Persistence of quantal synaptic vesicle recycling following dynamin depletion

Abstract

14Dynamins are GTPases required for pinching vesicles off the plasma membrane once a critical 15 curvature is reached during endocytosis. Here, we probed dynamin function in central synapses 16 by depleting all three dynamin isoforms in postnatal hippocampal neurons. We found a 17 decrease in the propensity of evoked neurotransmission as well as a reduction in synaptic 18 vesicle numbers. Using the fluorescent reporter vGluT1-pHluorin, we observed that 19 compensatory endocytosis after 20 Hz stimulation was arrested in ~40% of presynaptic 20 boutons, while remaining synapses showed only a modest effect suggesting the existence of a 21 dynamin-independent endocytic pathway in central synapses. Surprisingly, we found that the 22 retrieval of single synaptic vesicles, after either evoked or spontaneous fusion, was largely 23 impervious to disruption of dynamins. Overall, our results suggest that classical dynamin-24 dependent endocytosis is not essential for retrieval of synaptic vesicle proteins after quantal 25 single synaptic vesicle fusion. 26 27