Objective: After lesion of a peripheral nerve in neonatal mammals, motoneurons undergo a cell death. We wanted to ascertain if early surgery could influence such post-axotomy motoneuronal death and improve the functional outcome. In this study, we investigated the functional and anatomical results after immediate and delayed repair of the lower trunk of brachial plexus (BP) sectioned at birth in rats.
Methods: In neonate rats, the lower trunk of the left BP was cut. This nerve trunk was repaired either immediately [immediately-reconstructed group of rats (IR), or 30 days after, tardy reconstructed group of rats (TR)]; in the third group of animals, the nerve was not repaired (noreconstructed group of rats, NoR). In each group of animals, functional studies were performed at 90 days of age using the grooming test and the walking tracks analysis. Histologic studies of the C7-T1 spinal cord and lower trunk of BP were performed at 30 and 90 days of age; the numbers of motoneuron and axon were counted.
Results: Functional recovery was related to the difference in motoneuron number between the injured and the uninjured sides of the spinal cord of the operated animals. On the one side, only in the rats in which the inferior trunk was immediately repaired, the difference in motoneuron number between the two sides of the spinal cord was not statistically significant; these animals showed a good axonal regeneration and function recovery. On the other side, in the rats in which the inferior trunk was left unrepaired or tardy repaired, the decrease in motoneuron number in the injured side compared with the uninjured side of the spinal cord was statistically significant; these animals showed no axonal regeneration and no function recovery.
Discussion: The results cited above suggest that an important role in restoration of good neurological function after section of the lower trunk of BP in neonate rats is played by early nerve repair. Good neurological function was related more to a quite numerical balance of motoneurons between the two anterior gray horns of spinal cord than to the absolute number of rescued motoneurons.