Increased Seizure Susceptibility Research Articles

Inhibitory influence of agmatine on catamenial-like seizure susceptibility in progesterone withdrawn female rats

Catamenial epilepsy is a condition marked by an increased occurrence of seizures that coincide with the menstrual cycle in women. This study studies the role of neurotransmitter/neuromodulator agmatine in progesterone withdrawal induced increased seizure susceptibility that is one of the causes of catamenial epilepsy. Additionally, it investigates potential interactions between agmatine and the central neurosteroid system. The experiments involved the use of female Sprague-Dawley rats. To mime the seizure susceptibility as seen in catamenial epilepsy, rats were treated with PMSG and b-HCG which cause a higher release of progesterone and later injected with Finasteride on the 11th day of post-human chorionic gonadotropin administration to cause a sudden drop of progesterone. On the 12th day, seizure susceptibility was assessed through a low-dose (35 mg/kg) pentylenetetrazol (PTZ) injection. The results revealed that agmatine treatment showed a protective effect against seizures. Furthermore, this study explored the impact of neurosteroids such as allopregnanolone or progesterone (a precursor of allopregnanolone) and neurosteroidogenic drugs like FGIN 1–27 or metyrapone (an 11β-hydroxylase inhibitor) on the anticonvulsant effect of agmatine. The findings indicated that prior administration of these substances significantly enhanced the anticonvulsant effect of agmatine. In contrast, inhibiting neurosteroid production with drugs like trilostane (a 3β-hydroxysteroid dehydrogenase inhibitor) or indomethacin (a 3α-hydroxysteroid dehydrogenase inhibitor) completely nullified agmatine's effect. Seizures were associated with elevated progesterone levels and reduced allopregnanolone levels, which were normalized by agmatine treatment. Notably, agmatine exhibited seizure protection even in ovariectomized rats, affirming the involvement of neurosteroids in its anti-seizure effects in progesterone withdrawal increased seizure susceptibility. In conclusion, these findings emphasize central neurosteroid involvement in agmatine's pharmacological effects against seizure susceptibility in progesterone withdrawal in female rats.

Cannabidiol attenuates seizure susceptibility and behavioural deficits in adult CDKL5R59X knock-in mice.

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) is caused by a loss-of-function mutation in CDKL5 gene, encoding a serine-threonine kinase highly expressed in the brain. CDD manifests with early-onset epilepsy, autism, motor impairment and severe intellectual disability. While there are no known treatments for CDD, the use of cannabidiol has recently been introduced into clinical practice for neurodevelopmental disorders. Given the increased clinical utilization of cannabidiol, we examined its efficacy in the CDKL5R59X knock-in (R59X) mice, a CDD model based on a human mutation that exhibits both lifelong seizure susceptibility and behavioural deficits. We found that cannabidiol pre-treatment rescued the increased seizure susceptibility in response to the chemoconvulsant pentylenetetrazol (PTZ), attenuated working memory and long-term memory impairments, and rescued social deficits in adult R59X mice. To elucidate a potential mechanism, we compared the developmental hippocampal and cortical expression of common endocannabinoid (eCB) targets in R59X mice and their wild-type littermates, including cannabinoid type 1 receptor (CB1R), transient receptor potential vanilloid type 1 (TRPV1) and 2 (TRPV2), G-coupled protein receptor 55 (GPR55) and adenosine receptor 1 (A1R). Many of these eCB targets were developmentally regulated in both R59X and wild-type mice. In addition, adult R59X mice demonstrated significantly decreased expression of CB1R and TRPV1 in the hippocampus, and TRPV2 in the cortex, while TRPV1 was increased in the cortex. These findings support the potential for dysregulation of eCB signalling as a plausible mechanism and therapeutic target in CDD, given the efficacy of cannabidiol to attenuate hyperexcitability and behavioural deficits in this disorder.

Virus-Induced Epilepsy vs. Epilepsy Patients Acquiring Viral Infection: Unravelling the Complex Relationship for Precision Treatment.

