Oligodendrocytes (OLs) are the myelinating cells in the central nervous system (CNS) that extend long branchy processes to explore many different neurons 1−4. These myelinating cells provide support to the neuron which allows for messages to be sent rapidly from axon to axon. Without myelin, diseases such as multiple sclerosis effect millions of individuals. Neural impulses are potentiated by releasing synaptic vesicles at the terminal ends of neurons. An emerging area of interest within the field is that vesicle release occurs along the length of axons4 and works as a functional regulator of myelination1. OLs have heightened interactions at synaptic vesicle enrichment, a part of the neuron (unpublished data). Concurrently, OLs have heightened interactions at varicosities. The structure of these varicosities and vesicle enrichment sites are not well characterized. The aim of this study is to determine if the synaptic vesicle enrichments are localized within varicosities. Additionally, if there is an enrichment of synaptic vesicles located within the varicosities, are they motile or transient? The answers to these questions will give us a further insight as to how axons and their subdomains instruct or restrict myelination. These questions were addressed by obtaining short time lapses using in vivo, confocal microscopy of four-day old transgenic zebrafish embryos. From these time lapses, it was determined that synaptic vesicles can indeed reside in and enrich varicosities. We were also able to determine that individual vesicles can be motile while large areas of vesicle enrichments tend to remain transient in the time course observed.
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