BAER-101, a selective potentiator of α2- and α3-containing GABAA receptors, fully suppresses spontaneous cortical spike-wave discharges in Genetic Absence Epilepsy Rats from Strasbourg (GAERS).

BAER-101 (formerly AZD7325) is a selective partial potentiator of α2/3-containing γ-amino-butyric acid A receptors (GABAARs) and produces minimal sedation and dizziness. Antiseizure effects in models of Dravet and Fragile X Syndromes have been published. BAER-101 has been administered to over 700 healthy human volunteers and patients where it was found to be safe and well tolerated. To test the extent of the antiseizure activity of BAER-1010, we tested BAER-101 in the Genetic Absence Epilepsy Rats from Strasbourg (GAERS) model, a widely used and translationally relevant model. GAERS rats with recording electrodes bilaterally located over the frontal and parietal cortices were used. Electroencepholographic (EEG) signals in freely moving awake rats were analyzed for spike-wave discharges (SWDs). BAER-101 was administered orally at doses of 0.3-100 mg/kg and diazepam was used as a positive control using a cross-over protocol with a wash-out period between treatments. The number of SWDs was dose-dependently reduced by BAER-101 with 0.3 mg/kg being the minimally effective dose (MED). The duration of and total time in SWDs were also reduced by BAER-101. Concentrations of drug in plasma achieved an MED of 10.1 nM, exceeding the Ki for α2 or α3, but 23 times lower than the Ki for α5-GABAARs. No adverse events were observed up to a dose 300× MED. The data support the possibility of antiseizure efficacy without the side effects associated with other GABAAR subtypes. This is the first report of an α2/3-selective GABA PAM suppressing seizures in the GAERS model. The data encourage proceeding to test BAER-101 in patients with epilepsy.

Barrel cortex development lacks a key stage of hyperconnectivity from deep to superficial layers in a rat model of Absence Epilepsy.

During development of the sensory cortex, the ascending innervation from deep to upper layers provides a temporary scaffold for the construction of other circuits that remain at adulthood. Whether an alteration in this sequence leads to brain dysfunction in neuro-developmental diseases remains unknown. Using functional approaches in a genetic model of Absence Epilepsy (GAERS), we investigated in barrel cortex, the site of seizure initiation, the maturation of excitatory and inhibitory innervations onto layer 2/3 pyramidal neurons and cell organization into neuronal assemblies. We found that cortical development in GAERS lacks the early surge of connections originating from deep layers observed at the end of the second postnatal week in normal rats and the concomitant structuring into multiple assemblies. Later on, at seizure onset (1 month old), excitatory neurons are hyper-excitable in GAERS when compared to Wistar rats. These findings suggest that early defects in the development of connectivity could promote this typical epileptic feature and/or its comorbidities.

Molecular and Phenotypic Characterization of the RORB-Related Disorder.

BACKGROUND AND OBJECTIVES: Heterozygous variants in RAR-related orphan receptor B (RORB) have recently been associated with susceptibility to idiopathic generalized epilepsy. However, few reports have been published so far describing pathogenic variants of this gene in patients with epilepsy and intellectual disability (ID). In this study, we aimed to delineate the epilepsy phenotype associated with RORB pathogenic variants and to provide arguments in favor of the pathogenicity of variants. METHODS: Through an international collaboration, we analyzed seizure characteristics, EEG data, and genotypes of a cohort of patients with heterozygous variants in RORB. To gain insight into disease mechanisms, we performed ex vivo cortical electroporation in mouse embryos of 5 selected variants, 2 truncating and 3 missense, and evaluated on expression and quantified changes in axonal morphology. RESULTS: We identified 35 patients (17 male, median age 10 years, range 2.5-23 years) carrying 32 different heterozygous variants in RORB, including 28 single-nucleotide variants or small insertions/deletions (12 missense, 12 frameshift or nonsense, 2 splice-site variants, and 2 in-frame deletions), and 4 microdeletions; de novo in 18 patients and inherited in 10. Seizures were reported in 31/35 (89%) patients, with a median age at onset of 3 years (range 4 months-12 years). Absence seizures occurred in 25 patients with epilepsy (81%). Nineteen patients experienced a single seizure type: absences, myoclonic absences, or absences with eyelid myoclonia and focal seizures. Nine patients had absence seizures combined with other generalized seizure types. One patient had presented with absences associated with photosensitive occipital seizures. Three other patients had generalized tonic-clonic seizures without absences. ID of variable degree was observed in 85% of the patients. Expression studies in cultured neurons showed shorter axons for the 5 tested variants, both truncating and missense variants, supporting an impaired protein function. DISCUSSION: In most patients, the phenotype of the RORB-related disorder associates absence seizures with mild-to-moderate ID. In silico and in vitro evaluation of the variants in our cohort, including axonal morphogenetic experiments in cultured neurons, supports their pathogenicity, showing a hypomorphic effect.

