Mitochondrial changes in developing rat brain

Abstract

The cerebral energy requirement increases during neonatal maturation with a corresponding increase in mitochondrial protein. The question arises: do cerebral mitochondria change in number or in size during this period? Particulates prepared by differential centrifugation from rats of known ages were counted with phase contrast microscopy, also the dry weight and protein determined. The number of mitochondria per gram of brain is (12) (10¹⁰) in 1-day rats, (30) (10¹⁰) in 21-day rats, (33) (10¹⁰) in 50-day rats. The average dry weight in picograms of a mitochondrion is 0.387 in 1-day; 0.308 in 21-day; 0.288 in 50-day. The protein is 0.159 in 1-day; 0.122 in 21-day; and 0.107 in 50-day. Thus it appears there is a threefold increase in the number from 1 to 21 days but the mass per mitochondrion decreases. There is little change in number from 21- to 50-day and the mass continues to decrease. Calculation from the known total dry weight and protein increase per gram of brain shows that 66% of dry weight and 64% of the new protein synthesized is mitochondrial.