The intricate relationship between viruses and epilepsy involves a bidirectional interaction. Certain viruses can induce epilepsy by infecting the brain, leading to inflammation, damage, or abnormal electrical activity. Conversely, epilepsy patients may be more susceptible to viral infections due to factors, such as compromised immune systems, anticonvulsant drugs, or surgical interventions. Neuroinflammation, a common factor in both scenarios, exhibits onset, duration, intensity, and consequence variations. It can modulate epileptogenesis, increase seizure susceptibility, and impact anticonvulsant drug pharmacokinetics, immune system function, and brain physiology. Viral infections significantly impact the clinical management of epilepsy patients, necessitating a multidisciplinary approach encompassing diagnosis, prevention, and treatment of both conditions. We delved into the dual dynamics of viruses inducing epilepsy and epilepsy patients acquiring viruses, examining the unique features of each case. For virus-induced epilepsy, we specify virus types, elucidate mechanisms of epilepsy induction, emphasize neuroinflammation's impact, and analyze its effects on anticonvulsant drug pharmacokinetics. Conversely, in epilepsy patients acquiring viruses, we detail the acquired virus, its interaction with existing epilepsy, neuroinflammation effects, and changes in anticonvulsant drug pharmacokinetics. Understanding this interplay advances precision therapies for epilepsy during viral infections, providing mechanistic insights, identifying biomarkers and therapeutic targets, and supporting optimized dosing regimens. However, further studies are crucial to validate tools, discover new biomarkers and therapeutic targets, and evaluate targeted therapy safety and efficacy in diverse epilepsy and viral infection scenarios.

Early developmental changes in a rat model of malformations of cortical development: Abnormal neuronal migration and altered response to NMDA-induced excitotoxic injury

Malformations of cortical development (MCDs) are caused by abnormal neuronal migration processes during the fetal period and are a major cause of intractable epilepsy in infancy. However, the timing of hyperexcitability or epileptogenesis in MCDs remains unclear. To identify the early developmental changes in the brain of the MCD rat model, which exhibits increased seizure susceptibility during infancy (P12–15), we analyzed the pathological changes in the brains of MCD model rats during the neonatal period and tested NMDA-induced seizure susceptibility.Pregnant rats were injected with two doses of methylazoxymethanol acetate (MAM, 15 mg/kg, i.p.) to induce MCD, while controls were administered normal saline. The cortical development of the offspring was measured by performing magnetic resonance imaging (MRI) on postnatal days (P) 1, 5, and 8. At P8, some rats were sacrificed for immunofluorescence, Golgi staining, and Western analysis. In another set of rats, the number and latency to onset of spasms were monitored for 90 min after the NMDA (5 mg/kg i.p.) injection at P8.In MCD rats, in vivo MR imaging showed smaller brain volume and thinner cortex from day 1 after birth (p < 0.001). Golgi staining and immunofluorescence revealed abnormal neuronal migration, with a reduced number of neuronal cell populations and less dendritic arborization at P8. Furthermore, MCD rats exhibited a significant reduction in the expression of NMDA receptors and AMPAR4, along with an increase in AMPAR3 expression (p < 0.05). Although there was no difference in the latency to seizure onset between MCD rats and controls, the MCD rats survived significantly longer than the controls.These results provide insights into the early developmental changes in the cortex of a MCD rat model and suggest that delayed and abnormal neuronal development in the immature brain is associated with a blunted response to NMDA-induced excitotoxic injury. These developmental changes may be involved in the sudden onset of epilepsy in patients with MCD or prenatal brain injury.

Novel loss-of-function variants expand ABCC9-related intellectual disability and myopathy syndrome.

Loss-of-function mutation of ABCC9, the gene encoding the SUR2 subunit of ATP sensitive-potassium (KATP) channels, was recently associated with autosomal recessive ABCC9-related intellectual disability and myopathy syndrome (AIMS). Here we identify nine additional subjects, from seven unrelated families, harbouring different homozygous loss-of-function variants in ABCC9 and presenting with a conserved range of clinical features. All variants are predicted to result in severe truncations or in-frame deletions within SUR2, leading to the generation of non-functional SUR2-dependent KATP channels. Affected individuals show psychomotor delay and intellectual disability of variable severity, microcephaly, corpus callosum and white matter abnormalities, seizures, spasticity, short stature, muscle fatigability and weakness. Heterozygous parents do not show any conserved clinical pathology but report multiple incidences of intra-uterine fetal death, which were also observed in an eighth family included in this study. In vivo studies of abcc9 loss-of-function in zebrafish revealed an exacerbated motor response to pentylenetetrazole, a pro-convulsive drug, consistent with impaired neurodevelopment associated with an increased seizure susceptibility. Our findings define an ABCC9 loss-of-function-related phenotype, expanding the genotypic and phenotypic spectrum of AIMS and reveal novel human pathologies arising from KATP channel dysfunction.

