CHRONIC HYPOXEMIA CAUSES EXTRACELLULAR GLUTAMATE CONCENTRATION TO INCREASE IN THE CEREBRAL-CORTEX OF THE NEAR-TERM FETAL SHEEP

Fetal hypoxia is an important cause of neurologic morbidity and mortal ity. Hypoxia-induced increase in extracellular glutamate concentration can lead to excitotoxic neuronal death in adults. The objective of th is study was to test whether chronic fetal hypoxemia increases extrace llular glutamate concentration in the unanesthetized intact cerebral c ortex of the near-term fetal sheep. Microdialysis probes were implante d into the parasagittal parietal cortex and periventricular white matt er of near-term fetal sheep. At 124 +/- 1 days of gestation, extracell ular glutamate concentration was determined before and during 24 h of fetal hypoxemia. Chronic hypoxemia was produced by tightening a vascul ar occluder placed around the maternal common iliac artery. Larger dec reases in fetal arterial oxygen content were associated with larger in creases in extracellular glutamate concentration in the parietal corte x (Kendall's tau = 0.81, N = 7, p = 0.005). No such relationship was d etected in the periventricular white matter. Chronic hypoxemia increas es extracellular glutamate concentration in the intact cerebral cortex of the unanesthetized near-term fetal sheep. (C) 1998 Elsevier Scienc e B.V.