Seizures exacerbate excitatory: inhibitory imbalance in Alzheimer's disease and 5XFAD mice.

Approximately 22% of Alzheimer's disease (AD) patients suffer from seizures, and the co-occurrence of seizures and epileptiform activity exacerbates AD pathology and related cognitive deficits, suggesting that seizures may be a targetable component of AD progression. Given that alterations in neuronal excitatory:inhibitory (E:I) balance occur in epilepsy, we hypothesized that decreased markers of inhibition relative to those of excitation would be present in AD patients. We similarly hypothesized that in five times familial AD (5XFAD) mice, the E:I imbalance would progress from an early stage (prodromal) to later symptomatic stages, and be further exacerbated by pentylenetetrazol (PTZ) kindling. Post-mortem AD temporal cortical tissue from patients with or without seizure history were examined for changes in several markers of E:I balance, including levels of the inhibitory GABAA receptor, the sodium potassium chloride cotransporter 1 (NKCC1) and potassium chloride cotransporter 2 (KCC2), and the excitatory NMDA and AMPA type glutamate receptors. We performed patch clamp electrophysiological recordings from CA1 neurons in hippocampal slices and examined the same markers of E:I balance in prodromal 5XFAD mice. We next examined 5XFAD mice at chronic stages, after PTZ or control protocols, and in response to chronic mTORC1 inhibitor rapamycin, administered following kindled seizures, for markers of E:I balance. We found that AD patients with comorbid seizures had worsened cognitive and functional scores and had decreased GABAA receptor subunit expression, and increased NKCC1/KCC2 ratios, indicative of depolarizing GABA responses. Patch clamp recordings of prodromal 5XFAD CA1 neurons showed increased intrinsic excitability, along with decreased GABAergic inhibitory transmission and altered glutamatergic neurotransmission, indicating that E:I imbalance may occur in early disease stages. Furthermore, seizure induction in prodromal 5XFAD mice led to later dysregulation of NKCC1/KCC2 and a reduction in GluA2 AMPA glutamate receptor subunit expression, indicative of depolarizing GABA receptors and calcium permeable AMPA receptors. Finally, we found that chronic treatment with the mTORC1 inhibitor, rapamycin, at doses we have previously shown to attenuate seizure-induced ß-amyloid pathology and cognitive deficits, could also reverse elevations to NKCC1/KCC2 ratio in these mice. Our data demonstrate novel mechanisms of interaction between AD and epilepsy and indicate that targeting E:I balance, potentially with FDA-approved mTOR inhibitors, hold therapeutic promise for AD patients with a seizure history.

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.

Posttraumatic Epilepsy and Dementia Risk.

Importance: Although both head injury and epilepsy are associated with long-term dementia risk, posttraumatic epilepsy (PTE) has only been evaluated in association with short-term cognitive outcomes. Objective: To investigate associations of PTE with dementia risk. Design, Setting, and Participants: The Atherosclerosis Risk in Communities (ARIC) study initially enrolled participants from 1987 to 1989 and this prospective cohort study uses data through December 31, 2019, with a median follow-up of 25 years. Data were analyzed between March 14, 2023, and January 2, 2024. The study took place in 4 US communities in Minnesota, Maryland, North Carolina, and Mississippi. Of 15 792 ARIC study participants initially enrolled, 2061 were ineligible and 1173 were excluded for missing data, resulting in 12 558 included participants. Exposures: Head injury was defined by self-report and International Classification of Diseases (ICD) diagnostic codes. Seizure/epilepsy was defined using ICD codes. PTE was defined as a diagnosis of seizure/epilepsy occurring more than 7 days after head injury. Head injury, seizure/epilepsy, and PTE were analyzed as time-varying exposures. Main Outcomes and Measures: Dementia was defined using cognitive assessments, informant interviews, and ICD and death certificate codes. Adjusted Cox and Fine and Gray proportional hazards models were used to estimate dementia risk. Results: Participants had a mean (SD) age of 54.3 (5.8) years at baseline, 57.7% were female, 28.2% were of self-reported Black race, 14.4% were ultimately categorized as having head injury, 5.1% as having seizure/epilepsy, and 1.2% as having PTE. Over a median follow-up of 25 (25th to 75th percentile, 17-30) years, 19.9% developed dementia. In fully adjusted models, compared with no head injury and no seizure/epilepsy, PTE was associated with 4.56 (95% CI, 4.49-5.95) times the risk of dementia, while seizure/epilepsy was associated with 2.61 (95% CI, 2.21-3.07) times the risk and head injury with 1.63 (95% CI, 1.47-1.80) times the risk. The risk of dementia associated with PTE was significantly higher than the risk associated with head injury alone and with nontraumatic seizure/epilepsy alone. Results were slightly attenuated in models accounting for the competing risks of mortality and stroke, but patterns of association remained similar. In secondary analyses, the increased dementia risk associated with PTE occurring after first vs second head injury and after mild vs moderate/severe injury was similar. Conclusions and Relevance: In this community-based cohort, there was an increased risk of dementia associated with PTE that was significantly higher than the risk associated with head injury or seizure/epilepsy alone. These findings provide evidence that PTE is associated with long-term outcomes and supports both the prevention of head injuries via public health measures and further research into the underlying mechanisms and the risk factors for the development of PTE, so that efforts can also be focused on the prevention of PTE after a head injury.

