Hippocampal mossy fiber boutons (hMFBs) are presynaptic terminals displaying various forms of synaptic plasticity. The presynaptic mechanisms underlying synaptic plasticity still remain poorly understood. Here, we have combined high temporal resolution measurements of presynaptic capacitance and excitatory postsynaptic currents (EPSCs) to measure the kinetics of exocytosis. In addition, total internal reflection fluorescence (TIRF) microscopy was employed to directly visualize dynamics of single synaptic vesicles adjacent to the plasma membrane at high spatial resolution. Readily releasable vesicles mostly consisted of already-tethered vesicles in the TIRF field. Vesicle replenishment had fast and slow phases, and TIRF imaging suggests that the fast phase depends on vesicle priming from already-tethered vesicles. Application of cyclic AMP (cAMP), a molecule crucial for LTP, mainly increases the vesicular release probability rather than the number of readily releasable vesicles or their replenishment rate, likely by changing the coupling between Ca2+channels and synaptic vesicles. Thus, we revealed dynamic properties of synaptic vesicles at hMFBs.

中文翻译：

---

可释放突触囊泡的动力学及其在海马苔藓纤维突触中的塑性变化

海马长满苔藓的纤维钮扣（hMFBs）是突触前的终端，表现出各种形式的突触可塑性。突触可塑性潜在的突触前机制仍然知之甚少。在这里，我们结合了突触前电容和兴奋性突触后电流（EPSC）的高时间分辨率测量，以测量胞吐动力学。此外，采用全内反射荧光（TIRF）显微镜以高空间分辨率直接可视化与质膜相邻的单个突触囊泡的动力学。易于释放的囊泡主要由TIRF领域中已系链的囊泡组成。囊泡补充具有快速和慢速阶段，TIRF成像表明，快速阶段取决于已经束缚的囊泡的囊泡充盈。循环AMP（cAMP）的应用 对LTP至关重要的分子，主要是通过改变Ca2 +通道与突触小泡之间的偶联作用，增加了小泡释放的可能性，而不是增加了易于释放的小泡的数量或它们的补给率。因此，我们揭示了hMFBs突触小泡的动态特性。