Incorporation of amino acids into the axoplasm is enhanced by electrical stimulation of the fiber.

The effect of sustained electrical stimulation upon the incorporation of amino acids into the axoplasm was studied in the goldfish Mauthner (M) axon with light autoradiography. An extracellular pulse of tracers applied between M-axons in the medulla resulted in a local and substantial labeling of the M-axoplasm and a faint labeling of the M-perikaryon 4-5 mm away from the site of injection. After 18 h of direct electrical stimulation of the M-axon at 0.3-0.8 Hz, the local incorporation of amino acids into the M-axoplasm doubled. This enhancement declined to reach the baseline within 24 h. A 4 h electrical stimulation did not enhance the incorporation. Transynaptic activation of the M-neuron through the auditory input at 0.1-0.2 Hz for 18 h did not raise the amino acid incorporation in the M-axoplasm. We conclude that electrical discharge of the axon modulates the local incorporation of amino acids into the axoplasm.