Reversible synaptic adaptations in a subpopulation of murine hippocampal neurons following early-life seizures.

Early-life seizures (ELSs) can cause permanent cognitive deficits and network hyperexcitability, but it is unclear whether ELSs induce persistent changes in specific neuronal populations and whether these changes can be targeted to mitigate network dysfunction. We used the targeted recombination of activated populations (TRAP) approach to genetically label neurons activated by kainate-induced ELSs in immature mice. The ELS-TRAPed neurons were mainly found in hippocampal CA1, remained uniquely susceptible to reactivation by later-life seizures, and displayed sustained enhancement in α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor-mediated (AMPAR-mediated) excitatory synaptic transmission and inward rectification. ELS-TRAPed neurons, but not non-TRAPed surrounding neurons, exhibited enduring decreases in Gria2 mRNA, responsible for encoding the GluA2 subunit of the AMPARs. This was paralleled by decreased synaptic GluA2 protein expression and heightened phosphorylated GluA2 at Ser880 in dendrites, indicative of GluA2 internalization. Consistent with increased GluA2-lacking AMPARs, ELS-TRAPed neurons showed premature silent synapse depletion, impaired long-term potentiation, and impaired long-term depression. In vivo postseizure treatment with IEM-1460, an inhibitor of GluA2-lacking AMPARs, markedly mitigated ELS-induced changes in TRAPed neurons. These findings show that enduring modifications of AMPARs occur in a subpopulation of ELS-activated neurons, contributing to synaptic dysplasticity and network hyperexcitability, but are reversible with early IEM-1460 intervention.

Recognizing and Responding to the Needs of Future Child and Adult Neurology Care Through the Evolution of Residency Training.

Recent insights into the frequency of occurrence and the genetic and mechanistic basis of nervous system disease have demonstrated that neurologic disorders occur as a spectrum across all ages. To meet future needs of patients with neurologic disease of all ages and prepare for increasing implementaton of precision therapies, greater integration of child and adult neurology residency training is needed. ANN NEUROL 2023;94:1005-1007.

Discovery of E2730, a novel selective uncompetitive GAT1 inhibitor, as a candidate for anti-seizure medication.

