Synaptic vesicles fuse with the plasma membrane to release neurotransmitter following an action potential, after which new vesicles must ‘dock’ to refill vacated release sites. To capture synaptic vesicle exocytosis at cultured mouse hippocampal synapses, we induced single action potentials by electrical field stimulation, then subjected neurons to high-pressure freezing to examine their morphology by electron microscopy. During synchronous release, multiple vesicles can fuse at a single active zone. Fusions during synchronous release are distributed throughout the active zone, whereas fusions during asynchronous release are biased toward the center of the active zone. After stimulation, the total number of docked vesicles across all synapses decreases by ~40%. Within 14 ms, new vesicles are recruited and fully replenish the docked pool, but this docking is transient and they either undock or fuse within 100 ms. These results demonstrate that the recruitment of synaptic vesicles to release sites is rapid and reversible.

突触囊泡与质膜融合以在动作电位后释放神经递质，之后新囊泡必须“对接”以重新填充空出的释放位点。为了在培养的小鼠海马突触中捕获突触囊泡胞吐作用，我们通过电场刺激诱导单动作电位，然后对神经元进行高压冷冻以通过电子显微镜检查它们的形态。在同步释放期间，多个囊泡可以在单个活动区融合。同步释放期间的聚变分布在整个活动区，而异步释放期间的聚变偏向活动区的中心。刺激后，所有突触中停靠的囊泡总数减少约 40%。在 14 毫秒内，新的囊泡被招募并完全补充停靠的池，但这种对接是暂时的，它们要么在 100 毫秒内解除对接，要么融合。这些结果表明突触小泡向释放位点的募集是快速且可逆的。