Tetrodotoxin - A neurotoxin produced naturally by many strains of tetraodontiformes, such as the Japanese pufferfish (fugu), triggerfish, and others.

The toxin binds to (and blocks) the outside poor of voltage-gated sodium channels. It essentially blocks transmission of action potentials over nerves, which use voltage-gated Na⁺ channels to effect propagation.

TTX is a very useful toxin in the study of neuronal mechanisms at the cellular and molecular level.