In vivo patch-clamp analysis of developmental changes in the spinal nociceptive circuit.

使用切片和体内膜片钳记录检查脊髓伤害性突触传递的发育变化。在年轻大鼠和成年大鼠腰椎水平背根附着的横向脊髓切片上，应用背根电刺激记录明胶质（SG，脊髓II层）和深层（III-IV层）神经元的诱发突触反应。在体内膜片钳分析中，在氨基甲酸乙酯麻醉下进行胸腰椎椎板切除术后，将膜片电极插入SG的L3-L5脊柱水平。从SG神经元获得全细胞记录，然后记录皮肤自然机械刺激对同侧后肢引起的模态依赖性突触反应。在成年大鼠中，单突触Aβ和C纤维诱发的EPSCs在SG神经元中被诱导。此外，单突触Aβ纤维诱发的EPSCs在深层神经元中被激活，而在SG神经元中未被激活。另一方面，在幼龄大鼠中，除了Aβ和C纤维诱发的反应外，还在SG神经元中观察到单突触Aβ纤维诱发的EPSCs。在体内膜片钳分析中，捏刺激在年轻和成年大鼠的SG神经元中引发了大量EPSCs。即使在只接受a β纤维突触输入的SG神经元中，捏刺激也引起了大量epsc。成年大鼠的大多数深层神经元对触摸刺激有反应。本研究结果表明，除了Aδ和C纤维外，Aβ纤维还向幼鼠SG神经元传递有害的机械信息。在脊髓背角神经元回路进一步发育的成年大鼠中，无害的机械突触反应仅通过深层神经元中的Aβ纤维介导。

Developmental changes in the spinal nociceptive synaptic transmission were examined using slice and in vivo patch-clamp recordings. In transverse spinal cord slices of young and adult rats at lumbar spinal levels with an attached dorsal root, electrical dorsal root stimulation was applied to record the evoked-synaptic responses in substantia gelatinosa (SG, lamina II of the spinal cord)and deep lamina (lamina III-IV) neurons. In the in vivo patch-clamp analysis, patch electrodes were inserted into the SG at the spinal level of L3-L5 after a thoracolumbar laminectomy was performed under urethane anesthesia. Whole-cell recordings were obtained from SG neurons, and then modality-dependent synaptic responses evoked by cutaneous natural mechanical stimuli applied to the ipsilateral hind limb were recorded. In adult rats, monosynaptic Aβ and C fiber-evoked EPSCs were elicited in SG neurons. Additionally, monosynapitc Aβ fiber-evoked EPSCs were evoked in the deeper lamina neurons but not in SG neurons. In young rats, on the other hand, monosynaptic Aβ fiber-evoked EPSCs were observed in SG neurons in addition to Aβ and C fiber-evoked responses. In the in vivo patch-clamp analysis, pinch stimulation elicited a barrage of EPSCs in SG neurons in young and adult rats. Even in SG neurons that received synaptic inputs from only Aβ fibers, pinch stimulation evoked a barrage of EPSCs. Most deep neurons in adult rats responded to touch stimulation. The present results suggest that Aβ fibers, in addition to Aδ and C fibers, convey noxious mechanical information to SG neurons in young rats. In adult rats with further development of neuronal circuits in the spinal dorsal horn, innocuous mechanical synaptic responses are mediated only through Aβ fibers in deep lamina neurons.