Magnetic resonance proton spectroscopy and diffusion weighted imaging of chick embryo brain in ovo

Metabolic compensatory mechanisms may partly account for the decreased vulnerability to hypoxia observed in the developing brain. We used proton magnetic resonance spectroscopy and diffusion-weighted imaging to measure the cerebral concentrations of lactate and other metabolites, as well as the apparent diffusion coefficient (ADC) of tissue water, before, during and after hypoxia in anaesthetised chick embryos in ovo. Reducing the inspired oxygen concentration to 8% for 40 min caused a significant rise in both mean (+/-S.D.) lactate:creatine and alanine:creatine ratios from 0.58 (0.41) to 1.56 (0.56) and 0.14 (0.14) to 0.29 (0.17), respectively. Under similar hypoxic conditions, ADC did not change from a mean baseline value of 0.95 (0.09), but did fall to 0.40 (0.12) x 10(9) mm(2) s(-1) with further stepwise reductions in oxygenation. Moderate hypoxia increases lactate concentration in the developing chick brain without compromising cellular energy metabolism.