Sex differences in models of temporal lobe epilepsy: role of testosterone

The influence of sex hormones on seizures in dogs and humans

Epilepsy is the most common chronic neurological disorder in both humans and dogs. The effect of sex hormones on seizures is well documented in human medicine. Catamenial epilepsy is defined as an increase in frequency and severity of seizures during certain periods of the menstrual cycle. Oestradiol increases seizure activity and progesterone is believed to exhibit a protective effect. The role of androgens is controversial and there is a lack of research focusing on androgens and epilepsy. Indeed, little is known about the influence of sex hormones on epilepsy in dogs. Sterilisation is believed to improve seizure control, but no systematic research has been conducted in this field. This review provides an overview of the current literature on the influence of sex hormones on seizures in humans. The literature on idiopathic epilepsy in dogs was assessed to identify potential risk factors related to sex and sterilisation status. In general, there appears to be an over-representation of male dogs with idiopathic epilepsy but no explanation for this difference in prevalence between sexes has been reported. In addition, no reliable conclusions can be drawn on the effect of sterilisation due to the lack of focused research and robust scientific evidence.

Contribution of estradiol in sex-dependent differences of pentylenetetrazole-induced seizures in rats

In the present study the contribution of estradiol in sex-dependent differences of pentylenetetrazole (PTZ)-induced seizures was investigated in rats. The rats were divided into four groups: 1) sham, 2) ovariectomized (OVX), 3) ovariectomized-estradiol (OVX-Est) and 4) male. The OVX-Est group received estradiol valerate (2 mg/kg; i.m/4 weeks) while, male, sham and OVX groups received vehicle. The animals were injected by PTZ (90 mg/kg). The latencies to minimal clonic seizures (MCS) and generalized tonic-clonic seizures (GTCS), were recorded. Serum 17β-estradiol and testosterone levels were also determined using an Elisa kit. GTCS latency in OVX rats was higher than in sham-operated animals (P < 0.05). MCS and GTCS latency in the male group was significantly higher than in the sham, OVX and OVX-Est groups (P < 0.001 and P < 0.01). There was no significant difference in MCS or GTCS latencies among OVX-Est, sham and OVX groups. Serum 17β-estradiol level in the OVX group was significantly lower than in the sham (P < 0.01) and in the OVX-Est group it was higher than in the sham, OVX and male groups (P < 0.01 and P < 0.001). Serum testosterone level in the male group was significantly higher than in all the other three groups (P < 0.001). It seems that testosterone probably has a more efficient role than estradiol in the gender dependent difference in seizure caused by PTZ in rats.

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.

The effect of mental rotation on changes in plasma testosterone and cortisol levels

Testosterone level has an influence on cognitive functions, especially spatial abilities. The relationship is, however, bidirectional and brain activity also affects testosterone levels. The aim of this study was to analyze the effects of an intensive 3D mental rotation task on testosterone levels in young healthy men and women. In the mental rotation task, men reached a higher top score (P=0.027) and total score (P=0.004) compared to women. In 8 out of 9 women (P=0.008) but not in men (P=0.129) testosterone levels decreased after one hour of mental rotation testing. A significant gender difference was shown (P<0.0001). In all women, plasma cortisol levels was significantly lower after testing (P=0.004). In men cortisol levels decreased in 7 out of 9 subjects (P=0.039). A significant gender difference was not found (P=0.19). No association was found in women between baseline testosterone levels and mental rotation total score (P=0.810). In men there was a positive correlation between baseline testosterone and mental rotation total score (P=0.015). A significant difference gender difference was seen in the association between testosterone and mental rotation score (P<0.05). Mental rotation stimuli caused significant changes in hormonal levels of testosterone and cortisol. A gender-specific response was detected in testosterone fluctuation.

Estrogen-dependent effect of soy extract on pentylenetetrazole-induced seizures in rats

OBJECTIVE

To study the different effects of soy extract on pentylenetetrazole (PTZ)-induced seizures in the presence and absence of ovarian hormones in rats, and the gender-dependent differences in the effects of phytoestrogens on behavior.

METHODS

Male and female Wistar rats were randomly divided into nine groups with eight in each, namely, male-saline (M-saline), male-low-dose soy (M-LDS), male-high-dose soy (M-HDS), sham-saline (Sh-saline), sham-low-dose soy (Sh-LDS), sham-high-dose soy (Sh-HDS), ovariectomized-saline (OVX-saline), ovariectomized-low-dose soy (OVX-LDS) and ovariectomized-high-dose soy (OVX-HDS). The rats of groups 7 to 9 were ovariectomized under ketamine anesthesia. The rats of groups 2, 5 and 8 were treated by 20 mg/kg of soy extract while the animals of groups 3, 6 and 9 received 60 mg/kg of soy extract for two weeks. In groups 1, 4 and 7, saline was injected instead of soy extract. The animals were then injected by a single dose of PTZ (90 mg/kg body weight, intraperitoneally) and placed in a plexiglas cage and the latency to minimal clonic seizure (MCS) and generalized tonic-clonic seizure (GTCS) was recorded.

RESULTS

Both MCS and GTCS latency in M-LDS and M-HDS groups was significantly lower than that in M-saline group (P<0.05 or P<0.01). Treatment for female sham rats by soy extract did not affect MCS and GTCS latency. The animals of OVX-LDS and OVX-HDS groups had lower MCS and GTCS latency in comparison with OVX-saline group (P<0.05 or P<0.01).

CONCLUSION

It is concluded that the phytoestrogens of soy affect seizure severity induced by PTZ, but their effects are different in the presence or absence of ovarian hormones. However, further studies are necessary to be done.

