Abstract
In the central nerves system (CNS) synapses long- and short-term modification of synaptic vesicle exocytosis is one of basic mechanisms underlying learning and memory. Synaptic vesicles recycle through the elementary processes as docking, priming, fusion and endocytosis. The dynamics of these processes are physiologically quantified by two parameters; the readily releasable pool (RRP) which is assumed to be the number of docked/primed vesicles to plasma membrane and the fusion probability of a vesicle to plasma membrane. Here, we report the vesicular dynamics of a single mossy fiber presynaptic terminal in the acute slice of mouse hippocampus. We used a TV-42 transgenic mouse line that expresses synaptopHluorin, one of optical probes measuring exo-endocytosis, specifically in the hippocampal mossy fiber terminals. The mouse was deeply ether-anesthetized and the brain was removed. The hippocampal slices were made at 400 μm. Individual large mossy fiber terminals were identified under confocal microscopy and the activity-dependent changes of synaptopHluorin fluorescence were measured. The fusion probability of a vesicle was 0.02 on average whereas the RRP was large. It is suggested that the small fusion probability enables the stable neurotransmission during high frequency activity or potentiation. All animal procedures were conducted in accordance with the guiding principles of Physiological Society of Japan. [J Physiol Sci. 2007;57 Suppl:S154]
