Primary sensory and forebrain motor systems in the newborn brain are preferentially damaged by hypoxia-ischemia

Cerebral hypoxia-ischemia causes encephalopathy and neurologic disabilities in newborns by unclear mechanisms. We tested the hypothesis that hypoxia-ischemia causes brain damage in newborns that is system-preferential and related to regional oxidative metabolism. One-week-old piglets were subjected to 30 minutes of hypoxia and then seven minutes of airway occlusion, producing asphyxic cardiac arrest, followed by cardiopulmonary resuscitation and four-day recovery. Brain injury in hypoxic-ischemia piglets (n = 6) compared to controls (n = 5) was analyzed by hematoxylin-eosin, Nissl, and silver staining, relationships between regional vulnerability and oxidative metabolism were evaluated by cytochrome oxidase histochemistry. Profile counting-based estimates showed that 13% and 27% of neurons in layers II/III and layers of somatosensory cortex had ischemic cytopathology, respectively; CA1 neuronal perikarya appeared undamaged, and < 10% of CA3 and CA4 neurons were injured; and neuronal damage was 79% in putamen, 17% in caudate, but nucleus accumbens was undamaged. Injury was found preferentially in primary sensory neocortices (particularly somatosensory cortex), basal ganglia (predominantly putamen, subthalamic nucleus, and substantia nigra reticulata), ventral thalamus, geniculate nuclei, and tectal nuclei. In sham piglets, vulnerable region generally had higher cytochrome oxidase levels than less vulnerable areas. Postischemic alterations in cytochrome oxidase were regional and laminar, with reductions (31-66%) occurring in vulnerable regions and increases (20%) in less vulnerable areas. We conclude that neonatal hypoxia-ischemia causes highly organized, system-preferential and topographic encephalopathy, targeting regions that function in sensorimotor integration and movement control. This distribution of neonatal encephalopathy is dictated possibly by regional function, mitochondrial activity, and connectivity.