Early-life stress is associated with gender-based vulnerability to epileptogenesis in rat pups

During development, the risk of developing mesial temporal lobe epilepsy (MTLE) increases when the developing brain is exposed to more than one insult in early life. Early life insults include abnormalities of cortical development, hypoxic-ischemic injury and prolonged febrile seizures. To study epileptogenesis, we have developed a two-hit model of MTLE characterized by two early-life insults: a freeze lesion-induced cortical malformation at post-natal day 1 (P1), and a prolonged hyperthermic seizure (HS) at P10. As early life stressors lead to sexual dimorphism in both acute response and long-term outcome, we hypothesized that our model could lead to gender-based differences in acute stress response and long-term risk of developing MTLE. Male and female pups underwent a freeze-lesion induced cortical microgyrus at P1 and were exposed to HS at P10. Animals were monitored by video-EEG from P90 to P120. Pre and post-procedure plasma corticosterone levels were used to measure stress response at P1 and P10. To confirm the role of sex steroids, androgenized female pups received daily testosterone injections to the mother pre-natally and post-natally for nine days while undergoing both insults. We demonstrated that after both insults females did not develop MTLE while all males did. This correlated with a rise in corticosterone levels at P1 following the lesion in males only. Interestingly, all androgenized females showed a similar rise in corticosterone at P1, and also developed MTLE. Moreover, we found that the cortical lesion significantly decreased the latency to generalized convulsion during hyperthermia at P10 in both genders. The cortical dysplasia volumes at adulthood were also similar between male and female individuals. Our data demonstrate sexual dimorphism in long-term vulnerability to develop epilepsy in the lesion + hyperthermia animal model of MTLE and suggest that the response to early-life stress at P1 contributes significantly to epileptogenesis in a gender-specific manner.

Factors affecting outcomes of pilocarpine treatment in a mouse model of temporal lobe epilepsy

Pilocarpine-treated mice are an increasingly used model of temporal lobe epilepsy. However, outcomes of treatment can be disappointing, because many mice die or fail to develop status epilepticus. To improve animal welfare and outcomes of future experiments we analyzed results of previous pilocarpine treatments to identify factors that correlate with development of status epilepticus and survival. All treatments were performed by one investigator with mice of the FVB background strain. Results from 2413 mice were evaluated for effects of sex, age, body weight, and latency between administration of atropine methyl bromide and pilocarpine. All parameters correlated with effects on outcomes. Best results were obtained from male mice, 6-7 weeks old, and 21-25 g, with pilocarpine administered 18-30 min after atropine methyl bromide. In that group only 23% failed to develop status epilepticus, and 64% developed status epilepticus and survived. Those results are substantially better than that of the total sample in which 31% failed to develop status epilepticus and only 34% developed status epilepticus and survived.

β-Hydroxybutyrate increases the pilocarpine-induced seizure threshold in young mice

This study was designed to investigate the effects of β-hydroxybutyrate (BHB) on pilocarpine-induced seizures in young mice. Eighty-five male, postnatal day 21, ICR mice were used. All mice were pretreated with scopolamine methylbromide (1 mg/kg) 30 min prior to pilocarpine administration. Experimental mice (n=46) were injected intraperitoneally with BHB (20 mmol/kg), 15 min prior to pilocarpine administration; control animals (n=39) were administered normal saline. Pilocarpine (300 mg/kg) was then administered intraperitoneally to induce seizures. Mice were monitored for 2 h after pilocarpine injection, and seizure behavior grades were evaluated according to Racine's scale. All mice developed typical seizure behaviors of grade 3 or higher. Although the severity in terms of seizure behavior grade was not significantly different between groups, the mean (±SD) latency to the onset of seizure was significantly prolonged in BHB-treated mice (5.15±2.19 min) compared with controls (2.95±1.06 min; p<0.001). This study demonstrates that treatment with BHB significantly prolongs the latency to the onset of seizures induced by pilocarpine in mice and suggests that BHB, one of the ketone bodies, may be direct anticonvulsant.

Increased medial temporal lobe and striatal grey-matter volume in a rare disorder of androgen excess: a voxel-based morphometry (VBM) study

Major questions remain about how sex hormones influence human brain development and cognition. Studies in humans and animals suggest a strong impact of androgen on the structure and function of the medial temporal lobe (MTL) and striatum. Using voxel-based morphometry (DARTEL), we compared MTL and striatal structures in 13 [mean age (±S.D.) 12.7±3.2 yr, mean bone age 14.8±3.2 yr] boys with familial male precocious puberty (FMPP), characterized by early excess androgen secretion, and 39 healthy age-matched boys (mean age 14.3±2.5 yr). The FMPP group showed significantly larger grey-matter volume (GMV) in parahippocampal and fusiform gyri as well as putamen relative to controls. By comparison, larger GMV for controls relative to patients was only apparent in the precentral gyrus. Exploratory regression analyses that examined the impact of age on the current findings revealed a significant increase of GMV in the putamen with age in patients suffering from excess androgen but not in controls. Finally, current levels of free testosterone were obtained in the patient group. Analyses revealed a significant negative association indicating that FMPP boys with low levels of bioavailable testosterone exhibited high GMV in the bilateral striatum. The findings suggest a critical influence of androgen on human brain development and are discussed in relation to male-dominant psychiatric childhood disorders.

Epilepsy, sex hormones and antiepileptic drugs in female patients

Women with epilepsy have a higher incidence of reproductive endocrine disorders than the general female population. These alterations include polycystic ovary syndrome, hyperandrogenemia, infertility, hypothalamic amenorrhea and hyperprolactinemia. Reproductive dysfunction is attributed both to epilepsy itself and to antiepileptic drugs (AEDs). Focal epileptic discharges from the temporal lobe may have a direct influence on the function of the hypothalamic-pituitary axis, thus altering the release of sex steroid hormones, including the production of luteinizing hormone, follicle-stimulating hormone, gonadotropin-releasing hormone and prolactin. AEDs may modulate hormone release from the hypothalamic-pituitary-gonadal axis and they may alter the metabolism of sex hormones and their binding proteins. Hepatic enzyme-inducing AEDs, such as carbamazepine and phenytoin, may be most clearly linked to altered metabolism of sex steroid hormones, but valproic acid, an enzyme inhibitor, has also been associated with a frequent occurrence of polycystic ovary syndrome and hyperandrogenism in women with epilepsy. Therefore, treatment of epilepsy and selection of AEDs are important for reproductive health in female patients. The aim of the present review is to critically evaluate the recently published data concerning the interactions between sex hormones, epilepsy and AEDs.

