Effects of age on the metabolic, ionic and electrical responses to anoxia in the newborn dog brain in vivo

The interrelation between brain energy metabolism, electrical activity and ion homeostasis developing under experimental anoxia in animals of different ages is of significant value in the understanding of brain damage occurring under similar conditions of clinical neuropathology. The purpose of the present study was to compare brain energy states and extracellular ion homeostasis during anoxia in newborn puppies of various ages. We have developed and used a multiparametric monitoring device by which various functions of the brain can be recorded in a real-time mode from a 5 mm diameter area on the surface of the cortex. Intracellular oxygen balance was evaluated in newborn puppies of various ages by monitoring the intramitochondrial NADH redox state using a fluorescence techni-que. The electrical activity was measured by recording the spontaneous ECoG (electrocorticogram) and DC (direct current) steady potential. Ion homeostasis was evaluated using surface potassium and calcium mini-electrodes. Newborn puppies were anesthetized, the dura mater was removed and the multiprobe assembly was placed on the brain and cemented to the skull. Five groups of puppies (0–1, 2–7, 8–14, 15–21 days and 3–24 weeks) were exposed to 5 minutes of complete O₂ deprivation (100% nitrogen exposure) and were monitored during the recovery period until all parameters returned to baseline values. The results may be summarized as follows: 1. Resting baseline levels of extracellular K⁺ were in the same range as described for other young and adult mammals (2.9 ± 0.05 mM).