Secondary Energy Failure after Cerebral Hypoxia–Ischemia in the Immature Rat

Abstract

A delayed or secondary energy failure occurs during recovery from perinatal cerebral hypoxia–ischemia. The question remains as to whether the energy failure causes or accentuates the ultimate brain damage or is a consequence of cell death. To resolve the issue, 7-day postnatal rats underwent unilateral common carotid artery occlusion followed thereafter by systemic hypoxia with 8% oxygen for 2.5 hours. During recovery, the brains were quick frozen and individually processed for histology and the measurements of 1) high-energy phosphate reserves and 2) neuronal (MAP-2, SNAP-25) and glial (GFAP) proteins. Phosphocreatine (PCr) and ATP, initially depleted during hypoxia–ischemia, were partially restored during the first 18 hours of recovery, with secondary depletions at 24 and 48 hours. During the initial recovery phase (6 to 18 hours), there was a significant correlation between PCr and the histology score (0 to 3), but not for ATP. During the late recovery phase, there was a highly significant correlation between all measured metabolites and the damage score. Significant correlation also exhibited between the neuronal protein markers, MAP-2 and SNAP-25, and PCr as well as the sum of PCr and Cr at both phases of recovery. No correlation existed between the high-energy reserves and the glial protein marker, GFAP. The close correspondence of PCr to histologic brain damage and the loss of MAP-2 and SNAP-25 during both the early and late recovery intervals suggest evolving cellular destruction as the primary event, which precedes and leads to the secondary energy failure.