Metabolism of rat brain mitochondria during postnatal development

Abstract

Mitochondria from whole brains of female Sprague-Dawley rats 1–50 days old were examined for relative cellular quantity and oxidative-phosphorylative capacity. The concentration of mitochondrial protein (MP) is constant during the first 5 days after birth, i.e. the rate of synthesis of MP is the same as the rate of total brain growth. This is followed by a period of accelerated MP synthesis during which the MP, initially at 17%, increases to about 26% of total cerebral protein. By the 21st day (weaning), the rapid proliferation of MP tapers off. Calculation of the relative amount of MP per cell (assume a constant amount of desoxyribose nucleic acid in each cell) reveals an increase per cell throughout the entire age range studied, with a three-fold increase during the first 21 days. The rate of O₂ utilization per milligram MP is constant throughout the age range studied; the rate of high-energy phosphate synthesis per milligram MP declines slightly. Apparently, newly formed mitochondria are fully capable of oxidative-phosphorylation. Also, the well known acceleration of O₂ utilization with brain development can be accounted for by the increase in MP. The relative gain in MP per cell during development may be a prerequisite to the greater power cost of maintaining a larger surface area as the growing cells extend into the extracellular space.