Presynaptic membrane potential and transmitter release at the crayfish neuromuscular junction

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Abstract
Release of transmitter was evoked at neuromuscular junctions of the crayfish opener muscle by passage of current through an intracellular electrode impaling a branch of the motor axon close to a muscle fiber. Membrane-potential changes in the presynaptic axon branch were monitored, together with postsynaptic potentials. Morphological features of the terminals were investigated after injection of lucifer yellow into the axon. An electrical model incorporating the morphological features suggests that membrane-potential changes set up in the main axon reach the nearest terminals with 30-40% attenuation, while events originating in the terminals would be severely attenuated in the main axon. Comparison of the crayfish synapse with other frequently studied synapses shows both similarities and differences, suggesting that it is not possible to apply findings made in 1 synapse to all others.