Metabolic and ionic responses to global brain ischemia in the newborn dog in vivo: II. Post-natal age aspects

The main difference between newborn and adult brains is expressed in the relative resistance of the newborn brain to oxygen deprivation. The aim of the present study was to examine the effect of global ischemia in canine puppies of three different ages on the metabolic, ionic and electrical activity of the brain and to study the basic mechanisms underlying the relative resistance of the newborn brain in ischemic episode. The puppies were divided into three age groups. The young group included 0-6-day-old puppies (n = 16), the intermediate group included 7-19-day-old puppies (n = 21), and the 'adult' group included puppies aged 20 days or more (n = 17). Statistical analysis of the results led to the following conclusions: The younger the puppy, the longer is the time until the occurrence of the secondary reflectance increase SRI (13.0± 1.9 min vs. 5.3±0.5 min). The younger the puppy, the longer the time until onset of potassium leakage from the cells (0.9±0.1 min vs. 0.35±0.05 min) and the lower the amount of potassium leakage (9.6±2.8 mM vs. 21.7±4.8 mM). The rate of pumping of the potassium ions into the cells during the recovery stage was higher in the oldest group (1.2±0.2 mM min^-1 vs. 0.38±0.1 mM min^-1). It was possible to speculate that in the young puppies there is uncoupling of the oxidative phosphorylation from respiration and as a result, there is a lower, if any, rate of ATP synthesis. It seems that the newborn brain is able to cope with a decrease in available energy for a longer period of time. This is apparently due to differences in membrane characteristics and an improved ability to retain ionic equilibrium across both sides of the membrane.