Seizure susceptibility in intact and ovariectomized female rats treated with the convulsant pilocarpine

Evaluating the interplay between estrous cyclicity and flurothyl-induced seizure susceptibility in Scn2a K1422E mice

Recently, we demonstrated that Scn2a K1422E female mice showed a distinct distribution of flurothyl-induced seizure thresholds. To evaluate whether the estrous cycle contributes to this effect, estrous cycle monitoring was performed in mice that had undergone ovariectomy, sham surgery, or no treatment prior to seizure induction. Ovariectomy did not affect the non-unimodal distribution of flurothyl seizure thresholds observed in Scn2a K1422E females. Additionally, seizure thresholds were not associated with estrous cycle stage in mice that underwent sham surgery or in non-surgerized (intact) mice. Interestingly, intact Scn2a K1422E females showed evidence of disrupted estrous cyclicity, an effect not previously described in a genetic epilepsy model.

Sex and gonadectomy modify behavioral seizure susceptibility and mortality in a repeated low-dose kainic acid systemic injection paradigm in mice

OBJECTIVE

Sex differences in epilepsy appear driven in part due to effects of gonadal steroids, with varying results in experimental models based on species, strain, and method of seizure induction. Furthermore, removing the main source of these steroids via gonadectomy may impact seizure characteristics differently in males and females. Repeated low-dose kainic acid (RLDKA) systemic injection paradigms were recently shown to reliably induce status epilepticus (SE) and hippocampal histopathology in C57BL/6J mice. Here, we investigated whether seizure susceptibility in a RLDKA injection protocol exhibits a sex difference and whether gonadectomy differentially influences response to this seizure induction paradigm in males and females.

METHODS

Adult C57BL/6J mice were left gonad-intact as controls or gonadectomized (females: ovariectomized, OVX; males: orchidectomized, ORX). At least 2 weeks later, KA was injected ip, every 30 minutes at 7.5 mg/kg or less until the animal reached SE, defined by at least 5 generalized seizures (GS, Racine stage 3 or higher). Parameters of susceptibility to GS induction, SE development, and mortality rates were quantified.

RESULTS

No differences in seizure susceptibility or mortality were observed between control males and control females. Gonadectomized mice exhibited increased susceptibility and reduced latency to both GS and SE in comparison to corresponding controls of the same sex, but the effects were stronger in males. In addition, ORX males, but not OVX females, exhibited strongly increased seizure-induced mortality.

SIGNIFICANCE

The RLDKA protocol is notable for its efficacy in inducing SE and seizure-induced histopathology in C57BL/6J mice, the background for many transgenic strains in current use in epilepsy research. The present results indicate that this protocol may be beneficial for investigating the effects of gonadal hormone replacement on seizure susceptibility, mortality, and seizure-induced histopathology, and that gonadectomy unmasks sex differences in susceptibility to seizures and mortality not observed in gonad-intact controls.

Sex and gonadectomy modify behavioral seizure susceptibility and mortality in a repeated low-dose kainic acid systemic injection paradigm in mice

Objective

Sex differences in epilepsy appear driven in part due to effects of gonadal steroids, with varying results in experimental models based on species, strain, and method of seizure induction. Furthermore, removing a main source of these steroids via gonadectomy may impact seizure characteristics differently in males and females. Repeated low-dose kainic acid (RLDKA) systemic injection paradigms were recently shown to reliably induce status epilepticus (SE) and hippocampal histopathology in C57BL/6J mice. Here, we investigated whether seizure susceptibility in a RLDKA injection protocol exhibits a sex difference, and whether gonadectomy differentially influences response to this seizure induction paradigm in males and females.

Methods

Adult C57BL/6J mice were left gonad-intact as controls or gonadectomized (females: ovariectomized, OVX; males: orchidectomized, ORX). At least 2 weeks later, KA was injected i.p. every 30 minutes at 7.5 mg/kg or less until the animal reached SE, defined by at least 5 generalized seizures (GS, Racine stage 3 or higher). Parameters of susceptibility to GS induction, SE development, and mortality rates were quantified.

Results

No differences in seizure susceptibility or mortality were observed between control males and control females. ORX males exhibited increased susceptibility and reduced latency to both GS and SE, but OVX females exhibited increased susceptibility and reduced latency to SE only. However, ORX males, but not OVX females, exhibited strongly increased seizure-induced mortality.

Significance

The RLDKA protocol is notable for its efficacy in inducing SE and seizure-induced histopathology in C57BL/6J mice, the background for many transgenic strains in current use in epilepsy research. The present results indicate that this protocol may be beneficial for investigating the effects of gonadal hormone replacement on seizure susceptibility, mortality, and seizure-induced histopathology, and that gonadectomy unmasks sex differences in susceptibility to seizures and mortality not observed in gonad-intact controls.

Evaluating the interplay between estrous cyclicity and induced seizure susceptibility in Scn2aK1422E mice

Pathogenic variants in SCN2A are associated with a range of neurodevelopmental disorders (NDD). SCN2A-related NDD show wide phenotypic heterogeneity, suggesting that modifying factors must be considered in order to properly elucidate the mechanisms of pathogenic variants. Recently, we characterized neurological phenotypes in a mouse model of the variant SCN2A-p.K1422E. We demonstrated that heterozygous Scn2aK1422E female mice showed a distinct, reproducible distribution of flurothyl-induced seizure thresholds. Women with epilepsy often show a cyclical pattern of altered seizure susceptibility during specific phases of the menstrual cycle which can be attributed to fluctuations in hormones and corresponding changes in neurosteroid levels. Rodent models have been used extensively to examine the relationship between the estrous (menstrual) cycle, steroid hormones, and seizure susceptibility. However, the effects of the estrous cycle on seizure susceptibility have not been evaluated in the context of an epilepsy-associated genetic variant. To determine whether the estrous cycle affects susceptibility to flurothyl-induced seizures in Scn2aK1422E female mice, estrous cycle monitoring was performed in mice that had undergone ovariectomy (OVX), sham surgery, or no treatment prior to seizure induction. Removing the influence of circulating sex hormones via OVX did not affect the non-unimodal distribution of flurothyl seizure thresholds observed in Scn2aK1422E females. Additionally, flurothyl seizure thresholds were not associated with estrous cycle stage in mice that underwent sham surgery or were untreated. These data suggest that variation in Scn2aK1422E flurothyl seizure threshold is not significantly influenced by the estrous cycle and, by extension, fluctuations in ovarian hormones. Interestingly, untreated Scn2aK1422E females showed evidence of disrupted estrous cyclicity, an effect not previously described in a genetic epilepsy model. This unexpected result highlights the importance of considering sex specific effects and the estrous cycle in support of more inclusive biomedical research.

Non-Status Epilepticus female rats show seizure-like behaviors in the chronic phase of Pilocarpine experimental model

Abstract Only few studies have focus on animals that received Pilocarpine (Pilo) and did not develop behavioral status epilepticus (SE) and, whether they may become epileptic in the model’s chronic phase. Previews works observed mossy fiber sprouting in the hippocampus of Non-SE (NSE) rats, while others observed spontaneous and recurrent seizures (SRS) 6 - 8 months after animals received Pilo. It is known that neuronal excitability is influenced by female hormones, as well as, the occurrence of SE in castrated and non-castrated female rats. However, it is not known whether females that received Pilo and did not show SE, may have SRS. The aim of this work was to investigate whether castrated and non-castrated female rats that did not show behavioral SE after Pilo, will develop SRS in the following one-year. For that, animals received 360 mg/kg of Pilo and were video monitored for 12 months. SE females from castrated and non-castrated groups became epileptic since the first month after drug injection. Epileptic behaviors were identified watching video monitoring recordings in the fast speed. Castrated and Non-castrated NSE animals showed behaviors resembling seizures described by Racine Scale stages 1 - 3. Motor alterations showed by NSE groups could be observed only when recordings were analyzed in slow speed. In addition, behavioral manifestations as, rhythmic head movements, sudden head movements, whole body movements and immobility were also observed in both, SE and NSE groups. We concluded that NSE female rats may have become epileptic. Adding to it, slow speed analysis of motor alterations was essential for the observation of NSE findings, which suggests that possibly many motor alterations have been underestimated in epilepsy experimental research.