Inhibitory CCK+ basket synapse defects in mouse models of dystroglycanopathy.

Dystroglycan (Dag1) is a transmembrane glycoprotein that links the extracellular matrix to the actin cytoskeleton. Mutations in Dag1 or the genes required for its glycosylation result in dystroglycanopathy, a type of congenital muscular dystrophy characterized by a wide range of phenotypes including muscle weakness, brain defects, and cognitive impairment. We investigated interneuron (IN) development, synaptic function, and associated seizure susceptibility in multiple mouse models that reflect the wide phenotypic range of dystroglycanopathy neuropathology. Mice that model severe dystroglycanopathy due to forebrain deletion of Dag1 or Pomt2, which is required for Dystroglycan glycosylation, show significant impairment of CCK+/CB1R+ IN development. CCK+/CB1R+ IN axons failed to properly target the somatodendritic compartment of pyramidal neurons in the hippocampus, resulting in synaptic defects and increased seizure susceptibility. Mice lacking the intracellular domain of Dystroglycan have milder defects in CCK+/CB1R+ IN axon targeting, but exhibit dramatic changes in inhibitory synaptic function, indicating a critical postsynaptic role of this domain. In contrast, CCK+/CB1R+ IN synaptic function and seizure susceptibility was normal in mice that model mild dystroglycanopathy due to partially reduced Dystroglycan glycosylation. Collectively, these data show that inhibitory synaptic defects and elevated seizure susceptibility are hallmarks of severe dystroglycanopathy, and show that Dystroglycan plays an important role in organizing functional inhibitory synapse assembly.

Inhibitory CCK+ basket synapse defects in mouse models of dystroglycanopathy

Dystroglycan (Dag1) is a transmembrane glycoprotein that links the extracellular matrix to the actin cytoskeleton. Mutations in Dag1 or the genes required for its glycosylation result in dystroglycanopathy, a type of congenital muscular dystrophy characterized by a wide range of phenotypes including muscle weakness, brain defects, and cognitive impairment. We investigated interneuron (IN) development, synaptic function, and associated seizure susceptibility in multiple mouse models that reflect the wide phenotypic range of dystroglycanopathy neuropathology. Mice that model severe dystroglycanopathy due to forebrain deletion of Dag1 or Pomt2, which is required for Dystroglycan glycosylation, show significant impairment of CCK+/CB1R+ IN development. CCK+/CB1R+ IN axons failed to properly target the somatodendritic compartment of pyramidal neurons in the hippocampus, resulting in synaptic defects and increased seizure susceptibility. Mice lacking the intracellular domain of Dystroglycan have milder defects in CCK+/CB1R+ IN axon targeting, but exhibit dramatic changes in inhibitory synaptic function, indicating a critical postsynaptic role of this domain. In contrast, CCK+/CB1R+ IN synaptic function and seizure susceptibility was normal in mice that model mild dystroglycanopathy due to partially reduced Dystroglycan glycosylation. Collectively, these data show that inhibitory synaptic defects and elevated seizure susceptibility are hallmarks of severe dystroglycanopathy, and show that Dystroglycan plays an important role in organizing functional inhibitory synapse assembly.

