A foodborne outbreak of flaccid descending paralysis follows consumption of home-preserved vegetables. The toxin responsible acts at the neuromuscular junction by:
- A Competitive blockade of postsynaptic nicotinic receptors
- B Proteolytic cleavage of SNARE proteins preventing calcium-dependent acetylcholine release ✓
- C Irreversible inhibition of acetylcholinesterase
- D Blockade of voltage-gated sodium channels in motor nerve terminals
Correct answer: B. Proteolytic cleavage of SNARE proteins preventing calcium-dependent acetylcholine release
Explanation
Botulinum toxin is a zinc-dependent endopeptidase that cleaves SNARE proteins such as SNAP-25 and synaptobrevin, preventing fusion of acetylcholine-containing vesicles with the presynaptic membrane. Curare-like drugs act postsynaptically on nicotinic receptors, organophosphates inhibit cholinesterase, and tetrodotoxin blocks neuronal sodium channels. Management is supportive ventilation plus antitoxin; cholinesterase inhibitors do not help.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.