Hormonal regulation of atypical absence seizures

Atypical absence seizures and gene variants: A gene-based review of etiology, electro-clinical features, and associated epilepsy syndrome

Atypical absence seizures are generalized non-convulsive seizures that often occur in children with cognitive impairment. They are common in refractory epilepsy and have been recognized as one of the hallmarks of developmental epileptic encephalopathies. Notably, pathogenic variants associated with AAS, such as GABRG2, GABRG3, SLC6A1, CACNB4, SCN8A, and SYNGAP1, are also linked to developmental epileptic encephalopathies. Atypical absences differ from typical absences in that they are frequently drug-resistant and the prognosis is dependent on the etiology or related epileptic syndromes. To improve clinicians' understanding of atypical absences and provide novel perspectives for clinical treatment, we have reviewed the electro-clinical characteristics, etiologies, treatment, and prognosis of atypical absences, with a focus on the etiology of advancements in gene variants, shedding light on potential avenues for improved clinical management.

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.

The Natural History of Epilepsy in 163 Untreated Patients: Looking for "Oligoepilepsy"

The clinical evolution of untreated epilepsy has been rarely studied in developed countries, and the existence of a distinct syndrome characterized by rarely repeated seizures (oligoepilepsy) is debated. The aim of this study is to assess the natural history of 163 untreated patients with epilepsy in order to evaluate whether oligoepilepsy retains specific features. We retrospectively evaluated 7344 patients with ≥2 unprovoked seizures. Inclusion criteria: sufficient anamnestic/EEG data, disease duration ≥10 years, follow-up ≥3 years. Exclusion criteria: psychogenic seizures, natural history of disease <5 years. The 163 included subjects were divided into 2 groups according to seizure frequency: oligoepilepsy (≤1/year; 47 subjects) and controls (>1/year; 116 subjects). We also evaluated seizure frequency during the natural history. There were no differences between groups regarding duration of natural history, family history of epilepsy/febrile seizures, interictal EEG. Subjects with oligoepilepsy differed from controls in terms of sex (females 38% vs. 58%, p = 0.03) and drug resistance (6% vs 28%; p = 0.003). Juvenile myoclonic epilepsy was more frequent in controls (9.5% vs 0%, p = 0.04). Patients with oligoepilepsy, differently from controls, had stable seizure frequency. Oligoepilepsy represents a favourable evolution of different epileptic syndromes and keeps a stable seizure frequency over time.

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.

Dehydroepiandrosterone's antiepileptic action in FeCl3-induced epileptogenesis involves upregulation of glutamate transporters

Dehydroepiandrosterone (DHEA), a neuroactive androgen steroid, has antiepileptic action in iron-induced experimental epilepsy (which models post-traumatic clinical epilepsy). In iron-induced epilepsy increased extracellular glutamate resulting from its reduced glial uptake due to the down-regulation (decreased expression) of transporters (glial and or neuronal) is active during epileptogenesis. The present study was aimed at determining whether the mechanism of antiepileptic action of DHEA involved upregulation (increased expression) of glutamate transporters. Iron-induced epileptogenesis was performed in rats by FeCl3 injection into the cerebral cortex. DHEA was administered intraperitoneally to the iron-induced epileptic rats for 7, 14 and 21 days. Levels of glutamate transporters mRNAs expression were measured using quantitative PCR in the hippocampus during the chronic phase of iron-induced epileptogenesis. There were significant reductions in the glutamate transporter mRNAs in epileptogenesis. DHEA treatment resulted in a significant elevation of glutamate transporters: GLT-1, GLAST and EACC-1 mRNA indicating that the DHEA treatment induced upregulation of these transporters. The results are of significance in respect of the mechanism of the antiepileptic action of neurosteroids and the glutamate transporters as therapeutic targets in glutamatergic epileptogenesis.