OBJECTIVE: As of 2022, 36 anti-seizure medications (ASMs) have been licensed for the treatment of epilepsy, however, adverse effects (AEs) are commonly reported. Therefore, ASMs with a wide margin between therapeutic effects and AEs are preferred over ASMs that are associated with a narrow margin between efficacy and risk of AEs. E2730 was discovered using in vivo phenotypic screening and characterized as an uncompetitive, yet selective, inhibitor of γ-aminobutyric acid (GABA) transporter 1 (GAT1). Here, we describe the preclinical characteristics of E2730. METHODS: Anti-seizure effects of E2730 were evaluated in several animal models of epilepsy: corneal kindling, 6 Hz-44 mA psychomotor seizure, amygdala kindling, Fragile X syndrome, and Dravet syndrome models. Effects of E2730 on motor coordination were assessed in accelerating rotarod tests. The mechanism of action of E2730 was explored by [3 H]E2730 binding assay. The GAT1-selectivity over other GABA transporters was examined by GABA uptake assay of GAT1, GAT2, GAT3, or betaine/GABA transporter 1 (BGT-1) stably expressing HEK293 cells. To further investigate the mechanism for E2730-mediated inhibition of GAT1, in vivo microdialysis and in vitro GABA uptake assays were conducted under conditions of different GABA concentrations. RESULTS: E2730 showed anti-seizure effects in the assessed animal models with an approximately >20-|fold margin between efficacy and motor incoordination. [3 H]E2730 binding on brain synaptosomal membrane was abolished in GAT1-deficient mice, and E2730 selectively inhibited GAT1-mediated GABA uptake over other GABA transporters. In addition, results of GABA uptake assays showed that E2730-mediated inhibition of GAT1 positively correlated to the level of ambient GABA in vitro. E2730 also increased extracellular GABA concentration in hyperactivated conditions but not under basal levels in vivo. SIGNIFICANCE: E2730 is a novel, selective, uncompetitive GAT1 inhibitor, which acts selectively under the condition of increasing synaptic activity, contributing to a wide margin between therapeutic effect and motor incoordination.

Anti-seizure efficacy of perampanel in two established rodent models of early-life epilepsy.

Early-life seizures can be refractory to conventional antiseizure medications (ASMs) and can also result in chronic epilepsy and long-term behavioral and cognitive deficits. Treatments targeting age-specific mechanisms contributing to epilepsy would be of clinical benefit. One such target is the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) subtype of excitatory glutamate receptor, which is upregulated in the developing brain. Perampanel is a non-competitive, selective AMPAR antagonist that is FDA-approved for focal onset seizures (FOS) or primary generalized tonic-clonic seizures (PGTC) in children and adults. However, the efficacy of perampanel treatment in epilepsy patients younger than 4 years has been less documented. We thus tested the efficacy of perampanel in two early-life seizure models: (1) a rat model of hypoxia-induced neonatal seizures and (2) a mouse model of Dravet syndrome with hyperthermia-induced seizures. Pretreatment with perampanel conferred dose-dependent protection against early-life seizures in both experimental models. These findings suggest that AMPAR-mediated hyperexcitability could be involved in the pathophysiology of early-life seizures, which may be amenable to treatment with perampanel.

Shifting the trajectory of therapeutic development for neurological and psychiatric disorders.

Clinical trials for central nervous system disorders often enroll patients with unrecognized heterogeneous diseases, leading to costly trials that have high failure rates. Here, we discuss the potential of emerging technologies and datasets to elucidate disease mechanisms and identify biomarkers to improve patient stratification and monitoring of disease progression in clinical trials for neuropsychiatric disorders. Greater efforts must be centered on rigorously standardizing data collection and sharing of methods, datasets, and analytical tools across sectors. To address health care disparities in clinical trials, diversity of genetic ancestries and environmental exposures of research participants and associated biological samples must be prioritized.

Optical Redox Imaging of Ex Vivo Hippocampal Tissue Reveals Age-Dependent Alterations in the 5XFAD Mouse Model of Alzheimer's Disease.

