We investigated the effects of nitrous oxide (N₂O) on glycinergic inhibitory whole-cell and synaptic responses using a “synapse bouton preparation,” dissociated mechanically from rat spinal sacral dorsal commissural nucleus (SDCN) neurons. This technique can evaluate pure single- or multi-synaptic responses from native functional nerve endings and enable us to accurately quantify how N₂O influences pre- and postsynaptic transmission. We found that 70 % N₂O enhanced exogenous glycine-induced whole-cell currents (I_Gly) at glycine concentrations lower than 3 × 10^–5 M, but did not affect I_Gly at glycine concentrations higher than 10^–4 M. N₂O did not affect the amplitude and 1/e decay-time of both spontaneous and miniature glycinergic inhibitory postsynaptic currents recorded in the absence and presence of tetrodotoxin (sIPSCs and mIPSCs, respectively). The decrease in frequency induced by N₂O was observed in sIPSCs but not in mIPSCs, which was recorded in the presence of both tetrodotoxin and Cd²⁺, which block voltage-gated Na⁺ and Ca²⁺ channels, respectively. N₂O also decreased the amplitude and increased the failure rate and paired-pulse ratio of action potential-evoked glycinergic inhibitory postsynaptic currents. N₂O slightly decreased the Ba²⁺ currents mediated by voltage-gated Ca²⁺ channels in SDCN neurons. We found that N₂O suppresses glycinergic responses at synaptic levels with presynaptic effect having much more predominant role. The difference between glycinergic whole-cell and synaptic responses suggests that extrasynaptic responses seriously modulate whole-cell currents. Our results strongly suggest that these responses may thus in part explain analgesic effects of N₂O via marked glutamatergic inhibition by glycinergic responses in the spinal cord.

我们使用从大鼠脊髓骶骨背连合核 (SDCN) 神经元机械分离的“突触布顿制剂”研究了氧化亚氮 (N ₂ O) 对甘氨酸能抑制性全细胞和突触反应的影响。这种技术可以评估来自天然功能性神经末梢的纯单突触或多突触反应，并使我们能够准确量化 N ₂ O如何影响突触前和突触后传递。我们发现，70 % N ₂ O在甘氨酸浓度低于 3 × 10 ^–5 M 时增强了外源性甘氨酸诱导的全细胞电流 ( I _Gly ) ，但在甘氨酸浓度高于 10 ^{–4 时}不影响I _GlyM. N ₂ O 不影响在河豚毒素（分别为 sIPSC 和 mIPSC）不存在和存在下记录的自发和微型甘氨酸能抑制性突触后电流的振幅和1/e衰减时间。在 sIPSCs 中观察到由 N ₂ O诱导的频率降低，但在 mIPSCs 中未观察到，这在河豚毒素和 Cd ²⁺存在的情况下被记录，它们分别阻断电压门控 Na ⁺和 Ca ²⁺通道。N ₂ O 还降低了动作电位诱发的甘氨酸能抑制性突触后电流的幅度并增加了失败率和配对脉冲比。N ₂ O 略微降低了 Ba ²⁺SDCN 神经元中电压门控 Ca ²⁺通道介导的电流。我们发现 N ₂ O 在突触水平上抑制甘氨酸能反应，其中突触前效应具有更显着的作用。甘氨酸能全细胞和突触反应之间的差异表明突触外反应严重调节全细胞电流。我们的结果强烈表明，这些反应因此可以部分解释 N ₂ O 通过脊髓中甘氨酸能反应显着的谷氨酸能抑制作用而产生的镇痛作用。