Cortical Tonic Inhibition Gates the Expression of Spike-and-Wave Discharges Associated with Absence Epilepsy.

OBJECTIVE: Absence seizures result from aberrant thalamocortical processing that confers synchronous, bilateral spike-and-wave discharges (SWDs) and behavioral arrest. Previous work has demonstrated that SWDs can result from enhanced thalamic tonic inhibition, consistent with the mechanism of first-line antiabsence drugs that target thalamic low-voltage-activated calcium channels. However, nearly half of patients with absence epilepsy are unresponsive to first-line medications. In this study we evaluated the role of cortical tonic inhibition and its manipulation on absence seizure expression. METHODS: We used video-electroencephalogram (EEG) monitoring to show that mice with a γ-aminobutyric acid type A (GABAA) receptor mutation (γ2R43Q) display absence seizures. Voltage-clamp recordings in brain slices from wild type and γ2R43Q mice were used to evaluate the amount of tonic inhibition and its selective pharmacological modulation. Finally, we determined whether modulating tonic inhibition controls seizure expression. RESULTS: γ2R43Q mice completely lack tonic inhibition in principal neurons of both layer 2/3 cortex and ventrobasal thalamus. Blocking cortical tonic inhibition in wild type mice is sufficient to elicit SWDs. Tonic inhibition in slices from γ2R43Q mice could be rescued in a dose-dependent fashion by the synthetic neurosteroid ganaxolone. Low-dose ganaxolone suppressed seizures in γ2R43Q mice. CONCLUSIONS: Our data suggest that reduced cortical tonic inhibition promotes absence seizures and that normal function can be restored via selective pharmacological rescue. These results, together with previous findings, suggest that deviations of tonic inhibition either above or below an optimal set point can contribute to absence epilepsy. Returning the thalamocortical system to this set point may provide a novel treatment for refractory absence epilepsy.

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.

Transmembrane α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor regulatory protein expression during the development of absence seizures in genetic absence epilepsy rats from Strasbourg.

The transmembrane α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) regulatory proteins (TARPs), γ2 (stargazin), γ3, γ4, γ5, γ7, and γ8, are a family of proteins that regulate AMPAR trafficking, expression, and biophysical properties that could have a role in the development of absence seizures. Here, we evaluated the expression of TARPs and AMPARs across the development of epilepsy in the genetic absence epilepsy rats from Strasbourg (GAERS) model of idiopathic generalized epilepsy (IGE) with absence seizures. Pre-epileptic (7-day-old), early epileptic (6-week-old), and chronically epileptic (16-week-old) GAERS, and age-matched male nonepileptic control rats (NEC) were used. Electroencephalographic (EEG) recordings were acquired from the 6- and 16-week-old animals to quantify seizure expression. Somatosensory cortex (SCx) and whole thalamus were collected from all the animals to evaluate TARP and AMPAR mRNA expression. Analysis of the EEG demonstrated a gradual increase in the number and duration of seizures across GAERS development. mRNA expression of the TARPs γ2, γ3, γ4, γ5, and γ8 in the SCx, and γ4 and γ5 in the thalamus, increased as the seizures started and progressed in the GAERS compared to NEC. There was a temporal association between increased TARP expression and seizures in GAERS, highlighting TARPs as potential targets for developing novel treatments for IGE with absence seizures.

Lack of causal association between epilepsy and dementia: A Mendelian randomization analysis.