Antiseizure effects of 3alpha-androstanediol and/or 17beta-estradiol may involve actions at estrogen receptor beta

Testosterone (T), the principal androgen secreted by the testes, can have antiseizure effects. Some of these effects may be mediated by T's metabolites. T is metabolized to 3alpha-androstanediol (3alpha-diol). T, but not 3alpha-diol, binds androgen receptor. We investigated effects of 3alpha-diol (1 mg/kg, SC) and/or an androgen receptor blocker (flutamide 10 mg, SC), 1 hour prior to administration of pentylenetetrazol (85 mg/kg, IP). Juvenile male rats administered 3alpha-diol had less seizure activity than those administered vehicle. Flutamide had no effects. T is aromatized to 17beta-estradiol (E(2)), which, like 3alpha-diol, acts at estrogen receptors (ERs). Selective estrogen receptor modulators that favor ERalpha (propyl pyrazole triol, 17alpha-E(2)) or ERbeta (diarylpropionitrile, coumestrol, 3alpha-diol), or both (17beta-E(2)), were administered (0.1 mg/kg, SC) to juvenile male rats 1 hour before pentylenetetrazol. Estrogens with activity at ERbeta, but not those selective for ERalpha, produced antiseizure effects. Actions at ERbeta may underlie some antiseizure effects of T's metabolites.

Seizure susceptibility and the brain regional sensitivity to oxidative stress in male and female rats in the lithium-pilocarpine model of temporal lobe epilepsy

Several studies have shown the existence of sex differences in the sensitivity to various convulsants in animals and to the development of some epilepsy types in humans. The purpose of this study was to investigate whether there are sex differences in seizure susceptibility and sensitivity of different brain regions to oxidative stress in rats with status epilepticus (SE) induced by lithium-pilocarpine administration, that provides a common experimental model of temporal lobe epilepsy (TLE) in humans. Latencies to isolated full limbic seizures or SE onset as well as the number of the animals presenting full limbic seizures, SE or full limbic seizures that progressed to SE were recorded for 2 h after pilocarpine administration. Number of animals which survived 24 h after SE onset was also monitored. Levels of lipid peroxidation as well as the superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities in the piriform and entorhinal cortices, temporal neocortex, thalamus, and hippocampus in rats of both sexes, at 24 h after SE onset were determined. Results of our study showed that males developed full limbic seizures and SE more rapidly and in greater number than females. Levels of lipid peroxidation in all brain regions examined, the SOD activities in the piriform and entorhinal cortices, and temporal neocortex as well as the GSH-Px activities in the piriform and entorhinal cortices, and thalamus were significantly higher in rats with SE in comparison to the values of mentioned biochemical parameters in rats of the control groups. Lipid peroxidation level in the temporal neocortex as well as the GSH-Px activity in the hippocampus in male rats were significantly higher in comparison to the values registered in females. With the exception of the thalamus, where SOD activity in male rats with SE was significantly higher in relation to the respective control group and also to females with SE, sex differences in the response of other brain regions investigated to oxidative stress were not obtained, at 24 h after SE.

Hormonal influences on seizures: basic neurobiology

There are sex differences and effects of steroid hormones, such as androgens, estrogens, and progestogens, that influence seizures. Androgens exert early organizational and later activational effects that can amplify sex/gender differences in the expression of some seizure disorders. Female-typical sex steroids, such as estrogen (E2) and progestins, can exert acute activational effects to reduce convulsive seizures and these effects are mediated in part by the actions of steroids in the hippocampus. Some of these anticonvulsive effects of sex steroids are related to their formation of ligands which have agonist-like actions at gamma-aminobutyric acid (GABAA) receptors or antagonist actions at glutamatergic receptors. Differences in stress, developmental phase, reproductive status, endocrine status, and treatments, such as anti-epileptic drugs (AEDs), may alter levels of these ligands and/or the function of target sites, which may mitigate differences in sensitivity to, and/or tolerance of, steroids among some individuals. The evidence implicating sex steroids in differences associated with hormonal, reproductive, developmental, stress, seizure type, and/or therapeutics are discussed.

The pilocarpine model of temporal lobe epilepsy

Understanding the pathophysiogenesis of temporal lobe epilepsy (TLE) largely rests on the use of models of status epilepticus (SE), as in the case of the pilocarpine model. The main features of TLE are: (i) epileptic foci in the limbic system; (ii) an “initial precipitating injury”; (iii) the so-called “latent period”; and (iv) the presence of hippocampal sclerosis leading to reorganization of neuronal networks. Many of these characteristics can be reproduced in rodents by systemic injection of pilocarpine; in this animal model, SE is followed by a latent period and later by the appearance of spontaneous recurrent seizures (SRSs). These processes are, however, influenced by experimental conditions such as rodent species, strain, gender, age, doses and routes of pilocarpine administration, as well as combinations with other drugs administered before and/or after SE. In the attempt to limit these sources of variability, we evaluated the methodological procedures used by several investigators in the pilocarpine model; in particular, we have focused on the behavioural, electrophysiological and histopathological findings obtained with different protocols. We addressed the various experimental approaches published to date, by comparing mortality rates, onset of SRSs, neuronal damage, and network reorganization. Based on the evidence reviewed here, we propose that the pilocarpine model can be a valuable tool to investigate the mechanisms involved in TLE, and even more so when standardized to reduce mortality at the time of pilocarpine injection, differences in latent period duration, variability in the lesion extent, and SRS frequency.