Seizures exacerbate tau spread in the 5XFAD mouse model

AbstractBackgroundCentral to the progression of Alzheimer’s disease (AD) is the spread of pathological tau along neuronal connections. This aspect of pathological progression can be recapitulated in WT mice by intracerebral injection of human AD brain derived tau lysate (AD‐tau). AD‐tau spread is enhanced in the amyloidosis mouse model, five times familial AD (5XFAD), suggesting that tau propagation is facilitated by β‐amyloid (Aβ) plaques. Once assumed to simply be a biproduct of Aβ‐induced hyperexcitability, a bidirectional relationship between seizures and AD progression has been established. Our lab has demonstrated worsened tau and Aβ pathology and cognitive deficits in AD patients with seizure history and in seizure‐kindled 5XFAD mice. Thus, we hypothesized that seizures would exacerbate the spread of AD‐tau in the 5XFAD mouse model and that 5XFAD mice would show increased seizure susceptibility and related neuronal activity.MethodTo investigate seizure‐pathology interactions, we crossed the 5XFAD mouse model with targeted recombination in active populations (TRAP; 5X‐TRAP) mice to permanently label seizure‐activated neurons. We injected AD‐tau unilaterally into the hippocampus and overlying cortex (1 µg/site) at 3 months of age in 5X‐TRAP and WT‐TRAP littermates. Seizures were induced with pentylenetetrazol (PTZ) kindling 2‐3 weeks following surgery and seizure‐activated neurons were labeled (tdTomato) on the final day of kindling via 4‐hydroxytamoxifen administration (50 mg/kg). Mice were euthanized three months post AD‐tau injection and immunohistochemistry for phospho‐tau (AT8) was performed.ResultWe found that kindled 5X‐TRAP mice show increased pathological tau (% AT8 coverage) in the dentate gyrus (DG) and CA1 contralateral to injection site compared to non‐kindled mice (p&lt;0.05). We also found a trend towards elevated AT8 in the ipsilateral DG across seizure kindled groups (p = 0.083) and that 5X‐TRAP mice showed increased AT8 in the ipsilateral CA1 compared to WT‐TRAP (p&lt;0.05). Further, we found a trend towards increased seizure susceptibility (0.059) in 5X‐TRAP mice and significantly increased seizure activated neurons (tdTomato+) in the DG of kindled 5X‐TRAP mice compared to WT‐TRAP (p&lt;0.05).ConclusionOverall, our data further indicate a bidirectional relationship between seizures and AD. We also demonstrate that seizures facilitate the spread of pathological tau, thus suggesting that targeting seizure activity may slow AD progression.

ApoE variant associated with cognitive resilience alters AD associated hyperexcitability in dentate granule neurons

AbstractBackgroundCognitive decline in Alzheimer’s disease (AD) differs based on background genetics even with similar pathology. Using genetic linkage analysis, we identified a coding variant in the receptor binding domain of ApoE that leads to changes in cognitive performance across a genetically diverse population harboring familial (FAD) mutations known as the AD‐BXDs (Neuner et al., 2019). Using CRISPR‐based gene editing, we developed a C57BL/6J (B6) mouse carrying the ApoE allele from the DBA/2J (D2) strain (ApoEE163D) and determined that ApoEE163D mice with 5XFAD transgene (ApoEE163D‐5XFAD) are susceptible to cognitive decline compared to B6‐5XFAD mice (Kaczorowski, et al., 2022).Analysis of hippocampal RNA sequencing profiles from the hippocampus indicates robust transcriptomic changes in dentate gyrus (DG) granule cells associated with cognitive resilience to FAD mutations in the presence of the B6 ApoE genotype. Here we aim to evaluate the functional implications.MethodWe adapted the Patch‐Seq method (Cadwell et al., 2017) to investigate transcriptional and electrophysiological changes within the DG associated with both FAD mutations and ApoE genotype. Whole‐cell patch clamp was used to evaluate intrinsic excitability of granule cells from 14month old B6 mice carrying FAD mutations and ApoEE163D, compared to age matched controls. The cellular contents, including the nucleus, were collected after each recording to characterize the transcriptome, and the cells were filled and stained for downstream analysis of neuronal morphology.ResultWe observed a significant interaction of the 5XFAD and ApoE genotypes on DG granule cell excitability. Specifically, cells from ApoEE163D‐5XFAD required less current stimulus to both elicit a single action potential, and to fire in response to a current ramp (rheobase). Although input resistance was comparable across all 4 groups, the sag ratio of ApoEE163D‐5XFAD was also reduced.ConclusionEnhancement of DG excitability of ApoEE163D‐5XFAD mice may underlie increased seizure susceptibility that has been reported previously in FAD animal models on D2 genetic background and associated with increased risk of seizures in AD patients. Ongoing work will integrate DG excitability with single‐cell RNAseq, morphology, and behavior to dissect mechanisms underlying the modifier effect of ApoE genotype on susceptibility and resilience to cognitive deficits in FAD mutation carriers.

Neurodevelopmental deficits and cell-type-specific transcriptomic perturbations in a mouse model of HNRNPU haploinsufficiency.

