[Short and long term depression of neuromuscular transmission in crayfish]

Following single excitation of the abdominal giant motoneuron of crayfish, an important depression of neuro-muscular transmission is observed for about 15 mn. The time course of recovery is not modified even after low frequency (1/30 Hz) repetitive stimulation. Recovery curves obtained for different Mg++ concentration in physiological solutions show two phases of depression: short-term depression which is largely reduced in high Mg++ concentrations - thus probably depending on transmitter depletion in motoneuron terminals - long-term depression which is not modified by changing Mg++ concentration and seems to be independent of depletion.