Functional Motor Recovery from Motoneuron Axotomy Is Compromised in Mice with Defective Corticospinal Projections

This study investigates how the corticospinal tract (CST), a major brain pathway, affects motor recovery after nerve damage in mice. They used mice that genetically lack the CST to understand its role in restoring movement. The researchers tore off and re-implanted nerve roots in the mice to mimic a brachial plexus injury, which often causes loss of motor function. They then compared the recovery of elbow flexion between mice with and without the CST. The results showed that mice lacking the CST had impaired recovery of elbow flexion, reduced nerve regeneration, and fewer new connections between nerves and muscles, despite unexpectedly having a higher survival rate of motor neurons.

• 1
  Mice lacking the corticospinal tract (CST) showed impaired recovery of elbow flexion after brachial plexus injury and root re-implantation, as measured by grooming tests and Catwalk analysis.
• 2
  Mutant mice displayed reduced axonal regeneration, indicated by a lower number of small axons and a higher G-ratio in the myelin sheaths of peripheral nerves, compared to control mice.
• 3
  Surprisingly, a higher motoneuron survival rate was observed in mutant mice compared to controls after root avulsion/re-implantation, suggesting the absence of the CST may foster motoneuron survival.