OBJECTIVE: Epidemiological studies have reported an association between epilepsy and dementia. However, the causal relationship between epilepsy and the risk of dementia is not clear. We aimed to inspect the causal effect of epilepsy on memory loss and dementia. METHODS: We analyzed summary data of epilepsy, memory loss, and dementia from the genome-wide association study (GWAS) using the two-sample Mendelian randomization (MR) method. We used the estimated odds ratio of memory loss and dementia associated with each of the genetically defined traits to infer evidence for a causal relationship with the following exposures: all epilepsy, focal epilepsy (including focal epilepsy with hippocampal sclerosis, lesion-negative focal epilepsy, and focal epilepsy with other lesions), and genetic generalized epilepsy (including childhood absence epilepsy, generalized tonic-clonic seizures alone, Juvenile absence epilepsy, and Juvenile myoclonic epilepsy). RESULTS: According to the result of MR using the inverse variance weighted method (IVW), we found that genetically predicted epilepsy did not causally increase the risk of memory loss and dementia (p > 0.05). Results of the MR-Egger and weighted median method were consistent with the IVW method. CONCLUSIONS: No evidence has been found to support the notion that epilepsy can result in memory loss and dementia. The associations observed in epidemiological studies could be attributed, in part, to confounding or nongenetic determinants.

Precision medicine: Vinpocetine as a potential treatment for GABRG2-related epilepsy.

INTRODUCTION: Pathogenic variants of the GABRG2 gene, encoding a GABAA receptor subunit, have been associated with various epileptic syndromes and drug-resistant epilepsy. Vinpocetine has been previously reported efficacious in a patient harboring a GABRB3 pathogenic variant, encoding another GABAA receptor subunit. CASE PRESENTATION: We describe a patient with GABRG2-related drug-resistant epilepsy who improved after vinpocetine treatment. An 8-year-old boy with a family history of epilepsy was diagnosed with early onset absence epilepsy at 6 months of age and was treated unsuccessfully with sodium valproate and ethosuximide. At 6 years of age, he developed generalized tonic-clonic seizures and increasing absences despite lamotrigine add-on as well as learning difficulties. Brain MRI was normal and video-EEG telemetry showed multiple myoclonic absences. An epilepsy gene panel analysis showed a GABRG2 pathogenic variant, c.254 T > A p.(Ile85Lys) (NM_198903.2), inherited from the proband's father. Seizures were resistant to several medications. After treatment with vinpocetine add-on, the patient showed a dramatic initial response, further reduction of seizures, and improvement of his cognitive functions. CONCLUSION: This case illustrates that vinpocetine could be considered in drug-resistant epilepsies related to GABRG2 in accordance with the principles of precision medicine.

Effects of the T-type calcium channel CaV3.2 R1584P mutation on absence seizure susceptibility in GAERS and NEC congenic rats models.

RATIONALE: Low-voltage-activated or T-type Ca2+ channels play a key role in the generation of seizures in absence epilepsy. We have described a homozygous, gain of function substitution mutation (R1584P) in the CaV3.2 T-type Ca2+ channel gene (Cacna1h) in the Genetic Absence Epilepsy Rats from Strasbourg (GAERS). The non-epileptic control (NEC) rats, derived from the same original Wistar strains as GAERS but selectively in-breed not to express seizures, are null for the R1584P mutation. To study the effects of this mutation in rats who otherwise have a GAERS or NEC genetic background, we bred congenic GAERS-Cacna1hNEC (GAERS null for R1584P mutation) and congenic NEC-Cacna1hGAERS (NEC homozygous for R1584P mutation) and evaluated the seizure and behavioral phenotype of these strains in comparison to the original GAERS and NEC strains. METHODS: To evaluate seizure expression in the congenic strains, EEG electrodes were implanted in NEC, GAERS, GAERS-Cacna1hNEC without the R1584P mutation, and NEC-Cacna1hGAERS with the R1584P mutation rats. In the first study, continuous EEG recordings were acquired from week 4 (when seizures begin to develop in GAERS) to week 14 of age (when GAERS display hundreds of seizures per day). In the second study, the seizure and behavioral phenotype of GAERS and NEC-Cacna1hGAERS strains were evaluated during young age (6 weeks of age) and adulthood (16 weeks of age) of GAERS, NEC, GAERS-Cacna1hNEC and NEC-Cacna1hGAERS. The Open field test (OFT) and sucrose preference test (SPT) were performed to evaluate anxiety-like and depressive-like behavior, respectively. This was followed by EEG recordings at 18 weeks of age to quantify the seizures, and spike-wave discharge (SWD) cycle frequency. At the end of the study, the whole thalamus was collected for T-type calcium channel mRNA expression analysis. RESULTS: GAERS had a significantly shorter latency to first seizures and an increased number of seizures per day compared to GAERS-Cacna1hNEC. On the other hand, the presence of the R1584P mutation in the NEC-Cacna1hGAERS was not enough to generate spontaneous seizures in their seizure-resistant background. 6 and 16-week-old GAERS and GAERS-Cacna1hNEC rats showed anxiety-like behavior in the OFT, in contrast to NEC and NEC-Cacna1hGAERS. Results from the SPT showed that the GAERS developed depressive-like in the SPT compared to GAERS-Cacna1hNEC, NEC, and NEC-Cacna1hGAERS. Analysis of the EEG at 18 weeks of age showed that the GAERS had an increased number of seizures per day, increased total seizure duration and a higher cycle frequency of SWD relative to GAERS-Cacna1hNEC. However, the average seizure duration was not significantly different between strains. Quantitative real-time PCR showed that the T-type Ca2+ channel isoform CaV3.2 channel expression was significantly increased in GAERS compared to NEC, GAERS-Cacna1hNEC and NEC-Cacna1hGAERS. The presence of the R1584P mutation increased the total ratio of CaV3.2 + 25/-25 splice variants in GAERS and NEC-Cacna1hGAERS compared to NEC and GAERS-Cacna1hNEC. DISCUSSION: The data from this study demonstrate that the R1584P mutation in isolation on a seizure-resistant NEC genetic background was insufficient to generate absence seizures, and that a GAERS genetic background can cause seizures even without the mutation. However, the study provides evidence that the R1584P mutation acts as a modulator of seizures development and expression, and depressive-like behavior in the SPT, but not the anxiety phenotype of the GAERS model of absence epilepsy.

