Transmitter secretion varies between visualized release sites at amphibian neuromuscular junctions

Living amphibian (Bufo marinus) motor-nerve terminals have been stained and electrophysiological techniques have been used to determine the amount of transmitter secreted at selected release sites of the terminals. High secretion occurs at sites laid down near the origin of the terminals; very low or zero secretion occurs at more distal sites. The results indicate that some release sites may fail to secrete transmitter on arrival of a nerve impulse. It is suggested that functionally silent release sites may exist at synapses in the nervous system.