Electrographic spikes are common in wildtype mice

Dendrimer nanotherapy targeting of glial dysfunction improves inflammation and neurobehavioral phenotype in adult female Mecp2-heterozygous mouse model of Rett syndrome

Rett syndrome is an X-linked neurodevelopmental disorder caused by mutation of Mecp2 gene and primarily affects females. Glial cell dysfunction has been implicated in in Rett syndrome (RTT) both in patients and in mouse models of this disorder and can affect synaptogenesis, glial metabolism and inflammation. Here we assessed whether treatment of adult (5-6 months old) symptomatic Mecp2-heterozygous female mice with N-acetyl cysteine conjugated to dendrimer (D-NAC), which is known to target glia and modulate inflammation and oxidative injury, results in improved behavioral phenotype, sleep and glial inflammatory profile. We show that unbiased global metabolomic analysis of the hippocampus and striatum in adult Mecp2-heterozygous mice demonstrates significant differences in lipid metabolism associated with neuroinflammation, providing the rationale for targeting glial inflammation in this model. Our results demonstrate that treatment with D-NAC (10 mg/kg NAC) once weekly is more efficacious than equivalently dosed free NAC in improving the gross neurobehavioral phenotype in symptomatic Mecp2-heterozygous female mice. We also show that D-NAC therapy is significantly better than saline in ameliorating several aspects of the abnormal phenotype including paw clench, mobility, fear memory, REM sleep and epileptiform activity burden. Systemic D-NAC significantly improves microglial proinflammatory cytokine production and is associated with improvements in several aspects of the phenotype including paw clench, mobility, fear memory, and REM sleep, and epileptiform activity burden in comparison to saline-treated Mecp2-hetereozygous mice. Systemic glial-targeted delivery of D-NAC after symptom onset in an older clinically relevant Rett syndrome model shows promise in improving neurobehavioral impairments along with sleep pattern and epileptiform activity burden. These findings argue for the translational value of this approach for treatment of patients with Rett Syndrome.

Mouse model of focal cortical dysplasia type II generates a wide spectrum of high-frequency activities

High-frequency oscillations (HFOs) represent an electrographic biomarker of endogenous epileptogenicity and seizure-generating tissue that proved clinically useful in presurgical planning and delineating the resection area. In the neocortex, the clinical observations on HFOs are not sufficiently supported by experimental studies stemming from a lack of realistic neocortical epilepsy models that could provide an explanation of the pathophysiological substrates of neocortical HFOs. In this study, we explored pathological epileptiform network phenomena, particularly HFOs, in a highly realistic murine model of neocortical epilepsy due to focal cortical dysplasia (FCD) type II. FCD was induced in mice by the expression of the human pathogenic mTOR gene mutation during embryonic stages of brain development. Electrographic recordings from multiple cortical regions in freely moving animals with FCD and epilepsy demonstrated that the FCD lesion generates HFOs from all frequency ranges, i.e., gamma, ripples, and fast ripples up to 800 Hz. Gamma-ripples were recorded almost exclusively in FCD animals, while fast ripples occurred in controls as well, although at a lower rate. Gamma-ripple activity is particularly valuable for localizing the FCD lesion, surpassing the utility of fast ripples that were also observed in control animals, although at significantly lower rates. Propagating HFOs occurred outside the FCD, and the contralateral cortex also generated HFOs independently of the FCD, pointing to a wider FCD network dysfunction. Optogenetic activation of neurons carrying mTOR mutation and expressing Channelrhodopsin-2 evoked fast ripple oscillations that displayed spectral and morphological profiles analogous to spontaneous oscillations. This study brings experimental evidence that FCD type II generates pathological HFOs across all frequency bands and provides information about the spatiotemporal properties of each HFO subtype in FCD. The study shows that mutated neurons represent a functionally interconnected and active component of the FCD network, as they can induce interictal epileptiform phenomena and HFOs.

Seizure reduction in TSC2-mutant mouse model by an mTOR catalytic inhibitor

OBJECTIVE

Tuberous sclerosis complex (TSC) is a neurodevelopmental disorder caused by autosomal-dominant pathogenic variants in either the TSC1 or TSC2 gene, and it is characterized by hamartomas in multiple organs, such as skin, kidney, lung, and brain. These changes can result in epilepsy, learning disabilities, and behavioral complications, among others. The mechanistic link between TSC and the mechanistic target of the rapamycin (mTOR) pathway is well established, thus mTOR inhibitors can potentially be used to treat the clinical manifestations of the disorder, including epilepsy.

