Placental Ischemia increases Seizure Susceptibility through Reduced ASIC2a Expression

Abstract

Introduction Eclampsia is diagnosed in pregnant women and women with preeclampsia, a hypertensive pregnancy disorder, who experience new-onset seizures. Previous studies from our laboratory showed that the rat model of preeclampsia, induced by reducing uterine perfusion pressure (RUPP), displays reduced latency to drug-induced seizures. The factors that contribute to increased seizure sensitivity in pregnancy and preeclampsia are unknown. While acid sensing ion channels (ASIC1a and 3) were shown to be important for reducing seizure longevity and severity, the role of ASIC2a in seizures during pregnancy or RUPP has not been investigated. Thus, we hypothesized that RUPP in mice reduces seizure latency and hippocampal ASIC2a expression. We further hypothesize that mice with reduced ASIC2a (ASIC2a+/-) will display increased seizure severity and duration. Methods Hippocampi from 5 RUPP and 6 Sham C57BL/6 pregnant mice were harvested on gestational day 18.5 and processed for Western blot analysis to assess ASIC2a expression. Seizures were induced using pentylenetetrazol (40 mg/kg, i.p) in RUPP and sham mice (n=5 per group), as well as pregnant wild type (WT) and ASIC2a heterozygous (HET) mice (n=7 or 14 per genotype) and video recorded for 30 minutes. Seizure behavior was scored using a modified Racine scale ranging from 0-7 (0 = no seizure, 7 = respiratory arrest). Seizure severity was separated into two generalized behaviors: petite-mal (1-3), grand-mal (4-7). Data are shown as Mean ± SEM. Results RUPP mice show a trend for reduced latency to seizure activity (63.4 ± 21.3 vs 103.3 ± 5.6s; p=0.068) and had a significant reduction in hippocampal ASIC2a expression (0.5 ± 0.1 in RUPP vs 1 ± 0.2 in Sham; p=0.037). ASIC2a HET mice displayed reduced latency to seizure activity (101 ± 18 vs 248 ± 85s, p=0.033), increased seizure duration (1253 ± 467s vs 823 ± 137s; p=0.019), decreased seizure-free duration (552 ± 125s vs 950 ± 145s; p=0.023), increased grand-mal seizure duration (713 ± 188 vs 18 ± 13s; p=0.004), and higher maximum seizure scores (WT= 3 ± 0; HET= 5 ± 1, p=0.011). ASIC2a HET mice display seizure behavior suggesting increased seizure susceptibility. Conclusion Our findings of reduced hippocampal ASIC2a expression in RUPP mice and increased seizure severity and longevity in pregnant mice with reduced ASIC2a, support the hypothesis that reduced ASIC2a increases seizure sensitivity in the context of placental ischemia.