Circadian rhythms: interactions with seizures and epilepsy

Analysis of seizure-cluster circadian periodicity from a long-term, open-label safety study of diazepam nasal spray

OBJECTIVE

Seizure clusters require prompt medical treatment to minimize possible progression to status epilepticus, increased health care use, and disruptions to daily life. Isolated seizures may exhibit cyclical patterns, including circadian and longer rhythms. However, little is known about the cyclical patterns in seizure clusters. This post hoc analysis of data from a long-term, phase 3, open-label, repeat-dose safety study of diazepam nasal spray modeled the periodicity of treated seizure clusters.

METHODS

Mixed-effects cosinor analysis evaluated circadian rhythmicity, and single component cosinors using 12 and 24 h were used to calculate cosinor parameters (e.g., midline statistic of rhythm, wave ampitude, and acrophase [peak]). Analysis was completed for the full cohort and a consistent cohort of participants with two or more seizure clusters in each of four, 3-month periods. The influence of epilepsy type on cosinor parameters was also analyzed.

RESULTS

Seizure-cluster events plotted across 24 h showed a bimodal distribution with acrophases (peaks) at ~06:30 and ~18:30. A 12-h plot showed a single peak at ~06:30. Cosinor analyses of the full and consistent cohort aligned, with acrophases for both models predicting peak seizure activity at ~23:30 on a 24-h scale and ~07:30 on a 12-h scale. The consistent cohort was associated with increases in baseline and peak seizure-cluster activity. Analysis by epilepsy type identified distinct trends. Seizure clusters in the focal epilepsy group peaked in the evening (acrophase 19:19), whereas events in the generalized epilepsy group peaked in the morning (acrophase 04:46). Together they compose the bimodal clustering observed over 24 h.

SIGNIFICANCE

This analysis of seizure clusters treated with diazepam nasal spray demonstrated that seizure clusters occur cyclically in 12- and 24-h time frames similar to that reported with isolated seizures. Further elucidation of these patterns may provide important information for patient care, ranging from improved patient-centered outcomes to seizure-cluster prediction.

Circadian distribution of epileptiform discharges in epilepsy: Candidate mechanisms of variability

Epilepsy is a serious neurological disorder characterised by a tendency to have recurrent, spontaneous, seizures. Classically, seizures are assumed to occur at random. However, recent research has uncovered underlying rhythms both in seizures and in key signatures of epilepsy-so-called interictal epileptiform activity-with timescales that vary from hours and days through to months. Understanding the physiological mechanisms that determine these rhythmic patterns of epileptiform discharges remains an open question. Many people with epilepsy identify precipitants of their seizures, the most common of which include stress, sleep deprivation and fatigue. To quantify the impact of these physiological factors, we analysed 24-hour EEG recordings from a cohort of 107 people with idiopathic generalized epilepsy. We found two subgroups with distinct distributions of epileptiform discharges: one with highest incidence during sleep and the other during day-time. We interrogated these data using a mathematical model that describes the transitions between background and epileptiform activity in large-scale brain networks. This model was extended to include a time-dependent forcing term, where the excitability of nodes within the network could be modulated by other factors. We calibrated this forcing term using independently-collected human cortisol (the primary stress-responsive hormone characterised by circadian and ultradian patterns of secretion) data and sleep-staged EEG from healthy human participants. We found that either the dynamics of cortisol or sleep stage transition, or a combination of both, could explain most of the observed distributions of epileptiform discharges. Our findings provide conceptual evidence for the existence of underlying physiological drivers of rhythms of epileptiform discharges. These findings should motivate future research to explore these mechanisms in carefully designed experiments using animal models or people with epilepsy.

ECoG spiking activity and signal dimension are early predictive measures of epileptogenesis in a translational mouse model of traumatic brain injury

The latency between traumatic brain injury (TBI) and the onset of epilepsy (PTE) represents an opportunity for counteracting epileptogenesis. Antiepileptogenesis trials are hampered by the lack of sensitive biomarkers that allow to enrich patient's population at-risk for PTE. We aimed to assess whether specific ECoG signals predict PTE in a clinically relevant mouse model with ∼60% epilepsy incidence. TBI was provoked in adult CD1 male mice by controlled cortical impact on the left parieto-temporal cortex, then mice were implanted with two perilesional cortical screw electrodes and two similar electrodes in the hemisphere contralateral to the lesion site. Acute seizures and spikes/sharp waves were ECoG-recorded during 1 week post-TBI. These early ECoG events were analyzed according to PTE incidence as assessed by measuring spontaneous recurrent seizures (SRS) at 5 months post-TBI. We found that incidence, number and duration of acute seizures during 3 days post-TBI were similar in PTE mice and mice not developing epilepsy (No SRS mice). Control mice with cortical electrodes (naïve, n = 5) or with electrodes and craniotomy (sham, n = 5) exhibited acute seizures but did not develop epilepsy. The daily number of spikes/sharp waves at the perilesional electrodes was increased similarly in PTE (n = 15) and No SRS (n = 8) mice vs controls (p < 0.05, n = 10) from day 2 post-injury. Differently, the daily number of spikes/sharp waves at both contralateral electrodes showed a progressive increase in PTE mice vs No SRS and control mice. In particular, spikes number was higher in PTE vs No SRS mice (p < 0.05) at 6 and 7 days post-TBI, and this measure predicted epilepsy development with high accuracy (AUC = 0.77, p = 0.03; CI 0.5830-0.9670). The cut-off value was validated in an independent cohort of TBI mice (n = 12). The daily spike number at the contralateral electrodes showed a circadian distribution in PTE mice which was not observed in No SRS mice. Analysis of non-linear dynamics at each electrode site showed changes in dimensionality during 4 days post-TBI. This measure yielded the best discrimination between PTE and No SRS mice (p < 0.01) at the cortical electrodes contralateral to injury. Data show that epileptiform activity contralateral to the lesion site has the the highest predictive value for PTE in this model reinforcing the hypothesis that the hemisphere contralateral to the lesion core may drive epileptogenic networks after TBI.

