In a study published in Science on October 17, a team led by Prof. BI Guoqiang from the University of Science and Technology of China/Shenzhen Institutes of Advanced Technology of the Chinese Academy of Sciences (CAS), along with collaborators, delineated the intricate choreography of synaptic vesicle (SV) release and rapid recycling by using a self-developed, time-resolved cryo-electron tomography (cryo-ET) method, and identified a "kiss-shrink-run" pathway.
Our brain function relies on efficient and precise synaptic transmission between neurons. When an electrical signal, known as action potential, reaches a neuron's terminal, SV release neurotransmitters to relay the information across the synapse. Due to technical limitations, biophysical mechanisms governing this process are only partially understood, with a long-standing debate over the existence of transient "kiss-and-run" fusion versus irreversible "full-collapse" fusion in central synapses.
In this study, the researchers developed a time-resolved, cellular cryo-ET method by integrating optogenetic stimulation (light-controlled neural activation) with high-speed plunge-freezing to capture snapshots of cultured neuronal synapses. Using this method, they acquired over 1,000 tomograms of intact excitatory synapses, frozen at time points ranging from 0 to 300 milliseconds post-action potential.
Through structural and statistical analyses, the researchers reconstructed the complete timeline of vesicle exocytosis and rapid recycling. Within four milliseconds after action potential, the vesicle first fused with the presynaptic membrane to form a ~4 nanometer fusion pore ("kiss"), then shrank into a small vesicle with half its original surface area ("shrink"). By 70 milliseconds, most of these small vesicles began to be recycled via the "run" pathway, while the rest underwent "full-collapse" fusion with the presynaptic membrane.
The "kiss-shrink-run" mechanism unifies the much debated models and provides a structural basis for the efficiency and fidelity of synaptic transmission. This study offers a fresh perspective on neurotransmission, synaptic plasticity, and related brain functions and diseases.