Effect of age on kainate-induced seizure severity and cell death

While the onset and extent of epilepsy increases in the aged population, the reasons for this increased incidence remain unexplored. The present study used two inbred strains of mice (C57BL/6J and FVB/NJ) to address the genetic control of age-dependent neurodegeneration by building upon previous experiments that have identified phenotypic differences in susceptibility to hippocampal seizure-induced cell death. We determined if seizure induction and seizure-induced cell death are affected differentially in young adult, mature, and aged male C57BL/6J and FVB/NJ mice administered the excitotoxin, kainic acid. Dose response testing was performed in three to four groups of male mice from each strain. Following kainate injections, mice were scored for seizure activity and brains from mice in each age group were processed for light microscopic histopathologic evaluation 7 days following kainate administration to evaluate the severity of seizure-induced brain damage. Irrespective of the dose of kainate administered or the age group examined, resistant strains of mice (C57BL/6J) continued to be resistant to seizure-induced cell death. In contrast, aged animals of the FVB/NJ strain were more vulnerable to the induction of behavioral seizures and associated neuropathology after systemic injection of kainic acid than young or middle-aged mice. Results from these studies suggest that the age-related increased susceptibility to the neurotoxic effects of seizure induction and seizure-induced injury is regulated in a strain-dependent manner, similar to previous observations in young adult mice.

The impact of gonadectomy and adrenalectomy on acute withdrawal severity in male and female C57BL/6J and DBA/2J mice following a single high dose of ethanol

BACKGROUND

Steroid hormones can influence neuronal excitability and subsequent seizure susceptibility through genomic and nongenomic mechanisms. For example, there are proconvulsant steroids such as estradiol and corticosterone and anticonvulsant steroids such as testosterone, progesterone, and their GABAergic metabolites. Recent findings indicated that a single, acute administration of ethanol increased levels of GABAergic steroids and that the source of this increase was peripheral organs such as the adrenals and gonads. Thus, the purpose of the present study was to determine the impact of removal of the adrenals and/or gonads on withdrawal severity following a single high dose of ethanol in 2 genotypes that differ in ethanol withdrawal severity.

METHOD

Male and female C57BL/6J (B6) and DBA/2J (D2) mice were either left intact (SHAM), adrenalectomized (ADX), gonadectomized (GDX), or underwent ADX/GDX surgery. Seven days following surgery, baseline handling-induced convulsions (HICs) were measured prior to administration of a 4 g/kg dose of ethanol. HICs were assessed following the ethanol injection, then hourly for 12 hours and at 24 hours. A separate group of mice were used to measure the impact of surgical status on ethanol metabolism at 30, 60, 120, and 240 minutes after a single 4 g/kg dose of ethanol.

RESULTS

ADX and ADX/GDX treatments in male B6 and D2 mice increased ethanol withdrawal severity following a single dose of ethanol, measured by area under the withdrawal curve and peak HIC scores. Acute ethanol withdrawal also was increased in female D2 mice that had undergone ADX/GDX. In contrast, surgical status did not alter ethanol withdrawal severity in female B6 mice. Surgical status had only minor effects on ethanol metabolism.

CONCLUSIONS

Removal of peripherally derived steroids with anticonvulsant properties significantly increased HIC scores during acute ethanol withdrawal following a single dose of ethanol in male and female D2 mice and in male B6 mice. These increases were not due to changes in ethanol metabolism.

The acceleration of amygdala kindling epileptogenesis by chronic low-dose corticosterone involves both mineralocorticoid and glucocorticoid receptors

We have previously demonstrated that low-dose corticosterone (CS) administration, used as a model of the effect of chronic stress, accelerates epileptogenesis in the electrical amygdala kindling rat model of temporal lobe epilepsy (TLE). This current study examined the relative contributions to this effect of mineralocorticoid (MR) and glucocorticoid (GR) subtypes of glucocorticoid receptors. Female non-epileptic wistar rats 10-13 weeks of age were implanted with a bipolar electrode into the left amygdala. Five treatment groups were subjected to rapid amygdala kindling: water-control (n=9), CS treated (6 mg/100 ml added to drinking water; n=9), CS+spironolactone (MR antagonist, 50 mg/kg sc; n=9), CS+mifepristone (GR antagonist, 25 mg/kg sc; n=9), and CS+both antagonists (n=7). Rats were injected with vehicle or the relevant antagonist twice daily for the entire kindling period. Experimental groups differed significantly in the number of stimulations required to reach the 'fully kindled state' (Racine, 1972) ANOVA, F(4,38)=2.73, p=0.04). Amygdala kindling was accelerated in the CS-treated group compared with water controls (mean stimulations for full kindling: 45.2 vs. 86.5, p<0.01). This acceleration was inhibited by both the MR and GR antagonist treatments (mean stimulations: 69.6 and 70.4, p=0.04 and 0.04 vs. CS group, respectively), with the kindling rates in these groups not significantly different from water-treated subjects (p=0.26 and 0.29, respectively). The kindling rates in the MR and GR antagonist treatment groups did not significantly differ from each other (p=0.93), nor from the combined treatment group (mean stimulations: 62.8, p=0.59 and 0.54, respectively). This study demonstrates that activation of both high-affinity (MR) and low-affinity (GR) glucocorticoid receptors are involved in mediating CS-induced acceleration of amygdala kindling epileptogenesis.

Peri-ictal vegetative symptoms in temporal lobe epilepsy

We investigated peri-ictal vegetative symptoms (PIVS) in 141 patients with adult temporal lobe epilepsy (TLE) and assessed frequency, gender effect, and lateralizing value of peri-ictal autonomic signs. We recorded abdominal auras in 62%, goosebumps in 3%, hypersalivation in 12%, spitting in 1%, cold shivering in 3%, urinary urge in 3%, water drinking in 7%, postictal nose wiping (PNW) in 44%, and postictal coughing in 16%. At least one vegetative sign appeared in 86% of the patients. The presence of PIVS did not have a significant lateralizing value. PNW occurred in 52% of women and in 33% of men, whereas any PIVS was present in 93% of women and 77% of men. In summary, contradictory to previous studies, the presence of PIVS has no lateralizing value, which may be linked to a low frequency of occurrence of PIVS. PIVS, especially PNW, occurred more frequently in women, supporting the gender differences in epilepsy.

