Miles R, Wong R K
J Physiol. 1986 Apr;373:397-418. doi: 10.1113/jphysiol.1986.sp016055.
Excitatory synaptic interactions between CA3 neurones in slices from guinea-pig hippocampus were examined. Recurrent excitatory post-synaptic potentials (e.p.s.p.s) were evoked by action potentials in a single presynaptic neurone or by the antidromic activation of part of the CA3 pyramidal cell population. The peak amplitude of unitary e.p.s.p.s was 1-2 mV at potentials between -64 and -70 mV. Their time to peak was 7-12 ms and the initial phase of their decay was slower than that of a somatically injected voltage pulse. Recurrent e.p.s.p.s were often followed by a small (0.3 mV) hyperpolarization, or undershoot. Recurrent e.p.s.p.s were compared with e.p.s.p.s evoked by stimulating mossy fibres, which terminate proximally on apical dendrites of CA3 pyramidal cells. They were of slower time course and reversed at a more positive potential than mossy fibre e.p.s.p.s. Some synaptic terminals made by recurrent axon collaterals apparently terminate at distant locations on apical dendrites. The decay of both recurrent e.p.s.p.s and dendritic voltage pulses was prolonged by membrane depolarization within a 10-15 mV subthreshold potential range. Voltage-dependent inward currents activated by the synaptic depolarization may contribute to the slow initial decay of these synaptic events. The undershoot did not occur when transmission of a unitary e.p.s.p. failed and was of slower time course than the hyperpolarization due to an inhibitory post-synaptic potential (i.p.s.p.). It was suppressed by intracellular application of K+ channel blockers and probably reflects an intrinsic outward current activated as a consequence of the synaptic depolarization. Considerable temporal summation of synaptic potentials occurred when recurrent synapses were activated twice at an interval of 5-10 ms, typical of the spontaneous burst firing pattern of CA3 neurones. The mean facilitation of a second e.p.s.p. at this interval was about 0.6. The efficacy of a third and subsequent e.p.s.p.s at similar interval was reduced. Presynaptic bursts of three to five action potentials evoked summed e.p.s.p.s of amplitude 2-4 mV, with time to peak 20-40 ms and decaying phase of similar duration. Their rising phase was relatively smooth and summed events were succeeded by an undershoot. Presynaptic bursts could cause a post-synaptic neurone to discharge.
对豚鼠海马切片中CA3神经元之间的兴奋性突触相互作用进行了研究。单个突触前神经元的动作电位或CA3锥体细胞群的部分逆向激活可诱发反复出现的兴奋性突触后电位（e.p.s.p.s）。在-64至-70 mV的电位下，单个e.p.s.p.s的峰值幅度为1-2 mV。其达到峰值的时间为7-12 ms，衰减的初始阶段比体细胞注入的电压脉冲慢。反复出现的e.p.s.p.s之后通常会跟随一个小的（0.3 mV）超极化或负后电位。将反复出现的e.p.s.p.s与刺激苔藓纤维诱发的e.p.s.p.s进行了比较，苔藓纤维在CA3锥体细胞顶端树突的近端终止。它们的时间进程较慢，反转电位比苔藓纤维e.p.s.p.s更正。一些由反复出现的轴突侧支形成的突触终末显然终止于顶端树突的远处位置。在10-15 mV的阈下电位范围内，膜去极化会延长反复出现的e.p.s.p.s和树突电压脉冲的衰减。由突触去极化激活的电压依赖性内向电流可能导致这些突触事件的缓慢初始衰减。当单个e.p.s.p.的传递失败时，负后电位不会出现，并且其时间进程比由于抑制性突触后电位（i.p.s.p.）引起的超极化慢。它被细胞内应用钾通道阻滞剂所抑制，可能反映了由于突触去极化而激活的内在外向电流。当反复出现的突触以5-10 ms的间隔被激活两次时，会出现明显的突触电位时间总和，这是CA3神经元自发爆发式放电模式的典型间隔。在此间隔下，第二个e.p.s.p.的平均易化约为0.6。在相似间隔下，第三个及后续e.p.s.p.s的效能降低。三到五个动作电位的突触前爆发诱发了幅度为2-4 mV的总和e.p.s.p.s，达到峰值的时间为20-40 ms，衰减阶段持续时间相似。它们的上升阶段相对平滑，总和事件之后是负后电位。突触前爆发可导致突触后神经元放电。
