The Contribution of Normal Pregnancy to Eclampsia.

Eclampsia, clinically defined as unexplained seizure in a woman with preeclampsia, is a life threatening complication unique to the pregnant state. However, a subpopulation of women with seemingly uncomplicated pregnancies experience de novo seizure without preeclamptic signs or symptoms, suggesting pregnancy alone may predispose the brain to seizure. Here, we hypothesized that normal pregnancy lowers seizure threshold and investigated mechanisms by which pregnancy may affect seizure susceptibility, including neuroinflammation and plasticity of gamma-aminobutyric acid type A receptor (GABAAR) subunit expression. Seizure threshold was determined by quantifying the amount of pentylenetetrazole (PTZ) required to elicit electrical seizure in Sprague Dawley rats that were either nonpregnant (Nonpreg, n = 7) or pregnant (Preg; d20, n = 6). Seizure-induced vasogenic edema was also measured. Further, activation of microglia, a measure of neuroinflammation (n = 6-8/group), and GABAAR δ- and γ2-subunit protein expression in the cerebral cortex and hippocampus (n = 6/group) was determined. Seizure threshold was lower in Preg compared to Nonpreg rats (36.7±9.6 vs. 65.0±14.5 mg/kg PTZ; p<0.01) that was associated with greater vasogenic edema formation (78.55±0.11 vs. 78.04±0.19% water; p<0.05). The % of active microglia was similar between groups; however, pregnancy was associated with downregulation of cortical GABAAR-δ and hippocampal GABAAR-γ2 expression. Overall, pregnancy appears to be a state of increased seizure susceptibility that is not due to neuroinflammation, but rather is associated with reduced expression of GABAAR subunits and greater edema. Understanding neurophysiological changes occurring in normal pregnancy could allow for better prevention and management of de novo seizure, including pathologic states such as eclampsia

The effect of pregnancy on GABA_AR δ- and γ2-subunit protein expression in the hippocampus and cerebral cortex.

<p>(A) Representative Western blots showing protein expression of the GABA_AR <b>γ</b>2-subunit and δ-subunit in the cerebral cortex of nonpregnant (Nonpreg) and pregnant (Preg) rats. (B) GABA_AR <b>γ</b>2-subunit protein expression was significantly lower in the hippocampus from Preg compared to Nonpreg rats, and GABA_AR δ-subunit expression trended towards being decreased in the hippocampus of Preg compared to Nonpreg rats. (C) Cortical GABA_AR <b>γ</b>2-subunit expression was similar in Preg and Nonpreg rats, however, GABA_AR δ-subunit expression was decreased in the cerebral cortex of Preg compared to Nonpreg rats. ** p < 0.01; * p < 0.05 vs. Nonpreg using Student’s t-test.</p

Zinc-induced cardiomyocyte relaxation in a rat model of hyperglycemia is independent of myosin isoform

<p>Abstract</p> <p>It has been reported previously that diabetic cardiomyopathy can be inhibited or reverted with chronic zinc supplementation. In the current study, we hypothesized that total cardiac calcium and zinc content is altered in early onset diabetes mellitus characterized in part as hyperglycemia (HG) and that exposure of zinc ion (Zn²⁺) to isolated cardiomyocytes would enhance contraction-relaxation function in HG more so than in nonHG controls. To better control for differential cardiac myosin isoform expression as occurs in rodents after β-islet cell necrosis, hypothyroidism was induced in 16 rats resulting in 100% β-myosin heavy chain expression in the heart. β-Islet cell necrosis was induced in half of the rats by streptozocin administration. After 6 wks of HG, both HG and nonHG controls rats demonstrated similar myofilament performance measured as thin filament calcium sensitivity, native thin filament velocity in the myosin motility assay and contractile velocity and power. Extracellular Zn²⁺ reduced cardiomyocyte contractile function in both groups, but enhanced relaxation function significantly in the HG group compared to controls. Most notably, a reduction in diastolic sarcomere length with increasing pacing frequencies, i.e., incomplete relaxation, was more pronounced in the HG compared to controls, but was normalized with extracellular Zn²⁺ application. This is a novel finding implicating that the detrimental effect of HG on cardiomyocyte Ca²⁺ regulation can be amelioration by Zn²⁺. Among the many post-translational modifications examined, only phosphorylation of ryanodine receptor (RyR) at S-2808 was significantly higher in HG compared to nonHG. We did not find in our hypothyroid rats any differentiating effects of HG on myofibrillar protein phosphorylation, lysine acetylation, O-linked N-acetylglucosamine and advanced glycated end-products, which are often implicated as complicating factors in cardiac performance due to HG. Our results suggest that the relaxing effects of Zn²⁺ on cardiomyocyte function are more pronounced in the HG state due an insulin-dependent effect of enhancing removal of cytosolic Ca²⁺ via SERCA2a or NCX or by reducing Ca²⁺ influx via L-type channel or Ca²⁺ leak through the RyR. Investigations into the effects of Zn²⁺ on these mechanisms are now underway.</p