METHODS

In this study, we tested the efficacy of a novel mTOR catalytic inhibitor (here named Tool Compound 1 or TC1) previously reported to be more brain-penetrant compared with other mTOR inhibitors. Using a well-characterized hypomorphic Tsc2 mouse model, which displays a translationally relevant seizure phenotype, we tested the efficacy of TC1.

RESULTS

Our results show that chronic treatment with this novel mTOR catalytic inhibitor (TC1), which affects both the mTORC1 and mTORC2 signaling complexes, reduces seizure burden, and extends the survival of Tsc2 hypomorphic mice, restoring species typical weight gain over development.

INTERPRETATION

Novel mTOR catalytic inhibitor TC1 exhibits a promising therapeutic option in the treatment of TSC.

N-acetylcysteine treatment mitigates loss of cortical parvalbumin-positive interneuron and perineuronal net integrity resulting from persistent oxidative stress in a rat TBI model

Traumatic brain injury (TBI) increases cerebral reactive oxygen species production, which leads to continuing secondary neuronal injury after the initial insult. Cortical parvalbumin-positive interneurons (PVIs; neurons responsible for maintaining cortical inhibitory tone) are particularly vulnerable to oxidative stress and are thus disproportionately affected by TBI. Systemic N-acetylcysteine (NAC) treatment may restore cerebral glutathione equilibrium, thus preventing post-traumatic cortical PVI loss. We therefore tested whether weeks-long post-traumatic NAC treatment mitigates cortical oxidative stress, and whether such treatment preserves PVI counts and related markers of PVI integrity and prevents pathologic electroencephalographic (EEG) changes, 3 and 6 weeks after fluid percussion injury in rats. We find that moderate TBI results in persistent oxidative stress for at least 6 weeks after injury and leads to the loss of PVIs and the perineuronal net (PNN) that surrounds them as well as of per-cell parvalbumin expression. Prolonged post-TBI NAC treatment normalizes the cortical redox state, mitigates PVI and PNN loss, and - in surviving PVIs - increases per-cell parvalbumin expression. NAC treatment also preserves normal spectral EEG measures after TBI. We cautiously conclude that weeks-long NAC treatment after TBI may be a practical and well-tolerated treatment strategy to preserve cortical inhibitory tone post-TBI.

Loss of ARHGAP15 affects the directional control of migrating interneurons in the embryonic cortex and increases susceptibility to epilepsy

GTPases of the Rho family are components of signaling pathways linking extracellular signals to the control of cytoskeleton dynamics. Among these, RAC1 plays key roles during brain development, ranging from neuronal migration to neuritogenesis, synaptogenesis, and plasticity. RAC1 activity is positively and negatively controlled by guanine nucleotide exchange factors (GEFs), guanosine nucleotide dissociation inhibitors (GDIs), and GTPase-activating proteins (GAPs), but the specific role of each regulator in vivo is poorly known. ARHGAP15 is a RAC1-specific GAP expressed during development in a fraction of migrating cortical interneurons (CINs) and in the majority of adult CINs. During development, loss of ARHGAP15 causes altered directionality of the leading process of tangentially migrating CINs, along with altered morphology in vitro. Likewise, time-lapse imaging of embryonic CINs revealed a poorly coordinated directional control during radial migration, possibly due to a hyper-exploratory behavior. In the adult cortex, the observed defects lead to subtle alteration in the distribution of CALB2-, SST-, and VIP-positive interneurons. Adult Arhgap15-knock-out mice also show reduced CINs intrinsic excitability, spontaneous subclinical seizures, and increased susceptibility to the pro-epileptic drug pilocarpine. These results indicate that ARHGAP15 imposes a fine negative regulation on RAC1 that is required for morphological maturation and directional control during CIN migration, with consequences on their laminar distribution and inhibitory function.

Differential effects of mTOR inhibition and dietary ketosis in a mouse model of subacute necrotizing encephalomyelopathy

