A mouse kindling model of perimenstrual catamenial epilepsy

The impact of pregnancy-related hormonal and physiological changes on antiseizure medications: expert perspective

INTRODUCTION

Epilepsy is a disorder of recurrent, unprovoked seizures affecting approximately 15 million individuals of childbearing potential worldwide. Patients with epilepsy rely on regular daily therapy with antiseizure medications (ASMs). Furthermore, ASMs are also prescribed for other neuropsychiatric indications (e.g. bipolar disorder, pain, migraines) with over 2% of the pregnancies in the United States involving prenatal exposure to ASMs.

AREAS COVERED

ASM concentrations are affected by hormonal and physiological changes in pregnancy, including increases in renal and hepatic blood flow, decreased protein binding, and changes in enzyme activity. Clearance changes typically reverse within a few weeks after delivery. During pregnancy, many ASMs, such as lamotrigine, levetiracetam, and oxcarbazepine, should have serum concentrations monitored and doses increased to maintain the individualized target range for seizure control. ASMs metabolized via glucuronidation, primarily lamotrigine, undergo marked increases in clearance throughout pregnancy, requiring about 3-fold the pre-pregnancy daily dose by delivery. Postpartum, ASM doses are usually decreased over several weeks to prevent drug toxicity.

EXPERT OPINION

In the future, the development of a physiologically-based pharmacokinetic model for various ASMs may enable empiric dose adjustments in pregnancy without the difficulties of frequent therapeutic drug monitoring.

Neurosteroids as Novel Anticonvulsants for Refractory Status Epilepticus and Medical Countermeasures for Nerve Agents: A 15-Year Journey to Bring Ganaxolone from Bench to Clinic

This article describes recent advances in the use of neurosteroids as novel anticonvulsants for refractory status epilepticus (RSE) and as medical countermeasures (MCs) for organophosphates and chemical nerve agents (OPNAs). We highlight a comprehensive 15-year journey to bring the synthetic neurosteroid ganaxolone (GX) from bench to clinic. RSE, including when caused by nerve agents, is associated with devastating morbidity and permanent long-term neurologic dysfunction. Although recent approval of benzodiazepines such as intranasal midazolam and intranasal midazolam offers improved control of acute seizures, novel anticonvulsants are needed to suppress RSE and improve neurologic function outcomes. Currently, few anticonvulsant MCs exist for victims of OPNA exposure and RSE. Standard-of-care MCs for postexposure treatment include benzodiazepines, which do not effectively prevent or mitigate seizures resulting from nerve agent intoxication, leaving an urgent unmet medical need for new anticonvulsants for RSE. Recently, we pioneered neurosteroids as next-generation anticonvulsants that are superior to benzodiazepines for treatment of OPNA intoxication and RSE. Because GX and related neurosteroids that activate extrasynaptic GABA-A receptors rapidly control seizures and offer robust neuroprotection by reducing neuronal damage and neuroinflammation, they effectively improve neurologic outcomes after acute OPNA exposure and RSE. GX has been selected for advanced, Biomedical Advanced Research and Development Authority-supported phase 3 trials of RSE and nerve agent seizures. In addition, in mechanistic studies of neurosteroids at extrasynaptic receptors, we identified novel synthetic analogs with features that are superior to GX for current medical needs. Development of new MCs for RSE is complex, tedious, and uncertain due to scientific and regulatory challenges. Thus, further research will be critical to fill key gaps in evaluating RSE and anticonvulsants in vulnerable (pediatric and geriatric) populations and military persons. SIGNIFICANCE STATEMENT: Following organophosphate and nerve agent intoxication, refractory status epilepticus (RSE) occurs despite benzodiazepine treatment. RSE occurs in 40% of status epilepticus patients, with a 35% mortality rate and significant neurological morbidity in survivors. To treat RSE, neurosteroids are better anticonvulsants than benzodiazepines. Our pioneering use of neurosteroids for RSE and nerve agents led us to develop ganaxolone as a novel anticonvulsant and neuroprotectant with significantly improved neurological outcomes. This article describes the bench-to-bedside journey of bringing neurosteroid therapy to patients, with ganaxolone leading the way.

Neuroprotectant Activity of Novel Water-Soluble Synthetic Neurosteroids on Organophosphate Intoxication and Status Epilepticus-Induced Long-Term Neurological Dysfunction, Neurodegeneration, and Neuroinflammation

Organophosphates (OPs) and nerve agents are potent neurotoxic compounds that cause seizures, status epilepticus (SE), brain injury, or death. There are persistent long-term neurologic and neurodegenerative effects that manifest months to years after the initial exposure. Current antidotes are ineffective in preventing these long-term neurobehavioral and neuropathological changes. Additionally, there are few effective neuroprotectants for mitigating the long-term effects of acute OP intoxication. We have pioneered neurosteroids as novel anticonvulsants and neuroprotectants for OP intoxication and seizures. In this study, we evaluated the efficacy of two novel synthetic, water-soluble neurosteroids, valaxanolone (VX) and lysaxanolone (LX), in combating the long-term behavioral and neuropathological impairments caused by acute OP intoxication and SE. Animals were exposed to the OP nerve agent surrogate diisopropylfluorophosphate (DFP) and were treated with VX or LX in addition to midazolam at 40 minutes postexposure. The extent of neurodegeneration, along with various behavioral and memory deficits, were assessed at 3 months postexposure. VX significantly reduced deficits of aggressive behavior, anxiety, memory, and depressive-like traits in control (DFP-exposed, midazolam-treated) animals; VX also significantly prevented the DFP-induced chronic loss of NeuN(+) principal neurons and PV(+) inhibitory neurons in the hippocampus and other regions. Additionally, VX-treated animals exhibited a reduced inflammatory response with decreased GFAP(+) astrogliosis and IBA1(+) microgliosis in the hippocampus, amygdala, and other regions. Similarly, LX showed significant improvement in behavioral and memory deficits, and reduced neurodegeneration and cellular neuroinflammation. Together, these results demonstrate the neuroprotectant effects of the novel synthetic neurosteroids in mitigating the long-term neurologic dysfunction and neurodegeneration associated with OP exposure. SIGNIFICANCE STATEMENT: Survivors of nerve agents and organophosphate (OP) exposures suffer from long-term neurological deficits. Currently, there is no specific drug therapy for mitigating the impact of OP exposure. However, novel synthetic neurosteroids that activate tonic inhibition provide a viable option for treating OP intoxication. The data from this study indicates the neuroprotective effects of synthetic, water-soluble neurosteroids for attenuation of long-term neurological deficits after OP intoxication. These findings establish valaxanolone and lysaxanolone as potent and efficacious neuroprotectants suitable for injectable dosing.

