Which toxin increases exocytosis of acetyl choline containing vesicles?
**Core Concept**
The release of acetylcholine (ACh) from motor neurons is a critical step in neurotransmission, and its dysregulation can lead to various neurological disorders. The increase in exocytosis of ACh-containing vesicles is primarily mediated by a toxin that interferes with the normal functioning of the presynaptic neuron.
**Why the Correct Answer is Right**
Botulinum toxin (BoNT) is a potent neurotoxin produced by the bacterium Clostridium botulinum. It works by cleaving the synaptosomal-associated protein SNAP-25, which is a key component of the SNARE complex essential for vesicle fusion and exocytosis. By inhibiting the SNARE complex, BoNT prevents the release of ACh into the synaptic cleft, thereby reducing acetylcholine-mediated neurotransmission. This results in flaccid paralysis of the affected muscles.
**Why Each Wrong Option is Incorrect**
* **Option A:** Tetanus toxin also affects neurotransmitter release, but it primarily targets glycine and GABA receptors, leading to hyperexcitability and rigidity. Tetanus toxin does not increase exocytosis of ACh-containing vesicles.
* **Option B:** Diphtheria toxin inhibits protein synthesis by ADP-ribosylating elongation factor 2, leading to cell death. It does not directly affect neurotransmitter release or exocytosis.
* **Option C:** Anthrax toxin affects various cellular processes, including cell signaling and protein synthesis, but it does not specifically increase exocytosis of ACh-containing vesicles.
**Clinical Pearl / High-Yield Fact**
Botulinum toxin has been used therapeutically for various conditions, including blepharospasm, strabismus, and hyperhidrosis. Its mechanism of action provides a unique opportunity for targeted treatment of neurological disorders.
**Correct Answer:** C. Botulinum toxin.