Interleukin-17A Mediates Hippocampal Damage and Aberrant Neurogenesis Contributing to Epilepsy-Associated Anxiety

Anxiety disorder is one of the most common comorbidities in temporal lobe epilepsy (TLE), but its neurobiological mechanisms remain unclear. Here we identified a novel target, interleukin-17A (IL-17A), which can contribute to TLE-associated anxiety. Epileptic seizures were induced in 6-week-old IL-17A wild-type (WT) and knockout (KO) mice by pilocarpine injection. To evaluate anxiety level, we subjected mice to open field and elevated plus maze (EPM) tests and measured the time animals spent in center zone or open arms. Epileptic IL-17A WT mice showed thigmotaxis and reluctance to stay in open arms, whereas IL-17A KO mice spent more time in the center area and open arms, suggesting alleviated anxiety in epilepsy. Histological assessments revealed that hippocampal neuronal death as evaluated by Fluoro-Jade B staining was significantly reduced in IL-17A KO mice. Moreover, at 6 weeks after pilocarpine-induced status epilepticus, the number of hilar ectopic granule cells was also markedly decreased by IL-17A deficiency without a difference in the proliferation of neural progenitors or the generation of newborn neurons in the dentate gyrus. Taken together, our data demonstrated that IL-17A deletion mitigates TLE-associated anxiety behavior, possibly via the hippocampal neuroprotection and the reduction of seizure-induced aberrant neurogenesis.

Neuroglobin deficiency increases seizure susceptibility but does not affect basal behavior in mice

Neuroglobin (Ngb) is found in the neurones of several different brain areas and is known to bind oxygen and other gaseous molecules and reactive oxygen species (ROS) in vitro, but it does not seem to act as a respiratory molecule for neurones. Using male and female Ngb‐knockout (KO) mice, we addressed the role of Ngb in neuronal brain activity using behavioral tests but found no differences in general behaviors, memory processes, and anxiety−/depression‐like behaviors. Oxidative stress and ROS play key roles in epileptogenesis, and oxidative injury produced by an excessive production of free radicals is involved in the initiation and progression of epilepsy. The ROS binding properties led us to hypothesize that lack of Ngb could affect central coping with excitatory stimuli. We consequently explored whether exposure to the excitatory molecule kainate (KA) would increase severity of seizures in mice lacking Ngb. We found that the duration and severity of seizures were increased, while the latency time to develop seizures was shortened in Ngb‐KO compared to wildtype adult female mice. Consistently, c‐fos expression after KA was significantly increased in Ngb‐KO mice in the amygdala and piriform cortex, regions rich in Ngb and known to be centrally involved in seizure generation. Moreover, the measured c‐fos expression levels were correlated with seizure susceptibility. With these new findings combined with previous studies we propose that Ngb could constitute an intrinsic defense mechanism against neuronal hyperexcitability and oxidative stress by buffering of ROS in amygdala and other Ngb‐containing brain regions.

Differences in Evolution of Epileptic Seizures and Topographical Distribution of Tissue Damage in Selected Limbic Structures Between Male and Female Rats Submitted to the Pilocarpine Model

Epidemiological evidence shows that clinical features and comorbidities in temporal lobe epilepsy (TLE) may have different manifestations depending on the sex of patients. However, little is known about how sex-related mechanisms can interfere with the processes underlying the epileptic phenomenon. The findings of this study show that male rats with epilepsy in the pilocarpine model have longer-lasting and more severe epileptic seizures, while female rats have a higher frequency of epileptic seizures and a greater number of seizure clusters. Significant sex-linked pathological changes were also observed: epileptic brains of male and female rats showed differences in mass reduction of 41.8% in the amygdala and 18.2% in the olfactory bulb, while loss of neuronal cells was present in the hippocampus (12.3%), amygdala (18.1%), and olfactory bulb (7.5%). Another important sex-related finding was the changes in non-neuronal cells with increments for the hippocampus (36.1%), amygdala (14.7%), and olfactory bulb (37%). Taken together, our study suggests that these neuropathological changes may underlie the differences in the clinical features of epileptic seizures observed in male and female rats.

Cellular and behavioral effects of altered NaV1.2 sodium channel ion permeability in Scn2aK1422E mice

Genetic variants in SCN2A, encoding the Na_V1.2 voltage-gated sodium channel, are associated with a range of neurodevelopmental disorders with overlapping phenotypes. Some variants fit into a framework wherein gain-of-function missense variants that increase neuronal excitability lead to developmental and epileptic encephalopathy, while loss-of-function variants that reduce neuronal excitability lead to intellectual disability and/or autism spectrum disorder (ASD) with or without co-morbid seizures. One unique case less easily classified using this framework is the de novo missense variant SCN2A-p.K1422E, associated with infant-onset developmental delay, infantile spasms and features of ASD. Prior structure–function studies demonstrated that K1422E substitution alters ion selectivity of Na_V1.2, conferring Ca²⁺ permeability, lowering overall conductance and conferring resistance to tetrodotoxin (TTX). Based on heterologous expression of K1422E, we developed a compartmental neuron model incorporating variant channels that predicted reductions in peak action potential (AP) speed. We generated Scn2a^K1422E mice and characterized effects on neurons and neurological/neurobehavioral phenotypes. Cultured cortical neurons from heterozygous Scn2a^K1422E/+ mice exhibited lower current density with a TTX-resistant component and reversal potential consistent with mixed ion permeation. Recordings from Scn2a^K1442E/+ cortical slices demonstrated impaired AP initiation and larger Ca²⁺ transients at the axon initial segment during the rising phase of the AP, suggesting complex effects on channel function. Scn2a^K1422E/+ mice exhibited rare spontaneous seizures, interictal electroencephalogram abnormalities, altered induced seizure thresholds, reduced anxiety-like behavior and alterations in olfactory-guided social behavior. Overall, Scn2a^K1422E/+ mice present with phenotypes similar yet distinct from other Scn2a models, consistent with complex effects of K1422E on Na_V1.2 channel function.

Brain structural and neuroendocrine basis of sex differences in epilepsy

This chapter reviews the current information about sex differences in epilepsy and potential mechanisms underlying sex differences in seizure susceptibility and epilepsy. The susceptibility to and occurrence of seizures are generally higher in men than women. There is gender-specific epilepsies such as catamenial epilepsy, a neuroendocrine condition in which seizures are most often clustered around the perimenstrual or periovulatory period in adult women. Structural differences in cerebral morphology, the structural and functional circuits may render men and women differentially vulnerable to seizure disorders and epileptogenic processes. Changes in seizure sensitivity are evident at puberty, pregnancy, and menopause, often attributed to circulating steroid hormones and neurosteroids as well as neuroplasticity in receptor systems. An improved understanding of the sexual dimorphism in neural circuits and the neuroendocrine basis of sex differences or resistance to protective drugs is essential to develop sex-specific therapies for seizure conditions.

