Dudel J
Pflugers Arch. 1983 Jul;398(2):155-64. doi: 10.1007/BF00581065.
In opener muscles of the first walking leg of 3 species of crayfish, quantal synaptic currents were recorded focally at synaptic spots by means of a macro-patch-clamp electrode. Proximal stimulation of the motor axons elicited excitatory postsynaptic currents (nEPSCs). In addition, current pulses through the recording electrode depolarizing the nerve terminal elicited similar synaptic release (pEPSCs). Artefact waveforms generated in the recording electrode after a pulse were compensated by a special circuit, allowing the pEPSC to be recorded from 0.3 to 1.5 ms after the pulse. In all terminals identified by recording nEPSCs, pEPSCs were also elicited, with a threshold pulse amplitude between -0.1 and -2 microA at 2 ms pulse duration. Most of the investigated terminals showed graded pEPSCs to rising amplitudes and durations of depolarizing pulses, and no effect of tetrodotoxin (TTX) on the pEPSCs. In these inexcitable terminals pEPSCs and nEPSCs showed mutual facilitation, with no signs of refractoriness for intervals as short at 3 ms. Some excitable terminals were found also: in these the amplitude of the pEPSC rose very steeply in an approximately all-or-nothing response on passing a threshold, while application of TTX reduced this response to one similar to that of inexcitable terminals. However, stimulation of such excitable terminals did not lead to antidromic conduction of action potentials into the main axon. In both inexcitable and excitable terminals, approximately the product of suprathreshold pulse amplitude and pulse duration determined the rate of release. The dependence of this response on pulse amplitude showed characteristic differences in proximal and distal synapses. The maximal double-logarithmic slope of this relation (sD) was 3.3 on the average in proximal synapses, while for distal synapses the average sD was 6.3. Further, in proximal synapses the nEPSC reached on average 86% of the maximum pEPSC, while the nEPSC in distal synapses amounted to only 5% of the maximum pEPSC. Therefore, the point of block of conduction in the terminal branch seems to lie father from the terminal in distal than in proximal synapses.
在3种小龙虾第一步行足的 opener 肌肉中，通过宏膜片钳电极在突触位点局部记录量子突触电流。对运动轴突进行近端刺激可引发兴奋性突触后电流（nEPSCs）。此外，通过记录电极施加使神经末梢去极化的电流脉冲也能引发类似的突触释放（pEPSCs）。脉冲后记录电极中产生的伪迹波形由一个特殊电路进行补偿，从而能够在脉冲后0.3至1.5毫秒记录pEPSC。在所有通过记录nEPSCs鉴定出的终末中，也能引发pEPSCs，在2毫秒脉冲持续时间下，阈值脉冲幅度在 -0.1至 -2微安之间。大多数被研究的终末对去极化脉冲幅度和持续时间的增加呈现出分级的pEPSCs，并且河豚毒素（TTX）对pEPSCs没有影响。在这些不可兴奋的终末中，pEPSCs和nEPSCs表现出相互促进作用，对于短至3毫秒的间隔没有不应期迹象。也发现了一些可兴奋终末：在这些终末中，pEPSC的幅度在超过阈值时以近似全或无的反应急剧上升，而应用TTX会使这种反应降低到与不可兴奋终末类似的水平。然而，对这种可兴奋终末的刺激不会导致动作电位向主轴突的逆向传导。在不可兴奋和可兴奋终末中，超阈值脉冲幅度和脉冲持续时间的乘积大致决定了释放速率。这种反应对脉冲幅度的依赖性在近端和远端突触中表现出特征性差异。这种关系的最大双对数斜率（sD）在近端突触中平均为3.3，而在远端突触中平均sD为6.3。此外，在近端突触中，nEPSC平均达到最大pEPSC的86%，而在远端突触中nEPSC仅占最大pEPSC的5%。因此，终末分支中传导阻滞点在远端似乎比近端突触离终末更远。
