Abstract
Hypoxia alters cellular metabolism and although the effects of sustained hypoxia (SH) have been extensively studied, less is known about chronic intermittent hypoxia (IH), commonly associated with cardiovascular morbidity and stroke. We hypothesize that impaired glutamate homeostasis after chronic IH may underlie vulnerability to stroke-induced excitotoxicity. P16 organotypic hippocampal slices, cultured for 7 days were exposed for 7 days to IH (alternating 2 min 5% O2-15 min 21% O2), SH (5% O2) or RA (21% O2), then 3 glutamate challenges. The first and last exposures were intended as a metabolic stimulus (200 µM glutamate, 15 min); the second emulated excitotoxicity (10 mM glutamate, 10 min). GFAP, MAP2, and EAAT1, EAAT2 glutamate transporters expression were assessed after exposure to each hypoxic protocol. Additionally, cell viability was determined at baseline and after each glutamate challenge, in presence or absence of ceftriaxone that increases glutamate transporter expression. GFAP and MAP2 decreased after 7 days IH and SH. Long-term IH but not SH decreased EAAT1 and EAAT2. Excitotoxic glutamate challenge decreased cell viability and the following 200 µM exposure further increased cell death, particularly in IH-exposed slices. Ceftriaxone prevented glutamate transporter decrease and improved cell viability after IH and excitotoxicity. We conclude that IH is more detrimental to cell survival and glutamate homeostasis than SH. These findings suggest that impaired regulation of extracellular glutamate levels is implicated in the increased brain susceptibility to excitotoxic insult after long-term IH.