Contralateral denervation causes enhanced transmitter release from frog motor nerve terminals.

Abstract

It is becoming increasingly apparent that vertebrate neuromuscular junctions can exhibit considerable plasticity in transmitter release. Long-term changes in the level of release, and therefore the effectiveness of synaptic transmission, are seen in conditions of altered use1,2, ageing3,4, hibernation5, disease6, hormonal influence7 and as a result of competitive interaction8. We have previously shown that transmitter release at frog neuromuscular junctions can vary over a wide range depending on the type of muscle examined9,10 or motor unit size11,12. We now present evidence that unilateral denervation of the frog sartorius muscle causes a large increase in transmitter release from nerve terminals in the contralateral sartorius, without an increase in synaptic size. Consequently, the safety margin for neuromuscular transmission is enhanced13. Contralateral denervation also causes a significant increase in apparent poly-neuronal innervation; but in contrast to similar experiments with the frog cutaneous pectoris muscle14–17, the increase in polyneuronal innervation does not seem to be due to nerve terminal sprouting.