Axonal regeneration in dorsal spinal roots is accelerated by peripheral axonal transection

Regeneration of crushed axons in rat dorsal spinal roots was measured to investigate the transganglionic influence of an additional peripheral axonal injury. The right sciatic nerve was cut at the hip and the left sciatic nerve was left intact. One week later, both fifth lumbar dorsal roots were crushed and subsequently, regeneration in the two roots was assessed with one of two anatomical techniques. By anterograde tracing with horseradish peroxidase, the maximal rate of axonal regrowth towards the spinal cord was estimated to be 1.0 mm/day on the left and 3.1 mm/day on the right. Eighteen days after crush injury, new, thinly myelinated fibers in the root between crush site and spinal cord were 5–10 times more abundant ipsilateral to the sciatic nerve transection. The central axons of primary sensory neurons regenerate more quickly if the corresponding peripheral axons are also injured.