European Neuroscience Institute and Center for Molecular Physiology of the Brain, Georg August University, D-37077 Göttingen, Germany.
Proc Natl Acad Sci U S A. 2013 Aug 6;110(32):E3007-16. doi: 10.1073/pnas.1305679110. Epub 2013 Jul 22.
Local recycling of synaptic vesicles (SVs) allows neurons to sustain transmitter release. Extreme activity (e.g., during seizure) may exhaust synaptic transmission and, in vitro, induces bulk endocytosis to recover SV membrane and proteins; how this occurs in animals is unknown. Following optogenetic hyperstimulation of Caenorhabditis elegans motoneurons, we analyzed synaptic recovery by time-resolved behavioral, electrophysiological, and ultrastructural assays. Recovery of docked SVs and of evoked-release amplitudes (indicating readily-releasable pool refilling) occurred within ∼8-20 s (τ = 9.2 s and τ = 11.9 s), whereas locomotion recovered only after ∼60 s (τ = 20 s). During ∼11-s stimulation, 50- to 200-nm noncoated vesicles ("100nm vesicles") formed, which disappeared ∼8 s poststimulation, likely representing endocytic intermediates from which SVs may regenerate. In endophilin, synaptojanin, and dynamin mutants, affecting endocytosis and vesicle scission, resolving 100nm vesicles was delayed (>20 s). In dynamin mutants, 100nm vesicles were abundant and persistent, sometimes continuous with the plasma membrane; incomplete budding of smaller vesicles from 100nm vesicles further implicates dynamin in regenerating SVs from bulk-endocytosed vesicles. Synaptic recovery after exhaustive activity is slow, and different time scales of recovery at ultrastructural, physiological, and behavioral levels indicate multiple contributing processes. Similar processes may jointly account for slow recovery from acute seizures also in higher animals.
突触囊泡（SVs）的局部再循环使神经元能够维持递质释放。极端活动（例如癫痫发作期间）可能会耗尽突触传递，并且在体外诱导大体积内吞作用以恢复 SV 膜和蛋白质；但在动物中这种情况如何发生尚不清楚。在用光遗传学方法超刺激秀丽隐杆线虫运动神经元后，我们通过时间分辨行为、电生理和超微结构测定来分析突触恢复。停泊的 SVs 和诱发释放幅度（表明易释放池的再填充）的恢复发生在约 8-20 秒内（τ = 9.2 秒和 τ = 11.9 秒），而运动恢复仅在约 60 秒后（τ = 20 秒）。在约 11 秒的刺激期间，形成了 50-200nm 的无涂层囊泡（“100nm 囊泡”），这些囊泡在刺激后约 8 秒消失，可能代表 SV 可能再生的内吞作用中间产物。在影响内吞作用和囊泡分裂的内收蛋白、突触结合蛋白和 dynamin 突变体中，解决 100nm 囊泡的时间延迟（>20 秒）。在 dynamin 突变体中，100nm 囊泡丰富且持久，有时与质膜连续；较小的 100nm 囊泡从较小的囊泡不完全出芽进一步表明 dynamin 参与了从大体积内吞作用的囊泡中再生 SVs。极度活动后的突触恢复缓慢，超微结构、生理和行为水平的恢复具有不同的时间尺度，表明存在多种贡献过程。类似的过程可能共同解释了在高等动物中急性癫痫发作后的缓慢恢复。
