Role of moving growth cone-like "wave" structures in the outgrowth of cultured hippocampal axons and dendrites

Hippocampal neurons exhibit periodically recurring growth cone-like structu res, referred to as "waves," that emerge at the base of neurites and travel distally to the tip. As a wave nears the tip, the neurite undergoes retrac tion, and when it reaches the tip, the neurite undergoes a burst of growth. At 1 day in culture, during early axon outgrowth, axone undergo an average 7,5-mu m retraction immediately preceding wave arrival at the tip followed by 12-mu m growth immediately after arrival tan average net growth of 4.5 mu m). In branched axons, waves often selectively travel down one branch or the other, Growth selectively occurs in the branch chosen by the wave, In dendrites, which grow much slower on average, wave-associated retractions a re much greater, resulting in less net growth. In the presence of Brefeldin A, which disrupts membrane traffic through the Golgi apparatus and leads t o retraction of the axon, axonal waves continue to be associated with both growth spurts and retractions. The magnitude of the growth spurts is not si gnificantly different from untreated axons, but wave-associated retractions are significantly increased, The close association between waves and cycli cal elongation suggests that waves may act to bring about this pattern of g rowth. Our results also show that modulation of regularly occurring retract ion phases plays a prominent role in determining average outgrowth rates. ( C) 1999 John Wiley & Sons, Inc.