氯苯氨丁酸抑制脊髓背角神经元谷氨酸量子释放的机制

目的　研究GABAB 受体特异性激动剂氯苯氨丁酸(baclofen)在脊髓背角神经元抑制谷氨酸量子释放的机制。方法　在脊髓薄片标本上 ,采用全细胞电压钳法记录脊髓背角神经元谷氨酸能的微兴奋性突触后电流 (miniatureexcita torypostsynapticcurrents;mEPSCs) ,通过分析这些电流的变化来研究baclofen影响谷氨酸量子释放的机制。结果　ba clofen抑制mEPSCs的发放频率 ,但对平均幅度无明显影响 ,表明baclofen抑制谷氨酸释放的作用部位在突触前。在无钙溶液或者K+ 通道阻滞剂 4 AP存在的条件下 ,baclofen对mEPSCs发放频率的抑制作用不受影响 ,但腺苷酸环化酶激动剂foskolin (可使cAMP保持在较高水平 )能降低其抑制作用。而蛋白激酶C (PKC)激动剂PDBu对baclofen的抑制作用无影响。用NEM破坏G蛋白 ,则可取消baclofen的抑制效果。结论　baclofen不是通过影响突触前Ca2 + 通道或K+通道 ,或PKC途径 ,而是通过作用于G蛋白和 (或 )cAMP途径抑制谷氨酸的释放 ;这种抑制作用可能参与baclofen在脊髓水平的镇痛

Mechanism for baclofen inhibition on quantal glutamate release in spinal dorsal horn neurons

Aim To investigate the inhibition mechanisms of baclofen, a specific GABA B receptor agonist, on quantal glutamate release in the rat spinal dorsal horn neurons.Methods Whole-cell voltage-clamp technique was performed on dorsal horn neurons in rat spinal cord slice to record glutamatergic spontaneous miniature excitatory postsynaptic currents (mEPSCs). Baclofen action on quantal glutamate release was assessed by analyzing the change of mEPESC to baclofen perfusion.Results Baclofen(10 μmol·L -1,50 s) depressed the frequency, but not amplitude distribution of glutamatergic mEPSCs, indicating baclofen presynaptic depression on glutamate release. The depression on frequency of mEPSCs persisted in Ca 2+-free solution, or in the presence of K + conductance blocker, 4-AP. On the other hand, the depression was occluded by forskolin, an activator of adenylate cyclase, but not protein kinase C (PKC) activator phorbol 12,13-dibutyrate (PDBu). N-ethylmaleimide (NEM), a sulphydryl alkylating agent, which destroys G protein, abolished baclofen depression.Conclusion Not presynaptic K +, Ca 2+ conductance or PKC, but G protein and/or cAMP pathway are involved in the baclofen depression on glutamate release in rat spinal dorsal horn;this depression might contribute to the analgesic action of baclofen at spinal level.