Spike and wave discharges detection in genetic absence epilepsy rat from Strasbourg and patients with genetic generalized epilepsy.

OBJECTIVE: Generalised spike and wave discharges (SWDs) are pathognomonic EEG signatures for diagnosing absence seizures in patients with Genetic Generalized Epilepsy (GGE). The Genetic Absence Epilepsy Rats from Strasbourg (GAERS) is one of the best-validated animal models of GGE with absence seizures. METHODS: We developed an SWDs detector for both GAERS rodents and GGE patients with absence seizures using a neural network method. We included 192 24-hour EEG sessions recorded from 18 GAERS rats, and 24-hour scalp-EEG data collected from 11 GGE patients. RESULTS: The SWDs detection performance on GAERS showed a sensitivity of 98.01% and a false positive (FP) rate of 0.96/hour. The performance on GGE patients showed 100% sensitivity in five patients, while the remaining patients obtained over 98.9% sensitivity. Moderate FP rates were seen in our patients with 2.21/hour average FP. The detector trained within our patient cohort was validated in an independent dataset, TUH EEG Seizure Corpus (TUSZ), that showed 100% sensitivity in 11 of 12 patients and 0.56/hour averaged FP. CONCLUSIONS: We developed a robust SWDs detector that showed high sensitivity and specificity for both GAERS rats and GGE patients. SIGNIFICANCE: This detector can assist researchers and neurologists with the time-efficient and accurate quantification of SWDs.

Optogenetic stimulation of the superior colliculus suppresses genetic absence seizures.

While anti-seizure medications are effective for many patients, nearly one-third of individuals have seizures that are refractory to pharmacotherapy. Prior studies using evoked preclinical seizure models have shown that pharmacological activation or excitatory optogenetic stimulation of the deep and intermediate layers of the superior colliculus (DLSC) display multi-potent anti-seizure effects. Here we monitored and modulated DLSC activity to suppress spontaneous seizures in the WAG/Rij genetic model of absence epilepsy. Female and male WAG/Rij adult rats were employed as study subjects. For electrophysiology studies, we recorded single unit activity from microwire arrays placed within the DLSC. For optogenetic experiments, animals were injected with virus coding for channelrhodopsin-2 or a control vector, and we compared the efficacy of continuous neuromodulation to that of closed-loop neuromodulation paradigms. For each, we compared three stimulation frequencies on a within-subject basis (5, 20, 100 Hz). For closed-loop stimulation, we detected seizures in real time based on the EEG power within the characteristic frequency band of spike-and-wave discharges (SWDs). We quantified the number and duration of each SWD during each 2 h-observation period. Following completion of the experiment, virus expression and fibre-optic placement was confirmed. We found that single-unit activity within the DLSC decreased seconds prior to SWD onset and increased during and after seizures. Nearly 40% of neurons displayed suppression of firing in response to the start of SWDs. Continuous optogenetic stimulation of the DLSC (at each of the three frequencies) resulted in a significant reduction of SWDs in males and was without effect in females. In contrast, closed-loop neuromodulation was effective in both females and males at all three frequencies. These data demonstrate that activity within the DLSC is suppressed prior to SWD onset, increases at SWD onset, and that excitatory optogenetic stimulation of the DLSC exerts anti-seizure effects against absence seizures. The striking difference between open- and closed-loop neuromodulation approaches underscores the importance of the stimulation paradigm in determining therapeutic effects.