Mass spectrometric assay and physiological-pharmacological activity of androgenic neurosteroids

Steroid hormones play a key role in the pathophysiology of several brain disorders. Testosterone modulates neuronal excitability, but the underlying mechanisms are obscure. There is emerging evidence that testosterone-derived "androgenic neurosteroids", 3alpha-androstanediol and 17beta-estradiol, mediate the testosterone effects on neural excitability and seizure susceptibility. Testosterone undergoes metabolism to neurosteroids via two distinct pathways. Aromatization of the A-ring converts testosterone into 17beta-estradiol. Reduction of testosterone by 5alpha-reductase generates 5alpha-dihydrotestosterone, which is then converted to 3alpha-androstanediol, a powerful GABA(A) receptor-modulating neurosteroid with anticonvulsant properties. Although the 3alpha-androstanediol is an emerging neurosteroid in the brain, there is no specific and sensitive assay for determination of 3alpha-androstanediol in biological samples. This article describes the development and validation of mass spectrometric assay of 3alpha-androstanediol, and the molecular mechanisms underlying the testosterone modulation of seizure susceptibility. A liquid chromatography-tandem mass spectrometry assay to measure 3alpha-androstanediol is validated with excellent linearity, specificity, sensitivity, and reproducibility. Testosterone modulation of seizure susceptibility is demonstrated to occur through its conversion to neurosteroids with "anticonvulsant" and "proconvulsant" actions and hence the net effect of testosterone on neural excitability and seizure activity depends on the levels of distinct testosterone metabolites. The proconvulsant effect of testosterone is associated with increases in plasma 17beta-estradiol concentrations. The 5alpha-reduced metabolites of testosterone, 5alpha-dihydrotestosterone and 3alpha-androstanediol, had powerful anticonvulsant activity. Overall, the testosterone-derived neurosteroids 3alpha-androstanediol and 17beta-estradiol could contribute to the net cellular actions of testosterone in the brain. Because 3alpha-androstanediol is a potent positive allosteric modulator of GABA(A) receptors, it could serve as an endogenous neuromodulator of neuronal excitability in men. The 3alpha-androstanediol assay is an important tool in this area because of the growing interest in the potential to use adjuvant aromatase inhibitor therapy to improve treatment of epilepsy.

Hippocampal Seizure Resistance and Reduced Neuronal Excitotoxicity in Mice Lacking the Cav2.3 E/R-Type Voltage-Gated Calcium Channel

Voltage-gated calcium channels are key components in the etiology and pathogenesis of epilepsies. Former studies mainly focused on P/Q-type Cav2.1 and T-type Cav3.2 Ca2+ channels involved in absence epileptogenesis, but recent findings also point to an intriguing role of the Cav2.3 E/R-type Ca2+ channel in ictogenesis and seizure propagation. Based on the observation that Cav2.3 is thought to induce plateau potentials in CA1 pyramidal cells, which can trigger epileptiform activity, our recent investigation revealed reduced PTZ-seizure susceptibility and altered seizure architecture in Cav2.3−/− mice compared with controls. In the present study we tested hippocampal seizure susceptibility in Cav2.3-deficient mice using surface and deep intrahippocampal telemetric EEG recordings as well as phenotypic seizure video analysis. Administration of kainic acid (30 mg/kg ip) revealed clear alteration in behavioral seizure architecture and dramatic resistance to limbic seizures in Cav2.3−/− mice compared with controls, whereas no difference in hippocampal EEG seizure activity between both genotypes could be detected at this suprathreshold dosage. The same tendency was observed for NMDA seizure susceptibility (150 mg/kg ip) approaching the level of significance. In addition, histochemical analysis within the hippocampus revealed that excitotoxic effects after kainic acid administration are absent in Cav2.3−/− mice, whereas Cav2.3+/+ animals exhibited clear and typical signs of excitotoxic cell death. These findings clearly indicate that the Cav2.3 voltage-gated calcium channel plays a crucial role in both hippocampal ictogenesis and seizure generalization and is of central importance in neuronal degeneration after excitotoxic events.

Development of a rat pilocarpine model of seizure/status epilepticus that mimics chemical warfare nerve agent exposure

We developed a rat pilocarpine seizure/status epilepticus (SE) model, which closely resembles 1.6-2.0 x LD50 soman exposure, to analyse the molecular mechanism of neuronal damage and to screen effective neuroprotectants against cholinergic agonist and chemical warfare nerve agent (CWNA) exposure. Rats implanted with radiotelemetry probes capable of recording electroencephalogram (EEG), electrocardiogram (ECG), temperature, and physical activity were treated with lithium chloride (5 mEq/kg, im), followed 24 h later by (ip) doses of pilocarpine hydrochloride. Based on radiotelemetry analysis, a dose of 240 mg/kg (ip) pilocarpine generated seizure/SE analogous to 1.6-2.0 x LD50 of soman. The model was refined by reducing the peripheral convulsions without affecting the central nervous system (CNS) by administering methylscopolamine bromide (1 mg/kg, ip), an anti-cholinergic that does not cross the blood-brain barrier. However, when methylscopolamine bromide was administered, a higher dose of pilocarpine (320 mg/kg, ip) was required to generate the equivalent seizure/SE. Histopathology data indicated that pilocarpine induces significant damage to the hippocampal region of the brain, with similar neuropathology to that of 1.6-2.0 x LD50 soman exposure. There was a reduction in body temperature after the administration of pilocarpine, as observed in organophosphate (OP) nerve agents exposure. The heart-rate of pilocarpine-treated animals increased compared to the normal range. The pilocarpine seizure/SE model was also reproducible in the absence of lithium chloride. These results support that pilocarpine seizure/SE model is useful in studying the molecular mechanisms of neuropathology and screening neuroprotectants following cholinergic agonist and CWNA exposure.

