Summary Objective Sex differences are evident in the antiseizure activity of neurosteroids; however, the potential mechanisms remain unclear. In this study, we sought to determine whether differences in target extrasynaptic δ‐subunit γ‐aminobutyric acid type A (GABA‐A) receptor expression and function underlie the sex differences in seizure susceptibility and the antiseizure activity of neurosteroids. Methods Sex differences in seizure susceptibility and protective activity of three distinct neurosteroids—allopregnanolone (AP), androstanediol (AD), and ganaxolone—were evaluated in the pilocarpine model of status epilepticus (SE) and kindling seizure test in mice. Immunocytochemistry was used for δGABA‐A receptor expression analysis, and patch‐clamp recordings in brain slices evaluated its functional currents. Results Sex differences were apparent in kindling epileptogenic seizures, with males exhibiting a faster progression to a fully kindled state. Neurosteroids AP, AD, or ganaxolone produced dose‐dependent protection against SE and acute partial seizures. However, female mice exhibited strikingly enhanced sensitivity to the antiseizure activity of neurosteroids compared to males. Sex differences in neurosteroid protection were unrelated to pharmacokinetic factors, as plasma levels of neurosteroids associated with seizure protection were similar between sexes. Mice lacking extrasynaptic δGABA‐A receptors did not exhibit sex differences in neurosteroid protection. Consistent with a greater abundance of extrasynaptic δGABA‐A receptors, AP produced a significantly greater potentiation of tonic currents in dentate gyrus granule cells in females than males; however, such enhanced AP sensitivity was diminished in δGABA‐A receptor knockout female mice. Significance Neurosteroids exhibit greater antiseizure potency in females than males, likely due to a greater abundance of extrasynaptic δGABA‐A receptors that mediate neurosteroid‐sensitive tonic currents and seizure protection. These findings indicate the potential to develop personalized gender‐specific neurosteroid treatments for SE and epilepsy in men and women, including catamenial epilepsy.

This article describes the recent advances in epileptogenesis and novel therapeutic approaches for the prevention of epilepsy, with a special emphasis on the pharmacological basis of disease-modification of epileptogenesis for curing epilepsy. Here we assess animal studies and human clinical trials of epilepsy spanning 1982–2016. Epilepsy arises from a number of neuronal factors that trigger epileptogenesis, which is the process by which a brain shifts from a normal physiologic state to an epileptic condition. The events precipitating these changes can be of diverse origin, including traumatic brain injury, cerebrovascular damage, infections, chemical neurotoxicity, and emergency seizure conditions such as status epilepticus. Expectedly, the molecular and system mechanisms responsible for epileptogenesis are not well defined or understood. To date, there is no approved therapy for the prevention of epilepsy. Epigenetic dysregulation, neuroinflammation, and neurodegeneration appear to trigger epileptogenesis. Targeted drugs are being identified that can truly prevent the development of epilepsy in at-risk people. The promising agents include rapamycin, COX-2 inhibitors, TRK inhibitors, epigenetic modulators, JAK-STAT inhibitors, and neurosteroids. Recent evidence suggests that neurosteroids may play a role in modulating epileptogenesis. A number of promising drugs are under investigation for the prevention or modification of epileptogenesis to halt the development of epilepsy. Some drugs in development appear rational for preventing epilepsy because they target the initial trigger or related signaling pathways as the brain becomes progressively more prone to seizures. Additional research into the target validity and clinical investigation is essential to make new frontiers in curing epilepsy.

Midazolam is a benzodiazepine anticonvulsant with rapid onset and short duration of action. Midazolam is the current drug of choice for acute seizures and status epilepticus, including those caused by organophosphate nerve agents. The antiseizure activity of midazolam is thought to result from its allosteric potentiation of synaptic GABA A receptors in the brain. However, there are indications that benzodiazepines promote neurosteroid synthesis via the 18-kDa cholesterol transporter protein (TSPO). Therefore, we investigated the role of neurosteroids and their extrasynaptic GABA A receptor targets in the antiseizure activity of midazolam. Here, we used d-subunit knockout (DKO) mice bearing a targeted deletion of the extrasynaptic receptors to investigate the contribution of the extrasynaptic receptors to the antiseizure activity of midazolam using the 6-Hz and hippocampus kindling seizure models. In both models, midazolam produced rapid and dose-dependent protection against seizures (ED 50 , 0.4 mg/kg). Moreover, the antiseizure potency of midazolam was undiminished in DKO mice compared with control mice. Pretreatment with PK11195 [1-(2-chlorophenyl)-N-methyl-N-(1-methylpropyl)-3-isoquinolinecarboxamide], a TSPO blocker, or finasteride, a 5a-reductase neurosteroid inhibitor, did not affect the antiseizure effect of midazolam. The antiseizure activity of midazolam was significantly reversed by pretreatment with flumazenil, a benzodiazepine antagonist. Plasma and brain levels of the neurosteroid allopregnanolone were not significantly greater in midazolam-treated animals. These studies therefore provide strong evidence that neurosteroids and extrasynaptic GABA A receptors are not involved in the antiseizure activity of midazolam, which mainly occurs through synaptic GABA A receptors via direct binding to benzodiazepine sites. This study reaffirms midazolam's use for controlling acute seizures and status epilepticus.