The overall objective of this research component is to investigate the high energy biochemical mechanisms whereby the perinatal brain is damaged by hypoxia-ischemia and how brain injury can be prevented or reduced through specific modalities of therapy.
Specific aims i nclude: 1) to ascertain the relationship between the extent of alterations in high energy metabolites (ATP,PCr) during hypoxia-ischemia and neuropathologic outcome; 2) to determine whether or not specific therapeutic manipulations known to preserve high energy metabolites ultimately and consistently prevent or reduce hypoxic-ischemic brain damage; 3) to improve the spatial localization of NMR measurements to more accurately reflect the changes of high energy metabolism in discrete region of the immature brain; 4) to explore the spatial dependence of Mg++, an important co-factor in the regulation of many essential enzymatic reactions, including neurotransmission. To produce perinatal hypoxic- ischemic brain damage, 7-day postnatal rats will undergo unilateral common carotid artery ligation followed by hypoxia with 8% oxygen at 37degreesC for up to 3 hours; an insult known to produce selective neuronal necrosis or infarction in the majority of animals. During or following hypoxia-ischemic, the animals will undergo those procedures necessary to obtain sequential 31P and 1H NMR spectra which will allow for a semi-quantitative measure of the alterations in high-energy phosphate reserves and lactate which result from the insult. Following hypoxia-ischemia, the immature rats will be reared with their dams until 30 days of postnatal age at which time they will undergo perfusion- fixation of their brains for neuropathologic analysis and scoring of brain damage. Additional experiments will include the effect of mild hypothermia (34 or 31degreesC) or of fasting on the preservation of high- energy phosphate reserves during and following hypoxia-ischemia. Experiments also will include immature rats undergoing hypoxia-ischemia which have received either allopurinol (100 or 200 md g/kg), M-801 (0.5- 10 mg/kg), nimodipine )1-2 mg/kg), or MgS04 (0.3-0.6 mg/kg) s.c.; untreated littermates undergoing cerebral hypoxia-ischemia will serve as controls. Analytical procedures will include sequential measurements with 31P and 1H NMR spectroscopy as well as brain tissue analysis of high-energy phosphate reserves (phosphocreatine, ATP, ADP, AMP) and lactate using high pressure liquid chromatography or enzymatic, fluorometric methods. Finally, a technique will be developed to allow spatial localization of NMR signals within specific regions of immature rat brain.
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