Molecular mechanisms of sex differences in epilepsy and seizure susceptibility in chemical, genetic and acquired epileptogenesis

This article provides a succinct overview of sex differences in epilepsy and putative molecular mechanisms underlying sex differences in seizure susceptibility in chemical, genetic, and acquired epileptogenesis. The susceptibility to excitability episodes and occurrence of epileptic seizures are generally higher in men than women. The precise molecular mechanisms remain unclear, but differences in regional morphology and neural circuits in men and women may explain differential vulnerability to seizures and epileptogenic cascades. Changes in seizure sensitivity can be attributed to steroid hormones, including fluctuations in neurosteroids as well as neuroplasticity in their receptor signaling systems. Other potential neurobiological bases for sex differences in epilepsies include differences in brain development, neurogenesis, neuronal chloride homeostasis, and neurotrophic and glial responses. In catamenial epilepsy, a gender-specific neuroendocrine condition, epileptic seizures are most often clustered around a specific menstrual period in adult women. A deeper understanding of the molecular and neural network basis of sex differences in seizures and response to antiepileptic drugs is highly warranted for designing effective, sex-specific therapies for epilepsy, epileptogenesis, and seizure 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.

Progesterone modulates neuronal excitability bidirectionally

Progesterone acts on neurons directly by activating its receptor and through metabolic conversion to neurosteroids. There is emerging evidence that progesterone exerts excitatory effects by activating its cognate receptors (progesterone receptors, PRs) through enhanced expression of α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid receptors (AMPARs). Progesterone metabolite 5α,3α-tetrahydro-progesterone (allopregnanolone, THP) mediates its anxiolytic and sedative actions through the potentiation of synaptic and extrasynaptic γ-aminobutyric acid type-A receptors (GABAARs). Here, we review progesterone's neuromodulatory actions exerted through PRs and THP and their opposing role in regulating seizures, catamenial epilepsy, and seizure exacerbation associated with progesterone withdrawal.

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.

Role of Lacosamide in Preventing Pentylenetetrazole Kindling-Induced Alterations in the Expression of the Gamma-2 Subunit of the GABAA Receptor in Rats

Background:

Epilepsy remains challenging to treat still no etiologic treatment has been identified, however, some antiepileptic drugs (AEDs) are able to modify the pathogenesis of the disease. Lacosamide (LCM) has been shown to possess complex anticonvulsant and neuroprotective actions, being an enhancer of the slow inactivation of voltage-gated sodium channels, and it has the potential to prevent epileptogenesis. Recent evidence has shown that LCM indirectly improves the function of GABAA receptors. Receptors at most GABAergic synapses involve the gamma-2 subunit, which contributes to both phasic and tonic inhibition, and its presence assures benzodiazepine sensitivity. Moreover, mutant gamma-2 subunits were associated with generalized epilepsy syndromes. In animal models, the expression of the gamma-2 subunit of the gamma-aminobutyric acid A receptor (GABAAg2) was shown to be increased in pentylenetetrazole (PTZ)-induced chemical kindling in Wistar rats.

Objective:

This study hypothesized that LCM might affect the kindling process by influencing the expression of GABAA receptors in the hippocampus.

Methods:

The gene and protein expression levels of the GABAAg2 were studied using RT-qPCR and immunofluorescent staining.

Results:

It was found that LCM treatment (10 mg/kg i.p. daily for 57 days) reduced the maximal intensity of the PTZ-induced seizures but did not prevent kindling. On the other hand, LCM treatment reverted the increase of mRNA expression of GABAAg2 in the hippocampus and prevented the decrease of GABAAg2 protein in the hippocampal CA1 region.

Conclusion:

LCM could exhibit modulatory effects on the GABAergic system of the hippocampus that may be independent of the anticonvulsant action.

Two Distinct Hippocampal Astrocyte Morphotypes Reveal Subfield-Different Fate during Neurodegeneration Induced by Trimethyltin Intoxication

Astrocytes comprise a heterogenic group of glial cells, which perform homeostatic functions in the central nervous system. These cells react to all kind of insults by changing the morphology and function that result in a transition from the quiescent to a reactive phenotype. Trimethyltin (TMT) intoxication, which reproduces pathological events in the hippocampus similar to those associated with seizures and cognitive decline, has been proven as a useful model for studying responses of the glial cells to neurodegeneration. In the present study, we have explored morphological varieties of astrocytes in the hippocampal subregions of ovariectomized female rats exposed to TMT. We have demonstrated an early loss of neurons in CA1 and DG subfields. Distinct morphotypes of protoplasmic astrocytes observed in CA1/CA3 and the hilus of control animals developed different responses to TMT intoxication, as assessed by GFAP-immunohistochemistry. In CA1 subregion, GFAP⁺ astrocytes preserved their domain organization and responded with typical hypertrophy, while the hilar GFAP⁺ astrocytes developed atrophy-like phenotype and increased expression of vimentin and nestin 7 days after the exposure. Both reactive and atrophied-like astrocytes expressed Kir4.1 in CA1/CA3 and the hilus of DG, respectively, indicating that these cells did not change their potential for normal activity at this time point of pathology. Together, the results demonstrate the persistence of two protoplasmic morphotypes of astrocytes, with distinct appearance, function, and fate after TMT-induced neurodegeneration, suggesting their pleiotropic roles in the hippocampal response to neurodegeneration.

Adult neurogenesis in the mouse dentate gyrus protects the hippocampus from neuronal injury following severe seizures

Previous studies suggest that reducing the numbers of adult-born neurons in the dentate gyrus (DG) of the mouse increases susceptibility to severe continuous seizures (status epilepticus; SE) evoked by systemic injection of the convulsant kainic acid (KA). However, it was not clear if the results would be the same for other ways to induce seizures, or if SE-induced damage would be affected. Therefore, we used pilocarpine, which induces seizures by a different mechanism than KA. Also, we quantified hippocampal damage after SE. In addition, we used both loss-of-function and gain-of-function methods in adult mice. We hypothesized that after loss-of-function, mice would be more susceptible to pilocarpine-induced SE and SE-associated hippocampal damage, and after gain-of-function, mice would be more protected from SE and hippocampal damage after SE. For loss-of-function, adult neurogenesis was suppressed by pharmacogenetic deletion of dividing radial glial precursors. For gain-of-function, adult neurogenesis was increased by conditional deletion of pro-apoptotic gene Bax in Nestin-expressing progenitors. Fluoro-Jade C (FJ-C) was used to quantify neuronal injury and video-electroencephalography (video-EEG) was used to quantify SE. Pilocarpine-induced SE was longer in mice with reduced adult neurogenesis, SE had more power and neuronal damage was greater. Conversely, mice with increased adult-born neurons had shorter SE, SE had less power, and there was less neuronal damage. The results suggest that adult-born neurons exert protective effects against SE and SE-induced neuronal injury.

