ACUTE AND CHRONIC EFFECTS OF HYPOXIA ON THE DEVELOPING HIPPOCAMPUS

Perinatal hypoxia is associated with both seizures arising acutely and the subsequent development of temporal lobe epilepsy (as determined r etrospectively). We therefore attempted to identify acute and chronic morphological and/or electrophysiological hippocampal pathologies asso ciated with experimentally induced hypoxia in immature rats. Pups were exposed to 15 minutes of hypoxia on 3 successive days (starting on po stnatal day 8; P8), or to 60 minutes of hypoxia on P10 with either one or multiple hypoxia-induced seizures. For animals experiencing multip le seizures, flurothyl seizure threshold was significantly lower than that of controls at 60 to 80 days, but not at 10 days, after hypoxia. Acutely, there was a treatment-related increase in the number and the density of pyknotic dentate and hilar neurons, in particular in animal s experiencing multiple seizures. However, 60 to 80 days after the mul tiple-seizure protocol, the number of dentate and hilar neurons did no t differ between control and experimental animals. Electrophysiologica l measures of pyramidal cell properties showed no striking difference between experimental and control animals at any time point. These resu lts indicate that early postnatal hypoxia and hypoxia-induced seizure episodes decrease seizure threshold in the adult but produce minimal a cute or chronic morphological or functional changes in the hippocampus .