Ontogeny of Cerebral Oxidative Metabolism in the Chick Embryo

Abstract

The low cerebral energy requirements of most mammals at birth reflect an immaturity of the CNS; energy demands in fetuses seem even less well developed than in newborns. Fetal cerebral energy requirements are presumed to be met predominantly or exclusively by anaerobic glycolysis. Cerebral oxidative metabolism was investigated in 9-, 14-, 16-, and 19-day-old chick embryos and in newly hatched peeps. Animals were decapitated and quick-frozen in liquid Freon 0-5 min post-mortem. Forebrain extracts were prepared and assayed for ATP, phosphocreatine, glucose and lactate. Alterations in these metabolites post-decapitation were used to calculate cerebral metabolic rates (.DELTA. .apprx. P) and rates of maximal anaerobic glycolysis (.DELTA. lactate). Rates of lactate accumulation during cerebral ischemia increased progressively embryonic day 9 through hatching. Cerebral metabolic rates were not different in 9-, 14-, and 16-day-old embryos, but increased steadily thereafter. The extent to which total cerebral energy utilization could be derived from anaerobic glycolysis (.DELTA. lactate/.DELTA. .apprx. P) increased from a low at day 9 (0.29) to a maximum at day 16 (0.78). Despite the low cerebral metabolic activity of the chick embryo, at no time during development is anaerobic glycolysis capable of entirely supporting the energy needs of the developing brain.