[Nature of the hig-frequency (pessimal) block in the excitatory neuromuscular synapses of cray fish].

The characteristics of the excitatory neuromuscular transmission of the crayfish claw opener were studied with intracellular recording during high frequency stimulation . The high frequency block was of the presynaptic origin. The appearance of failures of transmission was correlated with the decrease of the conduction velocity in the axon and/or its branches. At the high rates of stimulation before the failures of transmission, the mean quantum content of the polysynaptic EPSPs on the plateau of potentiation was lower than that at the lower rates. There were no signs of the transmitter store depletion during high frequency stimulation. The stability of transmitter secretion mechanism is concluded to be higher than that of the nerve conduction.