Calcium Accumulation during the Evolution of Hypoxic—Ischemic Brain Damage in the Immature Rat

Abstract

An excessive accumulation of calcium in neuronal and other tissues has been postulated to represent a “final common pathway” for cell death arising from hypoxia-ischemia. To clarify the role of altered calcium flux into and distribution within the perinatal brain undergoing hypoxic-ischemic injury, 7-day postnatal rats underwent unilateral common carotid artery ligation followed by 3 h of hypoxia with 8% oxygen. This insult is known to produce brain damage confined to the cerebral hemisphere ipsilateral to the arterial occlusion in >90% of the animals. Either before or after hypoxia-ischemia, the animals received a subcutaneous injection of [⁴⁵Ca]Cl₂, and their brains were subjected to ⁴⁵Ca autoradiography at 0–1, 5, 24, and 72 h, 7 or 15 days thereafter. During hypoxia-ischemia, calcium flux into the ipsilateral cerebral hemisphere was prominent in 13 of 14 rat pups, especially in neocortex, hippocampus, striatum, and thalamus. Calcium accumulation also occurred to a variable degree (6 of 14 animals) in the contralateral cerebral hemisphere. During recovery, radioactivity in the contralateral cerebral hemisphere was no longer apparent, whereas in the ipsilateral hemisphere, the extent of calcium accumulation was mild in four of six at 1 h, moderate in three of six at 5 h, moderate to intense in six of seven and six of seven at 24 and 72 h, respectively, and intense in three of three and two of two animals at 7 and 15 days, respectively. As during hypoxia-ischemia, the distribution of the radioactivity was most prominent in those structures that are known to be vulnerable to hypoxic-ischemic injury. Thus, hypoxia-ischemia is associated with enhanced calcium uptake into the immature brain, which does not dissipate but rather progressively accumulates for up to 15 days of recovery. The findings implicate a disruption of intracellular calcium homeostasis as a major factor in the evolution of perinatal hypoxic-ischemic brain damage.