VPT 421: Veterinary Toxicology (2+0)

MECHANISM OF ACTION

• Botulinus toxin enters presynaptic membranes of cholinergic nerve endings via receptor mediated endocytosis.
• The toxin acts intracellularly via a metalloendoprotease action to cleave 3 proteins essential for neurotransmitter release.
• Thus the toxin inhibits degranulation or exocytosis of acetylcholine granules.
• A small number of molecules of this toxin binds irreversibly to the sites of action, producing an essentially irreversible cessation of all cholinergic transmission.

• Death results from respiratory failure.
• The toxin prevents exocytosis of acetylcholine.
• Lower motor neuron effects include paresis to paralysis, hypotonia and hyporeflexia.