Biosynthesis of proteins is essential for growth and continued maintenance of the entire neuron including axons, dendrites, and synaptic terminals, and it is clearly one of the important biochemical processes underlying adaptive changes in the nervous system. Studies in experimental animals with the quantitative autoradiographic L [1 (14)C]leucine method have demonstrated a number of the physiological and pathological conditions in which changes in regional rates of cerebral protein synthesis (rCPS) occur.