Neurochemical and behavioral features in genetic absence epilepsy and in acutely induced absence seizures

The absence epilepsy typical electroencephalographic pattern of sharp spikes and slow waves (SWDs) is considered to be due to an interaction of an initiation site in the cortex and a resonant circuit in the thalamus. The hyperpolarization-activated cyclic nucleotide-gated cationic I h pacemaker channels (HCN) play an important role in the enhanced cortical excitability. The role of thalamic HCN in SWD occurrence is less clear. Absence epilepsy in the WAG/Rij strain is accompanied by deficiency of the activity of dopaminergic system, which weakens the formation of an emotional positive state, causes depression-like symptoms, and counteracts learning and memory processes. It also enhances GABAA receptor activity in the striatum, globus pallidus, and reticular thalamic nucleus, causing a rise of SWD activity in the cortico-thalamo-cortical networks. One of the reasons for the occurrence of absences is that several genes coding of GABAA receptors are mutated. The question arises: what the role of DA receptors is. Two mechanisms that cause an infringement of the function of DA receptors in this genetic absence epilepsy model are proposed.

Development and persistence of limbic epileptogenesis are impaired in mice lacking progesterone receptors

Progesterone plays a key role in ovarian cycle-related synaptic plasticity and neuronal excitability. Progesterone receptors (PRs), which mediate the cellular actions of progesterone, are expressed in the hippocampus and other limbic regions, but their functional significance remains unknown. Here, we report a novel role of PRs as crucial mediators in the development of epileptogenesis, which is the process whereby a normal brain becomes progressively epileptic because of precipitating factors. The PR knock-out (PR(-/-)) mouse, which lacks both the PR-A and PR-B isoforms, exhibited an increased resistance to epileptogenesis in the hippocampus and amygdala kindling models. Lack of PRs markedly impaired the persistence of seizure expression at 4 weeks after kindling development. We further show that selective inhibition of PRs in the brain by antisense oligos or pharmacological blockade of PRs by RU-486 [11β-[p-(dimethylamino)phenyl]-17β-hydroxy-17-(1-propynyl)estra-4,9-dien-3-one] resulted in a significant decrease in epileptogenesis in wild-type (PR(+/+)) mice. The delayed epileptogenesis in PR knock-out mice was not substantially affected by inhibition of neurosteroid synthesis. Mice lacking PRs show supersensitivity to the antiseizure responses of progesterone. Collectively, these results suggest that PRs in the hippocampus are linked to signaling pathways that control susceptibility to epileptogenesis and possibly persistence of an epileptic-like state. The PR pathway may represent a unique target for preventing or retarding epileptogenesis in females.

Antiepileptic action of exogenous dehydroepiandrosterone in iron-induced epilepsy in rat brain

In the study described here, the antiepileptic effect of dehydroepiandrosterone (DHEA) treatment on iron-induced focal epileptiform activity in the rat brain was investigated. DHEA is a neuroactive corticosteroid hormone synthesized both in the adrenal cortex and in the brain. Its antioxidant properties are well known. As oxidative stress seems to play a major role in epileptogenesis in the iron-induced model of posttraumatic epilepsy, it was of interest to examine whether DHEA would exert antiepileptic activity. DHEA at a dose of 30 mg/kg/day administered intraperitoneally for 7, 14, and 21 days to iron-induced epileptic rats prevented epileptiform electrophysiological activity. Morris water maze and open-field tests on iron-induced epileptic rats revealed that DHEA also prevented behavioral alterations related to epileptiform activity. Thus, DHEA attenuated the cognitive defects produced by epileptic activity. Moreover, alterations in epileptogenesis-related biochemical parameters-lipid peroxidation, protein oxidation and Na(+), K(+)-ATPase (sodium pump) activity--were also countered by DHEA.

EEG recording in rodents, with a focus on epilepsy

This unit describes the materials, methods, and analytical techniques available for the study of electrical activity of neural tissue in rodents in both homeostatic and disease states, with emphasis on epileptogenesis. A table containing a list of suppliers of relevant materials and equipment is also provided.