Heterozygous de novo loss-of-function mutations in the gene expression regulator HNRNPU cause an early-onset developmental and epileptic encephalopathy. To gain insight into pathological mechanisms and lay the potential groundwork for developing targeted therapies, we characterized the neurophysiologic and cell-type-specific transcriptomic consequences of a mouse model of HNRNPU haploinsufficiency. Heterozygous mutants demonstrated global developmental delay, impaired ultrasonic vocalizations, cognitive dysfunction and increased seizure susceptibility, thus modeling aspects of the human disease. Single-cell RNA-sequencing of hippocampal and neocortical cells revealed widespread, yet modest, dysregulation of gene expression across mutant neuronal subtypes. We observed an increased burden of differentially-expressed genes in mutant excitatory neurons of the subiculum-a region of the hippocampus implicated in temporal lobe epilepsy. Evaluation of transcriptomic signature reversal as a therapeutic strategy highlights the potential importance of generating cell-type-specific signatures. Overall, this work provides insight into HNRNPU-mediated disease mechanisms and provides a framework for using single-cell RNA-sequencing to study transcriptional regulators implicated in disease.

The intracerebral injection of Aβ1-42 oligomers does not invariably alter seizure susceptibility in mice.

Epileptiform activity and seizures are present in patients with Alzheimer's disease (AD) and genetic animal models of AD. Amyloid beta 1-42 (Aβ1-42) oligomers are thought to be crucial in AD and can cause neuronal hyperexcitability in vitro. However, it is unclear whether these Aβ1-42 oligomers cause the increased seizure susceptibility in vivo in people with AD and in AD animal models, nor via which mechanisms it would do so. We investigated this question by injecting Aβ1-42 oligomers intracerebrally in mice and assessed its impact on seizure susceptibility. We performed a single intracerebral injection of synthetic Aβ1-42 oligomers or scrambled Aβ1-42 in NMRI mice in three different cohorts and subjected them to an i.v. infusion of a chemoconvulsant. We evoked the seizures 1.5 h, 1 week, or 3 weeks after the intracerebral injection of Aβ1-42 oligomers, covering also the timepoints and injection locations that were used by others in similar experimental set-ups. With a thioflavine T assay and transmission electron microscopy we confirmed that Aβ1-42 monomers spontaneously aggregated to oligomers. We did not find an effect of Aβ1-42 oligomers on susceptibility to seizures - evoked 1.5 h, 1 week or 3 weeks - after their intracerebral injection. The lack of effect of Aβ1-42 oligomers on seizure susceptibility in our experiments contrasts with recent findings in similar experimental set-ups. Contradicting conclusions are frequent in experiments with Aβ1-42 and they are often attributed to subtle differences in the various aggregation forms of the Aβ1-42 used in different experiments. We confirmed the presence of Aβ1-42 oligomers with state-of-the-art methods but cannot ascertain that the protein aggregates we used are identical to those used by others. Whether our findings or those previously published best represent the role of Aβ1-42 oligomers on seizures in AD remains unclear.

Suppressive Effects of Docosahexaenoic Acid Intake on Increased Seizure Susceptibility after Growth Due to Febrile Seizures in Infancy.

Febrile seizures are seizures accompanied by a fever and frequently occur in children six months to five years of age. Febrile seizures are classified as simple or complex, and complex febrile seizures increase the risk of temporal lobe epilepsy after growth. Therefore, it is important to interfere with epileptogenesis after febrile seizures to prevent post-growth epilepsy. The present study challenged nutritional intervention using docosahexaenoic acid (DHA). Febrile seizures were induced in mice at the age of 10 d using a heat chamber, and seizure sensitivity was examined using pentylenetetrazol (PTZ) administration after growth. PTZ increased the seizure score and shortened the latency in the complex febrile seizure group compared to the control, hyperthermia and simple febrile seizure groups. Mice in the complex febrile seizure group showed abnormal electroencephalograms pre- and post-PTZ administration. Therefore, seizure susceptibility increases the episodes of complex febrile seizures. DHA supplementation after febrile seizures clearly suppressed the increased seizure susceptibility due to complex febrile seizures experienced in infancy. DHA also attenuated microglial activation after complex febrile seizures. Taken together, DHA suppressed microglial activation following complex febrile seizures, which may contribute to protecting the brain from post-growth seizures. The intake of DHA in infancy may protect children from high fever-induced developmental abnormalities.