Preclinical and clinical pharmacology of brexanolone (allopregnanolone) for postpartum depression: a landmark journey from concept to clinic in neurosteroid replacement therapy

This article describes the critical role of neurosteroids in postpartum depression (PPD) and outlines the landmark pharmacological journey of brexanolone as a first-in-class neurosteroid antidepressant with significant advantages over traditional antidepressants. PPD is a neuroendocrine disorder that affects about 20% of mothers after childbirth and is characterized by symptoms including persistent sadness, fatigue, dysphoria, as well as disturbances in cognition, emotion, appetite, and sleep. The main pathology behind PPD is the postpartum reduction of neurosteroids, referred to as neurosteroid withdrawal, a concept pioneered by our preclinical studies. We developed neurosteroid replacement therapy (NRT) as a rational approach for treating PPD and other conditions related to neurosteroid deficiency, unveiling the power of neurosteroids as novel anxiolytic-antidepressants. The neurosteroid, brexanolone (BX), is a progesterone-derived allopregnanolone that rapidly relieves anxiety and mood deficits by activating GABA-A receptors, making it a transformational treatment for PPD. In 2019, the FDA approved BX, an intravenous formulation of allopregnanolone, as an NRT to treat PPD. In clinical studies, BX significantly improved PPD symptoms within hours of administration, with tolerable side effects including headache, dizziness, and somnolence. We identified the molecular mechanism of BX in a neuronal PPD-like milieu. The mechanism of BX involves activation of both synaptic and extrasynaptic GABA-A receptors, which promote tonic inhibition and serve as a key target for PPD and related conditions. Neurosteroids offer several advantages over traditional antidepressants, including rapid onset, unique mechanism, and lack of tolerance upon repeated use. Some limitations of BX therapy include lack of aqueous solubility, limited accessibility, hospitalization for treatment, lack of oral product, and serious adverse events at high doses. However, the unmet need for synthetic neurosteroids to address this critical condition supersedes these limitations. Recently, we developed novel hydrophilic neurosteroids with a superior profile and improved drug delivery. Overall, approval of BX is a major milestone in the field of neurotherapeutics, paving the way for the development of novel synthetic neurosteroids to treat depression, epilepsy, and status epilepticus.

Towards understanding the biology of premenstrual dysphoric disorder: From genes to GABA

Premenstrual dysphoric disorder (PMDD) is a severe mood disorder, with affective symptoms that rise and fall in concert with the hormonal fluctuations of the menstrual cycle. PMDD's pathophysiology is poorly understood. This review describes recent research on potential biological contributors to PMDD, with a focus on neuroactive steroids, genetics, neuroimaging and cellular studies. Studies suggest that a key contributor is abnormal central nervous system (CNS) response to fluctuations in neuroactive steroid hormones. Imaging studies are limited but support alterations in serotonergic and GABA transmission. Genetic studies suggest heritability, yet specific genetic contributors have not been characterized. Finally, recent cutting-edge cellular studies indicate an underlying vulnerability to the effect of sex hormones at a cellular level. Overall the findings across studies do not yet fit together into a complete description of the underlying biology of PMDD. It is possible that PMDD consists of biological subtypes, and future research may benefit from a subtyping approach.

Neurosteroid replacement therapy for catamenial epilepsy, postpartum depression and neuroendocrine disorders in women

Neurosteroids are involved in the pathophysiology of many neuroendocrine disorders in women. This review describes recent advancements in pharmacology of neurosteroids and emphasizes the benefits of neurosteroid replacement therapy for the management of neuroendocrine disorders such as catamenial epilepsy (CE), postpartum depression (PPD) and premenstrual brain conditions. Neurosteroids are endogenous modulators of neuronal excitability. A variety of neurosteroids are present in the brain including allopregnanolone (AP), allotetrahydro-deoxycorticosterone and androstanediol. Neurosteroids interact with synaptic and extrasynaptic GABA_A receptors in the brain. AP and related neurosteroids, which are positive allosteric modulators of GABA_A receptors, are powerful anticonvulsants, anxiolytic, antistress and neuroprotectant agents. In CE, seizures are most often clustered around a specific menstrual period in women. Neurosteroid withdrawal-linked plasticity in extrasynaptic receptors has been shown to play a key role in catamenial seizures, anxiety and other mood disorders. Based on our extensive research spanning two decades, we have proposed and championed neurosteroid replacement therapy as a rational strategy for treating disorders marked by neurosteroid-deficiency, such as CE and other related ovarian or menstrual disorders. In 2019, AP (renamed as brexanolone) was approved for treating PPD. A variety of synthetic neurosteroids are in clinical trials for epilepsy, depression and other brain disorders. Recent advancements in our understanding of neurosteroids have entered a new era of drug discovery and one that offers a high therapeutic potential for treating complex brain disorders.

Sex Differences in the Epilepsies and Associated Comorbidities: Implications for Use and Development of Pharmacotherapies

The epilepsies are common neurologic disorders characterized by spontaneous recurrent seizures. Boys, girls, men, and women of all ages are affected by epilepsy and, in many cases, by associated comorbidities as well. The primary courses of treatment are pharmacological, dietary, and/or surgical, depending on several factors, including the areas of the brain affected and the severity of the epilepsy. There is a growing appreciation that sex differences in underlying brain function and in the neurobiology of epilepsy are important factors that should be accounted for in the design and development of new therapies. In this review, we discuss the current knowledge on sex differences in epilepsy and associated comorbidities, with emphasis on those aspects most informative for the development of new pharmacotherapies. Particular focus is placed on sex differences in the prevalence and presentation of various focal and generalized epilepsies; psychiatric, cognitive, and physiologic comorbidities; catamenial epilepsy in women; sex differences in brain development; the neural actions of sex and stress hormones and their metabolites; and cellular mechanisms, including brain-derived neurotrophic factor signaling and neuronal-glial interactions. Further attention placed on potential sex differences in epilepsies, comorbidities, and drug effects will enhance therapeutic options and efficacy for all patients with epilepsy. SIGNIFICANCE STATEMENT: Epilepsy is a common neurological disorder that often presents together with various comorbidities. The features of epilepsy and seizure activity as well as comorbid afflictions can vary between men and women. In this review, we discuss sex differences in types of epilepsies, associated comorbidities, pathophysiological mechanisms, and antiepileptic drug efficacy in both clinical patient populations and preclinical animal models.

