Abstracts

Rationale: There is enhanced AMPA receptor (AMPAR)-mediated synaptic transmission of CA1 pyramidal neurons in animals in status epilepticus (SE). It is not known whether this plasticity of GluA1 subunit-containing AMPARs regulates severity of SE. We hypothesize that the GluA1 subunit plasticity helps sustain SE. Methods: SE was induced by continuous hippocampal stimulation (CHS) in adult male and female mice lacking the GluA1 subunit expression (GluA1^-/-) and wild-type littermates (GluA1^+/+). SE was assessed by continuous video-EEG. Duration of SE, death, frequency of stage 5 behavioral seizures, and high amplitude fast discharges (HAFDs) were assessed. In addition, sEPSCs were recorded from CA1 pyramidal neurons of GluA1^+/+ and GluA1^-/- animals in SE and at baseline. SE induced by CHS in C57Bl/6 mice was treated with IEM-1460, an antagonist of calcium-permeable AMPARs. Results: The GluA1^-/- and GluA1^+/+ mice were equally susceptible to seizures evoked by 10 sec stimulation of hippocampus; the afterdischarge threshold (86 ± 9 mA, n=19 and 105 ± 10 mA, n=20, p>0.05) and after discharge duration (18 ± 2 and 17 ± 2 sec, p>0.05) were comparable. Thirty min of CHS evoked SE in 50% of GluA1^+/+ mice (n=8) and none of the GluA1^-/- mice (n=8, p+/+ mice (17/25) and 46% of GluA1^-/- mice (12/26, p>0.05). All GluA1^-/- mice survived SE (n= 26), whereas 26% of GluA1^+/+ mice (9/34, p-/- mice (102 ± 17 min, n=12) than that in GluA1^+/+ mice (215 ± 24 min, n=14, p+/+ mice; but only in 42% (5/12) GluA1^-/- mice (p+/+ mice but rare in GluA1^-/- mice. The altered characteristics of SE in GluA1^-/- mice raised a possibility that the potentiation of synaptic AMPAR-currents of CA1 pyramidal neurons during SE may not occur in GluA1^-/- mice. Therefore we recorded sEPSCs from CA1 neurons of GluA1^-/- and GluA1^+/+ mice in SE. The sEPSCs were potentiated in GluA1^+/+ animals in SE (20 ± 1 pA, n=8 vs 16 ± 1 pA< n=8, p<0.05), but not in GluA1^-/- mice in SE (15 ± 0.5 pA, n=8 vs 16± 1 pA, n=5, p>0.05).We also determined whether CA1-specific deletion of GluA1 subunit exerted similar effect on SE severity. AAV expressing GFP-Cre or GFP were injected in the CA1 region of animals expressing floxed exon 11 of Gria1. Severe mortality was seen in GFP-expressing mice (7/10) whereas GFP-Cre expressing mice were resistant (1/9, p<0.05).Finally, we determined whether pharmacological blockade of AMPARs after induction of SE could alter the seizures. IEM-1460 administered at 15 or 30 min after the end of stimulation shortened the duration of SE (control: 215 ± 21 min, n=13, 15 min: 36 ± 6 min, n=7 p Conclusions: These studies revealed that the plasticity of GluA1 subunit-containing AMPARs regulates severity of SE and the associated mortality. Funding: RO1 NS 040337RO1 NS 044370