SPREAD OF SYNAPTIC DEPRESSION MEDIATED BY PRESYNAPTIC CYTOPLASMIC SIGNALING

Postsynaptic activity may modulate presynaptic functions by transsynap tic retrograde signals, At developing neuromuscular synapses in Xenopu s nerve-muscle cultures, a brief increase in the cytosolic calcium ion (Ca2+) concentration in postsynaptic myocytes induced persistent depr ession of presynaptic transmitter secretion, This depression spread to distant synapses formed by the same neuron, Clearance of extracellula r fluid did not prevent the spread of depression, and depression could not be induced by increasing the Ca2+ concentration in a nearby myocy te not in contact with the presynaptic neuron, Thus, the spread of dep ression is mediated by signaling in the presynaptic cytoplasm, rather than by a retrograde factor in the extracellular space.