Metyrapone abolishes spike-wave discharge seizures in genetic absence epilepsy rats from Strasbourg by reducing stress hormones.

OBJECTIVE: Stress is one of the most commonly reported triggers for seizures in patients with epilepsy, although the mechanisms that mediate this effect are not established. The clinical evidence supporting this is derived from patients' subjective experience of stress, and how this influences their own seizures. Animal models can be used to explore this phenomenon in controlled environments, free from subjective bias. Here, we used genetic absence epilepsy rats from Strasbourg (GAERS), a genetic rat model of absence epilepsy, to explore the influence of stress and stress hormones on spontaneous seizures. METHODS: Adult male GAERS (n = 38) and nonepileptic control (NEC) rats (n = 4) were used. First, rats were subjected to 30-min restraint stress to assess hypothalamic-pituitary-adrenal axis function. Next, we assessed the effects of 30-min noise stress, and cage tilt stress, on spike-wave discharge seizures in GAERS. We then performed pharmacological experiments to assess the direct effects of stress hormones on seizures, including corticosterone, metyrapone, and deoxycorticosterone. RESULTS: GAERS exhibited elevated baseline corticosterone levels, compared to NEC rats. Noise stress and cage tilt stress significantly enhanced seizure incidence (p < .05), but only during stress periods. Exogenous corticosterone administration also significantly increased seizure occurrence (p < .05). Metyrapone, an inhibitor of corticosterone synthesis, completely abolished seizures in GAERS, and seizures remained suppressed for >2 h. However, deoxycorticosterone, the precursor of corticosterone, increased seizures. SIGNIFICANCE: These results suggest that GAERS exhibit elevations in stress hormones, and this may contribute to seizures. Inhibiting corticosterone synthesis with metyrapone prevents seizures in GAERS, and shows potential for repurposing this drug as a future antiseizure medication.

HCN channels and absence seizures.

Hyperpolarization-activation cyclic nucleotide-gated (HCN) channels were for the first time implicated in absence seizures (ASs) when an abnormal Ih (the current generated by these channels) was reported in neocortical layer 5 neurons of a mouse model. Genetic studies of large cohorts of children with Childhood Absence Epilepsy (where ASs are the only clinical symptom) have identified only 3 variants in HCN1 (one of the genes that code for the 4 HCN channel isoforms, HCN1-4), with one (R590Q) mutation leading to loss-of-function. Due to the multi-faceted effects that HCN channels exert on cellular excitability and neuronal network dynamics as well as their modulation by environmental factors, it has been difficult to identify the detailed mechanism by which different HCN isoforms modulate ASs. In this review, we systematically and critically analyze evidence from established AS models and normal non-epileptic animals with area- and time-selective ablation of HCN1, HCN2 and HCN4. Notably, whereas knockout of rat HCN1 and mouse HCN2 leads to the expression of ASs, the pharmacological block of all HCN channel isoforms abolishes genetically determined ASs. These seemingly contradictory results could be reconciled by taking into account the well-known opposite effects of Ih on cellular excitability and network function. Whereas existing evidence from mouse and rat AS models indicates that pan-HCN blockers may provide a novel approach for the treatment of human ASs, the development of HCN isoform-selective drugs would greatly contribute to current research on the role for these channels in ASs generation and maintenance as well as offer new potential clinical applications.

The effect of quercetin on absence epilepsy in WAG/Rij rats.

