AN EXPLANATION OF THE FIVE STAGES OF NEUROMUSCULAR AND GANGLIONIC SYNAPTIC TRANSMISSION

Abstract

The threshold of skeletal muscle (cat''s quadriceps) to acetylcholine increases reversibly in the course of prolonged indirect stimulation (60 per sec.); that of the superior cervical ganglion first decreases and later increases. The increments of muscular response to indirect activation produced by sub-threshold doses of acetylcholine first decrease and later increase during prolonged stimulation. These increments are true contractions, since they are attended by increased muscular spike potentials timed with the nerve volleys. The acetylcholine content of the sciatic and the superior cervical ganglion first decreases and later increases in the course of prolonged stimulation. A brief rest period after such sub-threshold stimulation results in an increase of acetylcholine conc. On the basis of these results the 5 stages of transmission in the ganglionic and neuromuscular synapses can be explained by changes in the output of acetylcholine from the presynaptic nerve endings.