Physiological parameters of nonpregnant (Nonpreg) and late-pregnant (Preg) rats under chloral hydrate anesthesia for seizure threshold measurements.

<p>** p < 0.01 vs. Nonpreg using Student’s t-test</p><p>Physiological parameters of nonpregnant (Nonpreg) and late-pregnant (Preg) rats under chloral hydrate anesthesia for seizure threshold measurements.</p

Effect of severe preeclampsia and magnesium sulfate (MgSO₄) treatment on microglial activation.

<p>(A) Illustration of morphological changes occurring as microglia progress from their inactive state 1, marked by long ramified processes to their active state 4, indicated by a large, amoeboid-like shape. (B) Representative photomicrographs of microglial cells stained for ionized calcium-binding adapter molecule 1 (Iba1) in the posterior cerebral cortices of late-pregnant (Late-Preg) rats, rats with severe preeclampsia (RUPP+HC) and rats with severe preeclampsia treated with MgSO₄ (RUPP+HC+MgSO₄). (C) The number of Iba1⁺ microglia was similar between groups. (D) The percentage of microglia in active state 4 was significantly higher in RUPP+HC rats compared to Late-Preg controls. Treatment of RUPP+HC rats with MgSO₄ decreased the percentage of cells that were active and was similar to Late-Preg controls. <b>**</b> p<0.01 vs. Late-Preg and RUPP+HC+MgSO₄ by one-way ANOVA and <i>post-hoc</i> Bonferroni test.</p

Physiological parameters in models of normal pregnancy (Late-Preg) and severe preeclampsia (RUPP+HC).

<p>* p<0.05; ** p<0.01 vs. Late-Preg by ANOVA.</p><p>Physiological parameters in models of normal pregnancy (Late-Preg) and severe preeclampsia (RUPP+HC).</p

Effect of severe preeclampsia and magnesium sulfate (MgSO₄) on in vivo blood-brain barrier (BBB) permeability to different sized solutes.

<p>(A) BBB permeability to sodium fluorescein was increased in rats with severe preeclampsia (RUPP+HC) in the posterior cerebral cortex compared to late-pregnant (Late-Preg) control rats. MgSO₄ treatment in rats with severe preeclampsia (RUPP+HC+MgSO₄) had no effect on BBB permeability to sodium fluorescein. (B) Permeability of the BBB to 70 kDa Texas red dextran was similar between Late-Preg and RUPP+HC rats with and without MgSO₄ treatment. * p<0.05 vs. Late-Preg by one-way ANOVA with <i>post-hoc</i> Bonferroni test.</p

Assessment of seizure severity in late-pregnant (Late-Preg) rats, rats with severe preeclampsia (RUPP+HC), and severe preeclamptic rats treated with magnesium sulfate (RUPP+HC+MgSO₄).

<p>Assessment of seizure severity in late-pregnant (Late-Preg) rats, rats with severe preeclampsia (RUPP+HC), and severe preeclamptic rats treated with magnesium sulfate (RUPP+HC+MgSO₄).</p