The Relationship Between Epilepsy Control and the Duration of Nighttime Sleep and Afternoon Siesta

CONTEXT

The association between epilepsy control and the duration of sleep among people with epilepsy (PWE) is not well studied in Middle Eastern countries such as Oman.

AIMS

To describe the sleep habits of PWE in Oman and explore the association of their sleep habits at night and afternoon siesta with the level of seizure control achieved and antiseizure medications (ASMs) consumed.

METHODS

The subjects of this cross-sectional study were adult epilepsy patients attending a neurology clinic. Their sleep parameters were measured for one week using actigraphy. Home sleep apnea testing for one night was conducted to rule out obstructive sleep apnea (OSA).

RESULTS

A total of 129 PWE completed the study. Their mean age was 29.8 ± 9.2  years, and their mean body mass index (BMI) was 27.1 kg/m². There was no significant difference between the people with controlled and uncontrolled epilepsy as regards the duration of night sleep or afternoon siesta (p = 0.24 and 0.37, respectively). There was also no significant correlation between their nighttime sleep duration, afternoon siesta, and the number of ASMs they consumed (p = 0.402 and 0.717, respectively).

CONCLUSION

The study revealed that the sleep habits of PWE with uncontrolled epilepsy who consumed more ASMs were not significantly different from those with controlled epilepsy who consumed fewer ASMs.

Clocking Epilepsies: A Chronomodulated Strategy-Based Therapy for Rhythmic Seizures

Epilepsy is a neurological disorder characterized by hypersynchronous recurrent neuronal activities and seizures, as well as loss of muscular control and sometimes awareness. Clinically, seizures have been reported to display daily variations. Conversely, circadian misalignment and circadian clock gene variants contribute to epileptic pathogenesis. Elucidation of the genetic bases of epilepsy is of great importance because the genetic variability of the patients affects the efficacies of antiepileptic drugs (AEDs). For this narrative review, we compiled 661 epilepsy-related genes from the PHGKB and OMIM databases and classified them into 3 groups: driver genes, passenger genes, and undetermined genes. We discuss the potential roles of some epilepsy driver genes based on GO and KEGG analyses, the circadian rhythmicity of human and animal epilepsies, and the mutual effects between epilepsy and sleep. We review the advantages and challenges of rodents and zebrafish as animal models for epileptic studies. Finally, we posit chronomodulated strategy-based chronotherapy for rhythmic epilepsies, integrating several lines of investigation for unraveling circadian mechanisms underpinning epileptogenesis, chronopharmacokinetic and chronopharmacodynamic examinations of AEDs, as well as mathematical/computational modeling to help develop time-of-day-specific AED dosing schedules for rhythmic epilepsy patients.

Sleep quality and circadian rhythm profile of persons with juvenile myoclonic epilepsy in a tertiary epilepsy center: A case-control study

PURPOSE

This study evaluated sleep quality, chronotype, and excessive diurnal somnolence in persons with Juvenile Myoclonic Epilepsy (JME) and their possible association with clinical variables.

METHODS

This cross-sectional controlled study evaluated 49 consecutive patients (65% females, mean age 27.53 years) with an electroclinical diagnosis of JME and 49 healthy controls (55% females, mean age 28.55 years). The Pittsburgh Sleep Quality Inventory (PSQI) was used to assess sleep quality and the Epworth Sleepiness Scale (ESS) to evaluate excessive daytime sleepiness. The patients' chronotype was evaluated by the Morningness-Eveningness Questionnaire (MEQ). Epilepsy-related factors gathered from the medical chart and personal interview were epilepsy duration, age at onset, frequency of myoclonic (Mcl), generalized tonic-clonic (GTC) and absence (ABS) seizures, pharmacoresponse, and current antiseizure medication (ASM).

RESULTS

Persons with JME did not differ from the control group regarding daytime sleepiness (p=0.840); however, the JME group had worse sleep quality (p=0.01) than the controls. Persons with JME presented a more evening chronotype than controls (p = 0.003). The age at onset, epilepsy duration, frequency of Mcl seizure, frequency of GTC seizure, frequency of ABS seizure, and drug response did not predict ESS and MEQ scales. Pharmacoresponsive patients had lower PSQI scores compared with pharmacoresistant patients (p=0.036).

CONCLUSION

Persons with JME have worse sleep quality and a more evening chronotype. Notably, pharmacoresistant patients present a worse sleep quality that deserves attention and special care due to the relationship between sleep deprivation and seizure worsening.