Repeated brief epileptic seizures by pentylenetetrazole cause neurodegeneration and promote neurogenesis in discrete brain regions of freely moving adult rats

Recurrent epileptic seizures are known to provoke various forms of cellular reorganization in the brains of humans and experimental animals. However, little is known about the mechanism of neuronal cell death resulting from epileptic seizures elicited by GABA antagonists. In the present study, we explored the effect on the central nervous systems of freely moving adult rats, of repeated brief epileptic seizures induced by systemic injection of pentylenetetrazole, a GABA-A receptor antagonist. Starting with minor convulsions, repeated epileptic seizures elicited a progressive increase in seizure severity, culminating in the fully kindled state. Histological examination showed that the epileptic seizures caused overt neuronal cell death in the limbic system, including the hippocampus and amygdala, and its adjoining cortex. During the recurrent epileptic seizures, neurogenesis occurred in the subgranular zone of the hippocampus, the subventricular zone of the lateral ventricle, and the amygdala. This type of pentylenetetrazole-induced neurogenesis was seen at an early stage of epileptogenesis in some regions in which massive cell loss was not evident. This suggests that neurogenesis is not a secondary consequence of neuronal cell death, but rather an independent effect of recurrent epileptic seizures.

Leukemia inhibitory factor is a key regulator of astrocytic, microglial and neuronal responses in a low-dose pilocarpine injury model

Insult to the central nervous system (CNS) induces many changes, including altered neurotransmitter expression, activation of astrocytes and microglia, neurogenesis and cell death. Cytokines and growth factors are candidates to be involved in astrocyte and microglial activation, and the up-regulation of glial fibrillary acidic protein (GFAP) is associated with brain damage. One of these candidates is leukemia inhibitory factor (LIF), a pro-inflammatory cytokine that is induced in astrocytes by brain damage or seizure. LIF also regulates expression of both neuropeptide Y (NPY) and galanin following peripheral nerve injury. To test the hypothesis that LIF regulates astrocyte, microglial and neuropeptide responses to a mild insult, we used a low-dose pilocarpine model to induce a brief seizure in LIF knock-out (KO) mice. Compared to wild type mice, the LIF KO mouse displays reduced astrocyte and microglial activation in the hippocampus. In addition, LIF KO mice display dramatically altered NPY, but not galanin, expression in response to injury. Thus, LIF is required for normal glial responses to brain damage, and, as in the periphery, LIF regulates NPY expression in the CNS.

Gender differences in febrile seizure-induced proliferation and survival in the rat dentate gyrus

PURPOSE

Febrile seizures are fever-associated early-life seizures that are thought play a role in the development of epilepsy. Seizure-induced proliferation of dentate granule cells has been demonstrated in several adult animal models and is thought to be an integral part of epileptogenesis. The aim of the present study was to investigate proliferation and survival of dentate gyrus (DG) cells born after early-life hyperthermia (HT)-induced seizures in male and female rats.

METHODS

At postnatal day (PN) 10, male and female rats were exposed to heated air to induce seizures. Littermates were used as normothermia controls. Convulsive behavior was observed by two researchers. From PN11 to PN16, rats were injected with bromodeoxyuridine (BrdU) to label dividing cells. The number of BrdU-immunoreactive cells in the DG was counted at PN17 and PN66.

RESULTS

At PN17, male as well as female HT rats had the same amount of BrdU-positive cells compared with controls. At PN66, significantly more BrdU-positive cells were left in HT females (53%) than in controls (44%, percentage of BrdU-positive cells at PN17), whereas no difference was found between HT males and male controls. The net result of proliferation and survival at PN66 was that female HT rats had the same number of BrdU-immunoreactive cells as controls, whereas male HT rats had 25% more BrdU-immunoreactive cells than did controls (p < 0.05).

CONCLUSIONS

Early-life seizures cause a sexually dimorphic cytogenic response that results in an increased population of newborn DG cells in young adult males, while leaving that of young adult females unaltered.

Aromatase inhibitors as add-on treatment for men with epilepsy

Manipulation of neurosteroids to treat epilepsy has been an area of active research. The effect of testosterone on brain excitability and seizure threshold has been mixed; the estradiol metabolite of testosterone increases brain excitability, while the reduced metabolite of testosterone, 3alpha-androstanediol, decreases brain excitability, likely through an action at the gamma-amino butyric acid A receptor. Therefore, the metabolites of testosterone produce opposite effects on brain excitability in seizure models. Aromatase is the enzyme for the conversion of testosterone to 17beta-estradiol. Aromatase inhibitors could decrease brain excitability by decreasing local estradiol levels and therefore, could be beneficial for the treatment of epilepsy. Aromatase inhibitors are US Food and Drug Administration-approved and have a long history of safe use in menopausal women with breast cancer. This review presents the results of using anastrazole in an open-label, add-on manner in a small group of men with epilepsy in order to improve seizures. The results suggested some effect on reduction of seizures and no side effects. Testosterone levels did increase, but not to above the normal range. Letrozole used in a single case was also beneficial for seizures. It was concluded that aromatase inhibitors may be a useful adjunct to the treatment of epilepsy, but habituation to the treatment may be limiting. Many men with epilepsy have low testosterone, and aromatase inhibition may be helpful in restoring levels to normal. Modulation of reproductive hormones by aromatase inhibition as well as enhancement of the 3alpha-androstanediol pathway may be an avenue of epilepsy treatment that would not produce sedative side effects, which is often a limiting factor with standard antiseizure medications. A further interesting result is that elevated follicle stimulating hormone and luteal stimulating hormone levels were associated with seizure reduction, suggesting that they may be a biomarker for a beneficial effect of aromatase inhibition on brain excitability.

Seizure Frequency and Cortisol and Dehydroepiandrosterone Sulfate (DHEAS) Levels in Women with Epilepsy Receiving Antiepileptic Drug Treatment

PURPOSE

Hormonal changes occur in epilepsy because of seizures themselves and of antiepileptic drug (AED) effects on steroid production, binding, and metabolism. Conversely, steroids may influence neuron activity and excitability by acting as neuroactive steroids. This cross-sectional observational study aimed to evaluating cortisol and dehydroepiandrosterone sulfate (DHEAS) levels in female epilepsy patients with different disease severity, as assessed by a seizure frequency score (SFS).

