Abstracts

Rationale: : Neonatal seizures (NS) are the most common form of seizures during childhood, and NS are refractory to current treatment in > 50% of patients. Neonatal seizures contribute to severe long-term effects including epilepsy, cognitive impairment, mental retardation and behavioral deficits. Animal models that mimic the long-term consequences of early-life seizures, especially in mice strains that are amenable to gene manipulation, can be utilized to dissect the underlying molecular mechanisms. Methods: P 7-9 mice were subjected to hypoxic conditions (60 minutes of graded exposure to 9-5.5 % O2) and allowed to survive following seizures. Cortical and hippocampal tissue was collected from mice pups subjected to hypoxia, and their littermate controls in naccordance with institutional care protocols, membrane protein samples were isolated and electrophoretically separated. Expression of phosphorylated and total GluR1, GluR2 and Actin was analyzed using immunoblotting techniques. Spontaneous and evoked potantials in hippocampal slices from pups subjected to hypoxia induced seizures were recorded. A subset of mice pups exposed to hypoxia at P9 were subjected to kainate seizures at P 40, latency to different stages of behavioral seizures were analyzed using Racine scale. Results: Majority of transgenic lines that have specific genetic mutations have been created in mouse strains with a C57 BL/6 genetic background, we aimed to determine the age at which this strain optimally responded to the epileptogenic effects of hypoxia. Neurotransmitter receptor and transporter expression was used to determine the age window of P7-9 in mice pups for optimal neonatal seizure expression. Wild type mice (C57/BL6) subjected to graded global hypoxia at P9 exhibit electrographic and behavioral seizures (83 %, n= 22). Subsequently, mice exposed to early-life seizures display an increase in the phosphorylation of GluR1 Ser 831 (138 %, n=6, p < 0.05) and GluR1 Ser 845 (128 %, n= 6) up to 12 hours following seizures compared to littermate controls. Furthemore, mice experiencing these hypoxia-induced seizures exhibit a significantly lower latency to development of second-hit seizures following a challenge with Kainic acid (30 mg/kg i.p.) at P 40, with a lower latency to reaching Racine Stage 3 seizures (69 % 12, n = 10, p < 0.05) as compared to their normoxic littermates not exposed to early-life seizures (normalized 100%, n= 10). Conclusions: Our data suggests that subjecting C57 BL/ 6 mice pups to graded global hypoxia during early life leads to emergence of spontaneous seizures during the hypoxic insult. Furthemore, we observe early changes in the phosphorylation status of the neurotransmitter receptors similar to that observed in our well-established rodent model of hypoxic seizures. These results suggest that seizures can be induced in theC57 BL/6 mouse strain following early-life hypoxic insults, and this model can be used to dissect the molecular mechanisms involved in mediating seizure susceptibility, epileptogenesis and cognitive dysfunction in the immature brain.