Seizure burden fluctuates with the female reproductive cycle in a mouse model of chronic temporal lobe epilepsy

Women with catamenial epilepsy often experience increased seizure burden near the time of ovulation (periovulatory) or menstruation (perimenstrual). To date, a rodent model of chronic temporal lobe epilepsy (TLE) that exhibits similar endogenous fluctuations in seizures has not been identified. Here, we investigated whether seizure burden changes with the estrous cycle in the intrahippocampal kainic acid (IHKA) mouse model of TLE. Adult female IHKA mice and saline-injected controls were implanted with EEG electrodes in the ipsilateral hippocampus. At one and two months post-injection, 24/7 video-EEG recordings were collected and estrous cycle stage was assessed daily. Seizures were detected using a custom convolutional neural network machine learning process. Seizure burden was compared within each mouse between diestrus and combined proestrus and estrus days (pro/estrus) at two months post-injection. IHKA mice showed higher seizure burden on pro/estrus compared with diestrus, characterized by increased time in seizures and longer seizure duration. When all IHKA mice were included, no group differences were observed in seizure frequency or EEG power. However, increased baseline seizure burden on diestrus was correlated with larger cycle-associated differences, and when analyses were restricted to mice that showed the severe epilepsy typical of the IHKA model, increased seizure frequency on pro/estrus was also revealed. Controls showed no differences in EEG parameters with cycle stage. These results suggest that the stages of proestrus and estrus are associated with higher seizure burden in IHKA mice. The IHKA model may thus recapitulate at least some aspects of reproductive cycle-associated seizure clustering.

Allopregnanolone in premenstrual dysphoric disorder (PMDD): Evidence for dysregulated sensitivity to GABA-A receptor modulating neuroactive steroids across the menstrual cycle

Premenstrual dysphoric disorder (PMDD) is a severe mood disorder with core symptoms (affective lability, irritability, depressed mood, anxiety) and increased sensitivity to stress occurring in the luteal phase of the menstrual cycle. PMDD can be conceptualized as a disorder of suboptimal sensitivity to neuroactive steroid hormones (NASs). In this review, we describe the role of the NAS allopregnanolone (ALLO), a positive allosteric modulator of the GABA_A receptor (GABA_A-R), in PMDD's pathophysiology. We review evidence of impaired interaction between ALLO and GABA_A-Rs in terms of affective symptom expression, with evidence from rodent and human studies. We discuss evidence of increased luteal phase stress sensitivity as a result of poor ALLO-GABA control of the HPA axis. Finally, we describe how treatments such as selective serotonin reuptake inhibitors (SSRIs) and new drugs targeting GABA_A-Rs provide evidence for impaired ALLO-GABA function in PMDD. In sum, the literature supports the hypothesis that PMDD pathophysiology is rooted in impaired GABA_A-R response to dynamic ALLO fluctuations across the menstrual cycle, manifesting in affective symptoms and poor regulation of physiologic stress response.

Extrasynaptic γ-aminobutyric acid type A receptor-mediated sex differences in the antiseizure activity of neurosteroids in status epilepticus and complex partial seizures

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.

Role of β2/3-specific GABA-A receptor isoforms in the development of hippocampus kindling epileptogenesis

OBJECTIVE

Subunit-specific positive allosteric modulators (PAMs) of gamma-aminobutyric acid-A (GABA-A) receptors are commonly used to uncover the role of GABA-A receptor isoforms in brain function. Recently, we have designed novel PAMs selective for β_2/3-subunit containing GABA-A receptors (β_2/3-selective PAMs) that are nonbenzodiazepine site-mediated and do not show an α-subunit isoform selectivity, yet exhibit anxiolytic efficacy with reduced potential for sedation, cognitive impairment, and tolerance. In this study, we used three novel β_2/3-selective PAMs (2-261, 2-262, and 10029) with differential β_2/3-subunit potency to identify the role of β_2/3-selective receptor isoforms in limbic epileptogenesis.

METHODS

Experimental epileptogenesis was induced in mice by daily hippocampus stimulations until each mouse showed generalized (stage 5) seizures. Patch-clamp electrophysiology was used to record GABA-gated currents. Brain levels of β_2/3-selective PAMs were determined for mechanistic correlations.

RESULTS

Treatment with the β_2/3-selective PAMs 2-261 (30mg/kg), 2-262 (10mg/kg), and 10029 (30mg/kg), 30min prior to stimulations, significantly suppressed the rate of development of kindled seizure activity without affecting the afterdischarge (AD) signal, indicating their disease-modifying activity. The β_2/3-selective agents suppressed chemical epileptogenesis in the pentylenetetrazol model. Test doses of these agents were devoid of acute antiseizure activity in the kindling model.

CONCLUSION

These findings demonstrate that β_2/3-selective PAMs can moderately retard experimental epileptogenesis, indicating the protective role of β_2/3-subunit GABA-A receptor isoforms in the development of epilepsy.

3β-Methyl-Neurosteroid Analogs Are Preferential Positive Allosteric Modulators and Direct Activators of Extrasynaptic δ-Subunit γ-Aminobutyric Acid Type A Receptors in the Hippocampus Dentate Gyrus Subfield

