Journal of Neuroscience, Vol 14, 4694-4704, Copyright © 1994 by Society for Neuroscience
Depression of developing neuromuscular synapses induced by repetitive postsynaptic depolarizations
YJ Lo, YC Lin, DH Sanes and MM Poo
Department of Biological Sciences, Columbia University, New York, New York 10027.
Effect of postsynaptic activity on the synaptic efficacy was studied in
Xenopus nerve-muscle cultures. Repetitive postsynaptic depolarizations
induced by injection of current pulses into singly innervated myocytes
resulted in significant reduction in the frequency of spontaneous synaptic
currents and the amplitude of nerve-evoked synaptic currents at the
majority of synapses that showed immature synaptic properties. Repetitive
hyperpolarizations and steady depolarizations of similar duration were
without effect. The depolarization-induced synaptic depression appeared to
result predominantly from a reduced ACh secretion from the presynaptic
nerve terminal. Buffering the myocyte cytosolic Ca2+ at a low level with
intracellular loading of a Ca2+ buffer,
1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid (BAPTA),
significantly reduced the effect of the depolarizations. Thus postsynaptic
electrical activity can regulate the synaptic efficacy of the developing
neuromuscular synapases and the regulation may be mediated by retrograde
transsynaptic interactions.