Tetrodotoxin Blocks a Graded Sensory Response in the Eye of Limulus

Abstract
The generalization that tetrodotoxin selectively blocks all-or-none electrical activity of nerve and muscle but has negligible effect upon graded responses of sensory systems does not appear to be valid for the Limulus eye. Tetrodotoxin reversibly blocks the graded transient component of this visual response, while the steady-state component of the response is relatively unaffected by the drug.