How do strychnine rodenticides exert their toxic effect?

• A. Inhibition of acetylcholinesterase
• B. Antagonizes inhibitory glycine receptors (competitive and reversible)
• C. Blockade of GABA receptors
• D. Activates NMDA receptors

Answer: (B)

Strychnine’s toxicity comes from blocking the inhibitory action of glycine in the spinal cord and brainstem. It acts as a competitive antagonist at the glycine receptor, preventing glycine from opening the chloride channel that would normally hyperpolarize and dampen motor neurons. Without this glycinergic inhibition, motor neurons become highly excitable, producing drastic reflexes and severe generalized convulsions, often with opisthotonos and jaw stiffness. This mechanism is distinct from cholinesterase inhibition (which would cause a cholinergic crisis), GABA receptor blockade, or NMDA receptor activation, making the glycine receptor antagonism the correct explanation for the observed toxic effects.