The interaction between circadian rhythm and epilepsy

Evidence about the interaction between circadian rhythms (CR) and epilepsy has been expanded with the application of advanced detection technology. An adequate understanding of how circadian system and epilepsy interact with each other could contribute to more accurate seizure prediction as well as rapid development of potential treatment timed to specific phases of CR. In this review, we present the reciprocal relationship between CR and epileptic activities from aspects of sleep effect, genetic modulation and brain biochemistry. It has been found that sleep-wake patterns, circadian timing systems and multidien rhythms have essential roles in seizure activities and interictal epileptiform discharge (IED). For instance, specific distribution patterns of seizures and IED have been reported, i.e., lighter non-rapid eye movement (NREM) sleep stage (stage 2) induces seizures while deeper NREM sleep stage (stage 3) activates IEDs. Furthermore, the epilepsy type, seizure type and seizure onset zone can significantly affect the rhythms of seizure occurrence. Apart from the common seizure types, several specific epilepsy syndromes also have a close correlation with sleep-wakefulness patterns. Sleep influences the epilepsy rhythm, and conversely, epilepsy alters the sleep rhythm through multiple pathways. Clock genes accompanied by two feedback loops of regulation have an important role in cortical excitability and seizure occurrence, which may be involved in the mTORopathy. The suprachiasmatic nuclei (SCN) has a rhythm of melatonin and cortisol secretion under the circadian pattern, and then these hormones can feed back into a central oscillator to affect the SCN-dependent rhythms, leading to variable but prominent influence on epilepsy. Furthermore, we discuss the precise predictive algorithms and chronotherapy strategies based on different temporal patterns of seizure occurrence for patients with epilepsy, which may offer a valuable indication for non-invasive closed-loop treatment system. Optimization of the time and dose of antiseizure medications, and resynchronization of disturbed CR (by hormone therapy, light exposure, ketogenic diet, novel small molecules) would be beneficial for epileptic patients in the future. Before formal clinical practice, future large-scale studies are urgently needed to assist prediction and treatment of circadian seizure activities and address unsolved restrictions.

Chronic recording of the vagus nerve to analyze modulations by the light-dark cycle

OBJECTIVE

The vagus nerve is considered to play a key role in the circadian rhythm. Chronic continuous analysis of the vagus nerve activity could contribute to a better understanding of the role of the vagus nerve in light-dark modulations. This paper presents a continuous analysis of spontaneous vagus nerve activity performed in four rats.

APPROACH

We analyzed the vagus electroneurogram (VENG) and electroencephalogram (EEG) over a recording period of 28 days. Spike activity and heart rate estimation were derived from the VENG, and slow-wave activity was derived from the EEG. The presence of repetitive patterns was investigated with periodograms, cosinor fitting, autocorrelation, and statistical tests. The light-dark variations derived from the VENG spikes were compared with EEG slow waves, an established metric in circadian studies.

RESULTS

Our results demonstrate that light-dark variations can be detected in long-term vagus nerve activity monitoring. A recording period of about seven days is required to characterize accurately the VENG light-dark variations.

SIGNIFICANCE

As a major outcome of this study, vagus nerve recordings hold the promise to help understand circadian regulation.

Sleep Disruption Worsens Seizures: Neuroinflammation as a Potential Mechanistic Link

Sleep disturbances, such as insomnia, obstructive sleep apnea, and daytime sleepiness, are common in people diagnosed with epilepsy. These disturbances can be attributed to nocturnal seizures, psychosocial factors, and/or the use of anti-epileptic drugs with sleep-modifying side effects. Epilepsy patients with poor sleep quality have intensified seizure frequency and disease progression compared to their well-rested counterparts. A better understanding of the complex relationship between sleep and epilepsy is needed, since approximately 20% of seizures and more than 90% of sudden unexpected deaths in epilepsy occur during sleep. Emerging studies suggest that neuroinflammation, (e.g., the CNS immune response characterized by the change in expression of inflammatory mediators and glial activation) may be a potential link between sleep deprivation and seizures. Here, we review the mechanisms by which sleep deprivation induces neuroinflammation and propose that neuroinflammation synergizes with seizure activity to worsen neurodegeneration in the epileptic brain. Additionally, we highlight the relevance of sleep interventions, often overlooked by physicians, to manage seizures, prevent epilepsy-related mortality, and improve quality of life.

Sleep fragmentation and decreased REM sleep in a primate model of diurnal cortical seizures

Many people with epilepsy suffer from comorbid sleep disorders and sleep fragmentation. While the disruptive nature of seizures on sleep is well documented, it is unclear how diurnal seizures impact sleep quality and for how long these changes persist during the following nights. To better understand this relationship, the sleep architecture of two rhesus macaques were studied before and several nights after penicillin-induced diurnal seizures. These focal seizures stopped naturally, and none occurred at night. We scored sleep-stage during the nights immediately following the seizures, as well as several nights after seizure induction. We noted a significant increase in movement along with a decrease in sleep efficiency, both limited to the night of seizure induction. For both animals, we observed a significant decrease in the number of REM periods that manifested as a decrease in total REM sleep duration, and this phenomenon persisted up to 2 nights after the seizures. We also found a significant increase in the probability to transition from stage N2 to stage N1 on the night of the seizures. This study shows for the first time that the NHP model of penicillin-induced cortical seizures exhibits significant changes in sleep architecture, including an increase in nocturnal movement, change in sleep architecture and a prolonged decrease in REM activity. The prolonged decrease in REM periods compared to the temporary enhanced movement and reduction of sleep efficiency suggest that these seizures may affect two neural circuits, one controlling REM sleep entry and the other controlling nocturnal wakefulness.

