Synaptic vesicle dynamics in the mossy fiber-CA3 presynaptic terminals of mouse hippocampus

• Published in: Neuroscience research 2007-12, Vol.59 (4), p.481-490
• Main Authors: Suyama, Shigetomo, Hikima, Takuya, Sakagami, Hiroyuki, Ishizuka, Toru, Yawo, Hiromu
• Format: Article
• Language: English
• Subjects: Active zone; Animals; Animals, Newborn; Electron microscopy; Endocytosis; Exocytosis; Exocytosis - physiology; Fidelity; Green Fluorescent Proteins; Hippocampus - metabolism; Hippocampus - ultrastructure; Learning and memory; Membrane Fusion - physiology; Mice; Mice, Inbred C57BL; Mice, Transgenic; Microscopy, Electron, Transmission; Mossy Fibers, Hippocampal - metabolism; Mossy Fibers, Hippocampal - ultrastructure; Organ Culture Techniques; Plasticity; Presynaptic Terminals - metabolism; Presynaptic Terminals - ultrastructure; Recombinant Fusion Proteins - metabolism; Synaptic Membranes - metabolism; Synaptic Membranes - ultrastructure; Synaptic Transmission - physiology; Synaptic Vesicles - metabolism; Synaptic Vesicles - ultrastructure; SynaptopHluorin; Time Factors; Transmitter release; Vesicle recycling; Vesicle-Associated Membrane Protein 2 - metabolism
• ISSN: 0168-0102; 1872-8111
• DOI: 10.1016/j.neures.2007.08.019

The mossy fiber (MF)-CA3 synapse in the hippocampus is unique in the CNS because of its wide dynamic range of transmitter release during short- and long-term plasticity. The presynaptic mechanisms underlying the fidelity of transmission were investigated for the MF-CA3 synapses. The relative size of readily releasable pool ( RRP) of vesicles was estimated by counting the number of docked vesicles at an active zone (AZ) on the transmission electron microscopy (TEM) image. The size of the releasable pool and the exo-endocytosis kinetics were directly measured from individual large MF boutons in hippocampal slices of transgenic mice that selectively express synaptopHluorin (SpH), a pH-sensitive GFP fused to the lumenal aspect of one of the vesicular membrane proteins, VAMP-2, in these boutons. Here we found (1) there are distinct two vesicle pools, the resting pool which is resistant to exocytosis, and the releasable pool, (2) the initially docked vesicles are easily depleted and the RRP is maintained by refilling from the reserve subpopulation of releasable pool (“reserve” releasable pool), and (3) the contribution of rapid reuse of recycled vesicles is relatively small. Therefore, the fidelity of transmission is suggested to be ensured by the rapid refilling rate of RRP.