Cummings D D, Wilcox K S, Dichter M A
David Mahoney Institute of Neurological Sciences, School of Medicine, University of Pennsylvania, Philadelphia 19104, USA.
J Neurosci. 1996 Sep 1;16(17):5312-23. doi: 10.1523/JNEUROSCI.16-17-05312.1996.
Two forms of evoked neurotransmitter release at excitatory synapses between cultured hippocampal neurons have been described. After an action potential, it has been shown that transmitter initially is released synchronously, and this is followed by a period of "slow" asynchronous release. The "fast" synchronous component of release at these synapses has been found routinely to demonstrate paired-pulse and tetanic depression, whereas the short-term plasticity of asynchronous release has not been investigated. In the present experiments, we have used the whole-cell patch-clamp technique to record from pairs of neurons in a low-density hippocampal culture preparation to determine both the properties and underlying mechanisms of short-term plasticity of asynchronous release. It was found that an increase in miniature EPSC (mEPSC) frequency accompanied both single and multiple stimuli, and this mEPSC increase was facilitated during paired stimuli, even when the evoked synchronous release was depressed. In addition, both the activity-dependent depression of evoked EPSCs and facilitation of asynchronous mEPSC release were dependent on Ca accumulation in the nerve terminal. However, the Ca-dependent mechanisms underlying these two processes could be distinguished by the differential effects of two membrane-permeant calcium chelators, BAPTA-AM and EGTA-AM. Frequency-dependent depression of evoked EPSCs involves a rapid rise in intraterminal Ca, which likely triggers a process that proceeds in a Ca-independent manner, whereas the asynchronous release may be linked more directly to a sustained increase in intraterminal Ca.
在培养的海马神经元之间的兴奋性突触处，已描述了两种诱发神经递质释放的形式。动作电位后，已表明递质最初是同步释放的，随后是一段“缓慢”的异步释放期。在这些突触处释放的“快速”同步成分通常被发现表现出双脉冲和强直抑制，而异步释放的短期可塑性尚未被研究。在本实验中，我们使用全细胞膜片钳技术从低密度海马培养制剂中的成对神经元进行记录，以确定异步释放的短期可塑性的特性和潜在机制。发现微小兴奋性突触后电流（mEPSC）频率的增加伴随着单次和多次刺激，并且即使在诱发的同步释放被抑制时，这种mEPSC增加在双脉冲刺激期间也会增强。此外，诱发的兴奋性突触后电流的活动依赖性抑制和异步mEPSC释放的增强都依赖于神经末梢中的钙积累。然而，这两个过程背后的钙依赖性机制可以通过两种膜通透性钙螯合剂BAPTA-AM和EGTA-AM的不同作用来区分。诱发的兴奋性突触后电流的频率依赖性抑制涉及末梢内钙的快速升高，这可能触发一个以钙独立方式进行的过程，而异步释放可能更直接地与末梢内钙的持续增加有关。
