BRAIN PROTEINS: QUALITATIVE AND QUANTITATIVE CHANGES, SYNTHESIS AND DEGRADATION DURING FETAL DEVELOPMENT OF THE RABBIT

The composition and metabolism of the proteins of the cerebral pallium of the rabbit during the final one-third of the gestational period were measured. During this period, the brain increased in size almost 10-fold and the migration of neuroblasts to form the cerebral cortex became complete. Concurrent with the marked structural changes, the solubility characteristics and electrophoretic distribution of various brain proteins showed little change. However, at the time of birth and in the adult, significant differences in gel electrophoresis patterns were apparent. The rate of synthesis of protein in brain slices from the fetus of 20 days gestation was 3-fold higher per mg of tissue than in the neonate and about 30-fold higher than in the adult. Activities of acidic and neutral proteases per unit weight were virtually the same and nearly constant throughout the late fetal period. However, during this stage, while rapid growth persists, the total protein synthetic activity of the pallium predominated over the total proteolytic activity, whereas sometime after birth the ratios of these activities reversed consequent to a shutdown of the synthetic process.