A farmer develops descending flaccid paralysis after eating home-canned food, while his neighbour with a contaminated puncture wound develops spastic paralysis and risus sardonicus. Both toxins act on the same molecular target family. The difference in presentation is explained by:

• A Tetanus toxin enhances glycine release whereas botulinum toxin blocks it
• B Botulinum toxin blocks postsynaptic nicotinic receptors, tetanus toxin blocks presynaptic calcium channels
• C Both toxins block acetylcholine release, but tetanus toxin acts faster
• D Botulinum toxin cleaves SNAREs at the neuromuscular junction, tetanus toxin cleaves synaptobrevin in inhibitory spinal interneurons ✓

Explanation

Both are zinc-dependent proteases that cleave SNARE proteins, preventing vesicular transmitter release. Botulinum toxin acts mainly at peripheral cholinergic terminals, blocking ACh release and causing flaccid paralysis. Tetanus toxin is taken up retrogradely by motor neurons, transferred to inhibitory interneurons in the spinal cord, and blocks glycine and GABA release, removing reciprocal and recurrent inhibition and causing unopposed excitation with spasticity. Option A reverses the direction of the tetanus effect.

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.