4-AP challenge reveals that early intervention with brivaracetam prevents posttraumatic epileptogenesis in rats

PurposeThere are currently no clinical treatments to prevent posttraumatic epilepsy (PTE). Recently, our group has shown that administration of levetiracetam (LEV) or brivaracetam (BRV) shortly after cortical neurotrauma prevents the development of epileptiform activity in rats, as measured ex vivo in neocortical slices. Due to the low incidence of spontaneous seizures in rodent-based models of traumatic brain injury (TBI), chemoconvulsants have been used to test injured animals for seizure susceptibility. We used a low dose of the voltage-gated potassium channel blocker 4-aminopyridine (4-AP) to evaluate posttraumatic epileptogenesis after controlled cortical impact (CCI) injury. We then used this assessment to further investigate the efficacy of BRV as an antiepileptogenic treatment. MethodsSprague-Dawley rats aged P24–35 were subjected to severe CCI injury. Following trauma, one group received BRV-21 mg/kg (IP) at 0–2 min after injury and the other BRV-100 mg/kg (IP) at 30 min after injury. Four to eight weeks after injury, animals were given a single, low dose of 4-AP (3.0–3.5 mg/kg, IP) and then monitored up to 90 min for stage 4/5 seizures. ResultsThe chemoconvulsant challenge revealed that within four to eight weeks, CCI injury led to a two-fold increase in percentage of rats with 4-AP induced stage 4–5 seizures relative to sham-injured controls. Administration of a single dose of BRV within 30 min after trauma significantly reduced injury-induced seizure susceptibility, bringing the proportion of CCI-rats that exhibited evoked seizures down to control levels. ConclusionsThis study is the first to use a low dose of 4-AP as a chemoconvulsant challenge to test epileptogenicity within the first two months after CCI injury in rats. Our findings show that a single dose of BRV administered within 30 min after TBI prevents injury-induced increases in seizure susceptibility. This supports our hypothesis that early intervention with BRV may prevent PTE.

Preventing development of post-stroke hyperexcitability by optogenetic or pharmacological stimulation of cortical excitatory activity

Stroke is the most common cause of acquired epilepsy, but treatment for preventing the development of post-stroke epilepsy is still unavailable. Since stroke results in neuronal damage and death as well as initial loss of activity in the affected brain region, homeostatic plasticity may be trigged and contribute to an increase in network hyperexcitability that underlies epileptogenesis. Correspondingly, enhancing brain activity may inhibit hyperexcitability from enhanced homeostatic plasticity and prevent post-stroke epileptogenesis. To test these hypotheses, we first used in vivo two-photon and mesoscopic imaging of activity of cortical pyramidal neurons in Thy1-GCaMP6 transgenic mice to determine longitudinal changes in excitatory activity after a photothrombotic ischemic stroke. At 3-days post-stroke, there was a significant loss of neuronal activity in the peri-injury area as indicated by reductions in the frequency of calcium spikes and percentage of active neurons, which recovered to baseline level at day 7, supporting a homeostatic activity regulation of the surviving neurons in the peri-injury area. We further used optogenetic stimulation to specifically stimulate activity of pyramidal neurons in the peri-injury area of Thy-1 channelrhodopsin transgenic mice from day 5 to day 15 after stroke. Using pentylenetetrazole test to evaluate seizure susceptibility, we showed that stroke mice are more susceptible to Racine stage V seizures (time latency 54.3 ± 12.9 min) compared to sham mice (107.1 ± 13.6 min), but optogenetic stimulation reversed the increase in seizure susceptibility (114.0 ± 9.2 min) in mice with stroke. Similarly, administration of D-cycloserine, a partial N-methyl-d-aspartate (NMDA) receptor agonist that can mildly enhance neuronal activity without causing post-stroke seizure, from day 5 to day 15 after a stroke significantly reversed the increase in seizure susceptibility. The treatment also resulted in an increased survival of glutamic acid decarboxylase 67 (GAD67) positive interneurons and a reduced activation of glial fibrillary acidic protein (GFAP) positive reactive astrocytes. Thus, this study supports the involvement of homeostatic activity regulation in the development of post-stroke hyperexcitability and potential application of activity enhancement as a novel strategy to prevent post-stroke late-onset seizure and epilepsy through regulating cortical homeostatic plasticity.

