Effects of temperature and drugs on mammalian motor nerve terminals

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Abstract
The effects of temperature and drugs on spontaneous and stimulus-linked modes of transmitter release have been studied in the rat diaphragm. Miniature end-plate potential (MEPP) frequency increases with rising temperature whereas, in high magnesium concentration, the number of transmitter quanta liberated per nerve impulse decreases. The rate of increase in spontaneous release after heating does not change with removal of calcium, though the absolute frequency of MEEP''s is reduced by about 40%. If twitching is blocked by partial curarization the temperature activation of spontaneous release mechanisms is paralleled by both an increased number of quanta per nerve impulse and a lesser degree of transmitter depletion during a tetanus. Both the latter effects and the response of the MEPP''s to heating are thought to reflect increased production of transmitter quanta. Veratrine and guanidine may selectively activate one or more functions of the mammalian motor nerve terminal, but neither agent appears to increase synthesis or restore the activation of 20 m[image] K blocked by prior removal of calcium. It is suggested that the normal spontaneous "leakage" of acetylcholine quanta from nerve terminals represents mainly an overflow of production.