Abstract
1. Effects of tetrodotoxin on the neuromuscular junction have been studiedon the nerve sartorius preparation of frog.
2. Tetrodotoxin has a potent narcotic action on nerve and muscle, withoutdepolarizing them. But, it does not suppress the sensitivity of the end-plateto ACh even at much higher concentration than needed for the narcosis ofnerve and muscle. This point is rather different from many local anesthetics.
3. When a dilute solution of tetrodotoxin was applied, the size of curarinee.p.p.(recorded by an intracellular electrode) decreased gradually to about70% of the initial value, then e.p.p. was abolished abruptly due to a conductionblock in the nerve fiber. Sometimes a stepwise change in the size of e.p.p.was observed, which may be explained by a blockage of conduction in thenerve fiber near its terminal arborization (fig. 6).
4. In most cases, a selective neuromuscular block was produced by tetrodo-toxin, but not in some cases. A neuromuscular block seemed to be more easilyproduced in a preparation whose safety factor of transmission was low.
