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1. Mitochondria
2. synaptic vesicle with neurotransmitters
3. Autoreceptor
4. Synapse with neurotransmitter released (serotonin)
5. Postsynaptic receptors activated by neurotransmitter (induction of a postsynaptic potential)
6. Calcium channel
7. Exocytosis of a vesicle
8. Recaptured neurotransmitter
In a neuron, synaptic vesicles, also called neurotransmitter vesicles, store the various neurotransmitters that are released during calcium-regulated exocytosis at the presynaptic terminal into the synaptic cleft of a synapse. The vesicles are essential for the propagation of nerve impulses between neurons and are constantly recreated by the cell.
Formation
Synaptic vesicles are made of a lipid bilayer in which transport proteins specific to each type of neurotransmitter are inserted. Neurotransmitters are moved from the cell's cytoplasm into the vesicles by vesicular transporters that rely on active transport mechanisms involving an exchange of protons (H+ ions). The necessary proton gradient is created by V-ATPase, which breaks down ATP for energy. Vesicular glutamate transporters, for example, sequester glutamate into vesicles by this process.
The stoichiometry for the movement of different neurotransmitters into a vesicle is given in the following table.
| Neurotransmitter type(s) | Inward movement | Outward movement |
|---|---|---|
| norepinephrine, dopamine, histamine, serotonin and acetylcholine | neurotransmitter+ | 2 H+ |
| GABA and glycine | neurotransmitter | 1 H+ |
| glutamate | neurotransmitter- + Cl- | 1 H+ |
membranes are tethered to SNAP via ATPase.
Effects of neurotoxins
Some neurotoxins, such as batrachotoxin, are known to destroy synaptic vesicles. The tetanus toxin damages vesicle-associated membrane proteins (VAMP), a type of v-SNARE, while botulinum toxins damage t-SNARES and v-SNARES and thus inhibit synaptic transmission.[1] A spider toxin called α-Latrotoxin binds to neurexins, damaging vesicles and causing massive release of neurotransmitters.
References
- ^ Kandel et al, 2000
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- This page was last modified on 14 August 2008, at 03:49.
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