Amino acid uptake in the spinal cord and brain of the rat with long-term spinal hemisection

Abstract

Protein metabolism in brain and spinal cord of rats subjected to spinal cord hemisection or a control operation was examined using the incorporation of [ 3H]lysine into trichloracetic acid (TCA)-precipitable protein and TCA-soluble fractions as an indicator. Groups of animals were studied 30, 45, 60, and 90 days after a left spinal hemisection or laminectomy alone at T2. One hour prior to utilization, the animals were injected subcutaneously with 200 μCi [ 3H]lysine. Tissue samples were taken from left and right somatomotor and occipital cortex and in spinal cord as far as 14 mm rostral and caudal to the site of hemisection. In brain, the uptake of [ 3H]lysine into protein ant TCA-soluble fractions was greater ( P < 0.05) in normal animals than in any other experimental group. In spinal cord, the uptake of amino acid into protein and TCA-soluble fractions pooled over time differed ( P < 0.05) between treatment groups (normal > spinal hemisection > laminectomy controls). In rats with spinal hemisection of various durations, the average values of protein radioactivity fluctuated significantly ( P < 0.05) with time with peaks at 30 and 60 days postoperation. These differences did not appear in control groups with laminectomies. In localized regions of spinal cord, the site of spinal hemisection had the highest ( P < 0.05) protein and TCA-soluble radioactivity of all regions examined. Also, the left (lesion) side of the spinal cord had a greater average protein radioactivity than the right side in all groups of animals with spinal hemisection. These data indicate that spinal lesions produce long-term alterations in spinal cord amino acid metabolism both at the site of lesion and in regions not directly traumatized. The cyclic fluctuations of average protein radioactivity in spinal cord may correlate (Spearman rank correlation coefficient, 0.9 to 1.0) with the cyclic renewal of boutons in the rat with spinal hemisection described in earlier studies. This suggests that general metabolic factors may be important in the regenerative processes of the central nervous system.