Protein synthesis in experimental allergic encephalomyelitis

Amino acid incorporation into neurons and glia of guinea pigs with experimental allergic encephalomyelitis

After in vitro incubation of brain slices from guinea pigs in the intermediate (10 days postinduction) stage of experimental allergic encephalomyelitis (EAE), incorporation of [14C]leucine into protein was increased in a glial-enriched fraction. By the late (17-18 days postinduction) stage of the disease, when EAE symptoms were manifest, both the neuronal- and glial-enriched fractions showed increased specific activity of their total protein. SDS polyacrylamide gel electrophoresis showed that the increased leucine incorporation occurred in those proteins which labeled in a control material. After intraperitoneal injection of [3H]leucine the incorporated radioactivity was slightly increased in unfractionated brains from EAE animals. The neuronal-glial ratios for protein-bound radioactivity indicated that the increased incorporation resided mainly in the glial population.

Amino acid incorporation into brain subcellular fractions in experimental allergic encephalomyelitis

The in vitro protein synthetic capactiy of brain slices from guinea-pigs in the late stage (17-18 days post-induction) of experimental allergic encephalomyelitis was increased over that of Freund's adjuvant injected controls, as determined by the rate of (14C)-leucine incorporation into both tris-soluble and tris-insoluble proteins. All subcellular fractions prepared from incubated slices showed increased incorporation, with a crude nuclear fraction having the largest increase. Isolated brain mitochondria from EAE animals incorporated more amino acid into protein during the late stage of the disease, while isolated microsomes and "pH5 enzymes" show decreased amino acid incorporation compared with controls in the late stage of EAE. Polyacrylamide gel electrophoresis of acidic, soluble proteins isolated from (3H)-leucine labeled nuclear or synaptosomal fractions revealed that increases of incorporation were generalized, and not restricted to a few proteins.

Evidence for differential function of neuronal and glial cells in protein metabolism and amino acid transport

Amino acid incorporation in neuronal and glial cells has been investigated in several laboratories employing bulk-separation techniques to obtain cell-enriched fractions. The relative rates of incorporation into the proteins of both cell types vary substantially with the method of isotope administration. Through the use of single-pulse perfusions with a duration of 30-40 sec the early time course of labeling has been studied. The difference between neuronal and glial cells with respect to indicating cell interactions will be discussed. The in vitro amino acid incorporation has been measured in neurons and glia after slice incubation. In material from animals developing experimental allergic encephalitis the rate of 3H-leucine incorporation more than doubles in the unfractionated brain. Glial cells increased their rate of incorporation by approximately 400% under the same conditions. The involvement of specific proteins in the cells and organelles has been studied by gel electrophoresis. The high uptake capacity of glial cells for certain amino acids with possible transmitter function has been further characterized. The release of these substances is measured in a superfusion system where beds of cells, preloaded with the labeled substance, are used. High potassium pulses stimulate release of, for example, GABA in both neuronal and glial cells.