸能神经元的兴奋性，会导致有助于神经源性炎症的背根反射的产生。本研究旨在确定在麻醉大鼠的一只后爪无毛皮肤注射辣椒素后，腰骶脊髓中γ-氨基丁酸能神经元中Fos蛋白表达是否发生变化，以及用NMDA受体拮抗剂D-（-）-2-氨基-7-磷酸庚酸（AP7）或非NMDA受体拮抗剂6-氰基-7-硝基喹喔啉-2,3-二酮（CNQX）预处理是否会阻断这些神经元中的Fos表达。实验采用辣椒素或溶剂注射后的蛋白质免疫印迹法和免疫荧光双标记染色法。蛋白质免疫印迹法显示，辣椒素注射后0.5小时，脊髓组织同侧的Fos蛋白增加。用AP7或CNQX预处理可使辣椒素诱导的Fos表达降低。免疫荧光双标记显示，与溶剂注射（23.8±5.1%）相比，在腰骶脊髓同侧浅层中，辣椒素注射后Fos阳性γ-氨基丁酸能神经元轮廓比例显著增加（48.8±4.8%）（P<0.05）。然而，当脊髓用AP7（5微克）或CNQX（0.2微克）预处理时，辣椒素注射后仅9.1±0.6%或7.1±0.8%的γ-免疫反应性神经元轮廓被Fos染色。辣椒素诱发的Fos染色阻断呈剂量依赖性。这些发现表明，γ-氨基丁酸能神经元参与调节伤害性信息的背角回路，并且辣椒素注射后γ-氨基丁酸能神经元的功能部分由NMDA和非NMDA受体介导。
