Patch-Clamp Analysis on the Mechanism for Inhibitory Synaptic Transmission in Rat Spinal Motoneurone.

采用全细胞法记录新生大鼠脊髓运动神经元的抑制性突触后电流（IPSC）。通过细胞外刺激单个神经元诱发IPSC。当以各种频率（0.2-50 Hz）刺激时，从刺激伪影到IPSC发作所测量的潜伏期是稳定的，在37 ℃下平均潜伏期为0.6-0.8 ms，表明IPSC的单突触性质。当细胞外Ca^<2+>浓度（[Ca]_o）降低时，IPSCs的失活次数增加，IPSCs的平均振幅降低。[Ca]_0（0.35-1.4mM）与IPSCs的平均振幅在双对数坐标上呈线性关系，平均斜率为3.1。IPSCs的振幅随[Ca] o的降低而降低。然而，低于0.7 mM [Ca]_0时，观察到的IPSC（不包括故障）的幅度达到稳定的“最小”水平。在0.5mM [Ca]_0中测得的“最小”IPSC的平均电导为650 pS，这与在河豚毒素下从运动神经元记录到的自发微型IPSC的电导相当。结果表明，在低[Ca]_o时观察到的“最小”IPSC可能代表量子IPSC。量子IPSC的平均变异系数为0.50。量子IPSC的平均振幅不同的运动神经元之间的3倍。量子IPSC的上升时间和振幅之间没有观察到相关性，表明量子尺寸的分散不是由于释放位点的不同位置。IPSC的统计性质表明，IPSC的幅度不能拟合二项分布。结论：在新生大鼠脊髓抑制性突触中，IPSCs的量子大小可能不均匀。

Tight-seal whole-cell recordings of Inhibitory Postsynaptic Currents (IPSCs) were made from neonatal rat spinal motoneurones. The IPSCs were evoked by stimulating a single internuncial neurone extracellularly. The latency measured from the stimulus artifact to the onset of IPSCs was stable when stimulated at various frequencies (0.2-50 Hz) with the mean latency of 0.6-0.8 ms at 37 C, suggesting the monosynaptic nature of the IPSCs. When the external Ca^<2+> concentration ([Ca]_o) was reduced, the number of failures of IPSCs increased, and the mean amplitude of IPSCs decreased. The relation between [Ca]_o (0.35-1.4mM) and the mean amplitude of IPSCs was linear with a mean slope of 3.1 on double logarithmic co-ordinates. The amplitude of IPSCs decreased with a decrease in [Ca]_o. However, below 0.7 mM [Ca]_o, the amplitude of observed IPSCs (excluding failures) reached a steady 'minimum' level. The meah conductance of the 'minimum' IPSCs measured in 0.5 mM [Ca]_o was 650 pS, which was comparable to the conductance of spontaneous miniature IPSCs recorded from motoneurones under tetrodotoxin. It is suggested that the 'minimum' IPSCs observed at low [Ca]_o may represent the quantal IPSCs. The quantal IPSCs had a coefficient of variation of 0.50 on average. The mean amplitude of quantal IPSCs varied among different motoneuromes by a factor of 3. No correlation was observed between the rise time and amplitude of quantal IPSCs, indicating that the dispersion in quantal size is not due to different locations of release sites. The statistical nature of the IPSCs indicated that the amplitude of IPSCs cannot be fitted with a binomial distribution. It is concluded that the quantal size constututing IPSCs may not be uniform at individual inhibitory synapses of neonatal rat spinal cord.