Tetrodotoxin and neuromuscular transmission

1. The puffer fish poison, tetrodotoxin ( T . T .) was applied to eliminate impulse propagation in nerve and muscle fibre, and the physiological properties of the neuromuscular junction were studied under this condition. 2. Spontaneous miniature end-plate potentials of normal frequency and amplitude were recorded in the T . T .-paralysed muscle. 3. Depolarization of motor nerve endings by locally applied current still produces the usual increase in the frequency of miniature end-plate potentials (e. p. ps). 4. When brief current pulses are applied to the nerve endings e. p. ps can be evoked, whose size varies with the intensity of the current. The responses are composed, like normal e. p. ps, of a statistically varying number of miniature potentials. The response fails when calcium is removed from the bath. 5. When two identical pulses are applied at varying intervals, facilitation of the second e. p. p. occurs, similar to that observed normally with pairs of nerve impulses. 6. It is concluded that tetrodotoxin while blocking electric excitation in nerve and muscle does not interfere with the release of acetylcholine from nerve endings nor with its local action on the muscle fibre.