Investigating Presynaptic Activity using the SF-iGluSnFR Sensor: Measuring Kinetics and Plasticity of Glutamate Release Across Heterogeneous Population of Synapses

In this article, we introduce an integrated methodology to examine the kinetics and plasticity of glutamate release in small central synapses in culture. This technique combines patch-clamp electrophysiology with fluorescence imaging using the SF-iGluSnFR glutamate sensor. This enables monitoring of vesicular glutamate release across the axonal arbor of a selected pyramidal neuron at a 4 ms temporal resolution. By employing quantal optical analysis, the method determines the timing and vesicular content of glutamate release events at multiple synapses in parallel. This provides insights into key presynaptic functional properties such as release probability, short-term plasticity, and the balance between synchronous and asynchronous release modes for each imaged synapse. In conclusion, the described methodological approach offers a powerful tool to explore functional dynamics in diverse synaptic populations and to study molecular mechanisms of vesicular neurotransmitter release and synaptic plasticity at the single-synapse level.