BMI SEMINAR // Takeshi Sakaba - Biophysics of transmitter release at the mossy fiber synapse

Hippocampal mossy fiber synapses are an important element in the hippocampus and exhibit various forms of synaptic plasticity. To investigate the mechanism of transmitter release and its modulation, we used presynaptic capacitance measurements and EPSC recording to measure the kinetics of transmitter release. In addition, total internal reflection fluorescence (TIRF) microscopy was used to visualize single synaptic vesicle dynamics near the plasma membrane. Readily releasable synaptic vesicles are mediated by fusion of already-tethered vesicles in the TIRF field. Vesicle replenishment had fast and slow phases, and the fast phase depends on synaptic vesicle priming from already-tethered vesicles. cAMP, a molecule crucial for LTP, mainly increases the vesicular release probability, likely by changing the coupling between Ca²⁺ channels and synaptic vesicles. We compared these findings with those obtained at the calyx of Held synapse, one of the model synapses in the mammalian CNS, and discussed similarities and differences between two synapse types.