Drugs targeting metabotropic glutamate receptor 5 (mGluR5) have therapeutic potential in autism spectrum disorders (ASD), including tuberous sclerosis complex (TSC). The question whether inhibition ...or potentiation of mGluR5 could be beneficial depends, among other factors, on the specific indication. To facilitate the development of mGluR5 treatment strategies, we tested the therapeutic utility of mGluR5 negative and positive allosteric modulators (an mGluR5 NAM and PAM) for TSC, using a mutant mouse model with neuronal loss of Tsc2 that demonstrates disease-related phenotypes, including behavioral symptoms of ASD and epilepsy. This model uniquely enables the in vivo characterization and rescue of the electrographic seizures associated with TSC. We demonstrate that inhibition of mGluR5 corrects hyperactivity, seizures, and elevated de novo synaptic protein synthesis. Conversely, positive allosteric modulation of mGluR5 results in the exacerbation of hyperactivity and epileptic phenotypes. The data suggest a meaningful therapeutic potential for mGluR5 NAMs in TSC, which warrants clinical exploration and the continued development of mGluR5 therapies.
Abstract
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.
Abstract
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.
•Cerebral malaria is an important disease model for understanding epileptogenesis.•Spectral analyses from EEGs recorded in low resource regions is feasible.•Early EEG gamma power is associated with ...post-cerebral malaria epilepsy.•Combined, acute clinical and EEG features in cerebral malaria predict epilepsy risk.
Cerebral malaria (CM) affects 500,000 million children annually, 10% whom develop epilepsy within two years. Acute identification of biomarkers for post-CM epilepsy would allow for follow-up of the highest risk populations in resource-limited regions. We investigated the utility of electroencephalogram (EEG) and clinical metrics obtained during acute CM infection for predicting epilepsy.
We analyzed 70 EEGs recorded within 24 h of admission for CM hospitalization obtained during the Blantyre Malaria Project Epilepsy Study (2005–2007), a prospective cohort study of pediatric CM survivors. While all studies underwent spectral analyses for comparisons of mean power band frequencies, a subset of EEGs from the 10 subjects who developed epilepsy and 10 age- and sex-matched controls underwent conventional visual analysis. Findings were tested for relationships to epilepsy outcomes.
Ten of the 70 subjects developed epilepsy. There were no significant differences between groups that were analyzed via visual EEG review; however, spectral EEG analyses revealed a significantly higher gamma-delta power ratio in CM survivors who developed epilepsy (0.23 ± 0.10) than in those who did not (0.16 ± 0.06), p = 0.003. Excluding potential confounders, multivariable logistic-regression analyses found relative gamma power (p = 0.003) and maximum temperature during admission (p = 0.03) significant and independent predictors of post-CM epilepsy, with area under receiver operating characteristics (AUROC) curve of 0.854.
We found that clinical and EEG metrics acquired during acute CM presentation confer risk of post-CM epilepsy. Further studies are required to investigate the utility of gamma activity as a potential biomarker of epileptogenesis and study this process over time. Additionally, resource limitations currently prevent follow-up of all CM cases to surveil for epilepsy, and identification of acute biomarkers in this population would offer the opportunity to allocate resources more efficiently.
Abstract Background Status epilepticus (SE) is a condition of prolonged or recurrent and often drug-resistant seizures where nonsedating SE therapy remains an important unmet need. Repetitive ...transcranial magnetic stimulation (rTMS) is emerging as a means to suppress seizures but has not been extensively studied in models. Objectives We aimed to test the antiepileptic potential of high-frequency rTMS in SE. As a step toward eventual coupling of rTMS with antiepileptic pharmacotherapy, we also tested whether high-frequency rTMS in combination with a low (ineffective but less likely to cause a side effect) lorazepam dose is as effective as a full lorazepam dose in suppressing seizures in a rat SE model. Methods EEG was recorded to measure epileptic spike frequency in the rat kainate SE model. Epileptic spikes were counted before, during, and after either high-frequency rTMS treatment alone or high-frequency rTMS treatment in combination with lorazepam, a firstline SE treatment. Results We found that rTMS alone decreases epileptic spike frequency only acutely. However, combinatory treatment with half-dose lorazepam together with rTMS was as effective as a full lorazepam dose. Conclusion We report that high-frequency rTMS has modest antiepileptic potential alone but acts in complement with lorazepam to suppress seizures.
Objective
Cathodal direct current stimulation (cDCS) induces long‐term depression (LTD)‐like reduction of cortical excitability (DCS‐LTD), which has been tested in the treatment of epilepsy with ...modest effects. In part, this may be due to variable cortical neuron orientation relative to the electric field. We tested, in vivo and in vitro, whether DCS‐LTD occurs throughout the cortical thickness, and if not, then whether drug–DCS pairing can enhance the uniformity of the cortical response and the cDCS antiepileptic effect.