Neurosteroids are powerful modulators of γ-aminobutyric acid (GABA)-A receptors. Ganaxolone (3α-hydroxy-3β-methyl-5α-pregnan-20-one, GX) and synthetic analogs of the neurosteroid allopregnanolone (AP) are designed to treat epilepsy and related conditions. However, their precise mechanism of action in native neurons remains unclear. Here, we sought to determine the mode of action of GX and its analogs at GABA-A receptors in native hippocampal neurons by analyzing extrasynaptic receptor-mediated tonic currents and synaptic receptor-mediated phasic currents. Concentration-response profiles of GX were determined in two cell types: δ-containing dentate gyrus granule cells (DGGCs) and γ2-containing CA1 pyramidal cells (CA1PCs). GX produced significantly greater potentiation of the GABA-A receptor-activated chloride currents in DGGCs (500%) than CA1PCs (200%). In the absence of GABA, GX evoked 2-fold greater inward currents in DGGCs than CA1PCs, which were 2-fold greater than AP within DGGCs. In hippocampus slices, GX potentiated and directly activated tonic currents in DGGCs. These responses were significantly diminished in DGGCs from δ-subunit knockout (δKO) mice, confirming GX's selectivity for δGABA-A receptors. Like AP, GX potentiation of tonic currents was prevented by protein kinase C inhibition. Furthermore, GX's protection against hippocampus-kindled seizures was significantly diminished in δKO mice. GX analogs exhibited greater potency and efficacy than GX on δGABA-A receptor-mediated tonic inhibition. In summary, these results provide strong evidence that GX and its analogs are preferential allosteric modulators and direct activators of extrasynaptic δGABA-A receptors regulating network inhibition and seizures in the dentate gyrus. Therefore, these findings provide a mechanistic rationale for the clinical use of synthetic neurosteroids in epilepsy and seizure disorders.

Genetic and Molecular Regulation of Extrasynaptic GABA-A Receptors in the Brain: Therapeutic Insights for Epilepsy

GABA-A receptors play a pivotal role in many brain diseases. Epilepsy is caused by acquired conditions and genetic defects in GABA receptor channels regulating neuronal excitability in the brain. The latter is referred to as GABA channelopathies. In the last two decades, major advances have been made in the genetics of epilepsy. The presence of specific GABAergic genetic abnormalities leading to some of the classic epileptic syndromes has been identified. Advances in molecular cloning and recombinant systems have helped characterize mutations in GABA-A receptor subunit genes in clinical neurology. GABA-A receptors are the prime targets for neurosteroids (NSs). However, GABA-A receptors are not static but undergo rapid changes in their number or composition in response to the neuroendocrine milieu. This review describes the recent advances in the genetic and neuroendocrine control of extrasynaptic and synaptic GABA-A receptors in epilepsy and its impact on neurologic conditions. It highlights the current knowledge of GABA genetics in epilepsy, with an emphasis on the neuroendocrine regulation of extrasynaptic GABA-A receptors in network excitability and seizure susceptibility. Recent advances in molecular regulation of extrasynaptic GABA-A receptor-mediated tonic inhibition are providing unique new therapeutic approaches for epilepsy, status epilepticus, and certain brain disorders. The discovery of an extrasynaptic molecular mechanism represents a milestone for developing novel therapies such as NS replacement therapy for catamenial epilepsy.

Sex differences in the anticonvulsant activity of neurosteroids

Epilepsy is one of the leading causes of chronic neurological morbidity worldwide. Acquired epilepsy may result from a number of conditions, such as brain injury, anoxia, tumors, stroke, neurotoxicity, and prolonged seizures. Sex differences have been observed in many seizure types; however, some sex-specific seizure disorders are much more prevalent in women. Despite some inconsistencies, substantial data indicates that sensitivity to seizure stimuli differs between the sexes. Men generally exhibit greater seizure susceptibility than women, whereas many women with epilepsy experience a cyclical occurrence of seizures that tends to center around the menstrual period, which has been termed catamenial epilepsy. Some epilepsy syndromes show gender differences with female predominance or male predominance. Steroid hormones, endogenous neurosteroids, and sexually dimorphic neural networks appear to play a key role in sex differences in seizure susceptibility. Neurosteroids, such as allopregnanolone, reflect sex differences in their anticonvulsant activity. This Review provides a brief overview of the evidence for sex differences in epilepsy and how sex differences influence the use of neurosteroids in epilepsy and epileptogenesis. © 2016 Wiley Periodicals, Inc.

Catamenial-like seizure exacerbation in mice with targeted ablation of extrasynaptic δGABA-a receptors in the brain

Neurosteroids play a key role in catamenial epilepsy, a menstrual cycle-related seizure clustering in women with epilepsy. While neurosteroids act on all GABA-A receptor isoforms, they cause greater effects on extrasynaptic δGABA-A receptors that mediate tonic inhibition in the brain. Previously, we identified a potential GABA-A receptor mechanism for catamenial epilepsy. However, the precise functional role of extrasynaptic δGABA-A receptors in the pathophysiology of catamenial epilepsy remains unclear. In this study, we utilized mice lacking extrasynaptic δGABA-A receptors (δKO) to investigate whether reduction of tonic inhibition affects catamenial seizure susceptibility or intensity. Intact female wildtype (WT) and δKO mice were subjected to hippocampus kindling until they exhibited stage 5 seizures. Elevated gonadal hormone-based neurosteroid levels were induced by standard gonadotropin regimen and neurosteroid withdrawal (NSW) was triggered by finasteride. NSW increased susceptibility to, as well the intensity of evoked catamenial-like seizures in WT and δKO mice. However, fully kindled δKO mice exhibited an accelerated and augmented response to NSW, with a more rapid increase in seizure susceptibility and intensity than WT mice undergoing the NSW paradigm. Moreover, δKO mice in NSW showed reduced benzodiazepine sensitivity, but in stark contrast to the increased neurosteroid sensitivity observed in WT animals, δKO mice displayed no change in neurosteroid sensitivity in response to NSW. The increased catamenial seizure exacerbation and alterations in antiseizure drug responses are consistent with NSW-induced changes in the abundance of δGABA-A receptors. Collectively, these findings provide evidence of a potential protective role for extrasynaptic δGABA-A receptors in catamenial-like seizures. © 2017 Wiley Periodicals, Inc.

PR-independent neurosteroid regulation of α2-GABA-A receptors in the hippocampus subfields

Progesterone (P) binding to the intracellular progesterone receptors (PRs) plays a key role in epilepsy via modulation of GABA-A receptor plasticity in the brain. This is thought to occur via conversion of P to neurosteroids such as allopregnanolone, an allosteric modulator of GABA-A receptors. In the female brain, the composition of GABA-A receptors is not static and undergoes dynamic spatial changes in response to fluctuations in P and neurosteroid levels. Synaptic α2-containing GABA-A receptors contribute to phasic neuronal excitability and seizure susceptibility. However, the mechanisms underlying α2-subunit plasticity remain unclear. Here, we utilized the neurosteroid synthesis inhibitor finasteride and PR knockout mice to investigate the role of PRs in α2-subunit in the hippocampus. α2-Subunit expression was significantly upregulated during the high-P state of diestrous stage and with P treatment in wildtype and PR knockout mice. In contrast, there was no change in α2-subunit expression when metabolism of P into neurosteroids was blocked by finasteride in both genotypes. These findings suggest that ovarian cycle-related P and neurosteroids regulate α2-GABA-A receptor expression in the hippocampus via a non-PR pathway, which may be relevant to menstrual-cycle related brain conditions.

