indication

Used internally for relieving respiratory distress. Also for use as an antidote in poisoning by CNS depressants, especially barbiturates.

pharmacology

Picrotoxin is a toxin obtained from the seeds of the shrub Anamirta cocculus. It is used as a central nervous system stimulant, antidote, convulsant, and GABA (gamma aminobutyric acid) antagonist. It is a noncompetitive antagonist at GABA_A receptors and thus a convulsant. Picrotoxin blocks the GABA_Activated chloride ionophore. Although it is most often used as a research tool, it has been used as a CNS stimulant and an antidote in poisoning by CNS depressants, especially barbiturates.

mechanism of action

Picrotoxin antagonizes the GABA_A receptor channel directly, which is a ligand-gated ion channel concerned chiefly with the passing of chloride ions across the cell membrane. Therefore picrotoxin prevents Cl^- channel permeability and thus promtes an inhibitory influence on the target neuron. Picrotoxin reduces conductance through the channel by reducing not only the opening frequency but also the mean open time. Picrotoxin also antagonizes GABA_C receptors (also called GABA_A-rho receptors) but the result of this action is not known. The GABA_C receptor is also linked to chloride channels, with distinct physiological and pharmacological properties. In contrast to the fast and transient responses elicited from GABA_A receptors, GABA_C receptors mediate slow and sustained responses.

toxicity

Oral, mouse: LD₅₀ = 15 mg/kg. In large doses it is a powerful poison, causing unconsciousness, delirium, convulsions, gastro-enteritis and stimulation of the respiratory centre followed by paralysis, from which death sometimes results.