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Later, synaptic vesicles could also be isolated from other tissues such as the superior cervical ganglion, [40] or the octopus brain. [41] The isolation of highly purified fractions of cholinergic synaptic vesicles from the ray Torpedo electric organ [42] [43] was an important step forward in the study of vesicle biochemistry and function.
In nerve terminals, synaptic vesicles are produced quickly to compensate for their rapid depletion during neurotransmitter release. Their biogenesis involves segregating synaptic vesicle membrane proteins from other cellular proteins and packaging those distinct proteins into vesicles of appropriate size.
Calcium ions then bind to synaptotagmin proteins found within the membranes of the synaptic vesicles, allowing the vesicles to fuse with the presynaptic membrane. [16] The fusion of a vesicle is a stochastic process, leading to frequent failure of synaptic transmission at the very small synapses that are typical for the central nervous system.
The pre-synaptic axon shows an increase in synaptic volume and area, an increase of synaptic vesicles, clustering of vesicles at the active zone, and polarization of the pre-synaptic membrane. These changes are thought to be mediated by neurotrophin and cell adhesion molecule release from muscle cells, thereby emphasizing the importance of ...
About once every second in a resting junction randomly one of the synaptic vesicles fuses with the presynaptic neuron's cell membrane in a process mediated by SNARE proteins. Fusion results in the emptying of the vesicle's contents of 7000–10,000 acetylcholine molecules into the synaptic cleft, a process known as exocytosis. [6]
The calyx of Held and endbulb of Held hold vesicles containing glutamate on the presynaptic terminal; the vesicles are released upon stimulation (originating in the cochlea and AVCN). The glutamate then binds to two known glutamate receptors, AMPA-and NMDA receptors, rapidly initiating action potentials in the post-synaptic cell. [12]
Several proteins of the synaptic ribbon have also been found to be associated with conventional synapses. RIM (Rab3-interacting proteins) is a GTPase expressed on synaptic vesicles that is important in priming synaptic vesicles. [12]
Accordingly, various subproteomes of isolated synaptosomes, such as synaptic vesicles, synaptic membranes, or postsynaptic densities can now be studied by proteomic techniques, leading to a deeper understanding of the molecular machinery of brain neurotransmission and neuroplasticity. [12] [11] [13] [14]