Cholesterol synthesis inhibitor U18666A and the role of sterol metabolism and trafficking in numerous pathophysiological processes

The multiple actions of U18666A have enabled major discoveries in lipid research and contributed to understanding the pathophysiology of multiple diseases. This review describes these advances and the utility of U18666A as a tool in lipid research. Harry Rudney's recognition that U18666A inhibited oxidosqualene cyclase led him to discover a pathway for formation of polar sterols that he proved to be important regulators of 3-hydroxy-3-methyl-glutaryl coenzyme A reductase. Laura Liscum's recognition that U18666A inhibited the egress of cholesterol from late endosomes and lysosomes led to greatly improved perspective on the major pathways of intracellular cholesterol trafficking. The inhibition of cholesterol trafficking by U18666A mimicked the loss of functional Niemann-Pick type C protein responsible for NPC disease and thus provided a model for this disorder. U18666A subsequently became a tool for assessing the importance of molecular trafficking through the lysosomal pathway in other conditions such as atherosclerosis, Alzheimer's disease, and prion infections. U18666A also provided animal models for two important disorders: petite mal (absence) epilepsy and cataracts. This was the first chronic model of absence epilepsy. U18666A is also being used to address the role of oxidative stress in apoptosis. How can one molecule have so many effects? Perhaps because of its structure as an amphipathic cationic amine it can interact and inhibit diverse proteins. Restricting the availability of cholesterol for membrane formation through inhibition of cholesterol synthesis and intracellular trafficking could also be a mechanism for broadly affecting many processes. Another possibility is that through intercalation into membrane U18666A can alter membrane order and therefore the function of resident proteins. The similarity of the effects of natural and enantiomeric U18666A on cells and the capacity of intercalated U18666A to increase membrane order are arguments in favor of this possibility.

Severity of atypical absence phenotype in GABAB transgenic mice is subunit specific

Overexpression of GABA(B)R1a receptors in mice (R1a(+)) results in an atypical absence seizure phenotype characterized by 3- to 6-Hz slow spike-and-wave discharges (SSWDs), reduced synaptic plasticity, and cognitive impairment. Here we tested the hypothesis that increased R1 expression causes atypical absence epilepsy and is not subunit specific. GABA(B)R1b receptors were overexpressed in mouse forebrain (R1b(+)) and confirmed by immunoblot and (3)H-CGP54626A autoradiography. The R1b(+) mice showed a reduction in hippocampal long-term potentiation and GABA(A) receptor-mediated inhibitory postsynaptic currents. R1b(+) mice manifested an electrographic, pharmacological, and behavioral phenotype consistent with atypical absence seizures, though less robust than R1a(+) in terms of SSWD duration and severity of cognitive impairment. These results suggest that abnormal GABA(B)R1b function plays a lesser role in the development of atypical absence epilepsy.

Estrogen-priming can enhance progesterone's anti-seizure effects in part by increasing hippocampal levels of allopregnanolone

Estrogen can be proconvulsant, while progesterone and its metabolite allopregnanolone typically have anti-seizure effects. We investigated whether estrogen-priming also has anti-seizure effects by altering progesterone's metabolism to allopregnanolone, or levels of brain-derived neurotrophic factor (BDNF), in the hippocampus. Two experiments investigated effects of different estrogen-priming regimen (Experiment 1--10 microg; Experiment 2--2 microg) on pentylenetetrazole (PTZ)-induced seizures and levels of estrogen, progesterone and allopregnanolone in plasma and hippocampus. In Experiment 1, ovariectomized (ovx) rats were administered sesame oil vehicle or 10 microg 17beta-estrogen at hour 0. Forty-four hours later, progesterone (500 microg; s.c.) or vehicle was administered. At hour 47, PTZ (70 mg/kg i.p.) was administered. For Experiment 2, a similar protocol was used except that ovx rats were administered vehicle or 2 microg 17beta-estradiol at hours 0 and 24. Progesterone, alone or in conjunction with either 10 or 2 microg estrogen-priming, tended to increase the latency to, and significantly reduced the number of, tonic seizures and elevated levels of progestins in hippocampus and plasma. Two, but not 10, micrograms of estrogen alone had anti-seizure effects and increased levels of allopregnanolone in the hippocampus. BDNF levels in the hippocampus were increased by estrogen-priming, but reduced by progesterone administration. Thus, estrogen may have anti-seizure effects by enhancing formation of allopregnanolone.

