Special Seminar with Carolina Borges-Merjane, PhD

Zoom Link: https://mit.zoom.us/j/92977291818

Functional and structural analysis of synaptic vesicle pools

Synaptic vesicles in presynaptic terminals are a fundamental component of synapses, and are typically organized into different functional pools. The readily releasable pool (RRP) is the pool of vesicles ready to be released upon arrival of an action potential. The recycling pool is freely and actively participating in exocytosis and endocytosis, providing vesicles to the RRP. Finally, the reserve pool of vesicles is held immobile via scaffolding proteins and is not actively participating in neurotransmitter release. However, these pools are not as neatly distinguished and rather interact in a highly dynamic and activity dependent manner. An important question in neuroscience is how do structural and functional properties of synaptic vesicles relate and contribute to synaptic transmission mechanisms? Our work used an enhanced method for Flash and Freeze, which combines optogenetic stimulation of presynaptic neurons and high-pressure freezing for analysis of synaptic transmission with millisecond time scale and nanometer spatial resolution. For the first time, we applied this functional electron microscopy method to intact networks in acute brains slices to examine structural vesicle pool changes during transmitter release at an identified cortical synapse – the hippocampal mossy fiber-CA3 pyramidal neuron synapse in mice. Our results show release of vesicles after single and multiple stimuli, with depletion of the docked-vesicle pool as a structural correlated to the RRP, as well as fast endocytosis. Additionally, we showed that during post-tetanic potentiation, an increase in the functionally measured RRP is associated with an increase in the number of docked vesicles. This increase lasts for the time-course of this form of short-term plasticity, in line with in vivo activity of presynaptic granule cells. We demonstrated that this mechanism is protein kinase A (PKA) and actin-dependent, suggesting that the RRP might be increasing due to mobilization of vesicles from the reserve pool by phosphorylation of the scaffolding protein synapsin via PKA and changes in actin cytoskeleton.

Zoom Link: https://mit.zoom.us/j/92977291818