Cell Death in the Red Nucleus Following Spinal Cord Hemisection in the Adult Rat
Schmidt, Eric R.
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It is well known that the mammalian spinal cord has a very limited capacity for regeneration. This is thought to be, in part, a result of extensive glial and connective tissue scarring at the injury site, and because of specific morphological characteristics of the spinal cord. Recent studies have shown that neurons of the red nucleus in the brain, whose axons project contralaterally into the spinal cord as the rubrospinal tract, degenerate following thoracic spinal cord hemisection in the neonatal and adult rat. The loss of neuronal cells in the brain whose axons project to the spinal cord may therefore be another reason for the lack of regeneration in the injured mammalian spinal cord. The present study was designed·to confirm cell death in the red nucleus of the adult rat following spinal cord hemisection and to attempt to determine the earliest time after spinal injury during which a significant cell loss could be observed and quantified. Adult rats were subjected to right spinal cord hemisections at the level of the first thoracic vertebra which severed the axons of the rubrospinal tract. This was followed by a second more rostral right hemisection at the level of the second cervical vertebra. Horseradish peroxidase (0.2ul of 30% HRP in 2% DMSO) was injected into the rostral hemisection to label the rubrospinal neurons by the o-dianisidine method. In the control animals the rostral hemisection and HRP injection were carried out immediately after the T1 hemisection. In the experimental animals the rostral hemisection and HRP injection were carried out 2-26 days after the, T1 hemisection. The number of labeled and unlabeled neurons in the red nucleus contralateral to the lesion sites was counted. The results indicated that there was a significant decrease in the number of rubrospinal neurons in the experimental animals as compared to the control animals. The first significant decrease was seen during' the 9-14 day time period. The results further substantiate massive cell loss in the red nucleus following spinal cord hemisection in the adult rat and may serve to further the hypothesis that regeneration of the mammalian spinal cord is limited by the death of neurons in the brain.