Short term, low dose fluoxetine blocks estrous cycle-linked changes in responsiveness to diazepam in female rats

Anxiety behavior in female Wistar rats was assessed at different stages of the estrous cycle using the elevated plus maze (EPM). No differences were observed at any cycle stage. Pretreatment with diazepam (1 mg kg(-1) intraperitoneal (i.p.)) 30 min before testing produced an anxiolytic effect (significant increase in percentage of time in the open arms compared to control group in the same cycle phase) in animals in proestrus, estrus, and early diestrus but had no effect in rats in late diestrus. Locomotor activity (total arm entries) was unchanged at any cycle phase. When rats in the late diestrus phase were pretreated with the selective serotonin reuptake inhibitor fluoxetine (1.75 mg kg(-1) i.p. on the afternoon of early diestrus and again in the morning of late diestrus) diazepam produced an anxiolytic effect (increase percentage time in the open arms). This dose is sufficient to raise brain allopregnanolone concentration without affecting 5-hydroxytryptamine (5-HT) systems. We propose that insensitivity to diazepam in late diestrus is due to increased expression of benzodiazepine insensitive α4 subunit-containing gamma-aminobutyric acid A (GABAA) receptors triggered by a sharp decrease in brain allopregnanolone concentration. Pretreatment with fluoxetine to raise brain allopregnanolone concentration during late diestrus prevents the withdrawal effect.

A Treatment Approach to Catamenial Epilepsy

OPINION STATEMENT

The cyclic hormonal underpinnings of catamenial seizure exacerbations are consistent with the neurophysiologic activity of estrogen and progesterone. For women with catamenial epilepsy who have regular menses, intermittent treatment approaches may be utilized. These interventions are targeted at adding or increasing anti-seizure treatments during established vulnerable days of the menstrual cycle, such as perimenstrually (C1 pattern), at ovulation (C2 pattern), and during the luteal phase (C3 pattern). The single large study of natural progesterone treatment showed benefit for women with clear perimenstrual seizure exacerbations (C1 pattern), but not for subjects with other catamenial patterns or for randomized women with epilepsy of reproductive age who did not have catamenial seizure exacerbations. In this protocol, natural progesterone was given at a high dose during the luteal phase and was generally well tolerated. Other intermittent cyclic treatments include benzodiazepine use, increasing the dose of an anti-seizure drug already in use, or acetazolamide. For women with irregular menses, or those in which the intermittent cyclic treatments are not effective, pharmacologically stopping the menstrual cycle altogether by using synthetic hormones such as medroxyprogesterone (Depo-Provera) or sustained oral contraceptives may be considered.

Clinical Potential of Neurosteroids for CNS Disorders

Neurosteroids are key endogenous molecules in the brain that affect many neural functions. We describe here recent advances in US National Institutes of Health (NIH)-sponsored and other clinical studies of neurosteroids for CNS disorders. The neuronal GABA-A receptor chloride channel is one of the prime molecular targets of neurosteroids. Allopregnanolone-like neurosteroids are potent allosteric agonists as well as direct activators of both synaptic and extrasynaptic GABA-A receptors. Hence, neurosteroids can maximally enhance synaptic phasic and extrasynaptic tonic inhibition. The resulting chloride current conductance generates a form of shunting inhibition that controls network excitability, seizures, and behavior. Such mechanisms of neurosteroids are providing innovative therapies for epilepsy, status epilepticus (SE), traumatic brain injury (TBI), fragile X syndrome (FXS), and chemical neurotoxicity. The neurosteroid field has entered a new era, and many compounds have reached advanced clinical trials. Synthetic analogs have several advantages over natural neurosteroids for clinical use because of their superior bioavailability and safety trends.

Catamenial Epilepsy: Discovery of an Extrasynaptic Molecular Mechanism for Targeted Therapy

Catamenial epilepsy is a type of refractory epilepsy characterized by seizure clusters around perimenstrual or periovulatory period. The pathophysiology of catamenial epilepsy still remains unclear, yet there are few animal models to study this gender-specific disorder. The pathophysiology of perimenstrual catamenial epilepsy involves the withdrawal of the progesterone-derived GABAergic neurosteroids due to the decline in progesterone level at the time of menstruation. These manifestations can be faithfully reproduced in rodents by specific neuroendocrine manipulations. Since mice and rats, like humans, have ovarian cycles with circulating hormones, they appear to be suitable animal models for studies of perimenstrual seizures. Recently, we created specific experimental models to mimic perimenstrual seizures. Studies in rat and mouse models of catamenial epilepsy show enhanced susceptibility to seizures or increased seizure exacerbations following neurosteroid withdrawal. During such a seizure exacerbation period, there is a striking decrease in the anticonvulsant effect of commonly prescribed antiepileptics, such as benzodiazepines, but an increase in the anticonvulsant potency of exogenous neurosteroids. We discovered an extrasynaptic molecular mechanism of catamenial epilepsy. In essence, extrasynaptic δGABA-A receptors are upregulated during perimenstrual-like neuroendocrine milieu. Consequently, there is enhanced antiseizure efficacy of neurosteroids in catamenial models because δGABA-A receptors confer neurosteroid sensitivity and greater seizure protection. Molecular mechanisms such as these offer a strong rationale for the clinical development of a neurosteroid replacement therapy for catamenial epilepsy.