Estrogen and Serotonin: Complexity of Interactions and Implications for Epileptic Seizures and Epileptogenesis

A burgeoning literature documents the confluence of ovarian steroids and central serotonergic systems in the in-junction of epileptic seizures and epileptogenesis. Estrogen administration in animals reduces neuronal death from seizures by up-regulation of the prosurvival molecule i.e. Bcl-2, anti-oxidant potential and protection of NPY interneurons. Serotonin modulates epileptiform activity in either direction i.e administration of 5-HT agonists or reuptake inhibitors leads to the acti-vation of 5-HT3 and 5-HT1A receptors tending to impede focal and generalized seizures, while depletion of brain 5-HT along with the destruction of serotonergic terminals leads to expanded neuronal excitability hence abatement of seizure threshold in experimental animal models. Serotonergic neurotransmission is influenced by the organizational activity of ster-oid hormones in the growing brain and the actuation effects of steroids which come in adulthood. It is further established that ovarian steroids bring induction of dendritic spine proliferation on serotonin neurons thus thawing a profound effect on sero-tonergic transmission. This review features 5-HT1A and 5-HT3 receptors as potential targets for ameliorating seizure-induced neurodegeneration and recurrent hypersynchronous neuronal activity. Indeed 5-HT3 receptors mediate cross-talk be-tween estrogenic and serotonergic pathways, and could be well exploited for combinatorial drug therapy against epileptogen-esis.

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.

Behavioral and electrophysiological changes in female mice overexpressing ORAI1 in neurons

Orai proteins form highly selective Ca²⁺ release-activated channels (CRACs). They play a critical role in store-operated Ca²⁺ entry (SOCE; i.e., the influx of external Ca²⁺ that is induced by the depletion of endoplasmic reticulum Ca²⁺ stores). Of the three Orai homologs that are present in mammals (Orai1-3), the physiological function of Orai1 is the best described. CRACs are formed by both homomeric assemblies and heteromultimers of Orais. Orai1 and Orai2 can form heteromeric channels that differ in conductivity during SOCE, depending on their Orai1-to-Orai2 ratio. The present study explored the potential consequences of ORAI1 overexpression in neurons where the dominant isoform is Orai2. We established the Tg(ORAI1)Ibd transgenic mouse line that overexpresses ORAI1 in brain neurons. We observed seizure-like symptoms in aged (≥15-month-old) female mice but not in males of the same age. The application of kainic acid and bicuculline to slices that were isolated from 8-month-old (±1 month) female Tg(ORAI1)Ibd mice revealed a significantly lower frequency of interictal bursts compared with samples that were isolated from wildtype mice. No differences were observed in male mice of a similar age. A battery of behavioral tests showed that context recognition decreased only in female transgenic mice. The phenotype that was observed in female mice suggests that ORAI1 overexpression may affect neuronal activity in a sex-dependent manner. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.

Impact of strain, sex, and estrous cycle on gamma butyrolactone-evoked absence seizures in rats

Childhood absence epilepsy (CAE) is the most common pediatric epilepsy syndrome and is characterized by typical absence seizures (AS). AS are non-convulsive epileptic seizures characterized by a sudden loss of awareness and bilaterally generalized synchronous 2.5-4 Hz spike and slow-wave discharges (SWD). Gamma butyrolactone (GBL) is an acute pharmacological model of AS and induces bilaterally synchronous SWDs and behavioral arrest. Despite the long use of this model, little is known about its strain and sex-dependent features. We compared the dose-response profile of GBL-evoked SWDs in three rat strains (Long Evans, Sprague-Dawley, and Wistar), and examined the modulatory effects of estrous cycle on SWDs in female Wistar rats. We evaluated the number of seizures, the cumulative time seizing, and the average seizure duration as a function of dose, strain, and sex/estrous phase. Long Evans rats displayed the greatest sensitivity to GBL, followed by Wistar rats, and then by Sprague-Dawley rats. GBL-evoked SWDs were modulated by estrous cycle in female rats, with the lowest sensitivity to GBL occurring during metestrus. Wistar rats showed the greatest variability as a function of dose, and the least variability within dose; these features make this strain desirable for interventional studies. Moreover, our finding that the SWD response to GBL differs as a function of estrous cycle underscores the importance of cycle monitoring in studies examining female animals using this model. Together, these strain and sex-dependent findings provide guidance for future studies.

Understanding the controversial drug targets in epilepsy and pharmacoresistant epilepsy

Accumulating experimental data suggests a number of successful drug targets against epilepsy which eventually failed in the clinical setup. Mammalian target of rapamycin inhibitors, multi-drug resistance transporter inhibitors, cyclo-oxygenase-2 inhibitors, statins, etc. are the most promising and well studied among them. Drugs aiming at these targets produced beneficial response in most of the in vitro and in vivo seizure models. However, in certain situations, they have produced differential rather controversial results. Their effects varied with the seizure model, species, time and route of administration, different drugs from the same class, etc. This review emphasises on such drugs which presented with variability in their beneficial effects against seizures and epilepsy. This review critically summarises the preclinical evidence of these targets in the context of seizures and the probable reasons for their variability and clinical failures.

Glial source of nitric oxide in epileptogenesis: A target for disease modification in epilepsy

Epileptogenesis is the process of developing an epileptic condition and/or its progression once it is established. The molecules that initiate, promote, and propagate remarkable changes in the brain during epileptogenesis are emerging as targets for prevention/treatment of epilepsy. Epileptogenesis is a continuous process that follows immediately after status epilepticus (SE) in animal models of acquired temporal lobe epilepsy (TLE). Both SE and epileptogenesis are potential therapeutic targets for the discovery of anticonvulsants and antiepileptogenic or disease-modifying agents. For translational studies, SE targets are appropriate for screening anticonvulsive drugs prior to their advancement as therapeutic agents, while targets of epileptogenesis are relevant for identification and development of therapeutic agents that can either prevent or modify the disease or its onset. The acute seizure models do not reveal antiepileptogenic properties of anticonvulsive drugs. This review highlights the important components of epileptogenesis and the long-term impact of intervening one of these components, nitric oxide (NO), in rat and mouse kainate models of TLE. NO is a putative pleotropic gaseous neurotransmitter and an important contributor of nitro-oxidative stress that coexists with neuroinflammation and epileptogenesis. The long-term impact of inhibiting the glial source of NO during early epileptogenesis in the rat model of TLE is reviewed. The importance of sex as a biological variable in disease modification strategies in epilepsy is also briefly discussed.

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.

The pilocarpine model of temporal lobe epilepsy: Marked intrastrain differences in female Sprague-Dawley rats and the effect of estrous cycle

Rat strains such as Sprague-Dawley (SD) or Wistar are widely used in epilepsy research, including popular models of temporal lobe epilepsy in which spontaneous recurrent seizures (SRS), hippocampal damage, and behavioral alterations develop after status epilepticus (SE). Such rats are randomly outbred, and outbred strains are known to be genetically heterogeneous populations with a high intrastrain variation. Intrastrain differences may be an important reason for discrepancies between studies from different laboratories, but the extent to which such differences affect the development of seizures, neurodegeneration, and psychopathology in post-SE models of epilepsy has received relatively little attention. In the present study, we induced SE by systemic administration of pilocarpine (following pretreatment with lithium) in SD rats from different breeders (Harlan, Charles River [CRL], Taconic) as well as different breeding locations of the same breeder (Harlan-Winkelmann [HW] in Germany vs. Harlan Laboratories [HL] in the Netherlands). Some experiments were also performed in Wistar rats. Pilocarpine was administered by a ramp-up dosing protocol that allows determining interindividual differences in susceptibility to the convulsant. Marked intrastrain differences in induction of SE and its long-term consequences were found. Sprague-Dawley rats from HW were significantly more sensitive to SE induction than all other SD substrains. The majority of SD rats from different vendors developed SRS after SE except SD rats from HL. The CRL-SD rats markedly differed in basal behavior and SE-induced behavioral alterations from other SD substrains. Susceptibility to pilocarpine was hardly affected by the estrous cycle. The marked intrastrain differences provide an interesting tool to study the impact of genetic and environmental factors on seizure susceptibility, epileptogenesis, and relationship between behavior and epilepsy and vice versa.