Sleep and Epilepsy

Sleep and epilepsy have a complex interrelationship that is influenced by various factors, including the distinct stages of sleep. Non-rapid eye movement sleep promotes epileptic activity, while rapid eye movement sleep suppresses it. Seizures can be triggered by sleep, while sleep deprivation increases seizure susceptibility. Epilepsy disrupts sleep architecture and quality, leading to sleep disturbances and comorbidities, like sleep apnea and restless legs syndrome. Excessive daytime sleepiness and fatigue can result from epilepsy and the sedating effects of antiseizure medications. Sleep-related epilepsy exhibits seizures predominantly during sleep, with specific patterns related to sleep stages. Antiseizure medications can directly impact sleep quality and should be carefully considered when treating epilepsy patients with comorbid sleep disorders. Understanding the bidirectional relationship between sleep and epilepsy is crucial for effective management. Optimizing treatment strategies requires recognizing the effects of antiseizure medications on sleep, and addressing sleep-related issues in individuals with epilepsy.

Fine-tuning GPCR-mediated neuromodulation by biasing signaling through different G protein subunits

G-protein-coupled receptors (GPCRs) mediate neuromodulation through the activation of heterotrimeric G proteins (Gαβγ). Classical models depict that G protein activation leads to a one-to-one formation of Gα-GTP and Gβγ species. Each of these species propagates signaling by independently acting on effectors, but the mechanisms by which response fidelity is ensured by coordinating Gα and Gβγ responses remain unknown. Here, we reveal a paradigm of G protein regulation whereby the neuronal protein GINIP (Gα inhibitory interacting protein) biases inhibitory GPCR responses to favor Gβγ over Gα signaling. Tight binding of GINIP to Gαi-GTP precludes its association with effectors (adenylyl cyclase) and, simultaneously, with regulator-of-G-protein-signaling (RGS) proteins that accelerate deactivation. As a consequence, Gαi-GTP signaling is dampened,whereas Gβγ signaling is enhanced. We show that this mechanism is essential to prevent the imbalances of neurotransmission that underlie increased seizure susceptibility in mice. Our findings reveal an additional layer of regulation within a quintessential mechanism of signal transduction that sets the tone of neurotransmission.

Seizure susceptibility to various convulsant stimuli in the BTBR mouse model of autism spectrum disorders.

Background: Autism spectrum disorders (ASDs) are one of the most severe chronic childhood disorders in terms of prevalence, morbidity, and impact on society. Interestingly, several systematic reviews and meta-analyses documented a bidirectional link between epilepsy and ASD, supporting the hypothesis that both disorders may have common neurobiological pathways. According to this hypothesis, an imbalance of the excitatory/inhibitory (E/I) ratio in several brain regions may represent a causal mechanism underpinning the co-occurrence of these neurological diseases. Methods: To investigate this bidirectional link, we first tested the seizure susceptibility to chemoconvulsants acting on GABAergic and glutamatergic systems in the BTBR mice, in which an imbalance between E/I has been previously demonstrated. Subsequently, we performed the PTZ kindling protocol to study the impact of seizures on autistic-like behavior and other neurological deficits in BTBR mice. Results: We found that BTBR mice have an increased susceptibility to seizures induced by chemoconvulsants impairing GABAA neurotransmission in comparison to C57BL/6J control mice, whereas no significant difference in seizure susceptibility was observed after administration of AMPA, NMDA, and Kainate. This data suggests that deficits in GABAergic neurotransmission can increase seizure susceptibility in this strain of mice. Interestingly, BTBR mice showed a longer latency in the development of kindling compared to control mice. Furthermore, PTZ-kindling did not influence autistic-like behavior in BTBR mice, whereas it was able to significantly increase anxiety and worsen cognitive performance in this strain of mice. Interestingly, C57BL/6J displayed reduced sociability after PTZ injections, supporting the hypothesis that a tight connection exists between ASD and epilepsy. Conclusion: BTBR mice can be considered a good model to study epilepsy and ASD contemporarily. However, future studies should shed light on the mechanisms underpinning the co-occurrence of these neurological disorders in the BTBR model.

