Bilateral movement training promotes axonal remodeling of the corticospinal tract and recovery of motor function following traumatic brain injury in mice

Abstract

Traumatic brain injury (TBI) results in severe motor function impairment, and subsequent recovery is often incomplete. Rehabilitative training is considered to promote restoration of the injured neural network, thus facilitating functional recovery. However, no studies have assessed the effect of such trainings in the context of neural rewiring. Here, we investigated the effects of two types of rehabilitative training on corticospinal tract (CST) plasticity and motor recovery in mice. We injured the unilateral motor cortex with contusion, which induced hemiparesis on the contralesional side. After the injury, mice performed either a single pellet-reaching task (simple repetitive training) or a rotarod task (bilateral movement training). Multiple behavioral tests were then used to assess forelimb motor function recovery: staircase, ladder walk, capellini handling, single pellet, and rotarod tests. The TBI+rotarod group performed most forelimb motor tasks (staircase, ladder walk, and capellini handling tests) better than the TBI-only group did. In contrast, the TBI+reaching group did not perform better except in the single pellet test. After the injury, the contralateral CST, labeled by biotinylated dextran amine, formed sprouting fibers into the denervated side of the cervical spinal cord. The number of these fibers was significantly higher in the TBI+rotarod group, whereas it did not increase in the TBI+reaching group. These results indicate that bilateral movement training effectively promotes axonal rewiring and motor function recovery, whereas the effect of simple repetitive training is limited.