Decreased expression of the clock gene Bmal1 is involved in the pathogenesis of temporal lobe epilepsy

Clock genes not only regulate the circadian rhythm of physiological activities but also participate in the pathogenesis of many diseases. Previous studies have documented the abnormal expression of clock genes in epilepsy. However, the molecular mechanism of brain and muscle Arnt-like protein 1 (Bmal1), one of the core clock genes, in the epileptogenesis and seizures of temporal lobe epilepsy (TLE) remain unclear. We first investigated the levels of Bmal1 and other clock proteins in the hippocampus of subjects with epilepsy to define the function of Bmal1. The levels of Bmal1 were decreased during the latent and chronic phases in the experimental group compared with those in the control group. Knockout of Bmal1 in hippocampal dentate gyrus (DG) neurons of Bmal1flox/flox mice by Synapsin 1 (Syn1) promoter AAV (adeno-associated virus) lowered the threshold of seizures induced by pilocarpine administration. High-throughput sequencing analysis showed that PCDH19 (protocadherin 19), a gene associated with epilepsy, was regulated by Bmal1. PCDH19 expression was also decreased in the hippocampus of epileptic mice. Furthermore, the higher levels of Bmal1 and PCDH19 were detected in patients with no hippocampal sclerosis (no HS) than in patients with HS International League Against Epilepsy (ILAE) type I and III. Altogether, these data suggest that decreased expression of clock gene Bmal1 may participate in epileptogenesis and seizures via PCDH19 in TLE.

The Kainic Acid Models of Temporal Lobe Epilepsy

Experimental models of epilepsy are useful to identify potential mechanisms of epileptogenesis, seizure genesis, comorbidities, and treatment efficacy. The kainic acid (KA) model is one of the most commonly used. Several modes of administration of KA exist, each producing different effects in a strain-, species-, gender-, and age-dependent manner. In this review, we discuss the advantages and limitations of the various forms of KA administration (systemic, intrahippocampal, and intranasal), as well as the histologic, electrophysiological, and behavioral outcomes in different strains and species. We attempt a personal perspective and discuss areas where work is needed. The diversity of KA models and their outcomes offers researchers a rich palette of phenotypes, which may be relevant to specific traits found in patients with temporal lobe epilepsy.

Proceedings of the Sleep and Epilepsy Workshop: Section 1 Decreasing Seizures-Improving Sleep and Seizures, Themes for Future Research

Epileptic seizures, sleep, and circadian timing share bilateral interactions, but concerted work to characterize these interactions and to leverage them to the advantage of patients with epilepsy remains in beginning stages. To further the field, a multidisciplinary group of sleep physicians, epileptologists, circadian timing experts, and others met to outline the state of the art, gaps of knowledge, and suggest ways forward in clinical, translational, and basic research. A multidisciplinary panel of experts discussed these interactions, centered on whether improvements in sleep or circadian rhythms improve decrease seizure frequency. In addition, education about sleep was lacking in among patients, their families, and physicians, and that focus on education was an extremely important "low hanging fruit" to harvest. Improvements in monitoring technology, experimental designs sensitive to the rigor required to dissect sleep versus circadian influences, and clinical trials in seizure reduction with sleep improvements were appropriate.

The effect of time-of-day and circadian phase on vulnerability to seizure-induced death in two mouse models

KEY POINTS

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of premature death in patients with refractory epilepsy. SUDEP typically occurs during the night, although the reason for this is unclear. We found that, in normally entrained mice, time-of-day alters vulnerability to seizure-induced death. We found that, in free-running mice, circadian phase alters the vulnerability to seizure-induced death. These findings suggest that circadian rhythmicity may be responsible for the increased night-time prevalence of SUDEP ABSTRACT: Sudden unexpected death in epilepsy (SUDEP) is the leading cause of epilepsy-related death. SUDEP typically occurs during the night following a seizure. Many aspects of mammalian physiology are regulated by circadian rhythms in ways that might make seizures occuring during the night more dangerous. Using two mouse models of seizure-induced death, we demonstrate that time-of-day and circadian rhythms alter vulnerability to seizure-induced death. We exposed normally entrained DBA/1 mice to a potentially seizure-inducing acoustic stimulus at different times of day and compared the characteristics and outcomes of the seizures. Time-of-day did not alter the probability of a seizure but it did alter the probability of seizure-induced death. To determine whether circadian rhythms alter vulnerability to seizure-induced death, we induced maximal electroshock seizures in free-running C57BL/6J mice at different circadian time points at the same time as measuring breathing via whole body plethysmography. Circadian phase did not affect seizure severity but it did alter postictal respiratory outcomes and the probability of seizure-induced death. By contrast to our expectations, in entrained and free-running mice, vulnerability to seizure-induced death was greatest during the night and subjective night, respectively. These findings suggest that circadian rhythmicity may be responsible for the increased night-time prevalence of SUDEP and that the underlying mechanism is phase conserved between nocturnal and diurnal mammals. All of the seizures in the present study were induced during wakefulness, indicating that the effect of time point on vulnerability to seizure-induced death was not the result of sleep. Understanding why SUDEP occurs more frequently during the night may inform future preventative countermeasures.

Epilepsy: Workup and Management in Adults

When managing epilepsy, there is a temptation to focus care with respect to the last and the next seizure. However, epilepsy is a multifaceted chronic condition and should be treated as such. Epilepsy comes with many physical risks, psychological effects, and socioeconomic ramifications, demanding a long-term commitment from the treating physician. Patients with epilepsy, compared to other chronically ill patient populations, have a worse quality of life, family function, and less social support. The majority of patients are well controlled on antiseizure drugs. However, approximately one-third will continue to have seizures despite optimized medical management. The primary aim of this article is to explore the long-term management of chronic epilepsy, and to address some of the particular needs of patients with chronic epilepsy.

