Subcellular Distribution of Radioactivity in Neuronal and Glial‐enriched Fractions After Incorporation of [3h]leucine in Vivo and in Vitro

The distribution of protein‐bound radioactivity among subcellular organelles of cerebral cortex was followed after intravenous administration of [3H]leucine and after incubation of brain slices in the presence of [3H]leucine. Neuronal and glial cell‐enriched fractions were prepared by discontinuous sucroseFicol1 gradient centrifugation of cerebral cortex cell suspensions. Subcellular fractions were obtained from each of the cell prepara‐ tions and the protein‐bound radioactivity determined after in uiuo and in vitro incorporation of [3H]leucine. The unfractionated neuronal material had a considerably higher level of protein‐bound radioactivity than the glial material. The most marked neuronal‐glial dif‐ ferences were observed in microsomes and soluble proteins, while the radioactive labelling of the nuclear and mitochondria1 fractions was similar for the two cell types.