AIM: In the present study, the effect of quercetin, a powerful antioxidant flavonoid, on genetic absence epilepsy was studied in WAG/Rij rats. MATERIAL AND METHOD: Tripolar electrodes were implanted into WAG/Rij rats. Basal electrocorticography (ECoG) was recorded following a recovery period. After basal ECoG recording, different doses of quercetin (QRC) (25, 50 and 100 mg/kg) were injected intraperitoneally (i.p.) for 30 days. ECoG recording was continued for 31 days, three hours a day. After recording, the rats were anesthetized and euthanized through cervical dislocation and their brains were excised. Biochemically, TNF-alpha, IL-6 and NO were studied in whole rat brains. RESULTS: In WAG/Rij rats, low-dose quercetin (25 mg/kg) reduced the number and duration of spike-wave discharges (SWDs) compared to the control group. However, 50 and 100 mg/kg quercetin doses increased SWDs. Duration of SWDs was prolonged only with 100 mg/kg dose. None of the quercetin doses had any effect on average amplitude of SWDs. In addition, it was observed in biochemical analyses that 25 mg/kg quercetin reduced TNF-alpha, IL-6 and NO levels compared to the control group. While TNF-alpha and IL-6 levels in rat brains were not affected by 50 or 100 mg/kg doses, both doses were found to increase NO levels in rat brains. CONCLUSION: Based on the results of the present study, 25 mg/kg low-dose quercetin may have reduced absence seizures by reducing proinflammatory cytokines and NO, but high-dose quercetin may have increased absence seizures through increasing the NO level. This contrasting effect of quercetin on absence seizures needs to be investigated by advanced mechanisms.

Higher-order thalamic nuclei facilitate the generalization and maintenance of spike-and-wave discharges of absence seizures.

Spike-and-wave discharges (SWDs), generated by the cortico-thalamo-cortical (CTC) network, are pathological, large amplitude oscillations and the hallmark of absence seizures (ASs). SWDs begin in a cortical initiation network in both humans and animal models, including the Genetic Absence Epilepsy Rats from Strasbourg (GAERS), where it is located in the primary somatosensory cortex (S1). The behavioral manifestation of an AS occurs when SWDs spread from the cortical initiation site to the whole brain, however, the mechanisms behind this rapid propagation remain unclear. Here we investigated these processes beyond the principal CTC network, in higher-order (HO) thalamic nuclei (lateral posterior (LP) and posterior (PO) nuclei) since their diffuse connectivity and known facilitation of intracortical communications make these nuclei key candidates to support SWD generation and maintenance. In freely moving GAERS, multi-site LFP in LP, PO and multiple cortical regions revealed a novel feature of SWDs: during SWDs there are short periods (named SWD-breaks) when cortical regions far from S1, such the primary visual cortex (V1), become transiently unsynchronized from the ongoing EEG rhythm. Inactivation of HO nuclei with local muscimol injections or optogenetic perturbation of HO nuclei activity increased the occurrence of SWD-breaks and the former intervention also increased the SWD propagation-time from S1. The neural underpinnings of these findings were explored further by silicon probe recordings from single units of PO which uncovered two previously unknown groups of excitatory neurons based on their burst firing dynamics at SWD onset. Moreover, a switch from tonic to burst firing at SWD onset was shown to be an important feature since it was much less prominent for non-generalized events, i.e. SWDs that remained local to S1. Additionally, one group of neurons showed a reverse of this switch during SWD-breaks, demonstrating the importance of this firing pattern throughout the SWD. In summary, these results support the view that multiple HO thalamic nuclei are utilized at SWD onset and contribute to cortical synchrony throughout the paroxysmal discharge.

Developmental Inhibitory Changes in the Primary Somatosensory Cortex of the Stargazer Mouse Model of Absence Epilepsy.

Childhood absence epilepsy seizures arise in the cortico-thalamocortical network due to multiple cellular and molecular mechanisms, which are still under investigation. Understanding the precise mechanisms is imperative given that treatment fails in ~30% of patients while adverse neurological sequelae remain common. Impaired GABAergic neurotransmission is commonly reported in research models investigating these mechanisms. Recently, we reported a region-specific reduction in the whole-tissue and synaptic GABAA receptor (GABAAR) α1 subunit and an increase in whole-tissue GAD65 in the primary somatosensory cortex (SoCx) of the adult epileptic stargazer mouse compared with its non-epileptic (NE) littermate. The current study investigated whether these changes occurred prior to the onset of seizures on postnatal days (PN) 17-18, suggesting a causative role. Synaptic and cytosolic fractions were biochemically isolated from primary SoCx lysates followed by semiquantitative Western blot analyses for GABAAR α1 and GAD65. We found no significant changes in synaptic GABAAR α1 and cytosolic GAD65 in the primary SoCx of the stargazer mice at the critical developmental stages of PN 7-9, 13-15, and 17-18. This indicates that altered levels of GABAAR α1 and GAD65 in adult mice do not directly contribute to the initial onset of absence seizures but are a later consequence of seizure activity.