Genetic mitochondrial diseases are the most frequent cause of inherited metabolic disorders and one of the most prevalent causes of heritable neurological disease. Leigh syndrome is the most common clinical presentation of pediatric mitochondrial disease, typically appearing in the first few years of life, and involving severe multisystem pathologies. Clinical care for Leigh syndrome patients is difficult, complicated by the wide range of symptoms including characteristic progressive CNS lesion, metabolic sequelae, and epileptic seizures, which can be intractable to standard management. While no proven therapies yet exist for the underlying mitochondrial disease, a ketogenic diet has led to some reports of success in managing mitochondrial epilepsies, with ketosis reducing seizure risk and severity. The impact of ketosis on other aspects of disease progression in Leigh syndrome has not been studied, however, and a rigorous study of the impact of ketosis on seizures in mitochondrial disease is lacking. Conversely, preclinical efforts have identified the intracellular nutrient signaling regulator mTOR as a promising therapeutic target, with data suggesting the benefits are mediated by metabolic changes. mTOR inhibition alleviates epilepsies arising from defects in TSC, an mTOR regulator, but the therapeutic potential of mTOR inhibition in seizures related to primary mitochondrial dysfunction is unknown. Given that ketogenic diet is used clinically in the setting of mitochondrial disease, and mTOR inhibition is in clinical trials for intractable pediatric epilepsies of diverse causal origins, a direct experimental assessment of their effects is imperative. Here, we define the impact of dietary ketosis on survival and CNS disease in the Ndufs4(KO) mouse model of Leigh syndrome and the therapeutic potential of both dietary ketosis and mTOR inhibition on seizures in this model. These data provide timely insight into two important clinical interventions.

Altered synaptic glutamate homeostasis contributes to cognitive decline in young APP/PSEN1 mice

Non-convulsive epileptiform activity is a common and under-studied comorbidity of Alzheimer’s disease that may significantly contribute to onset of clinical symptoms independently of other neuropathological features such as β-amyloid deposition. We used repeated treatment with low dose kainic acid (KA) to trigger subthreshold epileptiform activity in young (less than 6 months) wild-type (WT) and APP/PSEN1 mice to test the role of disruption to the glutamatergic system in epileptiform activity changes and the development of memory deficits. Short-term repeated low-dose KA (five daily treatments with 5 mg/kg, IP) impaired long-term potentiation in hippocampus of APP/PSEN1 but not WT mice. Long-term repeated low-dose KA (fourteen weeks of bi-weekly treatment with 7.5–10 mg/kg) led to high mortality in APP/PSEN1 mice. KA treatment also impaired memory retention in the APP/PSEN1 mice in a Morris water maze task under cognitively challenging reversal learning conditions where the platform was moved to a new location. Four weeks of bi-weekly treatment with 5 mg/kg KA also increased abnormal spike activity in APP/PSEN1 and not WT mice but did not impact sleep/wake behavioral states. These findings suggest that hyperexcitability in Alzheimer’s disease may indeed be an early contributor to cognitive decline that is independent of heavy β-amyloid-plaque load, which is absent in APP/PSEN1 mice under 6 months of age.

Increase in Seizure Susceptibility After Repetitive Concussion Results from Oxidative Stress, Parvalbumin-Positive Interneuron Dysfunction and Biphasic Increases in Glutamate/GABA Ratio

Chronic symptoms indicating excess cortical excitability follow mild traumatic brain injury, particularly repetitive mild traumatic brain injury (rmTBI). Yet mechanisms underlying post-traumatic excitation/inhibition (E/I) ratio abnormalities may differ between the early and late post-traumatic phases. We therefore measured seizure threshold and cortical gamma-aminobutyric acid (GABA) and glutamate (Glu) concentrations, 1 and 6 weeks after rmTBI in mice. We also analyzed the structure of parvalbumin-positive interneurons (PVIs), their perineuronal nets (PNNs), and their electroencephalography (EEG) signature (gamma frequency band power). For mechanistic insight, we measured cortical oxidative stress, reflected in the reduced/oxidized glutathione (GSH/GSSG) ratio. We found that seizure susceptibility increased both early and late after rmTBI. However, whereas increased Glu dominated the E/I 1 week after rmTBI, Glu concentration normalized and the E/I was instead characterized by depressed GABA, reduced per-PVI parvalbumin expression, and reduced gamma EEG power at the 6-week post-rmTBI time point. Oxidative stress was increased early after rmTBI, where transient PNN degradation was noted, and progressed throughout the monitoring period. We conclude that GSH depletion, perhaps triggered by early Glu-mediated excitotoxicity, leads to late post-rmTBI loss of PVI-dependent cortical inhibitory tone. We thus propose dampening of Glu signaling, maintenance of redox state, and preservation of PVI inhibitory capacity as therapeutic targets for post-rmTBI treatment.

