Paired-pulse facilitation and depression at unitary synapses in rat hippocampus: Quantal fluctuation affects subsequent release
Paired-pulse facilitation and depression at unitary synapses in rat hippocampus: Quantal fluctuation affects subsequent release
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DOI：
10.1113/jphysiol.1996.sp021204
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发表时间：
1996-02-15
影响因子：
5.5
通讯作者：
Thompson, SM
中科院分区：
文献类型：
--
作者：
Debanne, D;Guerineau, NC;Thompson, SM
1.在培养的大鼠海马片上观察了两对单突触耦合锥体细胞之间的兴奋性突触传递。结果：1.微电极刺激单个CA3锥体细胞诱发动作电位，全细胞电压钳CA1或CA3细胞记录到单位兴奋性突触后电流(EPSCs)。连续的单位EPSCs对单个动作电位的反应幅度不同。腺苷或[Mg~(2+)]/[Ca~(2+)]比值改变对EPSCs TVa值的影响。我们得出结论，单动作电位触发了谷氨酸的多量子释放。当突触前细胞产生两个动作电位时，第二个动作电位的幅度与第一个动作电位的幅度成反比。当第一个EPSC较小时，出现双脉冲促进(PPF)，即第二个EPSC大于第一个EPSC，而当第一个EPSC较大时，则观察到双脉冲抑制(PPD)。显示PPD的试验次数随着释放概率TVas的增加而增加，随着释放概率的降低而减少。PPD不是突触后介导的，因为它不受6-氰基-7-硝基-2，3-二酮(CNQX)降低离子通量或阿尼西坦受体脱敏的影响。PPP在刺激间隔70ms时最大，在500ms内恢复。PPD的恢复在5-7秒内发生。我们认为CA3锥体细胞的轴突和单个突触后CA1或CA3细胞形成了多个释放部位。如果第一动作电位在大多数释放部位未能释放递质，则观察到PPF。如果第一动作电位在大多数释放部位成功触发释放，则观察PPD。我们对PPP的观察与剩余钙假说是一致的。我们的结论是，PPD是由于量子含量的减少，可能是由于易释放的囊泡短期耗尽所致。
1. Excitatory synaptic transmission between pairs of monosynaptically coupled pyramidal cells was examined in rat hippocampal slice cultures. Action potentials were elicited in single CA3 pyramidal cells impaled with microelectrodes and unitary excitatory postsynaptic currents (EPSCs) were recorded in whole-cell voltage-clamped CA1 or CA3 cells.2. The amplitude of successive unitary EPSCs in response to single action potentials varied. The amplitude of EPSCs tvas altered by adenosine or changes in the [Mg2+]/[Ca2+] ratio. We conclude that single action potentials triggered the release of multiple quanta of glutamate.3. When two action potentials were elicited in the presynaptic cell, the amplitude of the second EPSC was inversely related to the amplitude of the first. Paired-pulse facilitation (PPF) was observed when the first EPSC was small, i.e. the second EPSC was larger than the first, whereas paired-pulse depression (PPD) was observed when the first EPSC was large.4. The number of trials displaying PPD was greater when release probability tvas increased, and smaller when release probability was decreased.5. PPD was not postsynaptically mediated because it was unaffected by decreasing ionic flux with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) or receptor desensitization with aniracetam.6. PPP was maximal at an interstimulus interval of 70 ms and recovered within 500 ms. Recovery from PPD occurred within 5 s.7. We propose that multiple release sites are formed by the axon of a CA3 pyramidal cell and a single postsynaptic CA1 or CA3 cell. PPF is observed if the first action potential fails to release transmitter at most release sites. PPD is observed if the first action potential successfully triggers release at most release sites.8. Our observations of PPP are consistent with the residual calcium hypothesis. We conclude that PPD results from a decrease in quantal content, perhaps due to short-term depletion of readily releasable vesicles.