The neuroendocrine basis of sex differences in epilepsy

Epilepsy affects people of all ages and both genders. Sex differences are well known in epilepsy. Seizure susceptibility and the incidence of epilepsy are generally higher in men than women. In addition, there are gender-specific epilepsies such as catamenial epilepsy, a neuroendocrine condition in which seizures are most often clustered around the perimenstrual or periovulatory period in adult women with epilepsy. Changes in seizure sensitivity are also evident at puberty, pregnancy, and menopause. Sex differences in seizure susceptibility and resistance to antiseizure drugs can be studied in experimental models. An improved understanding of the neuroendocrine basis of sex differences or resistance to protective drugs is essential to develop targeted therapies for sex-specific seizure conditions. This article provides a brief overview of the current status of sex differences in seizure susceptibility and the potential mechanisms underlying the gender differences in seizure sensitivity.

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.

Stress Effects on Neuronal Structure: Hippocampus, Amygdala, and Prefrontal Cortex

The hippocampus provided the gateway into much of what we have learned about stress and brain structural and functional plasticity, and this initial focus has expanded to other interconnected brain regions, such as the amygdala and prefrontal cortex. Starting with the discovery of adrenal steroid, and later, estrogen receptors in the hippocampal formation, and subsequent discovery of dendritic and spine synapse remodeling and neurogenesis in the dentate gyrus, mechanistic studies have revealed both genomic and rapid non-genomic actions of circulating steroid hormones in the brain. Many of these actions occur epigenetically and result in ever-changing patterns of gene expression, in which there are important sex differences that need further exploration. Moreover, glucocorticoid and estrogen actions occur synergistically with an increasing number of cellular mediators that help determine the qualitative nature of the response. The hippocampus has also been a gateway to understanding lasting epigenetic effects of early-life experiences. These findings in animal models have resulted in translation to the human brain and have helped change thinking about the nature of brain malfunction in psychiatric disorders and during aging, as well as the mechanisms of the effects of early-life adversity on the brain and the body.

Oestradiol Regulates Neuropeptide Y Release and Gene Coupling with the GABAergic and Glutamatergic Synapses in the Adult Female Rat Dentate Gyrus

Neuropeptide Y (NPY) is an endogenous modulator of neuronal activity affecting both GABAergic and glutamatergic transmission. Previously, we found that oestradiol modifies the number of NPY immunoreactive neurones in the hippocampal dentate gyrus. In the present study, we investigated which oestrogen receptor type is responsible for these changes in the number of NPY-positive neurones. Furthermore, we determined the effects of oestrogen receptor activation on NPY release. Finally, we examined the contribution of oestrogen toward the remodelling of the GABAergic and glutamatergic gene networks in terms of coupling with Npy gene expression in ovariectomised rats. We found that activation of either oestrogen receptor type (ERα or ERβ) increases the number of NPY-immunopositive neurones and enhances NPY release in the dentate gyrus. We also found that, compared to oestrogen-lacking ovariectomised rats, oestrogen replacement increases the probability of synergistic/antagonistic coupling between the Npy and GABAergic synapse genes, whereas the glutamatergic synapse genes are less likely to be coupled with Npy under similar conditions. The data together suggest that oestrogens play a critical role in the regulation of NPY system activity and are also involved in the coupling/uncoupling of the Npy gene with the GABAergic and glutamatergic synapses in the female rat dentate gyrus.

Detrimental effect of post Status Epilepticus treatment with ROCK inhibitor Y-27632 in a pilocarpine model of temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is the most common type of epilepsy in adults where 20-30% of the patients are refractory to currently available anti-epileptic drugs. The RhoA/Rho-kinase signaling pathway activation has been involved in inflammatory responses, neurite outgrowth and neuronal death under pathological conditions such as epileptic insults. Acute preventive administration of ROCK inhibitor has been reported to have beneficial outcomes in Status Epilepticus (SE) epilepsy. In the present study, we evaluate the effect of chronic post SE treatment with the ROCK inhibitor Y-27632 in a rat pilocarpine model of TLE. We used chronic i.p. injections of Y-27632 for 5 days in 6 week old control rats or rats subjected to pilocarpine treatment as a model of TLE. Surprisingly, our findings demonstrate that a systemic administration of Y-27632 in pilocarpine-treated rats increases neuronal death in the CA3 region and ectopic recurrent mossy fiber sprouting (rMFS) in the dentate gyrus of the hippocampal formation. Interestingly, we found that chronic treatment with Y-27632 exacerbates the down-regulation and pathological distribution of the K(+)-Cl(-) cotransporter KCC2, thus providing a putative mechanism for post SE induced neuronal death. The involvement of astrogliosis in this mechanism appears to be intricate as ROCK inhibition reduces reactive astrogliosis in pilocarpine rats. Conversely, in control rats, chronic Y-27632 treatment increases astrogliosis. Together, our findings suggest that Y-27632 has a detrimental effect when chronically used post SE in a rat pilocarpine model of TLE.

Opportunities for improving animal welfare in rodent models of epilepsy and seizures

Animal models of epilepsy and seizures, mostly involving mice and rats, are used to understand the pathophysiology of the different forms of epilepsy and their comorbidities, to identify biomarkers, and to discover new antiepileptic drugs and treatments for comorbidities. Such models represent an important area for application of the 3Rs (replacement, reduction and refinement of animal use). This report provides background information and recommendations aimed at minimising pain, suffering and distress in rodent models of epilepsy and seizures in order to improve animal welfare and optimise the quality of studies in this area. The report includes practical guidance on principles of choosing a model, induction procedures, in vivo recordings, perioperative care, welfare assessment, humane endpoints, social housing, environmental enrichment, reporting of studies and data sharing. In addition, some model-specific welfare considerations are discussed, and data gaps and areas for further research are identified. The guidance is based upon a systematic review of the scientific literature, survey of the international epilepsy research community, consultation with veterinarians and animal care and welfare officers, and the expert opinion and practical experience of the members of a Working Group convened by the United Kingdom's National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3Rs).

Animal models of absence epilepsies: what do they model and do sex and sex hormones matter?

While epidemiological data suggest a female prevalence in human childhood- and adolescence-onset typical absence epilepsy syndromes, the sex difference is less clear in adult-onset syndromes. In addition, although there are more females than males diagnosed with typical absence epilepsy syndromes, there is a paucity of studies on sex differences in seizure frequency and semiology in patients diagnosed with any absence epilepsy syndrome. Moreover, it is unknown if there are sex differences in the prevalence or expression of atypical absence epilepsy syndromes. Surprisingly, most studies of animal models of absence epilepsy either did not investigate sex differences, or failed to find sex-dependent effects. However, various rodent models for atypical syndromes such as the AY9944 model (prepubertal females show a higher incidence than prepubertal males), BN model (also with a higher prevalence in males) and the Gabra1 deletion mouse in the C57BL/6J strain offer unique possibilities for the investigation of the mechanisms involved in sex differences. Although the mechanistic bases for the sex differences in humans or these three models are not yet known, studies of the effects of sex hormones on seizures have offered some possibilities. The sex hormones progesterone, estradiol and testosterone exert diametrically opposite effects in genetic absence epilepsy and pharmacologically-evoked convulsive types of epilepsy models. In addition, acute pharmacological effects of progesterone on absence seizures during proestrus are opposite to those seen during pregnancy. 17β-Estradiol has anti-absence seizure effects, but it is only active in atypical absence models. It is speculated that the pro-absence action of progesterone, and perhaps also the delayed pro-absence action of testosterone, are mediated through the neurosteroid allopregnanolone and its structural and functional homolog, androstanediol. These two steroids increase extrasynaptic thalamic tonic GABAergic inhibition by selectively targeting neurosteroid-selective subunits of GABAA receptors (GABAARs). Neurosteroids also modulate the expression of GABAAR containing the γ2, α4, and δ subunits. It is hypothesized that differences in subunit expression during pregnancy and ovarian cycle contribute to the opposite effects of progesterone in these two hormonal states.