Aged heterozygous Cdkl5 mutant mice exhibit spontaneous epileptic spasms

CDKL5 deficiency disorder (CDD) is a devastating neurodevelopmental disorder characterized by early-onset epilepsy, severe intellectual disability, cortical visual impairment and motor disabilities. Epilepsy is a central feature of CDD, with most patients having intractable seizures, but seizure frequency and severity can vary. Clinical reports demonstrate a diversity in seizure semiology and electrographic features, with no pattern diagnostic of CDD. Although animal models of CDD have shown evidence of hyperexcitability, spontaneous seizures have not been previously reported. Here, we present the first systematic study of spontaneous seizures in mouse models of CDD. Epileptic spasms, the most frequent and persistent seizure type in CDD patients, were recapitulated in two mouse models of CDD carrying heterozygous mutations, Cdkl5^R59X and Cdkl5^KO. Spasm-like events were present in a significant proportion of aged heterozygous female mice carrying either of the two Cdkl5 mutations with significant variability in seizure burden. Electrographically, spasms were most frequently associated with generalized slow-wave activity and tended to occur in clusters during sleep. CDD mice also showed interictal and background abnormalities, characterized by high-amplitude spiking and altered power in multiple frequency bands. These data demonstrate that aged female heterozygous Cdkl5 mice recapitulate multiple features of epilepsy in CDD and can serve to complement existing models of epileptic spasms in future mechanistic and translational studies.

Regulation of lifespan by neural excitation and REST

The mechanisms that extend lifespan in humans are poorly understood. Here we show that extended longevity in humans is associated with a distinct transcriptome signature in the cerebral cortex that is characterized by downregulation of genes related to neural excitation and synaptic function. In Caenorhabditis elegans, neural excitation increases with age and inhibition of excitation globally, or in glutamatergic or cholinergic neurons, increases longevity. Furthermore, longevity is dynamically regulated by the excitatory-inhibitory balance of neural circuits. The transcription factor REST is upregulated in humans with extended longevity and represses excitation-related genes. Notably, REST-deficient mice exhibit increased cortical activity and neuronal excitability during ageing. Similarly, loss-of-function mutations in the C. elegans REST orthologue genes spr-3 and spr-4 elevate neural excitation and reduce the lifespan of long-lived daf-2 mutants. In wild-type worms, overexpression of spr-4 suppresses excitation and extends lifespan. REST, SPR-3, SPR-4 and reduced excitation activate the longevity-associated transcription factors FOXO1 and DAF-16 in mammals and worms, respectively. These findings reveal a conserved mechanism of ageing that is mediated by neural circuit activity and regulated by REST.

Transcranial focused ultrasound pulsation suppresses pentylenetetrazol induced epilepsy in vivo

BACKGROUND

Epilepsy is a neurological disorder characterized by abnormal neuron discharge, and one-third of epilepsy patients suffer from drug-resistant epilepsy (DRE). The current management for DRE includes epileptogenic lesion resection, disconnection, and neuromodulation. Neuromodulation is achieved through invasive electrical stimulus including deep brain stimulation, vagus nerve stimulation, or responsive neurostimulation (RNS). As an alternative therapy, transcranial focused ultrasound (FUS) can transcranially and non-invasively modulate neuron activity.

OBJECTIVE

This study seeks to verify the use of FUS pulsations to suppress spikes in an acute epileptic small-animal model, and to investigate possible biological mechanisms by which FUS pulsations interfere with epileptic neuronal activity.

METHODS

The study used a total of 76 Sprague-Dawley rats. For the epilepsy model, rats were administered pentylenetetrazol (PTZ) to induce acute epileptic-like abnormal neuron discharges, followed by FUS exposure. Various ultrasound parameters were set to test the epilepsy-suppressing effect, while concurrently monitoring and analyzing electroencephalogram (EEG) signals. Animal behavior was monitored and histological examinations were conducted to evaluate the hazard posed by ultrasound exposure and the expression of neuronal activity markers. Western blotting was used to evaluate the correlation between FUS-induced epileptic suppression and the PI3K-mTOR signaling pathway.

RESULTS

We observed that FUS pulsations effectively suppressed epileptic activity and observed EEG spectrum oscillations; the spike-suppressing effect depended on the selection of ultrasound parameters and highly correlated with FUS exposure level. Expression level changes of c-Fos and GAD65 were confirmed in the cortex and hippocampus, indicating that FUS pulsations deactivated excitatory cells and activated GABAergic terminals. No tissue damage, inflammatory response, or behavioral abnormalities were observed in rats treated with FUS under these exposure parameters. We also found that the FUS pulsations down-regulated the S6 phosphorylation and decreased pAKT expression.

CONCLUSION

Our results suggest that pulsed FUS exposure effectively suppresses epileptic spikes in an acute epilepsy animal model, and finds that ultrasound pulsation interferes with neuronal activity and affects the PTZ-induced PI3K-Akt-mTOR pathway, which might help explain the mechanism underlying ultrasound-related epileptic spike control.