When neuroblastoma cells bearing neurites are incubated with colchicine or Nocodazole, the cytoplasmic microtubules are depolymerized and concomitantly the neurites retract. We report here that cytochalasin separates the two effects of these drugs: it quantitatively inhibits neurite retraction but does not inhibit microtubule assembly. The neurites that remain contain intermediate filaments and actin but are devoid of microtubules. Depletion of cellular ATP also blocks neurite retraction induced by colchicine or Nocodazole, but some assembled microtubules persist under these conditions. The results suggest that neurite retraction is an active cell process.

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