Methods
cDCS‐mediated changes in cortical excitability were measured in vitro in mouse motor cortex (M1) and in human postoperative neocortex, in vivo in mouse somatosensory cortex (S1), and in a mouse kainic acid (KA)‐seizure model. Contributions of N‐methyl‐D‐aspartate–type glutamate receptors (NMDARs) to cDCS‐mediated plasticity were tested with application of NMDAR blockers (memantine/D‐AP5).
Results
cDCS reliably induced DCS‐LTD in superficial cortical layers, and a long‐term potentiation (LTP)‐like enhancement (DCS‐LTP) was recorded in deep cortical layers. Immunostaining confirmed layer‐specific increase of phospho‐S6 ribosomal protein in mouse M1. Similar nonuniform cDCS aftereffects on cortical excitability were also found in human neocortex in vitro and in S1 of alert mice in vivo. Application of memantine/D‐AP5 either produced a more uniform DCS‐LTD throughout the cortical thickness or at least abolished DCS‐LTP. Moreover, a combination of memantine and cDCS suppressed KA‐induced seizures.
Interpretation
cDCS aftereffects are not uniform throughout cortical layers, which may explain the incomplete cDCS clinical efficacy. NMDAR antagonists may augment cDCS efficacy in epilepsy and other disorders where regional depression of cortical excitability is desirable. ANN NEUROL 2020;88:489–502
Paired-pulse transcranial magnetic stimulation (ppTMS) is a safe and noninvasive tool for measuring cortical inhibition in humans, particularly in patients with disorders of cortical inhibition such ...as epilepsy. However, ppTMS protocols in rodent disease models, where mechanistic insight into the ppTMS physiology and into disease processes may be obtained, have been limited due to the requirement for anesthesia and needle electromyography. To eliminate the confounding factor of anesthesia and to approximate human ppTMS protocols in awake rats, we adapted the mechanomyogram (MMG) method to investigate the ppTMS inhibitory phenomenon in awake rats and then applied differential pharmacology to test the hypothesis that long-interval cortical inhibition is mediated by the GABA(A) receptor. Bilateral hindlimb-evoked MMGs were elicited in awake rats by long-interval ppTMS protocols with 50-, 100-, and 200-ms interstimulus intervals. Acute changes in ppTMS-MMG were measured before and after intraperitoneal injections of saline, the GABA(A) agonist pentobarbital (PB), and GABA(A) antagonist pentylenetetrazole (PTZ). An evoked MMG was obtained in 100% of animals by single-pulse stimulation, and ppTMS resulted in predictable inhibition of the test-evoked MMG. With increasing TMS intensity, MMG amplitudes increased in proportion to machine output to produce reliable input-output curves. Simultaneous recordings of electromyography and MMG showed a predictable latency discrepancy between the motor-evoked potential and the evoked MMG (7.55 ± 0.08 and 9.16 ± 0.14 ms, respectively). With pharmacological testing, time course observations showed that ppTMS-MMG inhibition was acutely reduced following PTZ (P < 0.05), acutely enhanced after PB (P < 0.01) injection, and then recovered to pretreatment baseline after 1 h. Our data support the application of the ppTMS-MMG technique for measuring the cortical excitability in awake rats and provide the evidence that GABA(A) receptor contributes to long-interval paired-pulse cortical inhibition. Thus ppTMS-MMG appears a well-tolerated biomarker for measuring GABA(A)-mediated cortical inhibition in rats.
Objective
To confirm the critical factors affecting seizure susceptibility in acute pentylenetetrazole (PTZ) mouse epilepsy models and evaluate the prior literature for these factors.
Methods
Serial ...cohorts of wild‐type mice administered intraperitoneal (IP)‐PTZ were aggregated and analyzed by multivariate logistic regression for the effect of sex, age, background strain, dose, and physiologic stress (i.e., EEG implantation and/or single‐housing) on seizure response. We assessed the reporting of these factors in a comprehensive literature review over the last 10 years (2010–2020).
Results
We conducted aggregated analysis of pooled data of 307 mice (220 C57BL/6J mice and 87 mixed background mice; 202 males, 105 females) with median age of 10 weeks (range: 6–49 weeks) with acute PTZ injection (dose range 40–65 mg/kg). Significance in multivariate analysis was found between seizures and increased PTZ dose (odds ratio (OR) 1.149, 95% confidence interval (CI) 1.102–1.205), older age (OR 1.1, 95% CI 1.041–1.170), physiologic stress (OR 17.36, 95% CI 7.349–44.48), and mixed background strain (OR 0.4725, 95% CI 0.2315–0.9345). Literature review identified 97 papers using acute PTZ‐seizure models. Age, housing, sex, and background were omitted by 61% (59/97), 51% (49/97), 18% (17/97), and 8% (8/97) papers, respectively. Only 17% of publications specified all four factors (16/97).
Interpretation
Our analysis and literature review demonstrate a critical gap in standardization of acute PTZ‐induced seizure paradigm in mice. We recommend that future studies specify and control for age, background strain, sex, and housing conditions of experimental animals.
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