METHODS

Morning serum levels of cortisol and DHEAS were assayed in 113 consecutive women, aged 16 to 47 years, with varied epilepsy syndromes, receiving mono- or polytherapy with enzyme-inducing and/or noninducing antiepileptic drugs (AEDs). Hormonal data were correlated with clinical parameters (age, body mass index, epilepsy syndrome, disease onset and duration, SFS, AED therapy, and AED serum levels) and compared with those of 30 age-matched healthy women.

RESULTS

In epilepsy patients, cortisol levels and cortisol-to-DHEAS ratios (C/Dr) were significantly higher, whereas DHEAS levels were significantly lower than those in controls. Patients with more frequent seizures showed higher cortisol and C/Dr values and lower DHEAS levels than did those with rarer or absent seizures during the previous 6 months. SFS mainly explained the increase of cortisol levels and C/Dr in patients with more active disease. Changes in DHEAS levels correlated with SFS and epilepsy syndrome, as well as with AED treatments and ages.

CONCLUSIONS

Women with more frequent seizures had alterations of their adrenal steroids characterized by an increase of cortisol and a decrease of DHEAS levels. Such hormonal changes might be relevant in seizure control and in patient health.

GABA receptors as broadcasters of sexually differentiating signals in the brain

Epileptic seizures are more common in males than in females. One of the areas that has recently been implicated in the higher susceptibility of males to seizures is the substantia nigra reticulata (SNR). Several studies support the existence of phenotypic differences between male and female infantile SNR neurons, and particularly in several aspects of the GABAergic system, including its ability to control seizures. We have recently found that at postnatal day 14-17 (PN14-17) rats, which are equivalent to infants, activation of GABA(A) receptors has different physiological effects in male and female SNR neurons. This is likely due to the differences in the expression of the neuronal-specific potassium-chloride co-transporter KCC2, which regulates the intracellular chloride concentration. In male PN14-17 SNR neurons, GABA(A)-receptor activation with muscimol causes depolarization and increments in intracellular calcium concentration and the expression of calcium regulated genes, such as KCC2. Blockade of L-type voltage-sensitive calcium channels (L-VSCC) by nifedipine decreases KCC2 mRNA expression. However, in PN14-17 females, muscimol hyperpolarizes the SNR neurons, does not increase intracellular calcium, and decreases KCC2 mRNA expression. In PN15 females, nifedipine has no effect on KCC2 mRNA expression in the SNR. This sexually dimorphic function of GABA(A) receptors also creates divergent patterns of estradiol signaling. In male PN15 rats, estradiol decreases KCC2 mRNA expression in SNR neurons. Pretreatment with the GABA(A)-receptor antagonist bicuculline or with nifedipine, prevents the appearance of estradiol-mediated downregulation of KCC2 mRNA expression. In contrast, in PN15 females, estradiol does not influence KCC2 expression. These findings show that, in infantile rats, drugs or conditions that modulate the activity of GABA(A) receptors or L-VSCCs have different effects on the differentiation of the SNR. As a result, they have the potency of causing long-term changes in the function of the SNR in the control of seizures, movement, and the susceptibility to and course of epilepsy and movement disorders.

Sex and estrus cycle differences in the modulatory effects of morphine on seizure susceptibility in mice

PURPOSE

To evaluate the effects of sex and estrus cycle on biphasic anticonvulsant and proconvulsant modulation of seizure threshold by morphine.

METHODS

The threshold for the clonic seizures (CST) induced by acute intravenous administration of gamma-aminobutyric acid (GABA)-antagonist pentylenetetrazole (PTZ) was assessed in male and female mice. Estrus cycle was assessed by vaginal smears. The effect of removing circulating sex hormones was assessed by gonadectomy.

RESULTS

At baseline, diestrus females had a higher CST compared with males and estrus females. Morphine at lower doses (0.5-3 mg/kg) had a significant anticonvulsant effect in males and estrus females compared with that in vehicle-treated controls, whereas female mice in diestrus phase showed a relative subsensitivity to this effect. Morphine at higher doses (30 and 60 mg/kg) significantly decreased CST in males and diestrus females, with less relative effect in estrus mice. In both phases, morphine exerted stronger effects in males compared with females. Ovariectomy brought the baseline CST to the male level and resulted in significant expression of both phases of morphine effect but did not abolish the sex difference in responsiveness to morphine.

CONCLUSIONS

The biphasic modulation of seizure threshold is subject to both constitutive sex differences in sensitivity to morphine and hormonal fluctuations during the estrus cycle.

Aromatase inhibition, testosterone, and seizures

The effect of testosterone on brain excitability is unclear. The excitatory aspect of testosterone's action in the brain may be due to its conversion to estrogen via aromatase. We report herein a 61-year-old man with temporal lobe epilepsy and sexual dysfunction due to low testosterone levels. Use of an aromatase inhibitor, letrozole, normalized his testosterone level and improved his sexual functioning. Letrozole, in addition to standard antiseizure medication, was also associated with improved seizure control. This was sustained and, further, was associated with seizure exacerbation after withdrawing letrozole, and subsequent seizure improvement after restarting it. During the course of treatment, his serum testosterone level increased, sex hormone-binding globulin decreased (SHBG), luteinizing hormone (LH), and follicle-stimulating hormone (FSH) levels increased, while serum estradiol levels remained undetectable. Letrozole may, therefore, have produced a central alteration in the testosterone/estrogen ratio, thereby impairing estrogen-mediated feedback control of the pituitary, resulting in the observed increase in circulating LH and FSH levels. This experience suggests that aromatase inhibitors should be further investigated as a beneficial treatment modality for male patients with epilepsy.

