Abstracts

Rationale: Hypoxic encephalopathy is the most common cause of neonatal seizures and can lead to development of epilepsy and cognitive disorders. We have previously established a model of hypoxia-induced neonatal seizures that exhibits increased susceptibility to later-life seizure susceptibility and seizure-induced neuronal death. Here, we hypothesize hypoxia-induced neonatal seizures may lead to the development of spontaneous epileptiform seizures in later life as well as long-term alterations in the expression of glutamate receptor subunits in hippocampus. Methods: Postnatal day (P) 10 Long Evans rats were subjected to hypoxic conditions (15 min of graded exposure to 7-4% O2) and video/electroencephalograms (video/EEG) were obtained (3-6 hours each) from rats at specific intervals from 24 hours to 5 weeks following seizures. Hippocampal and cortical tissue was collected from animals that had been allowed to survive for 1, 2, 3 and 4 weeks following hypoxia-induced seizures at P 10. Crude membrane protein lysates were obtained and electrophoretically separated on SDS-PAGE gels as described previously (Talos D.M. et. al., 2006, J. Comp. Neurology). The expression of neurotransmitter receptor subunits NR1, NR2A, NR2B, NR3A, GluR1, and GluR2, in hippocampus was quantified using immunoblot analysis. Results: In the early time points following hypoxia-induced seizures (1-2 days), spontaneous epileptiform/ictal EEG discharges were observed in 85.7 % (n=7, 1.34 ± 0.40 seizures/hr) followed by a latent period with little to no seizure activity from P13-22: less than 8% of pups exhibited seizures (n = 13, 0.25 seizures/hr). Beginning at P22, spontaneous epileptiform discharges were increasingly frequent with time, with an incidence of 18.2% at P22-31 (n=11, 1.41 ± 0.60 seizures/hr), 50% incidence at P 32-37 (n=6, 2.29 ± 1.05 seizures/hr) and higher incidence of 67.1% at P38-78 (n=14, 2.7 ± 0.77 seizures/hr). Furthermore, alterations were observed in the expression of neurotransmitter receptor subunits, concurrent around the time of end of latent phase and appearance of spontaneous epileptiform discharges in animals experiencing early-life seizures. At 2 weeks post hypoxic seizures, we observed increases in hippocampal expression of NR2A (128 %, n =6, p = 0.06, 2 weeks post hypoxia) and GluR1 (136 %, n = 6, p = 0.03, 2 weeks post hypoxia). Conclusions: Our results here suggest that hypoxia-induced early-life seizures in the rat result in the development of spontaneous epilepsy later in life. Notably after a period of increase seizures for 1-2 days following hypoxia, there is a 12-24 day latent period, followed by a gradual increase in the incidence of seizure activity. This process of epileptogenesis appears to be accompanied by alterations in the expression of glutamate neurotransmitter receptor subunits NR2A and GluR1. Early-life seizures can lead to altered neurotransmitter receptor expression that may be involved in modulating the excitability of the brain and coincident with epileptogenesis.