SOME CONDITIONS AFFECTING THE LATE STAGES OF NEUROMUSCULAR TRANSMISSION

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Abstract
The muscular response in stages 4 (fatigue) and 5 (recovery while tetanic stimulation is continued) was studied in rela-tion to certain conditioning factors. Prostigmin has an augmentive action on the muscular response during stage 5; the depressive effect is more marked as stage 5 progresses. Prostigmin advances the onset of stage 6 and accelerates its development. Curare has an early and precipitate de-pressive influence in stage 4, but the recovery from the depression is sooner and faster than in fresh muscle; i.e., the fatigued synapse is more resistant to curare than the fresh one. Post-tetanic decurarization does not occur in stage 4 as it does in the fresh state of the synapse. Wedensky inhibition (induced by maximal stimuli applied 2 per sec.) occurs to a more marked degree and at a faster rate in fresh than in fatigued muscle. In stage 5 conditions are more like those of the fresh state than of stage 4; i.e., the muscle in stage S is less resistant to curare than in stage 4, and Wedensky inhibition (induced as described above) is more prominent in stage 6 than in stage 4- The post-tetanic increment of responses to single nerve volleys, which is evident in fresh preps., disappears in stage 4, if the test is made immediately after the fatiguing tetanus. A short period of rest, however, allows the phenomenon to reappear. The increment is absent also in stage 6, and a longer rest is required for its return than in stage 4-These results are considered in relation to the chemical and electrical theories of neuromuscular transmission.

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