The epileptogenic effect of seizures induced by hypoxia: the role of NMDA and AMPA/KA antagonists.

Hypoxia of the brain may alter further seizure susceptibility in a different way. In this study, we tried to answer the question how episode of convulsion induced by hypoxia (HS) changes further seizure susceptibility, and how N-methyl-D-aspartic acid (NMDA) and AMPA/KA receptor antagonists influence this process. Adult Albino Swiss mice exposed to hypoxia (5% O(2)) developed clonic/tonic convulsions after about 340 s. Mice which underwent 10 s but not 5 s seizures episode subsequently exhibited significantly increased seizure susceptibility to low doses (equal ED(16)) of bicuculline (BCC) and NMDA during a 3-week observation period. No morphological signs of brain tissue damage were seen in light microscope on the third day after a hypoxia-induced seizure (HS). Learning abilities assessed in passive avoidance test as well as spontaneous alternation were not disturbed after an HS episode. Pretreatment with AMPA/KA receptor antagonist NBQX effectively prolonged latency to HS and given immediately after seizure episode also attenuated subsequent convulsive susceptibility rise, however, NMDA receptor antagonist, MK-801, appeared to be ineffective. These results suggest that a seizure episode induced by hypoxia, depending on its duration, may play an epileptogenic role. The AMPA/KA receptor antagonist prolongs the latency to HS, and given after this episode, prevents the long-term epileptogenic effect.