Cold Blockade of Axonal Transport Activates Premitotic Activity of Schwann Cells and Wallerian Degeneration

Between 3 and 4 days after transection of cat sciatic nerve, Schwann cell‐associated premitotic activity spreads anterogradely along degenerating distal nerve stumps at a rate of approximately 200 mm/day. We investigated whether fast anterograde axonal transport contributes to the initiation of this component of Wallerian degeneration. Axonal transport was blocked in intact and transected cat sciatic nerves by focally chilling a proximal segment to temperatures below 11°C for 24 hr. Incorporation of [³H]thymidine (a marker of premitotic DNA synthesis) was then measured 3 and 4 days posttransection in cold blocked‐ and control‐degenerating nerves. Effects of cold block prior to and concomitant with nerve transection were studied. Results failed to support the hypothesis that Schwann‐cell premitotic activity after axotomy is associated with entry into the axon of mitogenic substances and their anterograde fast transport along the distal stump. Instead, data suggested that progressive anterograde failure of fast anterograde transport distal to transection serves to effect the Schwann‐cell premitotic response to axotomy.