The Instigation of the Associations Between Melatonin, Circadian Genes, and Epileptic Spasms in Infant Rats

Background: Infantile spasm (IS) is one of the most common catastrophic epilepsy syndromes in infancy characterized by epileptic spasm. While adrenocorticotropic hormone (ACTH) is the first-line treatment for IS, it is evident that the seizures associated with IS exhibit a clear circadian rhythm; however, the precise mechanisms underlying such seizures remain unclear. Melatonin is an important amine hormone and is regulated by circadian rhythm. Circadian proteins, especially Aryl Hydrocarbon Receptor Nuclear Trasnslocator-like Protein (ARNTL or BMAL1) and Circadian Locomotor Output Cycles Kaput (CLOCK), and their target proteins Period Circadian Regulator 1 (PER1), Period Circadian Regulator 2 (PER2), Cryptochrome 1 (CRY1), and Cryptochrome 2 (CRY2), play key roles in circadian rhythm. This study explored the relationships between melatonin, genes associated with circadian rhythm, and epileptic spasm.

Materials and Methods: Eighteen female rats were mated with nine male rats and 16 became pregnant. Twelve pregnant rats were subjected to prenatal stress by forced swimming in cold water from the day of conception. Rat pups produced by stressed mothers received an intraperitoneal injection of N-methyl-D-aspartate (NMDA) on the 13th day after birth and were divided into four groups: NMDA (15 mg/kg), NMDA+ACTH (20 IU/kg), NMDA+melatonin (55 mg/kg), and NMDA+ACTH+melatonin (n = 36/group). Offspring from four dams that were not subjected to prenatal stress were used as controls. We then recorded latency and the frequency of flexion seizures. All offspring were sacrificed on the 14th day after birth and CLOCK, BMAL1, PER1, PER2, CRY1, and CRY2 expression was analyzed by western blotting, immunohistochemistry, and immunofluorescence.

Results: NMDA induced spasm-like symptoms in rats. ACTH and melatonin significantly increased seizure latency and significantly reduced the frequency of seizures (P < 0.05). CLOCK, BMAL1, PER1, PER2, CRY1, and CRY2 expression was significantly lower in the NMDA group than the controls (P < 0.05). ACTH significantly increased the expression of CLOCK, BAML1, PER1, and CRY1 (P < 0.05) and melatonin significantly increased the expression of CLOCK, BMAL1, PER1, PER2, CRY1, and CRY2 (P < 0.05) compared with those of the NMDA group. There were no significant differences in the expression of BMAL1, CRY2, PER1, and PER2 when compared between the NMDA+ACTH+melatonin and control groups (P > 0.05).

Conclusion: ACTH and melatonin significantly increased the expression of circadian genes and improved NMDA-induced seizures. The anticonvulsant effects of ACTH and melatonin are likely to involve regulation of the expression of these genes.

Decoding Circadian Rhythm and Epileptic Activities: Clues From Animal Studies

The relationship between circadian rhythm and epilepsy has been recognized for decades. Yet many questions underlying the complex mechanisms of their interaction remain elusive. A better understanding on this topic allows the development of accurate seizure-detection algorithm and alternative precise therapeutic strategies. Preclinical laboratory studies based on epileptic animal models, with controllable epileptogenic pathology and an array of intervention strategies, shed light on the bidirectional effects between circadian rhythm and epileptic seizures as well as their underlying mechanisms. Here, we reviewed findings on the interaction between circadian rhythm and epileptic seizures in the preclinical setting. We present the possible mechanisms at molecular, cellular and circuitry levels. We propose that future experimental designs should take into account the relationship between circadian rhythm and epilepsy as well as the underlying mechanisms in different types of animal models, which may have a translational significance as stepping stones for clinical benefits.

The Molecular Genetic Interaction Between Circadian Rhythms and Susceptibility to Seizures and Epilepsy

Seizure patterns observed in patients with epilepsy suggest that circadian rhythms and sleep/wake mechanisms play some role in the disease. This review addresses key topics in the relationship between circadian rhythms and seizures in epilepsy. We present basic information on circadian biology, but focus on research studying the influence of both the time of day and the sleep/wake cycle as independent but related factors on the expression of seizures in epilepsy. We review studies investigating how seizures and epilepsy disrupt expression of core clock genes, and how disruption of clock mechanisms impacts seizures and the development of epilepsy. We focus on the overlap between mechanisms of circadian-associated changes in SCN neuronal excitability and mechanisms of epileptogenesis as a means of identifying key pathways and molecules that could represent new targets or strategies for epilepsy therapy. Finally, we review the concept of chronotherapy and provide a perspective regarding its application to patients with epilepsy based on their individual characteristics (i.e., being a “morning person” or a “night owl”). We conclude that better understanding of the relationship between circadian rhythms, neuronal excitability, and seizures will allow both the identification of new therapeutic targets for treating epilepsy as well as more effective treatment regimens using currently available pharmacological and non-pharmacological strategies.

