Editing Synaptic vesicle (section)

==== Full collapse fusion ====
It has been shown that periods of intense stimulation at neural synapses deplete vesicle count as well as increase cellular capacitance and surface area.<ref>{{Cite journal | doi = 10.1083/jcb.57.2.315 | last1 = Heuser | first1 = J. E. | title = Evidence for Recycling of Synaptic Vesicle Membrane During Transmitter Release at the Frog Neuromuscular Junction | last2 = Reese | first2 = T. S. | journal = The Journal of Cell Biology | volume = 57 | issue = 2 | pages = 315–344 | year = 1973 | pmid = 4348786 | pmc = 2108984}}</ref> This indicates that after synaptic vesicles release their neurotransmitter payload, they merge with and become part of, the cellular membrane. After tagging synaptic vesicles with HRP ([[horseradish peroxidase]]), Heuser and Reese found that portions of the cellular membrane at the frog [[neuromuscular junction]] were taken up by the cell and converted back into synaptic vesicles.<ref>{{Cite journal | last1 = Miller | first1 = T. M. | last2 = Heuser | first2 = J. E. | title = Endocytosis of synaptic vesicle membrane at the frog neuromuscular junction | journal = The Journal of Cell Biology | volume = 98 | issue = 2 | pages = 685–698 | year = 1984 | pmid = 6607255 | pmc = 2113115 | doi=10.1083/jcb.98.2.685}}</ref> Studies suggest that the entire cycle of exocytosis, retrieval, and reformation of the synaptic vesicles requires less than 1 minute.<ref>{{Cite journal | last1 = Ryan | first1 = T. A. | last2 = Smith | first2 = S. J. | last3 = Reuter | first3 = H. | title = The timing of synaptic vesicle endocytosis | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 93 | issue = 11 | pages = 5567–5571 | year = 1996 | pmid = 8643616 | pmc = 39287 | doi=10.1073/pnas.93.11.5567| bibcode = 1996PNAS...93.5567R | doi-access = free }}</ref>

In full collapse fusion, the synaptic vesicle merges and becomes incorporated into the cell membrane. The formation of the new membrane is a protein mediated process and can only occur under certain conditions. After an [[action potential]], Ca<sup>2+</sup> floods to the presynaptic membrane. Ca<sup>2+</sup> binds to specific proteins in the cytoplasm, one of which is [[synaptotagmin]], which in turn trigger the complete fusion of the synaptic vesicle with the cellular membrane. This complete fusion of the pore is assisted by [[SNARE (protein)|SNARE]] proteins. This large family of proteins mediate docking of synaptic vesicles in an ATP-dependent manner. With the help of [[synaptobrevin]] on the synaptic vesicle, the t-SNARE complex on the membrane, made up of [[syntaxin]] and [[SNAP-25]], can dock, prime, and fuse the synaptic vesicle into the membrane.<ref>{{Cite journal | last1 = Xu | first1 = H. | last2 = Zick | first2 = M. | last3 = Wickner | first3 = W. T. | last4 = Jun | first4 = Y. | title = A lipid-anchored SNARE supports membrane fusion | doi = 10.1073/pnas.1113888108 | journal = Proceedings of the National Academy of Sciences | volume = 108 | issue = 42 | pages = 17325–17330 | year = 2011 | pmid = 21987819 | pmc =3198343 | bibcode = 2011PNAS..10817325X | doi-access = free }}</ref>

The mechanism behind full collapse fusion has been shown to be the target of the [[Botulinum toxin|botulinum]] and [[tetanus]] toxins. The botulinum toxin has [[protease]] activity which degrades the [[SNAP-25]] protein. The [[SNAP-25]] protein is required for vesicle fusion that releases neurotransmitters, in particular acetylcholine.<ref>{{Cite journal | last1 = Foran | first1 = P. G. | last2 = Mohammed | first2 = N. | last3 = Lisk | first3 = G. O. | last4 = Nagwaney | first4 = S. | last5 = Lawrence | first5 = G. W. | last6 = Johnson | first6 = E. | last7 = Smith | first7 = L. | last8 = Aoki | first8 = K. R. | last9 = Dolly | first9 = J. O. | title = Evaluation of the Therapeutic Usefulness of Botulinum Neurotoxin B, C1, E, and F Compared with the Long Lasting Type A. BASIS FOR DISTINCT DURATIONS OF INHIBITION OF EXOCYTOSIS IN CENTRAL NEURONS | doi = 10.1074/jbc.M209821200 | journal = Journal of Biological Chemistry | volume = 278 | issue = 2 | pages = 1363–1371 | year = 2002 | pmid = 12381720 | doi-access = free }}</ref> Botulinum toxin essentially cleaves these SNARE proteins, and in doing so, prevents synaptic vesicles from fusing with the cellular synaptic membrane and releasing their neurotransmitters. Tetanus toxin follows a similar pathway, but instead attacks the protein [[synaptobrevin]] on the synaptic vesicle. In turn, these [[neurotoxin]]s prevent synaptic vesicles from completing full collapse fusion. Without this mechanism in effect, muscle spasms, paralysis, and death can occur.{{cn|date=December 2022}}