A substantial decline in nicotinamide adenine dinucleotide (NAD) has been reported in brain tissue homogenates or neurons isolated from Alzheimer's disease (AD) models. NAD, together with flavin adenine dinucleotide (FAD), critically supports energy metabolism and maintains mitochondrial redox homeostasis. Optical redox imaging (ORI) of the intrinsic fluorescence of reduced NAD (NADH) and oxidized FAD yields cellular redox and metabolic information and provides biomarkers for a variety of pathological conditions. However, its utility in AD has not been characterized at the tissue level. We performed ex vivo ORI of freshly dissected hippocampi from a well-characterized AD mouse model with five familial Alzheimer's disease mutations (5XFAD) and wild type (WT) control littermates at various ages. We found (1) a significant increase in the redox ratio with age in the hippocampi of both the WT control and the 5XFAD model, with a more prominent redox shift in the AD hippocampi; (2) a higher NADH in the 5XFAD versus WT hippocampi at the pre-symptomatic age of 2 months; and (3) a negative correlation between NADH and Aß42 level, a positive correlation between Fp and Aß42 level, and a positive correlation between redox ratio and Aß42 level in the AD hippocampi. These findings suggest that the ORI can be further optimized to conveniently study the metabolism of freshly dissected brain tissues in animal models and identify early AD biomarkers.

The role of mTORC1 activation in seizure-induced exacerbation of Alzheimer's disease.

The risk of seizures is 10-fold higher in patients with Alzheimer's disease than the general population, yet the mechanisms underlying this susceptibility and the effects of these seizures are poorly understood. To elucidate the proposed bidirectional relationship between Alzheimer's disease and seizures, we studied human brain samples (n = 34) from patients with Alzheimer's disease and found that those with a history of seizures (n = 14) had increased amyloid-ß and tau pathology, with upregulation of the mechanistic target of rapamycin (mTOR) pathway, compared with patients without a known history of seizures (n = 20). To establish whether seizures accelerate the progression of Alzheimer's disease, we induced chronic hyperexcitability in the five times familial Alzheimer's disease mouse model by kindling with the chemoconvulsant pentylenetetrazol and observed that the mouse model exhibited more severe seizures than the wild-type. Furthermore, kindled seizures exacerbated later cognitive impairment, Alzheimer's disease neuropathology and mTOR complex 1 activation. Finally, we demonstrated that the administration of the mTOR inhibitor rapamycin following kindled seizures rescued enhanced remote and long-term memory deficits associated with earlier kindling and prevented seizure-induced increases in Alzheimer's disease neuropathology. These data demonstrated an important link between chronic hyperexcitability and progressive Alzheimer's disease pathology and suggest a mechanism whereby rapamycin may serve as an adjunct therapy to attenuate progression of the disease.

Dysregulation of GABAA Receptor-Mediated Neurotransmission during the Auditory Cortex Critical Period in the Fragile X Syndrome Mouse Model.

Fragile X syndrome (FXS) is the leading monogenic form of intellectual disability and autism, with patients exhibiting numerous auditory-related phenotypes during their developmental period, including communication, language development, and auditory processing deficits. Despite FXS studies describing excitatory-inhibitory (E-I) imbalance in the auditory circuit and an impaired auditory critical period, evaluation of E-I circuitry maturation in the auditory cortex of FXS models remains limited. Here, we examined GABAA receptor (GABAAR)-mediated inhibitory synaptic transmission within the auditory cortex, characterizing normal intracortical circuit development patterns in wild-type (WT) mice and examining their dysregulation in developing Fmr1 knock-out (KO) mice. Electrophysiological recordings revealed gradual developmental shifts in WT L4-L2/3 connectivity, where circuit excitability significantly increased after critical period onset. KO mice exhibited accelerated developmental shifts related to aberrant GABAergic signaling. Specifically, Fmr1 KO L2/3 pyramidal neurons have enhanced developmental sensitivity to pharmacological GABAAR modulators, altered maturation of GABAAR voltage-dependent conductance, with additional presynaptic GABA release alterations. These differences are further accompanied by alterations in developmental long-term potentiation. Together, our results suggest that altered GABAergic signaling within developing Fmr1 KOs impairs the normal patterning of E-I circuit and synaptic plasticity maturation to contribute to the impaired auditory cortex critical period and functional auditory deficits in FXS.

Altered hippocampal dendritic spine maturation after hypoxia-induced seizures in neonatal rats.