Sex differences in the neurobiology of epilepsy: a preclinical perspective

When all of the epilepsies are considered, sex differences are not always clear, despite the fact that many sex differences are known in the normal brain. Sex differences in epilepsy in laboratory animals are also unclear, although robust effects of sex on seizures have been reported, and numerous effects of gonadal steroids have been shown throughout the rodent brain. Here we discuss several reasons why sex differences in seizure susceptibility are unclear or are difficult to study. Examples of robust sex differences in laboratory rats, such as the relative resistance of adult female rats to the chemoconvulsant pilocarpine compared to males, are described. We also describe a novel method that has shed light on sex differences in neuropathology, which is a relatively new technique that will potentially contribute to sex differences research in the future. The assay we highlight uses the neuronal nuclear antigen NeuN to probe sex differences in adult male and female rats and mice. In females, weak NeuN expression defines a sex difference that previous neuropathological studies have not described. We also show that in adult rats, social isolation stress can obscure the normal effects of 17β-estradiol to increase excitability in area CA3 of the hippocampus. These data underscore the importance of controlling behavioral stress in studies of seizure susceptibility in rodents and suggest that behavioral stress may be one factor that has led to inconsistencies in outcomes of sex differences research. These and other issues have made it difficult to translate our increasing knowledge about the effects of gonadal hormones on the brain to improved treatment for men and women with epilepsy.

Are patterns of cortical hyperexcitability altered in catamenial epilepsy?

OBJECTIVE

We used transcranial magnetic stimulation to determine menstrual cycle-related changes in cortical excitability in women with and without catamenial epilepsy and investigated whether these changes differed between ovulatory and anovulatory cohorts.

METHODS

Healthy nonepilepsy women and women with generalized and focal epilepsy were investigated during ovulatory (n=11, 46, and 43, respectively) and anovulatory (n=9, 42, and 41) cycles. Patients were divided based on seizure pattern into catamenial (C1=perimenstrual, C2=periovulatory, C3=luteal seizure exacerbation), noncatamenial, and seizure free. Cortical excitability was assessed using motor threshold (MT) and paired pulse stimulation at short (2-15 milliseconds) and long (100-300 milliseconds) interstimulus intervals twice, at the (1) late follicular and (2) mid luteal phases of the menstrual cycle.

RESULTS

In controls, cortical excitability was greatest in the follicular study, where intracortical facilitation was increased (p<0.05). The opposite was seen in women with epilepsy, where intracortical facilitation was greatest and intracortical inhibition was least in the luteal studies (p<0.05). There were no differences between the ovulatory and anovulatory groups in any of the cohorts. No changes were observed in MT.

INTERPRETATION

Nonhormonal factors are involved in the cyclicity of cortical excitability across the menstrual cycle. Normal menstrual cycle variations in cortical excitability are altered in a similar pattern in ovulatory and anovulatory women with epilepsy regardless of seizure patterns. The underlying neural changes associated with epilepsy may alter responses to sex hormones. This may be an important underlying mechanism for catamenial seizure clustering.

Sex and hormonal influences on seizures and epilepsy

Epilepsy is the third most common chronic neurological disorder. Clinical and experimental evidence supports the role of sex and influence of sex hormones on seizures and epilepsy as well as alterations of the endocrine system and levels of sex hormones by epileptiform activity. Conversely, seizures are sensitive to changes in sex hormone levels, which in turn may affect the seizure-induced neuronal damage. The effects of reproductive hormones on neuronal excitability and seizure-induced damage are complex to contradictory and depend on different mechanisms, which have to be accounted for in data interpretation. Both estradiol and progesterone/allopregnanolone may have beneficial effects for patients with epilepsy. Individualized hormonal therapy should be considered as adjunctive treatment in patients with epilepsy to improve seizure control as well as quality of life.

A mouse kindling model of perimenstrual catamenial epilepsy

Catamenial epilepsy is caused by fluctuations in progesterone-derived GABA(A) receptor-modulating anticonvulsant neurosteroids, such as allopregnanolone, that play a significant role in the pathophysiology of epilepsy. However, there is no specific mouse model of catamenial epilepsy. In this study, we developed and characterized a mouse model of catamenial epilepsy by using the neurosteroid-withdrawal paradigm. It is hypothesized that seizure susceptibility decreases when neurosteroid levels are high (midluteal phase) and increases during their withdrawal (perimenstrual periods) in close association with GABA(A) receptor plasticity. A chronic seizure condition was created by using the hippocampus kindling model in female mice. Elevated neurosteroid levels were induced by sequential gonadotropin treatment, and withdrawal was induced by the neurosteroid synthesis inhibitor finasteride. Elevated neurosteroid exposure reduced seizure expression in fully kindled mice. Fully kindled mice subjected to neurosteroid withdrawal showed increased generalized seizure frequency and intensity and enhanced seizure susceptibility. They also showed reduced benzodiazepine sensitivity and enhanced neurosteroid potency, similar to the clinical catamenial seizure phenotype. The increased susceptibility to seizures and alterations in antiseizure drug responses are associated with increased abundance of the α4 and δ subunits of GABA(A) receptors in the hippocampus. These findings demonstrate that endogenous neurosteroids protect against seizure susceptibility and their withdrawal, such as that which occurs during menstruation, leads to exacerbation of seizure activity. This is possibly caused by specific changes in GABA(A) receptor-subunit plasticity and function, therefore providing a novel mouse model of human perimenstrual catamenial epilepsy that can be used for the investigation of disease mechanisms and new therapeutic approaches.

Ovariectomy in the developing rat decelerates cortical spreading depression in adult brain

The brain of mammals is one important target organ for the action of gonadal steroids and, when occurring during development, this hormonal influence may result in important repercussion on the brain electrophysiological properties at adulthood, some of which depending on the brain excitability. Here we have characterized in early-ovariectomized adult rats the brain ability to propagate the excitability-related phenomenon known as cortical spreading depression (CSD), as an index of the cerebral electrophysiological effects of the early-induced absence of the ovarian hormones. Wistar female rat pups (7-day old) underwent bilateral ovariectomy (Ovx group; n=21) or Sham surgery (Sham group; n=22), or no surgery (Naive group; n=22). When the pups became adult (90-130 days), they were submitted to the recording of CSD (electrocorticogram and slow DC-voltage variation) in two points of the cortical surface during 4h. Compared with both Naïve and Sham controls, bilateral ovariectomy early in life resulted in significantly higher body weights (from days 50-65 onwards) and severely reduced uterus weights at adulthood. Furthermore, in the Ovx animals the amplitudes and durations of the DC-potential changes of CSD were higher, and the CSD propagation velocities were reduced. Another group of rats ovariectomized in adulthood did not present such CSD alterations. It is concluded that ovariectomy during brain development is causally associated with the CSD changes in the adult brain, indicating a long-lasting effect, which we suggest as being related to the long-term suppression of the action of the ovarian hormones on brain excitability.

Effects of soy extract on pentylenetetrazol-induced seizures in ovariectomized rats

OBJECTIVE

To investigate the effects of soy extract on pentylenetetrazol (PTZ)-induced seizures in ovariectomized (OVX) rats.