Control of neuronal excitability by GSK-3beta: Epilepsy and beyond

Glycogen synthase kinase 3beta (GSK-3β) is an enzyme with a variety of cellular functions in addition to the regulation of glycogen metabolism. In the central nervous system, different intracellular signaling pathways converge on GSK-3β through a cascade of phosphorylation events that ultimately control a broad range of neuronal functions in the development and adulthood. In mice, genetically removing or increasing GSK-3β cause distinct functional and structural neuronal phenotypes and consequently affect cognition. Precise control of GSK-3β activity is important for such processes as neuronal migration, development of neuronal morphology, synaptic plasticity, excitability, and gene expression. Altered GSK-3β activity contributes to aberrant plasticity within neuronal circuits leading to neurological, psychiatric disorders, and neurodegenerative diseases. Therapeutically targeting GSK-3β can restore the aberrant plasticity of neuronal networks at least in animal models of these diseases. Although the complete repertoire of GSK-3β neuronal substrates has not been defined, emerging evidence shows that different ion channels and their accessory proteins controlling excitability, neurotransmitter release, and synaptic transmission are regulated by GSK-3β, thereby supporting mechanisms of synaptic plasticity in cognition. Dysregulation of ion channel function by defective GSK-3β activity sustains abnormal excitability in the development of epilepsy and other GSK-3β-linked human diseases.

Semi-supervised Training Data Selection Improves Seizure Forecasting in Canines with Epilepsy

Objective

Conventional selection of pre-ictal EEG epochs for seizure prediction algorithm training data typically assumes a continuous pre-ictal brain state preceding a seizure. This is carried out by defining a fixed duration, pre-ictal time period before seizures from which pre-ictal training data epochs are uniformly sampled. However, stochastic physiological and pathological fluctuations in EEG data characteristics and underlying brain states suggest that pre-ictal state dynamics may be more complex, and selection of pre-ictal training data segments to reflect this could improve algorithm performance.

Methods

We propose a semi-supervised technique to select pre-ictal training data most distinguishable from interictal EEG according to pre-specified data characteristics. The proposed method uses hierarchical clustering to identify optimal pre-ictal data epochs.

Results

In this paper we compare the performance of a seizure forecasting algorithm with and without hierarchical clustering of pre-ictal periods in chronic iEEG recordings from six canines with naturally occurring epilepsy. Hierarchical clustering of training data improved results for Time In Warning (TIW) (0.18 vs. 0.23) and False Positive Rate (FPR) (0.5 vs. 0.59) when evaluated across all subjects (p<0.001, n=6). Results were mixed when evaluating TIW, FPR, and Sensitivity for individual dogs.

Conclusion

Hierarchical clustering is a helpful method for training data selection overall, but should be evaluated on a subject-wise basis.

Significance

The clustering method can be used to optimize results of forecasting towards sensitivity or TIW or FPR, and therefore can be useful for epilepsy management.

The onset of pediatric refractory status epilepticus is not distributed uniformly during the day

PURPOSE

To evaluate whether the onset of pediatric refractory status epilepticus (rSE) is related to time of day.

METHOD

We analyzed the time of day for the onset of rSE in this prospective observational study performed from June 2011 to May 2019 in pediatric patients (1 month to 21 years of age). We evaluated the temporal distribution of pediatric rSE utilizing a cosinor analysis. We calculated the midline estimating statistic of rhythm (MESOR) and amplitude. MESOR is the estimated mean number of rSE episodes per hour if they were evenly distributed. Amplitude is the difference between MESOR and maximum rSE episodes/hour, or between MESOR and minimum rSE episodes/hour. We also evaluated the temporal distribution of time to treatment.

RESULTS

We analyzed 368 patients (58% males) with a median (p₂₅ - p₇₅) age of 4.2 (1.3-9.7) years. The MESOR was 15.3 (95% CI: 13.9-16.8) and the amplitude was 3.2 (95% CI: 1.1-5.3), p = 0.0024, demonstrating that the distribution is not uniform, but better described as varying throughout the day with a peak in the morning (11am-12 pm) and trough at night (11 pm-12 am). The duration from rSE onset to application of the first non-benzodiazepine antiseizure medication peaked during the early morning (2am-3 am) with a minimum during the afternoon (2 pm-3 pm) (p = 0.0179).

CONCLUSIONS

The distribution of rSE onset is not uniform during the day. rSE onset shows a 24-h distribution with a peak in the mid-morning (11am-12 pm) and a trough at night (11 pm-12am).

Semiology, clustering, periodicity and natural history of seizures in an experimental occipital cortical epilepsy model

Focal neocortical epilepsy is a common form of epilepsy and there is a need to develop animal models that allow the evaluation of novel therapeutic strategies to treat this type of epilepsy. Tetanus toxin (TeNT) injection into the rat visual cortex induces focal neocortical epilepsy without preceding status epilepticus. The latency to first seizure ranged from 3 to 7 days. Seizure duration was bimodal, with both short (approximately 30 s) and long-lasting (>100 s) seizures occurring in the same animals. Seizures were accompanied by non-motor features such as behavioural arrest, or motor seizures with or without evolution to generalized tonic-clonic seizures. Seizures were more common during the sleep phase of a light-dark cycle. Seizure occurrence was not random, and tended to cluster with significantly higher probability of recurrence within 24 h of a previous seizure. Across animals, the number of seizures in the first week could be used to predict the number of seizures in the following 3 weeks. The TeNT model of occipital cortical epilepsy is a model of acquired focal neocortical epilepsy that is well-suited for preclinical evaluation of novel anti-epileptic strategies. We provide here a detailed analysis of the epilepsy phenotypes, seizure activity, electrographic features and the semiology. In addition, we provide a predictive framework that can be used to reduce variation and consequently animal use in preclinical studies of potential treatments.