Cognitive comorbidities often follow early-life seizures (ELS), especially in the setting of autism and other neurodevelopmental syndromes. However, there is an incomplete understanding of whether neuronal and synaptic development are concomitantly dysregulated. We have previously shown that hypoxia-induced seizures (HS) in postnatal day (P)10 rats increase acute and later-life hippocampal glutamatergic neurotransmission and spontaneous recurrent seizures, and impair cognition and behavior. As dendritic spines critically regulate synaptic function, we hypothesized that ELS can induce developmentally specific changes in dendritic spine maturation. At intervals during one month following HS in P10 rats, we assessed dendritic spine development on pyramidal neurons in the stratum radiatum of hippocampal area CA1. Compared to control rats in which spine density significantly decreased from P10 to early adulthood (P38), post-seizure rats failed to show a developmental decrease in spine density, and spines from P38 post-seizure rats appeared more immature-shaped (long, thin). In addition, compared to P38 control rats, post-seizure P38 rats expressed significantly more synaptic PSD-95, a marker of mature synapses. These changes were preceded by a transient increase in hippocampal expression of cofilin phosphorylated at Ser3, representing a decrease in cofilin activity. These results suggest that early-life seizures may impair normal dendritic spine maturation and pruning in CA1 during development, resulting in an excess of less efficient synapses, via activity-dependent modification of actin-regulating proteins such as cofilin. Given that multiple neurodevelopmental disorders show similar failures in developmental spine pruning, the current findings may represent a deficit in structural plasticity that could be a component of a mechanism leading to later-life cognitive consequences associated with early-life seizures.

Adults with Cerebral Palsy Require Ongoing Neurologic Care: A Systematic Review.

Cerebral palsy (CP) neurologic care and research efforts typically focus on children. However, most people with CP are adults. Adults with CP are at increased risk of new neurologic conditions, such as stroke and myelopathy, that require ongoing neurologic surveillance to distinguish them from baseline motor impairments. Neurologic factors could also contribute to the motor function decline, chronic pain, and chronic fatigue that are commonly experienced by adults with CP. Based on a systematic literature review, we suggest (1) guidelines for neurologic surveillance and neurologist referral and (2) clinical research questions regarding the evolving neurologic risks for adults with CP. ANN NEUROL 2021;89:860-871.

A Pilot Randomized, Controlled, Double-Blind Trial of Bumetanide to Treat Neonatal Seizures.

OBJECTIVE: In the absence of controlled trials, treatment of neonatal seizures has changed minimally despite poor drug efficacy. We tested bumetanide added to phenobarbital to treat neonatal seizures in the first trial to include a standard-therapy control group. METHODS: A randomized, double-blind, dose-escalation design was employed. Neonates with postmenstrual age 33 to 44 weeks at risk of or with seizures were eligible. Subjects with electroencephalography (EEG)-confirmed seizures after ≥20 and <40mg/kg phenobarbital were randomized to receive additional phenobarbital with either placebo (control) or 0.1, 0.2, or 0.3mg/kg bumetanide (treatment). Continuous EEG monitoring data from ≥2 hours before to ≥48 hours after study drug administration (SDA) were analyzed for seizures. RESULTS: Subjects were randomized to treatment (n = 27) and control (n = 16) groups. Pharmacokinetics were highly variable among subjects and altered by hypothermia. The only statistically significant adverse event was diuresis in treated subjects (48% vs 13%, p = 0.02). One treated (4%) and 3 control subjects died (19%, p = 0.14). Among survivors, 2 of 26 treated subjects (8%) and 0 of 13 control subjects had hearing impairment, as did 1 nonrandomized subject. Total seizure burden varied widely, with much higher seizure burden in treatment versus control groups (median = 3.1 vs 1.2 min/h, p = 0.006). There was significantly greater reduction in seizure burden 0 to 4 hours and 2 to 4 hours post-SDA (both p < 0.01) compared with 2-hour baseline in treatment versus control groups with adjustment for seizure burden. INTERPRETATION: Although definitive proof of efficacy awaits an appropriately powered phase 3 trial, this randomized, controlled, multicenter trial demonstrated an additional reduction in seizure burden attributable to bumetanide over phenobarbital without increased serious adverse effects. Future trials of bumetanide and other drugs should include a control group and balance seizure severity. ANN NEUROL 2021;89:327-340.