Clinical and neurophysiologic spectrum associated with atypical absence seizures in children with intractable epilepsy

The aim of this study was to describe the clinical and neurophysiologic correlates of atypical absence seizures in children with intractable epilepsy. In a retrospective review, 19 children with videoelectroencephalographic monitoring (female n=14; male n=5) fulfilled the electroclinical criteria for this seizure type. Atypical absence seizures occurred in a spectrum of clinical conditions associated with educational disability and intractable seizures. In comparison with children with only atypical absence seizures, children with atypical absence in association with multiple seizure types were more likely to have severe educational disability (n=11 of 13; P = .01), a slower ictal frequency (n=10 of 13; P = .01), and slow background rhythms for age (n = 13 of 13; P = .03). This study illustrates the broad clinical spectrum in which atypical absence seizures are encountered. Differentiation between children with only atypical absence seizures and children with multiple seizure types can be useful with respect to potential academic ability.

Attenuating 5alpha-pregnane-3alpha-ol-20-one formation in the hippocampus of female rats increases pentylenetetrazole-induced seizures

Progesterone has antiseizure effects, which may be due to the actions of its 5alpha-reduced metabolite, 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP). Whether metabolism of progesterone to 3alpha,5alpha-THP in the hippocampus is essential for its antiseizure effects was investigated. In Experiment 1, ovariectomized rats were administered subcutaneous progesterone (500 microg) or vehicle (sesame oil), followed 1 hour later by subcutaneous administration of an inhibitor of the 5alpha-reductase enzyme, finasteride (50 mg/kg), or vehicle (90% sesame oil, 10% ethanol). Administration of progesterone increased the latency to, and decreased the number of, tonic seizures and increased hippocampal 3alpha,5alpha-THP levels, compared with vehicle. Administration of finasteride with progesterone attenuated progesterone's antiseizure effects and decreased levels of 3alpha,5alpha-THP in the hippocampus. Finasteride administration alone did not alter ictal behavior or 3alpha,5alpha-THP levels compared with vehicle. In Experiment 2, ovariectomized rats were administered subcutaneous progesterone (500 microg) or vehicle (sesame oil), followed 1 hour later by bilateral infusions of finasteride (10 microg) or vehicle (beta-cyclodextran) into the hippocampus. Administration of finasteride to the hippocampus of progesterone-primed rats significantly increased ictal activity and decreased hippocampal 3alpha,5alpha-THP levels, compared with progesterone administration alone. These data suggest that formation of 3alpha,5alpha-THP in the hippocampus is important for progesterone's antiseizure effects.

Progesterone: the forgotten hormone in men?

'Classical' genomic progesterone receptors appear relatively late in phylogenesis, i.e. it is only in birds and mammals that they are detectable. In the different species, they mediate manifold effects regarding the differentiation of target organ functions, mainly in the reproductive system. Surprisingly, we know little about the physiology, endocrinology, and pharmacology of progesterone and progestins in male gender or men respectively, despite the fact that, as to progesterone secretion and serum progesterone levels, there are no great quantitative differences between men and women (at least outside the luteal phase). In a prospective cohort study of 1026 men with and without cardiovascular disease, we were not able to demonstrate any age-dependent change in serum progesterone concentrations. Progesterone influences spermiogenesis, sperm capacitation/acrosome reaction and testosterone biosynthesis in the Leydig cells. Other progesterone effects in men include those on the central nervous system (CNS) (mainly mediated by 5alpha-reduced progesterone metabolites as so-called neurosteroids), including blocking of gonadotropin secretion, sleep improvement, and effects on tumors in the CNS (meningioma, fibroma), as well as effects on the immune system, cardiovascular system, kidney function, adipose tissue, behavior, and respiratory system. A progestin may stimulate weight gain and appetite in men as well as in women. The detection of progesterone receptor isoforms would have a highly diagnostic value in prostate pathology (benign prostatic hypertrophy and prostate cancer). The modulation of progesterone effects on typical male targets is connected with a great pharmacodynamic variability. The reason for this is that, in men, some important effects of progesterone are mediated non-genomically through different molecular biological modes of action. Therefore, the precise therapeutic manipulation of progesterone actions in the male requires completely new endocrine-pharmacological approaches.