Small voltage changes at nerve terminals travel up axons to affect action potential initiation

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Abstract
At the calyx of Held nerve terminal, Wu and Paradiso show that small hyperpolarizations or depolarizations can travel back up the axon and influence the threshold for action potential initiation. Nerve terminals are generally considered to be the destination points for electrical signals, which propagate unidirectionally from the soma to nerve terminals. We found that small hyperpolarizations or depolarizations (∼10 mV) generated under physiological conditions in rat nerve terminals backpropagated up the axon (∼400–800 μm) and changed the threshold for initiating action potentials and thus firing patterns. These results suggest a mechanism for information processing in neurons and neuronal circuits.