A patient-derived mutation of epilepsy-linked LGI1 increases seizure susceptibility through regulating Kv1.1

BackgroundAutosomal dominant lateral temporal epilepsy (ADLTE) is an inherited syndrome caused by mutations in the leucine-rich glioma inactivated 1 (LGI1) gene. It is known that functional LGI1 is secreted by excitatory neurons, GABAergic interneurons, and astrocytes, and regulates AMPA-type glutamate receptor-mediated synaptic transmission by binding ADAM22 and ADAM23. However, > 40 LGI1 mutations have been reported in familial ADLTE patients, more than half of which are secretion-defective. How these secretion-defective LGI1 mutations lead to epilepsy is unknown.ResultsWe identified a novel secretion-defective LGI1 mutation from a Chinese ADLTE family, LGI1-W183R. We specifically expressed mutant LGI1W183R in excitatory neurons lacking natural LGI1, and found that this mutation downregulated Kv1.1 activity, led to neuronal hyperexcitability and irregular spiking, and increased epilepsy susceptibility in mice. Further analysis revealed that restoring Kv1.1 in excitatory neurons rescued the defect of spiking capacity, improved epilepsy susceptibility, and prolonged the life-span of mice.ConclusionsThese results describe a role of secretion-defective LGI1 in maintaining neuronal excitability and reveal a new mechanism in the pathology of LGI1 mutation-related epilepsy.

Pre-existing Toxoplasma gondii infection increases susceptibility to pentylenetetrazol-induced seizures independent of traumatic brain injury in mice.

Post-traumatic epilepsy (PTE) is a debilitating chronic outcome of traumatic brain injury (TBI), and neuroinflammation is implicated in increased seizure susceptibility and epileptogenesis. However, how common clinical factors, such as infection, may modify neuroinflammation and PTE development has been understudied. The neurotropic parasite, Toxoplasma gondii (T. gondii) incurably infects one-third of the world's population. Thus, many TBI patients have a pre-existing T. gondii infection at the time of injury. T. gondii infection results in chronic low-grade inflammation and altered signaling pathways within the brain, and preliminary clinical evidence suggest that it may be a risk factor for epilepsy. Despite this, no studies have considered how a pre-existing T. gondii infection may alter the development of PTE. This study aimed to provide insight into this knowledge gap by assessing how a pre-existing T. gondii infection alters susceptibility to, and severity of, pentylenetetrazol (PTZ)-induced seizures (i.e., a surrogate marker of epileptogenesis/PTE) at a chronic stage of TBI recovery. We hypothesized that T. gondii will increase the likelihood and severity of seizures following PTZ administration, and that this would occur in the presence of intensified neuroinflammation. To test this, 6-week old male and female C57BL/6 Jax mice were intraperitoneally injected with 50,000 T. gondii tachyzoites or with the PBS vehicle only. At 12-weeks old, mice either received a severe TBI via controlled cortical impact or sham injury. At 18-weeks post-injury, mice were administered 40 mg/kg PTZ and video-recorded for evaluation of seizure susceptibility. Fresh cortical tissue was then collected for gene expression analyses. Although no synergistic effects were evident between infection and TBI, chronic T. gondii infection alone had robust effects on the PTZ-seizure response and gene expression of markers related to inflammatory, oxidative stress, and glutamatergic pathways. In addition to this, females were more susceptible to PTZ-induced seizures than males. While TBI did not impact PTZ responses, injury effects were evident at the molecular level. Our data suggests that a pre-existing T. gondii infection is an important modifier of seizure susceptibility independent of brain injury, and considerable attention should be directed toward delineating the mechanisms underlying this pro-epileptogenic factor.

Microglial pattern recognition via IL-33 promotes synaptic refinement in developing corticothalamic circuits in mice.

Microglia are critical regulators of brain development that engulf synaptic proteins during postnatal synapse remodeling. However, the mechanisms through which microglia sense the brain environment are not well defined. Here, we characterized the regulatory program downstream of interleukin-33 (IL-33), a cytokine that promotes microglial synapse remodeling. Exposing the developing brain to a supraphysiological dose of IL-33 altered the microglial enhancer landscape and increased binding of stimulus-dependent transcription factors including AP-1/FOS. This induced a gene expression program enriched for the expression of pattern recognition receptors, including the scavenger receptor MARCO. CNS-specific deletion of IL-33 led to increased excitatory/inhibitory synaptic balance, spontaneous absence-like epileptiform activity in juvenile mice, and increased seizure susceptibility in response to chemoconvulsants. We found that MARCO promoted synapse engulfment, and Marco-deficient animals had excess thalamic excitatory synapses and increased seizure susceptibility. Taken together, these data define coordinated epigenetic and functional changes in microglia and uncover pattern recognition receptors as potential regulators of postnatal synaptic refinement.