Abstracts

Rationale: Neonatal seizures (NS) have been shown to contribute to severe long-term effects including epilepsy, cognitive impairment, mental retardation and behavioral deficits. We have previously shown that early alterations in protein kinase activity and enhanced phosphorylation of the AMPA receptors at GluR1S831 andGluR1S845 play a critical role in mediating the hyperexcitability and epileptogenesis following NS in the rat (Rakhade SN et al, J Neurosci. 2008). We hypothesized that eliminating the phosphorylation of GluR1 receptors will attenuate the epileptogenesis following neonatal seizures. To unambiguously determine the role of these phosphorylation sites in seizures, we compared seizure thresholds/latencies between GluR1 phosphomutant mice (GluR1 DPM -/-) and their wild-type littermates (GluR1 DPM / ). Methods: GluR1 phosphomutant mice (GluR1 DPM -/-) and their wild-type siblings (GluR1 DPM / ) were obtained by mating heterozygous mice as described previously (Cell. 2003 Mar 7; 112(5):631-43.). Pentylenetetrazol (PTZ, 50 mg/kg i.p.) was used to induce generalized tonic-clonic seizures at postnatal day 7. Seizures were recorded and latency to behavioral seizures calculated. Hippocampal slices obtained from the GluR1 DPM -/- mice and their wild-type siblings at P7 and subjected to hypoxic conditions, single cell patch clamp recordings were made as described previously ( J Neurosci. 200525(13):3442-51.) The degree of phosphorylation of the GluR1 reecptor subtype in the hippocampus and cortex were analyzed by immunoblotting. Results: Transgenic knock-in mice with mutations in GluR1 phosphorylation sites S831 and S845 have been shown to have deficits in LTP, LTD and spatial memory tasks ( Lee HK et al, Cell ,2003 Mar 7;112(5):631-43). GluR1 DPM -/- mice exhibit an increased latency to onset of first behavioral seizure following PTZ injection (6.54 min 0.75, p <0.005, n=23) as compared to wild-type littermates subjected to same conditions (3.75 min 0.39). Wild-type mice subjected to PTZ induced neonatal seizures at post-natal day (P) 7 exhibit an increase in the phosphorylation of GluR1 Ser 831 (128 %, n=4) and GluR1 Ser 845 (134%, n=4, p<0.05) at 1 day following seizures s. There is a significant increase in expression of PSD-95 (192%, n=6, p<0.05) at 24 hours after induction of PTZ seizures, compared to littermate controls. Conclusions: These data suggest that GluR1 DPM -/- mice exhibit less excitability and are less prone to synaptic potentiation following neonatal seizures as compared to wild type littermate controls. The attenuated response to PTZ and the lack of neuronal hyperexcitability in area CA1 in GluR1 DPM transgenic mice supports the hypothesis that phosphorylation of the GluR1 receptor subunit is an early and critical step in the process of epileptogenesis following early life seizures. Furthermore, the phosphorylation event may be targeted as a potential antiepileptogenic target for preventing the long-term consequences of early life seizures.