Neurosteroid Structure-Activity Relationships for Functional Activation of Extrasynaptic δGABA(A) Receptors

Synaptic GABAA receptors are primary mediators of rapid inhibition in the brain and play a key role in the pathophysiology of epilepsy and other neurologic disorders. The δ-subunit GABAA receptors are expressed extrasynaptically in the dentate gyrus and contribute to tonic inhibition, promoting network shunting as well as reducing seizure susceptibility. However, the neurosteroid structure-function relationship at δGABA(A) receptors within the native hippocampus neurons remains unclear. Here we report a structure-activity relationship for neurosteroid modulation of extrasynaptic GABAA receptor-mediated tonic inhibition in the murine dentate gyrus granule cells. We recorded neurosteroid allosteric potentiation of GABA as well as direct activation of tonic currents using a wide array of natural and synthetic neurosteroids. Our results shows that, for all neurosteroids, the C3α-OH group remains obligatory for extrasynaptic receptor functional activity, as C3β-OH epimers were inactive in activating tonic currents. Allopregnanolone and related pregnane analogs exhibited the highest potency and maximal efficacy in promoting tonic currents. Alterations at the C17 or C20 region of the neurosteroid molecule drastically altered the transduction kinetics of tonic current activation. The androstane analogs had the weakest modulatory response among the analogs tested. Neurosteroid potentiation of tonic currents was completely (approximately 95%) diminished in granule cells from δ-knockout mice, suggesting that δ-subunit receptors are essential for neurosteroid activity. The neurosteroid sensitivity of δGABA(A) receptors was confirmed at the systems level using a 6-Hz seizure test. A consensus neurosteroid pharmacophore model at extrasynaptic δGABA(A) receptors is proposed based on a structure-activity relationship for activation of tonic current and seizure protection.

Seizure facilitating activity of the oral contraceptive ethinyl estradiol

Contraceptive management is critical in women with epilepsy. Although oral contraceptives (OCs) are widely used by many women with epilepsy, little is known about their impact on epileptic seizures and epileptogenesis. Ethinyl estradiol (EE) is the primary component of OC pills. In this study, we investigated the pharmacological effect of EE on epileptogenesis and kindled seizures in female mice using the hippocampus kindling model. Animals were stimulated daily with or without EE until generalized stage 5 seizures were elicited. EE treatment significantly accelerated the rate of epileptogenesis. In acute studies, EE caused a significant decrease in the afterdischarge threshold and increased the incidence and severity of seizures in fully-kindled mice. In chronic studies, EE treatment caused a greater susceptibility to kindled seizures. Collectively, these results are consistent with moderate proconvulsant-like activity of EE. Such excitatory effects may affect seizure risk in women with epilepsy taking OC pills.

Antiseizure Activity of Midazolam in Mice Lacking δ-Subunit Extrasynaptic GABA(A) Receptors

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 δ-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 (ED50, 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 5α-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.

Perimenstrual-like hormonal regulation of extrasynaptic δ-containing GABAA receptors mediating tonic inhibition and neurosteroid sensitivity

Neurosteroids are endogenous regulators of neuronal excitability and seizure susceptibility. Neurosteroids, such as allopregnanolone (AP; 3α-hydroxy-5α-pregnan-20-one), exhibit enhanced anticonvulsant activity in perimenstrual catamenial epilepsy, a neuroendocrine condition in which seizures are clustered around the menstrual period associated with neurosteroid withdrawal (NSW). However, the molecular mechanisms underlying such enhanced neurosteroid sensitivity remain unclear. Neurosteroids are allosteric modulators of both synaptic (αβγ2-containing) and extrasynaptic (αβδ-containing) GABAA receptors, but they display greater sensitivity toward δ-subunit receptors in dentate gyrus granule cells (DGGCs). Here we report a novel plasticity of extrasynaptic δ-containing GABAA receptors in the dentate gyrus in a mouse perimenstrual-like model of NSW. In molecular and immunofluorescence studies, a significant increase occurred in δ subunits, but not α1, α2, β2, and γ2 subunits, in the dentate gyrus of NSW mice. Electrophysiological studies confirmed enhanced sensitivity to AP potentiation of GABA-gated currents in DGGCs, but not in CA1 pyramidal cells, in NSW animals. AP produced a greater potentiation of tonic currents in DGGCs of NSW animals, and such enhanced AP sensitivity was not evident in δ-subunit knock-out mice subjected to a similar withdrawal paradigm. In behavioral studies, mice undergoing NSW exhibited enhanced seizure susceptibility to hippocampus kindling. AP has enhanced anticonvulsant effects in fully kindled wild-type mice, but not δ-subunit knock-out mice, undergoing NSW-induced seizures, confirming δ-linked neurosteroid sensitivity. These results indicate that perimenstrual NSW is associated with striking upregulation of extrasynaptic, δ-containing GABAA receptors that mediate tonic inhibition and neurosteroid sensitivity in the dentate gyrus. These findings may represent a molecular rationale for neurosteroid therapy of catamenial epilepsy.

Neurosteroids and their role in sex-specific epilepsies

Neurosteroids are involved in sex-specific epilepsies. Allopregnanolone and related endogenous neurosteroids in the brain control excessive neuronal excitability and seizure susceptibility. Neurosteroids activate GABA-A receptors, especially extrasynaptic αγδ-GABA-A receptor subtypes that mediate tonic inhibition and thus dampen network excitability. Our studies over the past decade have shown that neurosteroids are broad-spectrum anticonvulsants and confer seizure protection in various animal models. Neurosteroids also exert antiepileptogenic effects. There is emerging evidence on a critical role for neurosteroids in the pathophysiology of the sex-specific forms of epilepsies such as catamenial epilepsy, a menstrual cycle-related seizure disorder in women. Catamenial epilepsy is a neuroendocrine condition in which seizures are clustered around specific points in the menstrual cycle, most often around the perimenstrual or periovulatory period. Apart from ovarian hormones, fluctuations in neurosteroid levels could play a critical role in this gender-specific epilepsy. Neurosteroids also regulate the plasticity of synaptic and extrasynaptic GABA-A receptors in the hippocampus and other regions involved in epilepsy pathology. Based on these studies, we proposed a neurosteroid replacement therapy for catamenial epilepsy. Thus, neurosteroids are novel drug targets for pharmacotherapy of epilepsy.

