—The metabolic activity of proteins from myelin and non‐myelin fractions of slices of lesions in monkey brains and in spinal cords of Lewis rats with acute experimental allergic encephalomyelitis was investigated using [1‐14C]leucine as a protein precursor. The uptake in vitro of [1‐14C]leucine into the monkey EAE lesions was greatly increased in both the myelin and non‐myelin fractions. Similar findings were made in spinal cord slices of the EAE rat with an average specific activity 341 per cent of control measured in proteins of purified myelin and 415 per cent of control in the non‐myelin protein. The increased uptake appeared with the onset of paralytic symptoms 10–14 days after injection. The increased uptake did not appear to be a result of an increased amino acid pool size as measured with uniformly labelled l‐leucine, valine, arginine and phenylalanine. The increase in specific activity of the myelin protein of the EAE rats was shown to be associated with the peaks characteristic of myelin protein when separated on polyacrylamide gels and the serial slices counted. Most of the radioactivity of both the control and EAE myelin protein migrated with the high molecular weight fraction, and the largest increase in radioactivity in myelin protein appeared in this fraction. Some increase in specific activity was also found in the basic and proteolipid proteins. Four different guinea‐pig antigens were used to induce EAE: whole spinal cord, purified basic protein, purified myelin and basic protein + cerebroside. All caused paralytic symptoms and greatly increased incorporation in vitro of [1‐14C]leucine into spinal cord proteins. The incorporation of [1‐14C]leucine into slices of the inguinal and popliteal lymph nodes of the EAE and Freund's adjuvant control rats were measured and compared with the incorporation into the spinal cord non‐myelin fractions. The specific activity of lymph node proteins was of the order of 10 × that of the non‐myelin protein of the control spinal cord. Invasion of a moderate number of cells of the order of activity of these lymph nodes could account for the large increase in rate of protein synthesis in the EAE nervous tissue. It is concluded that much of the increased protein synthesis could be due to the inflammatory cells, although a small amount of the total increase appears to be associated with myelin protein. Other changes in metabolism of the CNS tissue of the EAE rat include a lower rate of lipid synthesis and a decreased activity of the tricarboxylic acid cycle.
M. Smith, H. C. Rauch
Journal of Neurochemistry