Ultrastructural membrane dynamics of mouse and human cortical synapses.

Live human brain tissues provide unique opportunities for understanding the physiology and pathophysiology of synaptic transmission. Investigations have been limited to anatomy, electrophysiology, and protein localization-while crucial parameters such as synaptic vesicle dynamics were not visualized. Here we utilize zap-and-freeze time-resolved electron microscopy to overcome this hurdle. First we validate the approach with acute mouse brain slices to demonstrate that axons parallel to the electrical field can be stimulated to produce calcium signaling. Next we show that ultrafast endocytosis is induced and can be captured in both mouse and human brain slices. Crucially, in both species a protein essential for ultrafast endocytosis Dynamin 1xA (Dyn1xA) localizes to the region peripheral to the active zone, the putative endocytic zone, indicating a likely mechanism conservation between mouse and human. This approach has the potential to reveal dynamic, high-resolution information about synaptic membrane trafficking in intact human brain slices.