Dead in the Night: Sleep-Wake and Time-Of-Day Influences on Sudden Unexpected Death in Epilepsy

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of epilepsy-related death in patients with refractory epilepsy. Convergent lines of evidence suggest that SUDEP occurs due to seizure induced perturbation of respiratory, cardiac, and electrocerebral function as well as potential predisposing factors. It is consistently observed that SUDEP happens more during the night and the early hours of the morning. The aim of this review is to discuss evidence from patient cases, clinical studies, and animal research which is pertinent to the nocturnality of SUDEP. There are a number of factors which might contribute to the nighttime predilection of SUDEP. These factors fall into four categories: influences of (1) being unwitnessed, (2) lying prone in bed, (3) sleep-wake state, and (4) circadian rhythms. During the night, seizures are more likely to be unwitnessed; therefore, it is less likely that another person would be able to administer a lifesaving intervention. Patients are more likely to be prone on a bed following a nocturnal seizure. Being prone in the accouterments of a bed during the postictal period might impair breathing and increase SUDEP risk. Sleep typically happens at night and seizures which emerge from sleep might be more dangerous. Lastly, there are circadian changes to physiology during the night which might facilitate SUDEP. These possible explanations for the nocturnality of SUDEP are not mutually exclusive. The increased rate of SUDEP during the night is likely multifactorial involving both situational factors, such as being without a witness and prone, and physiological changes due to the influence of sleep and circadian rhythms. Understanding the causal elements in the nocturnality of SUDEP may be critical to the development of effective preventive countermeasures.

Circadian and circaseptan rhythms in human epilepsy: a retrospective cohort study

BACKGROUND

Epilepsy has long been suspected to be governed by cyclic rhythms, with seizure rates rising and falling periodically over weeks, months, or even years. The very long scales of seizure patterns seem to defy natural explanation and have sometimes been attributed to hormonal cycles or environmental factors. This study aimed to quantify the strength and prevalence of seizure cycles at multiple temporal scales across a large cohort of people with epilepsy.

METHODS

This retrospective cohort study used the two most comprehensive databases of human seizures (SeizureTracker [USA] and NeuroVista [Melbourne, VIC, Australia]) and analytic techniques from circular statistics to analyse patients with epilepsy for the presence and frequency of multitemporal cycles of seizure activity. NeuroVista patients were selected on the basis of having intractable focal epilepsy; data from patients with at least 30 clinical seizures were used. SeizureTracker participants are self selected and data do not adhere to any specific criteria; we used patients with a minimum of 100 seizures. The presence of seizure cycles over multiple time scales was measured using the mean resultant length (R value). The Rayleigh test and Hodges-Ajne test were used to test for circular uniformity. Monte-Carlo simulations were used to confirm the results of the Rayleigh test for seizure phase.

FINDINGS

We used data from 12 people from the NeuroVista study (data recorded from June 10, 2010, to Aug 22, 2012) and 1118 patients from the SeizureTracker database (data recorded from Jan 1, 2007, to Oct 19, 2015). At least 891 (80%) of 1118 patients in the SeizureTracker cohort and 11 (92%) of 12 patients in the NeuroVista cohort showed circadian (24 h) modulation of their seizure rates. In the NeuroVista cohort, patient 8 had a significant cycle at precisely 1 week. Two others (patients 1 and 7) also had approximately 1-week cycles. Patients 1 and 4 had 2-week cycles. In the SeizureTracker cohort, between 77 (7%) and 233 (21%) of the 1118 patients showed strong circaseptan (weekly) rhythms, with a clear 7-day period. Between 151 (14%) and 247 (22%) patients had significant seizure cycles that were longer than 3 weeks. Seizure cycles were equally prevalent in men and women, and peak seizure rates were evenly distributed across all days of the week.

INTERPRETATION

Our results suggest that seizure cycles are robust, patient specific, and more widespread than previously understood. They align with the accepted consensus that most epilepsies have some diurnal influence. Variations in seizure rate have important clinical implications. Detection and tracking of seizure cycles on a patient-specific basis should be standard in epilepsy management practices.

FUNDING

Australian National Health and Medical Research Council.

Rhythms of Core Clock Genes and Spontaneous Locomotor Activity in Post-Status Epilepticus Model of Mesial Temporal Lobe Epilepsy

The interaction of Mesial Temporal Lobe Epilepsy (mTLE) with the circadian system control is apparent from an oscillatory pattern of limbic seizures, daytime's effect on seizure onset and the efficacy of antiepileptic drugs. Moreover, seizures per se can interfere with the biological rhythm output, including circadian oscillation of body temperature, locomotor activity, EEG pattern as well as the transcriptome. However, the molecular mechanisms underlying this cross-talk remain unclear. In this study, we systematically evaluated the temporal expression of seven core circadian transcripts (Bmal1, Clock, Cry1, Cry2, Per1, Per2, and Per3) and the spontaneous locomotor activity (SLA) in post-status epilepticus (SE) model of mTLE. Twenty-four hour oscillating SLA remained intact in post-SE groups although the circadian phase and the amount and intensity of activity were changed in early post-SE and epileptic phases. The acrophase of the SLA rhythm was delayed during epileptogenesis, a fragmented 24 h rhythmicity and extended active phase length appeared in the epileptic phase. The temporal expression of circadian transcripts Bmal1, Cry1, Cry2, Per1, Per2, and Per3 was also substantially altered. The oscillatory expression of Bmal1 was maintained in rats imperiled to SE, but with lower amplitude (A = 0.2) and an advanced acrophase in the epileptic phase. The diurnal rhythm of Cry1 and Cry2 was absent in the early post-SE but was recovered in the epileptic phase. Per1 and Per2 rhythmic expression were disrupted in post-SE groups while Per3 presented an arrhythmic profile in the epileptic phase, only. The expression of Clock did not display rhythmic pattern in any condition. These oscillating patterns of core clock genes may contribute to hippocampal 24 h cycling and, consequently to seizure periodicity. Furthermore, by using a pool of samples collected at 6 different Zeitgeber Times (ZT), we found that all clock transcripts were significantly dysregulated after SE induction, except Per3 and Per2. Collectively, altered SLA rhythm in early post-SE and epileptic phases implies a possible role for seizure as a nonphotic cue, which is likely linked to activation of hippocampal–accumbens pathway. On the other hand, altered temporal expression of the clock genes after SE suggests their involvement in the MTLE.

