Noradrenaline synchronizes evoked quantal release at frog neuromuscular junctions

1. Noradrenaline (NA) increases synaptic efficacy at the frog neuromuscular junction. To test the hypothesis that one of the actions of NA is to short en the period over which evoked quanta are released, we measured the latenc ies of focally recorded uniquantal endplate currents (EPCs). 2. NA shortened the release period for evoked quantal release. The interval between the time when responses with minimal delay appeared and the point at which 90% of all latencies had occurred was shortened in the presence of 1 x 10(-5) ar NA by about 35% at 20 degrees C and by about 45% at 8 degree s C. Inhibitor and agonist experiments showed that NA acts on a beta-adreno receptor. 3. The better synchronization of release significantly increased the size o f reconstructed multi quantal EPCs. This suggests that NA facilitates synap tic transmission by making the release of quanta more synchronous. 4. The synchronizing action of NA might potentiate neuromuscular transmissi on during nerve regeneration, transmitter exhaustion and other extreme phys iological states where the quantal content is reduced, such as survival in cold and hibernation.