Gender issues in antiepileptogenic treatments

Disease modification of epilepsy refers to the alleviation of epileptogenesis or comorbidities after genetic or acquired epileptogenic brain insults. There are currently 30 proof-of-concept experimental pharmacologic studies that have demonstrated some beneficial disease-modifying effects. None of these studies, however, has yet passed from the laboratory to the clinic. The International League Against Epilepsy and American Epilepsy Society working groups on antiepileptogenic (AEG) therapies recently released recommendations for conducting preclinical AEG studies, taking into account many of the critiques raised by previous study designs. One of the issues relates to the lack of analysis of AEG efficacy in both sexes. A review of the literature reveals that most of the preclinical studies have been performed using male rodents, whereas clinical study cohorts include both males and females. Therefore, it is important to determine whether sex differences should be taken into account to a greater extent than they have been historically at different phases of experimental studies. Here we address the following questions based on analysis of available experimental AEG studies: (a) whether sex differences should be considered when searching for novel AEG targets, (b) how sex differences can affect the preclinical AEG study designs and analysis of outcome measures, and (c) what factors should be considered when examining the effect of sex on outcome of clinical AEG trials or the clinical use of AEGs.

Neuroactive steroids for the treatment of status epilepticus

Benzodiazepines are the current first-line standard-of-care treatment for status epilepticus but fail to terminate seizures in about one third of cases. Synaptic GABAA receptors, which mediate phasic inhibition in central circuits, are the molecular target of benzodiazepines. As status epilepticus progresses, these receptors are internalized and become functionally inactivated, conferring benzodiazepine resistance, which is believed to be a major cause of treatment failure. GABAA receptor positive allosteric modulator neuroactive steroids, such as allopregnanolone, also potentiate synaptic GABAA receptors, but in addition they enhance extrasynaptic GABAA receptors that mediate tonic inhibition. Extrasynaptic GABAA receptors are not internalized, and desensitization of these receptors does not occur during continuous seizures in status epilepticus models. Here we review the broad-spectrum antiseizure activity of allopregnanolone in animal seizure models and the evidence for its activity in models of status epilepticus. We also demonstrate that allopregnanolone inhibits ongoing behavioral and electrographic seizures in a model of status epilepticus, even when there is benzodiazepine resistance. Parenteral allopregnanolone may provide an improved treatment for refractory status epilepticus.

Neurosteroid interactions with synaptic and extrasynaptic GABA(A) receptors: regulation of subunit plasticity, phasic and tonic inhibition, and neuronal network excitability

RATIONALE

Neurosteroids are steroids synthesized within the brain with rapid effects on neuronal excitability. Allopregnanolone, allotetrahydrodeoxycorticosterone, and androstanediol are three widely explored prototype endogenous neurosteroids. They have very different targets and functions compared to conventional steroid hormones. Neuronal γ-aminobutyric acid (GABA) type A (GABA(A)) receptors are one of the prime molecular targets of neurosteroids.

OBJECTIVE

This review provides a critical appraisal of recent advances in the pharmacology of endogenous neurosteroids that interact with GABA(A) receptors in the brain. Neurosteroids possess distinct, characteristic effects on the membrane potential and current conductance of the neuron, mainly via potentiation of GABA(A) receptors at low concentrations and direct activation of receptor chloride channel at higher concentrations. The GABA(A) receptor mediates two types of inhibition, now characterized as synaptic (phasic) and extrasynaptic (tonic) inhibition. Synaptic release of GABA results in the activation of low-affinity γ2-containing synaptic receptors, while high-affinity δ-containing extrasynaptic receptors are persistently activated by the ambient GABA present in the extracellular fluid. Neurosteroids are potent positive allosteric modulators of synaptic and extrasynaptic GABA(A) receptors and therefore enhance both phasic and tonic inhibition. Tonic inhibition is specifically more sensitive to neurosteroids. The resulting tonic conductance generates a form of shunting inhibition that controls neuronal network excitability, seizure susceptibility, and behavior.

CONCLUSION

The growing understanding of the mechanisms of neurosteroid regulation of the structure and function of the synaptic and extrasynaptic GABA(A) receptors provides many opportunities to create improved therapies for sleep, anxiety, stress, epilepsy, and other neuropsychiatric conditions.

Role of hormones and neurosteroids in epileptogenesis

This article describes the emerging evidence of hormonal influence on epileptogenesis, which is a process whereby a brain becomes progressively epileptic due to an initial precipitating event of diverse origin such as brain injury, stroke, infection, or prolonged seizures. The molecular mechanisms underlying the development of epilepsy are poorly understood. Neuroinflammation and neurodegeneration appear to trigger epileptogenesis. There is an intense search for drugs that truly prevent the development of epilepsy in people at risk. Hormones play an important role in children and adults with epilepsy. Corticosteroids, progesterone, estrogens, and neurosteroids have been shown to affect seizure activity in animal models and in clinical studies. However, the impact of hormones on epileptogenesis has not been investigated widely. There is emerging new evidence that progesterone, neurosteroids, and endogenous hormones may play a role in regulating the epileptogenesis. Corticosterone has excitatory effects and triggers epileptogenesis in animal models. Progesterone has disease-modifying activity in epileptogenic models. The antiepileptogenic effect of progesterone has been attributed to its conversion to neurosteroids, which binds to GABA-A receptors and enhances phasic and tonic inhibition in the brain. Neurosteroids are robust anticonvulsants. There is pilot evidence that neurosteroids may have antiepileptogenic properties. Future studies may generate new insight on the disease-modifying potential of hormonal agents and neurosteroids in epileptogenesis.

GABAergic neuroactive steroids and resting-state functional connectivity in postpartum depression: a preliminary study

Postpartum depression (PPD) affects up to 1 in 8 women. The early postpartum period is characterized by a downward physiological shift from relatively elevated levels of sex steroids during pregnancy to diminished levels after parturition. Sex steroids influence functional brain connectivity in healthy non-puerperal subjects. This study tests the hypothesis that PPD is associated with attenuation of resting-state functional connectivity (rs-fc) within corticolimbic regions implicated in depression and alterations in neuroactive steroid concentrations as compared to healthy postpartum women. Subjects (n = 32) were prospectively evaluated during pregnancy and in the postpartum with repeated plasma neuroactive steroid measurements and mood and psychosocial assessments. Healthy comparison subjects (HCS) and medication-free subjects with unipolar PPD (PPD) were examined using functional magnetic resonance imaging (fMRI) within 9 weeks of delivery. We performed rs-fc analysis with seeds placed in the anterior cingulate cortex (ACC), and bilateral amygdala (AMYG), hippocampi (HIPP) and dorsolateral prefrontal cortices (DLPFCs). Postpartum rs-fc and perinatal neuroactive steroid plasma concentrations, quantified by liquid chromatography/mass spectrometry, were compared between groups. PPD subjects showed attenuation of connectivity for each of the tested regions (i.e. ACC, AMYG, HIPP and DLPFC) and between corticocortical and corticolimbic regions vs. HCS. Perinatal concentrations of pregnanolone, allopregnanolone and pregnenolone were not different between groups. This is the first report of a disruption in the rs-fc patterns in medication-free subjects with PPD. This disruption may contribute to the development of PPD, at a time of falling neuroactive steroid concentrations.