Opportunities and limitations of genetically modified nonhuman primate models for neuroscience research.

The recently developed new genome-editing technologies, such as the CRISPR/Cas system, have opened the door for generating genetically modified nonhuman primate (NHP) models for basic neuroscience and brain disorders research. The complex circuit formation and experience-dependent refinement of the human brain are very difficult to model in vitro, and thus require use of in vivo whole-animal models. For many neurodevelopmental and psychiatric disorders, abnormal circuit formation and refinement might be at the center of their pathophysiology. Importantly, many of the critical circuits and regional cell populations implicated in higher human cognitive function and in many psychiatric disorders are not present in lower mammalian brains, while these analogous areas are replicated in NHP brains. Indeed, neuropsychiatric disorders represent a tremendous health and economic burden globally. The emerging field of genetically modified NHP models has the potential to transform our study of higher brain function and dramatically facilitate the development of effective treatment for human brain disorders. In this paper, we discuss the importance of developing such models, the infrastructure and training needed to maximize the impact of such models, and ethical standards required for using these models.

Alzheimer-like amyloid and tau alterations associated with cognitive deficit in temporal lobe epilepsy.

Temporal lobe epilepsy represents a major cause of drug-resistant epilepsy. Cognitive impairment is a frequent comorbidity, but the mechanisms are not fully elucidated. We hypothesized that the cognitive impairment in drug-resistant temporal lobe epilepsy could be due to perturbations of amyloid and tau signalling pathways related to activation of stress kinases, similar to those observed in Alzheimer's disease. We examined these pathways, as well as amyloid-ß and tau pathologies in the hippocampus and temporal lobe cortex of drug-resistant temporal lobe epilepsy patients who underwent temporal lobe resection (n = 19), in comparison with age- and region-matched samples from neurologically normal autopsy cases (n = 22). Post-mortem temporal cortex samples from Alzheimer's disease patients (n = 9) were used as positive controls to validate many of the neurodegeneration-related antibodies. Western blot and immunohistochemical analysis of tissue from temporal lobe epilepsy cases revealed increased phosphorylation of full-length amyloid precursor protein and its associated neurotoxic cleavage product amyloid-ß*56. Pathological phosphorylation of two distinct tau species was also increased in both regions, but increases in amyloid-ß1-42 peptide, the main component of amyloid plaques, were restricted to the hippocampus. Furthermore, several major stress kinases involved in the development of Alzheimer's disease pathology were significantly activated in temporal lobe epilepsy brain samples, including the c-Jun N-terminal kinase and the protein kinase R-like endoplasmic reticulum kinase. In temporal lobe epilepsy cases, hippocampal levels of phosphorylated amyloid precursor protein, its pro-amyloidogenic processing enzyme beta-site amyloid precursor protein cleaving enzyme 1, and both total and hyperphosphorylated tau expression, correlated with impaired preoperative executive function. Our study suggests that neurodegenerative and stress-related processes common to those observed in Alzheimer's disease may contribute to cognitive impairment in drug-resistant temporal lobe epilepsy. In particular, we identified several stress pathways that may represent potential novel therapeutic targets.

AMPA Receptor Dysregulation and Therapeutic Interventions in a Mouse Model of CDKL5 Deficiency Disorder.

