Activity-dependent modulation of nerve terminal excitation in a mammalian peptidergic system.

Transmitter release at nerve terminals is triggered by voltage-gated calcium influx upon arrival of an action potential. Changes in coupling between axonal impulse discharge and depolarization of the nerve ending might therefore regulate exocytotic secretion. In the magnocellular neurosecretory system of the rat, the pattern of electrical activity can modify the duration of action potentials within individual nerve endings, and alter the spatial spread of excitation into the branching terminal field of neurohypophysial axons. The observed effects are consistent with the effects of firing rate and pattern on peptide release, indicating that activity-dependent changes in axon-terminal coupling may modulate secretion in this neuroendocrine system.