Estrous cycle regulation of extrasynaptic δ-containing GABA(A) receptor-mediated tonic inhibition and limbic epileptogenesis

The ovarian cycle affects susceptibility to behavioral and neurologic conditions. The molecular mechanisms underlying these changes are poorly understood. Deficits in cyclical fluctuations in steroid hormones and receptor plasticity play a central role in physiologic and pathophysiologic menstrual conditions. It has been suggested that synaptic GABA(A) receptors mediate phasic inhibition in the hippocampus and extrasynaptic receptors mediate tonic inhibition in the dentate gyrus. Here we report a novel role of extrasynaptic δ-containing GABA(A) receptors as crucial mediators of the estrous cycle-related changes in neuronal excitability in mice, with hippocampus subfield specificity. In molecular and immunofluorescence studies, a significant increase occurred in δ-subunit, but not α4- and γ2-subunits, in the dentate gyrus during diestrus. However, δ-subunit upregulation was not evident in the CA1 region. The δ-subunit expression was undiminished by age and ovariectomy and in mice lacking progesterone receptors, but it was significantly reduced by finasteride, a neurosteroid synthesis inhibitor. Electrophysiologic studies confirmed greater potentiation of GABA currents by progesterone-derived neurosteroid allopregnanolone in dissociated dentate gyrus granule cells in diestrus than in CA1 pyramidal cells. The baseline conductance and allopregnanolone potentiation of tonic currents in dentate granule cells from hippocampal slices were higher than in CA1 pyramidal cells. In behavioral studies, susceptibility to hippocampus kindling epileptogenesis was lower in mice during diestrus. These results demonstrate the estrous cycle-related plasticity of neurosteroid-sensitive, δ-containing GABA(A) receptors that mediate tonic inhibition and seizure susceptibility. These findings may provide novel insight on molecular cascades of menstrual disorders like catamenial epilepsy, premenstrual syndrome, and migraine.

Neuroendocrine aspects of catamenial epilepsy

This review describes the neuroendocrinological aspects of catamenial epilepsy, a menstrual cycle-related seizure disorder in women with epilepsy. Catamenial epilepsy is a multifaceted neuroendocrine condition in which seizures are clustered around specific points in the menstrual cycle, most often around perimenstrual or periovulatory period. Three types of catamenial seizures (perimenstrual, periovulatory and inadequate luteal) have been identified. The molecular pathophysiology of catamenial epilepsy remains unclear. Cyclical changes in the circulating levels of estrogens and progesterone (P) play a central role in the development of catamenial epilepsy. Endogenous neurosteroids such as allopregnanolone (AP) and allotetrahydrodeoxycorticosterone (THDOC) that modulate seizure susceptibility could play a critical role in catamenial epilepsy. In addition, plasticity in GABA-A receptor subunits could play a role in the enhanced seizure susceptibility in catamenial epilepsy. P-derived neurosteroids such as AP and THDOC potentiate synaptic GABA-A receptor function and also activate extrasynaptic GABA-A receptors in the hippocampus and thus may represent endogenous regulators of catamenial seizure susceptibility. Experimental studies have shown that neurosteroids confer greater seizure protection in animal models of catamenial epilepsy, especially without evident tolerance to their actions during chronic therapy. In the recently completed NIH-sponsored, placebo controlled phase 3 clinical trial, P therapy proved to be beneficial only in women with perimenstrual catamenial epilepsy but not in non-catamenial subjects. Neurosteroid analogs with favorable profile may be useful in the treatment of catamenial epilepsy.

Neuroendocrine considerations in the treatment of men and women with epilepsy

Complex, multidirectional interactions between hormones, seizures, and the medications used to control them can present a challenge for clinicians treating patients with epilepsy. Many hormones act as neurosteroids, modulating brain excitability via direct binding sites. Thus, changes in endogenous or exogenous hormone levels can affect the occurrence of seizures directly as well as indirectly through pharmacokinetic effects that alter the concentrations of antiepileptic drugs. The underlying structural and physiological brain abnormalities of epilepsy and the metabolic activity of antiepileptic drugs can adversely affect hypothalamic and gonadal functioning. Knowledge of these complex interactions has increased and can now be incorporated in meaningful treatment approaches for men and women with epilepsy.

Finasteride inhibits the disease-modifying activity of progesterone in the hippocampus kindling model of epileptogenesis

Progesterone (P) plays an important role in seizure susceptibility in women with epilepsy. Preclinical and experimental studies suggest that P appears to interrupt epileptogenesis, which is a process whereby a normal brain becomes progressively susceptible to recurrent, unprovoked seizures due to precipitating risk factors. Progesterone has not been investigated widely for its potential disease-modifying activity in epileptogenic models. Recently, P has been shown to exert disease-modifying effects in the kindling model of epileptogenesis. However, the mechanisms underlying the protective effects of P against epileptogenesis remain unclear. In this study, we investigated the role of P-derived neurosteroids in the disease-modifying activity of P. It is hypothesized that 5α-reductase converts P to allopregnanolone and related neurosteroids that retard epileptogenesis in the brain. To test this hypothesis, we utilized the mouse hippocampus kindling model of epileptogenesis and investigated the effect of finasteride, a 5α-reductase and neurosteroid synthesis inhibitor. Progesterone markedly retarded the development of epileptogenesis and inhibited the rate of kindling acquisition to elicit stage 5 seizures. Pretreatment with finasteride led to complete inhibition of the P-induced retardation of the limbic epileptogenesis in mice. Finasteride did not significantly influence the acute seizure expression in fully kindled mice expressing stage 5 seizures. Thus, neurosteroids that potentiate phasic and tonic inhibition in the hippocampus, such as allopregnanolone, may mediate the disease-modifying effect of P, indicating a new role of neurosteroids in acquired limbic epileptogenesis and temporal lobe epilepsy.