SOME STUDIES ON RAT BRAIN MICROSOMES IN RELATION TO GROWTH AND DEVELOPMENT

Microsomes have been prepared from rat cerebral cortex and from cerebellum at various developmental stages varying from 7 g to 250 g body weight. The results show that the microsomal RNA content per cerebral cortex or cerebellum increases from 7 g to 25-28 g body weight and then declines. Changes also occur in the relative rates of incorporation of [14C]orotic acid into nuclear and microsome fractions between 7 and 28 g body weight. After 40 g body weight there is no further change. DOC treatment of young microsomes prepared 1 h after the intracerebral injection of orotic acid reduced the specific activity of the subsequently isolated RNA by 50%. The effect of DOC treatment decreases progressively, and by 28 g body weight the effect is small. Changes also occur in the nature of the polypeptides produced in the amino acid incorporating system between 7 and 28 g body weight. © 1969.