This is the second revision of a competitive renewal application to study basic mechanisms of hypoxic brain damage in newborn pigs. Experiments were designed to investigate specific cellular mechanisms of brain cell injury in the piglet by correlating the degree of hypoxia with alterations in the activity and structure of the N-methyl-D-aspartate (NMDA) receptor-ion channel complex and tissue histopathologic changes. The investigators hypothesize that the severity of hypoxia will have a specific impact on the function and possibly the structure of the NMDA receptor, which is a unique aspect of the grant application. The determination of the degree of hypoxia in vivo will be achieved by the continuous monitoring of brain high energy phosphate reserves using 31-P nuclear magnetic resonance spectroscopy as well as the determination of cerebral cortical oxygen pressure by oxygen- dependent quenching of phosphorescence. Measurements of cell membrane lipid peroxidation, sodium/potassium- ATPase activity and the presence of oxygen free radicals will be used as indices of brain cell injury. Light microscopy will be performed to assess histopathologic changes at 48 hours of recovery from hypoxia. All experiments will be conducted in newborn pigs to investigate: 1) the relationship between quantitative tissue hypoxia and the structure of the recognition and modulatory sites and the activation of the receptor/ion channel complex; 2) the effect of hypoxia on NMDA-mediated influx of calcium into synaptoneurosomes; 3) the relationship between the occurrence of lipid peroxidation and alterations in the recognition and modulatory sites of the NMDA receptor; 4) the relationship between quantitative tissue hypoxia and the release of specific monoamines and amino acid neurotransmitters; and 5) the effect of increased release of amino acid and monoamine neurotransmitters during hypoxia on the activity of brain cell sodium/potassium-ATPase and alterations in NMDA activity.Additional experiments will investigate the potentiating effect of hypoglycemia during hypoxia on both NMDA receptor activity and cell membrane function. The proposed experiments will be performed using well- established techniques for the determination of ligand binding and enzyme kinetics, microdialysis, HPLC, histopathologic methods and others. It is proposed that the findings of the experiments will provide new insights into brain cell membrane function and will lead to a better understanding of basic mechanisms contributing to hypoxic neuronal injury in the newborn human infant.
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