The continual administration of neostigmine and the neuromuscular junction.

The effect of continual administration of neostigmine on the neuromuscular junction of the rat diaphragm was examined by determining the number of quanta of acetylcholine released by each nerve impulse, the effect of differing repetition rats on quantal release and the amplitude and frequency of miniature end-plate potentials. The number of quanta of acetylcholine released at a nerve impulse repetition rate of 1/sec was reduced to 51% of normal in treated animals. The reduction was greater at faster repetition rates. The amplitude of miniature end-plate potentials was reduced to 75% of normal. This reduction appears to be due to blocking of receptor sites rather than the reduction in the amount of acetylcholine in each quantum. The frequency of spontaneous miniature end-plate potentials was reduced in treated animals.