METHODS

Female Wistar rats were randomly divided into 4 groups (n=15 in each group) as follows: sham-operated, OVX, low-dose soy (LDS) and high-dose soy (HDS). The rats in each group were divided into two subgroups and received daily injection of a low dose of PTZ (40 mg/kg body weight, intraperitoneally, n=7 in each subgroup) for 14 d or a single injection of a high dose of PTZ (90 mg/kg body weight, intraperitoneally, n=8 in each subgroup). The rats of LDS and HDS groups were injected with 20 and 60 mg/kg body weight of soy extract intraperitoneally, respectively, just 30 min before each PTZ injection. The rats of the sham-operated and the OVX groups received saline instead of soy extract. After treatment, the rats were placed in a plexiglas cage and their behaviors were observed for 60 min.

RESULTS

The results of repeated injection of low dose of PTZ during 14 d showed that the seizure score of the rats of OVX group on days 3, 5, 8, 10, 11, 12, and 13 was lower than that of the sham-operated group (P<0.05 or P<0.01). However, the rats of both LDS and HDS groups had higher score compared with the OVX group on the mentioned days (P<0.05 or P<0.01). The results of a single injection of a high dose of PTZ showed a significant increase (P<0.01) in the generalized tonic-clonic seizure (GTCS), but not the minimal clonic seizure (MCS) in the OVX rats compared with the sham-operated rats. Treatment with both low and high doses of soy extract significantly decreased the GTCS and MCS latencies compared with the OVX group (P<0.01).

CONCLUSION

Female hormones affect seizure severity induced by PTZ, and phytoestrogens of soy mimic this effects. However, more investigations need to be done in the future.

Neurosteroid withdrawal regulates GABA-A receptor α4-subunit expression and seizure susceptibility by activation of progesterone receptor-independent early growth response factor-3 pathway

Neurosteroids regulate GABA-A receptor plasticity. Neurosteroid withdrawal occurs during menstruation and is associated with a marked increase in expression of GABA-A receptor α4-subunit, a key subunit linked to enhanced neuronal excitability, seizure susceptibility and benzodiazepine resistance. However, the molecular mechanisms underlying the upregulation of α4-subunit expression remain unclear. Here we utilized the progesterone receptor (PR) knockout mouse to investigate molecular pathways of PR and the transcription factor early growth response factor-3 (Egr3) in regulation of the GABA-A receptor α4-subunit expression in the hippocampus in a mouse neurosteroid withdrawal paradigm. Neurosteroid withdrawal induced a threefold increase in α4-subunit expression in wild-type mice, but this upregulation was unchanged in PR knockout mice. The expression of Egr3, which controls α4-subunit transcription, was increased significantly following neurosteroid withdrawal in wild-type and PR knockout mice. Neurosteroid withdrawal-induced α4-subunit upregulation was completely suppressed by antisense Egr3 inhibition. In the hippocampus kindling model of epilepsy, there was heightened seizure activity, significant reduction in the antiseizure sensitivity of diazepam (a benzodiazepine insensitive at α4βγ-receptors) and conferral of increased seizure protection of flumazenil (a low-affinity agonist at α4βγ-receptors) in neurosteroid-withdrawn wild-type and PR knockout mice. These observations are consistent with enhanced α4-containing receptor abundance in vivo. Neurosteroid withdrawal-induced seizure exacerbation, diazepam insensitivity, and flumazenil efficacy in the kindling model were reversed by inhibition of Egr3. These results indicate that neurosteroid withdrawal-induced upregulation of GABA-A receptor α4-subunit expression is mediated by the Egr3 via a PR-independent signaling pathway. These findings help advance our understanding of the molecular basis of catamenial epilepsy, a neuroendocrine condition that occurs around the perimenstrual period and is characterized by neurosteroid withdrawal-linked seizure exacerbations in women with epilepsy.

A rat model of epilepsy in women: a tool to study physiological interactions between endocrine systems and seizures

Epilepsy in women is influenced by endocrine status and antiepileptic drugs, but without an animal model, the effects of endocrine variables and antiepileptic drugs cannot be easily dissociated from the influence of epilepsy itself. Animal models have had limited utility because experimentally induced seizures typically result in reproductive failure. This study was conducted to develop an improved animal model. The muscarinic convulsant pilocarpine was used to elicit status epilepticus (SE) in adult female Sprague Dawley rats. The selective estrogen receptor modulator raloxifene was administered 30 min before pilocarpine. An anticonvulsant barbiturate, pentobarbital, was injected 5-10 min after the onset of SE and at least once thereafter to minimize acute convulsions. Mortality, morbidity, estrous cyclicity, and the ultimate success of the procedure (i.e. induction of recurrent, spontaneous seizures) were monitored. The combination of raloxifene and pentobarbital led to significantly improved estrous cyclicity compared with previous methods. Animals treated with raloxifene and pentobarbital became epileptic, as defined by the recurrence of spontaneous convulsions in the weeks after SE. The results of this study provide an improved animal model to examine the interactions between seizures and ovarian hormone secretion. The results also suggest that treatment of SE with raloxifene may benefit women with SE.

Seizures and reproductive function: insights from female rats with epilepsy

OBJECTIVE

Chronic seizures in women can have adverse effects on reproductive function, such as polycystic ovarian syndrome, but it has been difficult to dissociate the effects of epilepsy from the role of antiepileptic drugs. To distinguish the effects of chronic seizures from medication, we used the laboratory rat, because an epileptic condition can be induced without concomitant anticonvulsant drug treatment.

METHODS

Adult female rats were administered the chemoconvulsant pilocarpine to initiate status epilepticus, which was decreased in severity by the anticonvulsant diazepam. These rats developed spontaneous seizures in the ensuing weeks, and are therefore termed epileptic. Controls were saline-treated rats, or animals that were injected with pilocarpine but did not develop status epilepticus. Ovarian cyclicity and weight gain were evaluated for 2 to 3 months. Serum hormone levels were assayed from trunk blood, which was collected at the time of death. Paraformaldehyde-fixed ovaries were evaluated quantitatively.

RESULTS

Rats that had pilocarpine-induced seizures had an increased incidence of acyclicity by the end of the study, even if status epilepticus did not occur. Ovarian cysts and weight gain were significantly greater in epileptic than control rats, whether rats maintained cyclicity or not. Serum testosterone was increased in epileptic rats, but estradiol, progesterone, and prolactin were not.

INTERPRETATIONS

The results suggest that an epileptic condition in the rat leads to increased body weight, cystic ovaries, and increased testosterone levels. Although caution is required when comparing female rats with women, the data suggest that recurrent seizures have adverse effects, independent of antiepileptic drugs.

