Onaka M, Minami T, Nishihara I, Ito S
Department of Anesthesiology, Osaka Medical College, Takatsuki, Japan.
Anesthesiology. 1996 May;84(5):1215-22. doi: 10.1097/00000542-199605000-00024.
Glycine and gamma-aminobutyric acid (GABA) are inhibitory neurotransmitters that appear to be important in sensory processing in the spinal dorsal horn. Intrathecal administration of strychnine (strychnine-sensitive glycine receptor antagonist) or bicuculline (GABAA antagonist) was reported to induce allodynia. Although the strychnine-induced allodynia was shown to be mediated through the N-methyl-D-aspartate (NMDA)-type glutamate receptor, it is not clear whether the bicuculline-evoked-allodynia is mediated through the glutamate receptor system or how different the allodynia induced by strychnine and bicuculline are.
Male ddY mice weighing 20 +/- 2 g were used in this study. A 27-G stainless-steel needle attached to a microsyringe was inserted between the L5 and L6 vertebrae by a slight modification of the method of Hylden and Wilcox. Drugs in vehicle were injected slowly into the subarachnoid space to conscious mice at 22 +/- 2 degrees C. The volume of the intrathecal injection was 5 microliters. Studies on allodynia were carried out essentially according to the method of Yaksh and Harty.
The intrathecal administration of strychnine or bicuculline in conscious mice resulted in allodynia elicited by nonnoxious brushing of the flanks. The maximum allodynia induced by strychnine was observed 5 min after intrathecal injection, but that induced by bicuculline was observed 10 min after intrathecal injection. Both responses gradually decreased over the experimental period of 50 min. The allodynia induced by strychnine was dose-dependently relieved by NMDA receptor antagonists (D-AP5, ketamine, and 7-C1-KYNA) and non-NMDA receptor antagonists (GAMS and CNQX) but not by metabotropic receptor antagonists (L-AP3 and L-AP4). On the other hand, allodynia induced by bicuculline was dose-dependently relieved by GAMS, L-AP3, and L-AP4, but not by D-AP5, ketamine, 7-C1-KYNA, and CNQX. Whereas the strychnine-evoked allodynia was dose-dependently relieved by the nitric oxide synthase inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) and the soluble guanylate cyclase inhibitor methylene blue, the bicuculline-induced one was dose-dependently relieved by methylene blue but not by L-NAME.
These results demonstrate that both strychnine- and bicuculline-evoked allodynia were mediated through pathways that include the glutamate receptor and nitric oxide systems but in a different manner. the current study suggests that GABA and glycine may modulate responses to an innocuous tactile stimulus as inhibitory neurotransmitters at presynaptic and postsynaptic sites in the spinal cord, respectively.
甘氨酸和γ-氨基丁酸（GABA）是抑制性神经递质，在脊髓背角的感觉处理中似乎很重要。据报道，鞘内注射士的宁（士的宁敏感的甘氨酸受体拮抗剂）或荷包牡丹碱（GABAA拮抗剂）可诱发痛觉过敏。尽管已表明士的宁诱发的痛觉过敏是通过N-甲基-D-天冬氨酸（NMDA）型谷氨酸受体介导的，但尚不清楚荷包牡丹碱诱发的痛觉过敏是否通过谷氨酸受体系统介导，以及士的宁和荷包牡丹碱诱发的痛觉过敏有何不同。
本研究使用体重为20±2 g的雄性ddY小鼠。通过对Hylden和Wilcox方法进行轻微修改，将连接到微量注射器的27G不锈钢针插入L5和L6椎骨之间。将溶解在溶媒中的药物缓慢注入22±2℃清醒小鼠的蛛网膜下腔。鞘内注射体积为5微升。基本上按照Yaksh和Harty的方法进行痛觉过敏研究。
清醒小鼠鞘内注射士的宁或荷包牡丹碱会导致胁腹非伤害性轻刷诱发痛觉过敏。鞘内注射士的宁后5分钟观察到最大痛觉过敏，而鞘内注射荷包牡丹碱后10分钟观察到最大痛觉过敏。在50分钟的实验期内，两种反应均逐渐降低。士的宁诱发的痛觉过敏可被NMDA受体拮抗剂（D-AP5、氯胺酮和7-C1-KYNA）和非NMDA受体拮抗剂（GAMS和CNQX）剂量依赖性缓解，但不能被代谢型受体拮抗剂（L-AP3和L-AP4）缓解。另一方面，荷包牡丹碱诱发的痛觉过敏可被GAMS、L-AP3和L-AP4剂量依赖性缓解，但不能被D-AP5、氯胺酮、7-C1-KYNA和CNQX缓解。士的宁诱发的痛觉过敏可被一氧化氮合酶抑制剂N（ω）-硝基-L-精氨酸甲酯（L-NAME）和可溶性鸟苷酸环化酶抑制剂亚甲蓝剂量依赖性缓解，而荷包牡丹碱诱发的痛觉过敏可被亚甲蓝剂量依赖性缓解，但不能被L-NAME缓解。
这些结果表明，士的宁和荷包牡丹碱诱发的痛觉过敏均通过包括谷氨酸受体和一氧化氮系统的途径介导，但方式不同。当前研究表明，GABA和甘氨酸可能分别作为脊髓中突触前和突触后部位的抑制性神经递质，调节对无害触觉刺激的反应。
