Delayed cerebral atrophy following moderate hypoxia-ischemia in the immature rat

Hypoxia-ischemia (H/I) damages cells in the immature brain and interferes with subsequent brain development; the extent of the damage has been related to the severity, or duration, of the initial insult. This study examined the effects of both severe and moderate duration of H/I on the evolution of damage through 8 weeks of recovery. Seven-day-old rat pups were subjected to either 75 min or 2 h of 8% oxygen following a unilateral carotid artery ligation. Evaluation of brain damage included morphometric analysis of hemispheric diameter at 2, 4, and 8 weeks of recovery, and hematoxylin and eosin for evaluation of pathology at 8 weeks. Two hours of H/I produced severe infarction in the ipsilateral hemisphere in the majority of the survivors, apparent by 2 weeks of recovery with no change at 4 or 8 weeks. In marked contrast, 75 min of H/I produced no significant damage during the initial 2 weeks of recovery but resulted in progressive cerebral atrophy with delayed infarction such that the extent of damage at 8 weeks was not different from the 2-hour group. Thus, even a mild-moderate ischemic insult to the perinatal brain establishes a vulnerable region which ultimately dies without intervention.