Impact of Reduced ASIC2 and Pregnancy on Seizure Susceptibility in Mice

Abstract

RationalePreeclampsia, a hypertensive disorder of pregnancy, can advance to eclampsia with the occurrence of new‐onset seizures in the mother. What induces this progression is unknown. Previous research found that utero‐placental ischemia, modeled by reducing uterine perfusion pressure (RUPP) in the rat, reduced latency to drug‐induced seizures. While acid sensing ion channels (ASICs) have been implicated in reducing seizure longevity and severity, the role ASICs have in seizure susceptibility in the context of pregnancy or placental ischemia has not been investigated.HypothesisIn this study, we tested the hypothesis that placental ischemia reduces hippocampal ASIC2 expression and that reduced ASIC2 increases seizure severity and longevity in pregnancy.MethodsUtero‐placental ischemia was induced in female C57BL/6 mice by ligating the uterine arteries between the ovaries and the first pup at day 13.5 post coitus. Hippocampi (SHAM=6, RUPP=5) were harvested on day 18.5 and processed for Western blot analysis to assess ASIC2a expression. Using Image Lab software, ASIC2a expression was normalized to total protein on the Western blot. The role of ASIC2 in seizure activity was assessed by inducing seizures using pentylenetetrazol (PTZ, 40mg/kg, i.p.) in pregnant and non‐pregnant ASIC2 wild type (WT) and heterozygous (HET) transgenic mice (n=4–11). After injection, mice were video monitored for 30 minutes. Using Observer XT software, seizure behavior was scored using a modified Racine Scale with scores ranging from 0 to 7, where 0 indicates normal behavior and 7 indicates respiratory arrest. Seizure activity was determined based on the following: latency to first seizure behavior, duration of all seizures, highest seizure severity score, and duration of seizure behavior associated with grand mal seizures (scores 4–7). Unpaired t‐test was used to analyze ASIC2a expression, and 2‐way ANOVA using a Sidak’s multiple comparison test was used to assess seizure behavior (factors: genotype and pregnancy status).ResultsHippocampal ASIC2a expression was reduced in RUPP (0.47±0.088) compared to SHAM (1±0.19; p= 0.021) mice. In WT mice, pregnancy increased latency to first seizure (116±43.3 vs 50±10.5s; p=0.057), decreased seizure duration (1026±142 vs.1643±44s; p=0.053), and decreased duration of grand‐mal associated seizure scores (23.5±23.5 vs1092±205s; p=0.018) compared to non‐pregnant mice. There was no effect of pregnancy on any of the seizure activity measures within the HET mice (p>0.05). However, there was a significant increase in duration of grand‐mal associated seizures in HET (1065±238s) vs WT pregnant mice (23.5±23.5; p=0.038). No significant difference in highest seizure severity score or survival was observed with pregnancy or reduced ASIC2.ConclusionOur finding of reduced hippocampal ASIC2 in placental ischemic mice and the absence of improved seizure latency and severity with pregnancy in HET mice, support the hypothesis that reduced ASIC2 contributes to increased seizure severity and longevity in placental ischemia.SignificanceASIC2a is a potential novel therapeutic target for the treatment of seizures in pregnancy as occurs in eclampsia.Support or Funding InformationNIH R00HL129192 and R00HL129192‐S1