Regional and cellular differences in rat brain protein synthesis in vivo and in slices during development.

We compared the rate of protein synthesis in immature and adult rat brain in vivo to that in brain slices. After the incorporation of a flooding dose of [14C]valine, in vivo and in brain slices, the label in proteins was measured in CNS regions and in neuron- and glia-enriched fractions. In regions in vivo in the adult, incorporation rates in corpus callosum were lower than in other regions, which were similar; in the young, cerebellum showed the highest rates and hypothalamus and cord the lowest. Since hypothalamus and cord were low in the young, there was no change during development in these two areas; in other areas incorporation rates in young were 2-3 times higher than in adult brain proteins. Incorporation rates in slices were lower than in vivo. In the young, cerebellum, olfactory bulb, and cord were close to in vivo, and other areas in slices from young incorporated at 60-90% of in vivo rates. In adult slices incorporation was 5-15% of that in vivo except in olfactory bulb, where it was 30%. In the cellular fractions, incorporation in vivo in young was close in the neuronal and glial fractions; in adults incorporation rates in neurons were higher, as the decrease in development was less in neurons than astrocytes. In slices in young, astrocytes incorporated amino acids at 100% of the in vivo rates, neurons at 60%; in adult slices, incorporation was at only 4-7% of the in vivo rate. The results show that developmental changes in protein metabolism occur in all brain areas and brain cells, with metabolic rates in young 2-3 times that in adult.(ABSTRACT TRUNCATED AT 250 WORDS)