FIGURE 4.

Axon regeneration in the lamprey spinal cord. (Left) Confocal projection of an uninjured, control lamprey spinal cord where the RS axons were anterogradely labeled with Alexa488-dextran. The descending RS axons typically exhibit straight, non-branching projection patterns. (Right) Confocal projection of a transected (Trans) spinal cord at 11 weeks post-injury (wpi). Anterograde labeling shows that the regenerating axons exhibit vastly different projection patterns. While some regenerating axons traverse the transection site (arrowhead) and cross into the distal spinal cord (below the transection site), other axons fail to regenerate, branch, or turn rostrally, demonstrating the imperfectness of structural regeneration. Despite this, the functional recovery of swimming behaviors is remarkably robust in these animals. Rostral is to the top. Adapted from Haspel et al., 2021 and used with permission by Wiley.