Effect of hormonal replacement therapy in the hippocampus of ovariectomized epileptic female rats using the pilocarpine experimental model

Amado and Cavalheiro [Amado, D., Cavalheiro, E.A., 1998. Hormonal and gestational parameters in female rats submitted to the pilocarpine model of epilepsy. Epilepsy Res. 32, 266-274], studying the establishment of the pilocarpine epilepsy model in female rats observed that the estrous cycle was dramatically altered during the three periods of this experimental model. This work was delineated to study the function of sexual hormones in the development of the epilepsy model induced by pilocarpine in ovariectomized rats. Experimental groups were: (a) control animals during estrus phase of the estrous cycle (E) and ovariectomized female rats (OVX) treated with saline instead of pilocarpine in the same volume, (b) experimental animals, that developed status epilepticus (SE) and were studied during the chronic phase of this model: intact chronic rats (CHRON) and ovariectomized chronic rats (OVX+CHRON) and (c) ovariectomized chronic rats, that were submitted to hormonal replacement therapy treated with: medroxyprogesterone (OVX+CHRON+MPA); 17beta-estradiol (OVX+CHRON+E2), or both (OVX+CHRON+E2+MPA). All ovariectomized animals showed genital atrophy 4 days after the surgical procedure. Moreover, all animals that developed SE and survived showed spontaneous recurrent seizures during the chronic phase. Concerning to seizure frequency, animals receiving medroxyprogesterone associated with 17beta-estradiol showed decreased seizures' number. However, animals that received only medroxyprogesterone therapy also showed reduction in the number of seizures. In addition, hormonal treatment was also able to stabilize the mossy fibers sprouting process, showing the importance of these hormones in the development of the epilepsy in female rats.

Decreases in HCN mRNA expression in the hippocampus after kindling and status epilepticus in adult rats

PURPOSE

Studies in animal models and patients have implicated changes in hyperpolarization-activated cyclic nucleotide-gated cation channel (HCN) expression in the pathogenesis of temporal lobe epilepsy (TLE). However, the nature of HCN changes during the epileptogenic process and their commonality across different TLE models is unknown. Here HCN1 and HCN2 mRNA expression was quantitatively measured at different time points during epileptogenesis in two distinct animal models of TLE; the kainic acid (KA)-induced status epilepticus (SE) and amygdala kindling models.

METHODS

Hippocampal subregions (CA1, CA3, and dentate gyrus [DG]) and entorhinal cortex were dissected at different time-points. For KA-induced SE animals this was 24 h, 7 days (preepileptic), and 6 weeks (epileptic) post status. For amygdala kindling animals this was 2 weeks after reaching either "partially kindled" (one class II/III seizure) or "fully kindled" (five class V seizures) states. Quantification of regional hippocampal neuronal loss in the KA-treated animals was done using NeuN immunofluorescence and confocal microscopy.

RESULTS

HCN mRNA levels decreased in an isoform and region specific manner at all time points after KA-induced SE. The decrease in neuronal number could not account for all reductions in HCN mRNA levels post-KA insult, implicating transcriptional changes. A reduction in HCN2 mRNA levels was also observed in fully kindled animals in the CA3 region.

CONCLUSIONS

A reduction in HCN mRNA levels is present in two different models of TLE. This supports the case that a reduction in HCN channel expression is an accompaniment of epileptogenesis in different adult models of TLE.

Hormone replacement therapy: will it affect seizure control and AED levels?

Interest in the years of reproductive changes for women with epilepsy (WWE), specifically perimenopause, menopause and postmenopause has been emerging in the epilepsy community. This article discusses evidence for changes in seizure frequency during perimenopause and postmenopause. Further, a catamenial epilepsy pattern during the reproductive years may be a hallmark for the observed seizure frequency change during these years; that is, an increase at perimenopause but a decrease at menopause. This finding implies that a subset of WWE are particularly susceptible to endogenous reproductive hormonal changes. An adverse effect on seizure frequency with the use of hormone replacement therapy (HRT) during postmenopause for WWE was reported in questionnaires, and was later borne out in a clinical trial. The laboratory counterpart of this human trial, HRT in ovariectomized rodent seizure models, shows that estrogen and progesterone are neuroprotective and do not uniformly increase seizure frequency. Possible reasons for the discrepancy between "the lab and the clinic" are presented. Strategies for managing HRT in symptomatic postmenopausal WWE using estrogenic and progestogenic compounds that may be less likely to promote seizures are discussed.

The current state of postmenopausal hormone therapy: update for neurologists and epileptologists

Appropriate and safe use of hormone replacement therapy (HRT) in postmenopausal women is an evolving saga, triggered by the unexpected results from the first publication of the Women's Health Initiative (WHI) Trial in 2002. These results showed a slight but significantly increased risk of breast cancer, stroke, and dementia with standard HRT compared with placebo. A reanalysis of these results shows that use of HRT within the first few years after the onset of menopause may be associated with decreased risk of dementia and coronary artery disease. However, HRT in its commonly used form of conjugated equine estrogen and medroxyprogesterone acetate can increase seizure frequency in menopausal women with epilepsy; this outcome may be an adverse effect of these neuroactive steroids on the epileptic female brain, which is already in a hormonally deprived state. To explore this possibility, more information about the neurophysiologic activity of medroxyprogesterone acetate is needed and alternatives to this specific HRT regimen should be considered for women with epilepsy.

The role of ovarian steroid hormones in the regulation of basal and stress induced absence seizures

Ovarian hormones play an important role in the regulation of absence seizures in patients as well as in animal models. The present study examined whether chronic progesterone exposure would induce tolerance for the occurrence of absence seizures and whether reduction in gonadal steroids (via ovariectomy) would alter the number of basal and stress induced absence seizures in WAG/Rij rats, a genetic model for absence epilepsy.

METHODS

In Experiment 1, female WAG/Rij rats equipped with EEG electrodes received progesterone (P) (20 mg/kg) or cyclodextrin (CD, solvent) i.p. injections once a day for 3 days while a third group received CD injections on Days 1 and 2 and P on Day 3. The EEG was recorded on the day preceding the injections and at each day after injections. In Experiment 2, female WAG/Rij rats equipped with EEG electrodes, were ovariectomized (OVX) or sham operated. EEG recordings were made before and at the 4th, 8th, 10th, 20th, and 35th day after surgery. Rats were then exposed to three series of 10 foot-shocks (FS, 1.5 mA, 1 s) over 3 days. The EEG was recorded 1 h before and 2 h after each FS series.

RESULTS

Tolerance developed after a single P injection and the effect of P on SWDs was facilitated by two preceding control injections. No differences were found between OVX and sham-operated females in the occurrence of SWDs either in resting conditions or after acute FS exposure. However, OVX females showed a more prominent day-to-day aggravation in SWDs after repeated FS administration.

CONCLUSIONS

The data suggest an important interaction between hormones of the hypothalamo-pituitary-adrenal and hypothalamo-pituitary-gonadal axes in seizure control. On the one hand, stress interferes with and facilitates the acute effects of progesterone on the occurrence of SWDs and, on the other hand, rats with an intact hypothalamo-pituitary-gonadal axis can better regulate the stress response and develop tolerance to the stressor.

Estrogens and epilepsy: why are we so excited?

Estrogens are essential for normal brain function throughout life. The source of estrogens is not only from the periphery, but local production has also been demonstrated in the CNS. Actions of estrogens involve a variety of effects, which include modulation of gene expression, regulation of neurotransmitter release, or direct inter-actions with neurotransmitter receptors. By these effects, estrogens affect neuronal excitability and thus may play an important role in seizure disorders. Although the original clinical as well as animal studies suggest that estrogens have exclusively proconvulsant properties, it has now become clear that estrogens also produce anticonvulsant effects. These opposite effects of estrogens on seizures may depend on treatment duration, latency prior to seizure testing, mode of administration, estrogen dose and hormonal status, estrogenic species, the region/neurotransmitter system involved, seizure type/model used, and sex. Animal data also suggest that estrogens, specifically beta-estradiol, have neuroprotective effects on seizure-induced hippocampal damage. Further studies are necessary to understand the role of estrogens in seizure disorders. Such under-standing is important, especially for women with epilepsy, to make qualified decisions regarding administration of contraceptives and hormonal replacement therapy as well as for the design of new therapeutic strategies for better seizure control and prevention of seizure-induced neuronal damage.