Pathogenic mutations in cyclin-dependent kinase-like 5 (CDKL5) result in CDKL5 deficiency disorder (CDD), a rare disease marked by early-life seizures, autistic behaviors, and intellectual disability. Although mouse models of CDD exhibit dendritic instability and alterations in synaptic scaffolding proteins, studies of glutamate receptor levels and function are limited. Here we used a novel mouse model of CDD, the Cdkl5R59X knock-in mouse (R59X), to investigate changes in synaptic glutamate receptor subunits and functional consequences. Male mice were used for all experiments to avoid the confounding effects of X-inactivation that would be present in female heterozygous mice. We showed that adult male R59X mice recapitulated the behavioral outcomes observed in other mouse models of CDD, including social deficits and memory and learning impairments, and exhibited decreased latency to seizure upon pentylenetetrazol administration. Furthermore, we observed a specific increase in GluA2-lacking α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid)-type glutamate receptors (AMPARs) in the adult R59X hippocampus, which is accompanied electrophysiologically by increased rectification ratio of AMPAR EPSCs and elevated early-phase long term potentiation (LTP). Finally, we showed that acute treatment with the GluA2-lacking AMPAR blocker IEM-1460 decreased AMPAR currents, and rescued social deficits, working memory impairments, and seizure behavior latency in R59X mice.SIGNIFICANCE STATEMENT CDKL5 deficiency disorder (CDD) is a rare disease marked by autistic-like behaviors, intellectual disability, and seizures. While synaptic dysfunction has been observed in mouse models of CDD, there is limited information on how synaptic alterations contribute to behavioral and functional changes in CDD. Here we reveal elevated hippocampal GluA2-lacking AMPAR expression in a novel mouse model of CDD that is accompanied by changes in synaptic AMPAR function and plasticity. We also show, for the first time, that acutely targeting GluA2-lacking AMPAR dysregulation rescues core synaptic and neurobehavioral deficits in CDD.

Regulation of seizure-induced MeCP2 Ser421 phosphorylation in the developing brain.

Neonatal seizures disrupt normal synaptic maturation and often lead to later-life epilepsy and cognitive deficits. During early life, the brain exhibits heightened synaptic plasticity, in part due to a developmental overabundance of CaV1.2 L-type voltage gated calcium (Ca2+) channels (LT-VGCCs) and Ca2+-permeable AMPARs (CP-AMPARs) lacking GluA2 subunits. We hypothesized that early-life seizures overactivate these channels, in turn dysregulating Ca2+-dependent signaling pathways including that of methyl CPG binding protein 2 (MeCP2), a transcription factor implicated in the autism spectrum disorder (ASD) Rett Syndrome. Here, we show that in vivo hypoxia-induced seizures (HS) in postnatal day (P)10 rats acutely induced phosphorylation of the neuronal-specific target of activity-dependent MeCP2 phosphorylation, S421, as well as its upstream activator CaMKII T286. We next identified mechanisms by which activity-dependent Ca2+ influx induced MeCP2 phosphorylation using in vitro cortical and hippocampal neuronal cultures at embryonic day (E)18 + 10 days in vitro (DIV). In contrast to the prevalent role of NMDARs in the adult brain, we found that both CP-AMPARs and LT-VGCCs mediated MeCP2 S421 and CaMKII T286 phosphorylation induced by kainic acid (KA) or high potassium chloride (KCl) stimulation. Furthermore, in vivo post-seizure treatment with the broad-spectrum AMPAR antagonist NBQX, the CP-AMPAR blocker IEM-1460, or the LT-VGCC antagonist nimodipine blocked seizure-induced MeCP2 phosphorylation. Collectively, these results demonstrate that early-life seizures dysregulate critical activity-dependent developmental signaling pathways, in part via CP-AMPAR and LT-VGCC activation, providing novel age-specific therapeutic targets for convergent pathways underlying epilepsy and ASDs.

Early Seizures Prematurely Unsilence Auditory Synapses to Disrupt Thalamocortical Critical Period Plasticity.

Heightened neural excitability in infancy and childhood results in increased susceptibility to seizures. Such early-life seizures are associated with language deficits and autism that can result from aberrant development of the auditory cortex. Here, we show that early-life seizures disrupt a critical period (CP) for tonotopic map plasticity in primary auditory cortex (A1). We show that this CP is characterized by a prevalence of "silent," NMDA-receptor (NMDAR)-only, glutamate receptor synapses in auditory cortex that become "unsilenced" due to activity-dependent AMPA receptor (AMPAR) insertion. Induction of seizures prior to this CP occludes tonotopic map plasticity by prematurely unsilencing NMDAR-only synapses. Further, brief treatment with the AMPAR antagonist NBQX following seizures, prior to the CP, prevents synapse unsilencing and permits subsequent A1 plasticity. These findings reveal that early-life seizures modify CP regulators and suggest that therapeutic targets for early post-seizure treatment can rescue CP plasticity.