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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Counting the number of releasable synaptic vesicles in a presynaptic terminal
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Counting the number of releasable synaptic vesicles in a presynaptic terminal

机译：计数突触前末端中可释放的突触小泡的数量

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Synaptic transmission depends on the continued availability of neurotransmitter-filled synaptic vesicles (SVs) for triggered release from presynaptic boutons. Surprisingly, small boutons in the brain, that already contain comparatively few SVs, are thought to retain the majority of these SVs in a "reserve" pool that is not mobilized under physiological conditions. Why such a scarce synaptic resource is normally inaccessible has been a matter of debate. Here, we readdress this issue by developing an electrophysiological approach for counting SVs released from boutons formed by a single, isolated neuron on itself ("autapses"). We show that, after treatment with Bafilomycin A1 to prevent reloading of discharged SVs with glutamate, each SV is counted only once on first-time release. Hence, by integrating all autaptic currents as they run down over time, we can estimate the total number of SVs released by a single neuron. This total can be normalized to the number of boutons on the neuron, giving the mean number of SVs released per bouton. We estimate that up to ≈130 vesicles can be released per bouton over ≈10 min of stimulation at 0.2 Hz. This number of vesicles represents a substantial proportion of the total number of SVs (100-200) that have been counted in these boutons by using electron microscopy. Thus, mild electrical stimulation, when maintained for sufficient time, causes the eventual release of many of the SVs in a bouton, including those in the putative reserve pool. This result suggests that SVs are functionally homogeneous in that the majority can contribute to basal synaptic transmission.
机译：突触传递依赖于神经递质填充的突触囊泡（SVs）从突触前钮扣触发释放的持续可用性。令人惊讶的是，脑中已经含有相对较少的SV的小钮扣被认为将这些SV的大部分保留在“储备”池中，该池在生理条件下无法动员。为什么通常无法获得这种稀有的突触资源一直是一个辩论的问题。在这里，我们通过开发一种电生理方法来解决这个问题，该方法用于对从单个孤立神经元自身形成的按钮（“突触”）释放的SV进行计数。我们显示，在用Bafilomycin A1治疗以防止排出的SVs用谷氨酸重新装载后，每个SV在首次释放时仅计数一次。因此，通过对所有自发电流随着时间的流逝进行积分，我们可以估计单个神经元释放的SV的总数。可以将总数归一化为神经元上的boutons数量，从而得出每个bouton释放的SV的平均数量。我们估计，在0.2 Hz的刺激下约10分钟内，每个bouton最多可以释放约130个囊泡。通过使用电子显微镜，这些囊泡中的囊泡数量占已在这些囊中计数的SV总数（100-200）的很大一部分。因此，轻度的电刺激在维持足够的时间后，最终会释放出布通中的许多SV，包括假定储藏池中的SV。该结果表明，SV在功能上是同质的，因为大多数可以促成基础突触传递。

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