Investigating the mechanism of action of ginkgolides and bilobalide on absence seizures in male WAG/Rij rats.

The effects of a single and multiple doses of ginkgolide A, B, C, and bilobalide, active components of Ginkgo biloba extract (EGb 761), on absence seizures were investigated in male WAG/Rij rats, a genetic animal model of absence epilepsy. Furthermore, the interactions of ginkgolide A together with NMDA receptor antagonist MK-801, AMPA/kainate receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), or L-type calcium channel blocker nicardipine were studied to figure out how ginkgolide A affects spike-wave discharges (SWDs) in the brain. The experiments were done using 6-8-month-old male WAG/Rij rats with infusion cannula and EEG electrode implanted. Ginkgolide A, B, C, and bilobalide were administered intraperitoneally for 7 days at a dose of 6 mg/kg. In interaction groups, 6 µg ginkgolide A was injected intracerebroventricularly in combination with MK-801 (10 µg), CNQX (1 µg), and nicardipine (50 µg) for 7 days. EEG was recorded from animals at the baseline, first dose, and seventh dose periods for 4 h. Ginkgolide A (p = .028), C (p = .046), and bilobalide (p = .043) significantly increased the frequency of SWDs in WAG/Rij rats. Ginkgolide A injected into the lateral ventricle with MK-801 (p = .046), CNQX (p = .043), and nicardipine (p = .046) significantly increased the number of SWDs after seventh dose. Finally, the EGb 761-related increase in absence epilepsy was determined to be caused by ginkgolide A, C, and bilobalide. All three receptor antagonists/channel blockers do not inhibit the pro-absence effect of ginkgolide A. The findings revealed that ginkgolide A's pro-absence effect is mediated by brain circuits other than ionotropic glutamate receptors or L-type calcium channels.

mGlu3 Metabotropic Glutamate Receptors as a Target for the Treatment of Absence Epilepsy: Preclinical and Human Genetics Data.

BACKGROUND: Previous studies suggest that different metabotropic glutamate (mGlu) receptor subtypes are potential drug targets for treating absence epilepsy. However, no information is available on mGlu3 receptors. OBJECTIVE: To examine whether (i) changes of mGlu3 receptor expression/signaling are found in the somatosensory cortex and thalamus of WAG/Rij rats developing spontaneous absence seizures; (ii) selective activation of mGlu3 receptors with LY2794193 affects the number and duration of spikewave discharges (SWDs) in WAG/Rij rats; and (iii) a genetic variant of GRM3 (encoding the mGlu3 receptor) is associated with absence epilepsy. METHODS: Animals: immunoblot analysis of mGlu3 receptors, GAT-1, GLAST, and GLT-1; realtime PCR analysis of mGlu3 mRNA levels; assessment of mGlu3 receptor signaling; EEG analysis of SWDs; assessment of depressive-like behavior. Humans: search for GRM3 and GRM5 missense variants in 196 patients with absence epilepsy or other Idiopathic Generalized Epilepsy (IGE)/ Genetic Generalized Epilepsy (GGE) and 125,748 controls. RESULTS: mGlu3 protein levels and mGlu3-mediated inhibition of cAMP formation were reduced in the thalamus and somatosensory cortex of pre-symptomatic (25-27 days old) and symptomatic (6-7 months old) WAG/Rij rats compared to age-matched controls. Treatment with LY2794193 (1 or 10 mg/kg, i.p.) reduced absence seizures and depressive-like behavior in WAG/Rij rats. LY2794193 also enhanced GAT1, GLAST, and GLT-1 protein levels in the thalamus and somatosensory cortex. GRM3 and GRM5 gene variants did not differ between epileptic patients and controls. CONCLUSION: We suggest that mGlu3 receptors modulate the activity of the cortico-thalamo-cortical circuit underlying SWDs and that selective mGlu3 receptor agonists are promising candidate drugs for absence epilepsy treatment.