Testosterone modulation of seizure susceptibility is mediated by neurosteroids 3α-androstanediol and 17β-estradiol

Testosterone modulates seizure susceptibility in animals and humans, but the underlying mechanisms are obscure. Here, testosterone modulation of seizure susceptibility is hypothesized to occur through its conversion to neurosteroids with "anticonvulsant" and "proconvulsant" actions, and hence the net effect of testosterone on neural excitability and seizure activity depends on the levels of distinct testosterone metabolites. Testosterone undergoes metabolism to neurosteroids via two distinct pathways. Aromatization of the A-ring converts testosterone into 17beta-estradiol. Reduction of testosterone by 5alpha-reductase generates 5alpha-dihydrotestosterone (DHT), which is then converted to 3alpha-androstanediol (3alpha-Diol), a powerful GABA(A) receptor-modulating neurosteroid with anticonvulsant properties. Systemic doses of testosterone decreased seizure threshold in rats and increased the incidence and severity of pentylenetetrazol (PTZ)-induced seizures in mice. These proconvulsant effects of testosterone were associated with increases in plasma 17beta-estradiol and 3alpha-Diol concentrations. Pretreatment with letrozole, an aromatase inhibitor that blocks the conversion of testosterone to 17beta-estradiol, significantly inhibited testosterone-induced exacerbation of seizures. The 5alpha-reductase inhibitor finasteride significantly reduced 3alpha-Diol levels and also blocked letrozole's ability to inhibit the proconvulsant effects of testosterone. The 5alpha-reduced metabolites of testosterone, DHT and 3alpha-Diol, had powerful anticonvulsant activity in the PTZ test. Letrozole or finasteride had no effect on seizure protection by DHT and 3alpha-Diol, but indomethacin partially reversed DHT actions. 3alpha-Diol but not 3beta-androstanediol, a GABA(A) receptor-inactive stereoisomer, suppressed 4-aminopyridine-induced spontaneous epileptiform bursting in rat hippocampal slices. Thus, testosterone-derived neurosteroids 3alpha-Diol and 17beta-estradiol could contribute to the net cellular actions of testosterone on neural excitability and seizure susceptibility.

Gender-specific Differences of Hypometabolism in mTLE: Implication for Cognitive Impairments

PURPOSE

To determine gender differences of hypometabolism and their implications for cognitive impairment in patients with medically refractory mesial temporal lobe epilepsy (mTLE).

METHODS

Regional cerebral glucose metabolism (rCMRGlu) was studied in 42 patients (21 male, 21 female) with either left- or right-sided mTLE (22 left, 20 right) and in 12 gender- and age-matched healthy controls during resting wakefulness and in 12 sex- and age-matched healthy controls. Clinical characteristics were balanced across the patient subgroups. All patients were subjected to neuropsychological assessment: 41 patients had histologic changes of definite or probable hippocampal sclerosis.

RESULTS

Data analysis based on pixel-by-pixel comparisons and on a laterality index of regions of interest (ROIs) showed significant depressions of the mean rCMRGlu extending beyond the mesiotemporal region and temporolateral cortex to extratemporal regions including the frontoorbital and insular cortex in mTLE patients. Extramesiotemporal hypometabolism prevailed in the male patients. Metabolic asymmetry in temporal and frontal regions was related to performance in the Trail-Making Test and WAIS-R subitems.

CONCLUSIONS

Our data showed a gender-specific predominance of extramesiotemporal hypometabolism in male patients with mTLE related to abnormalities of temporal and frontal lobe functions.

Exercise increases the vulnerability of rat hippocampal neurons to kainate lesion

Available evidence suggests that regular, moderate-intensity exercise has beneficial effects on neural health, perhaps including neuroprotection. To evaluate this idea further, we compared the severity of kainate-induced neuronal loss in exercised versus sedentary female rats. Stereological estimations of neuron number revealed that rats in the exercise condition exhibited significantly greater neuron loss in hippocampal region CA2/3, suggesting that high levels of physical activity may increase neuronal vulnerability to excitotoxicity.

Assessment of the seizure susceptibility of Wistar Audiogenic rat to electroshock, pentyleneterazole and pilocarpine

This work evaluates the seizure susceptibility of nai;ve female Wistar Audiogenic rats (WARs), a genetic model of reflex epilepsy in which seizures are induced by high-intensity sound stimulation (120 dB SPL), to other pro-convulsive stimuli: transauricular electroshock (ES), pentylenetetrazole (PTZ) and pilocarpine (PILO). Normal Wistar rats from the main breeding stock of the Institute of Biological Sciences, UFMG were taken as controls. Electroshock seizures were induced through a pair of ear-clip electrodes (10 mA, at a frequency of 60 Hz, applied for 1 s). In order to test WAR susceptibility to chemically induced seizures, animals were treated either with PTZ (37.5 mg/kg i.p.) or PILO (200, 270 and 300 mg/kg i.p.). Seizure severity was evaluated by appropriate behavioral severity index scales (SI) specific to each epilepsy model and tested for statistical significance using the non-parametric Mann-Whitney Rank Sum test. Results show a significantly greater susceptibility of WARs for ES (SI(WAR)=3+/-3/3, SI(Wistar)=1+/-1/1; median+/-interquartile range 25%/75%, P<0.01) and PTZ (SI(WAR)=4+/-4/4, SI(Wistar)=1+/-1/4; median+/-interquartile range 25%/75%, P<0.02), as indicated by significantly higher SI scores and shorter latencies for seizure onset (T(WAR)=71+/-7 s, T(Wistar)=94+/-8 s; P<0.05 Student t-test, mean+/-S.E.M.). Although PILO also caused higher SI scores in WARs (WAR(200 mg)=1+/-1/1, Wistar(200 mg)=1+/-1/1; WAR(270 mg)=1.5+/-1/2, Wistar(270 mg)=1+/-1/1.25; WAR(300 mg)=9+/-1/9, Wistar(300 mg)=4+/-1.5/7.5; median+/-interquartile range 25%/75%), statistically significant differences were not observed. In conclusion, our results show that WARs have an inherited broader predisposition for seizures.