NMDA-antagonists reverse increased hypoxic tolerance by preceding chemical hypoxia.

Glutamate antagonists mitigate hypoxic damage upon acute inhibition of energy metabolism. The goal of this study was to investigate their effect on increased hypoxic tolerance induced by preceding chemical inhibition of energy metabolism. While recovery of population spike amplitude (psap) is 30% of onset in slices prepared from control animals (15 min hypoxia, 45 min recovery), recovery exceeds 90% in slices prepared from animals that underwent mild chemical hypoxia in vivo by treatment with 20 mg/kg 3-nitropropionic acid 1 h prior to slice preparation (p-slices). In p-slices perfused for 5 min with D(-)-2-amino-5-phosphonopentanoic acid (APV) (100 microM) 45 min prior to hypoxia, recovery declines to 42 +/- 13% (mean +/- SEM). In contrast, posthypoxic recovery after similar perfusion with 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) (10 microM) is 72 +/- 15% (P < 0.05). We conclude that increased hypoxic tolerance is abolished by N-methyl-D-aspartate (NMDA)-antagonists but not non-NMDA-antagonists.