A forward-looking review of seizure prediction

PURPOSE OF REVIEW

Seizure prediction has made important advances over the last decade, with the recent demonstration that prospective seizure prediction is possible, though there remain significant obstacles to broader application. In this review, we will describe insights gained from long-term trials, with the aim of identifying research goals for the next decade.

RECENT FINDINGS

Unexpected results from these studies, including strong and highly individual relationships between spikes and seizures, diurnal patterns of seizure activity, and the coexistence of different seizure populations within individual patients exhibiting distinctive dynamics, have caused us to re-evaluate many prior assumptions in seizure prediction studies and suggest alternative strategies that could be employed in the search for algorithms providing greater clinical utility. Advances in analytical approaches, particularly deep-learning techniques, harbour great promise and in combination with less-invasive systems with sufficiently power-efficient computational capacity will bring broader clinical application within reach.

SUMMARY

We conclude the review with an exercise in wishful thinking, which asks what the ideal seizure prediction dataset would look like and how these data should be manipulated to maximize benefits for patients. The motivation for structuring the review in this way is to create a forward-looking, optimistic critique of the existing methodologies.

Circadian and Brain State Modulation of Network Hyperexcitability in Alzheimer's Disease

Network hyperexcitability is a feature of Alzheimer' disease (AD) as well as numerous transgenic mouse models of AD. While hyperexcitability in AD patients and AD animal models share certain features, the mechanistic overlap remains to be established. We aimed to identify features of network hyperexcitability in AD models that can be related to epileptiform activity signatures in AD patients. We studied network hyperexcitability in mice expressing amyloid precursor protein (APP) with mutations that cause familial AD, and compared a transgenic model that overexpresses human APP (hAPP) (J20), to a knock-in model expressing APP at physiological levels (APP^NL/F). We recorded continuous long-term electrocorticogram (ECoG) activity from mice, and studied modulation by circadian cycle, behavioral, and brain state. We report that while J20s exhibit frequent interictal spikes (IISs), APP^NL/F mice do not. In J20 mice, IISs were most prevalent during daylight hours and the circadian modulation was associated with sleep. Further analysis of brain state revealed that IIS in J20s are associated with features of rapid eye movement (REM) sleep. We found no evidence of cholinergic changes that may contribute to IIS-circadian coupling in J20s. In contrast to J20s, intracranial recordings capturing IIS in AD patients demonstrated frequent IIS in non-REM (NREM) sleep. The salient differences in sleep-stage coupling of IIS in APP overexpressing mice and AD patients suggests that different mechanisms may underlie network hyperexcitability in mice and humans. We posit that sleep-stage coupling of IIS should be an important consideration in identifying mouse AD models that most closely recapitulate network hyperexcitability in human AD.

Seizure semiology: an important clinical clue to the diagnosis of autoimmune epilepsy

Objective

The purpose of this study is to analyze the seizure semiologic characteristics of patients with autoimmune epilepsy (AE) and describe the investigation characteristics of AE using a larger sample size.

Methods

This observational retrospective case series study was conducted from a tertiary epilepsy center between May 2014 and March 2017. Cases of new‐onset seizures were selected based on laboratory evidence of autoimmunity. At the same time, typical mesial temporal lobe epilepsy (MTLE) patients with hippocampal sclerosis (HS) were recruited as the control group from the subjects who underwent presurgical evaluation during the same period.

Results

A total of 61 patients with AE were identified. Specific autoimmune antibodies were detected in 39 patients (63.93%), including anti‐VGKC in 23 patients (37.70%), anti‐NMDA‐R in 9 patients (14.75%), anti‐GABA_B‐R in 6 patients (9.84%), and anti‐amphiphysin in 1 patient (1.64%). Regarding the seizure semiology, no significant differences were noted between AE patients with autoantibody and patients with suspected AE without antibody. Compared to typical MTLE patients with HS, both AE patients with autoantibody and patients with suspected AE without antibody had the same seizure semiologic characteristics, including more frequent SPS or CPS, shorter seizure duration, rare postictal confusion, and common sleeping SGTC seizures.

Significance

This study highlights important seizure semiologic characteristics of AE. Patients with autoimmune epilepsy had special seizure semiologic characteristics. For patients with autoimmune epilepsy presenting with new‐onset seizures in isolation or with a seizure‐predominant neurological disorder, the special seizure semiologic characteristics may remind us to test neuronal nuclear/cytoplasmic antibodies early and initiate immunomodulatory therapies as soon as possible. Furthermore, the absence of neural‐specific autoantibodies does not rule out AE.

The Need for Antiepileptic Drug Chronotherapy to Treat Selected Childhood Epilepsy Syndromes and Avert the Harmful Consequences of Drug Resistance

Antiepileptic drug (AED) chronotherapy involves the delivery of a greater AED dose at the time of greatest seizure susceptibility usually associated with predictable seizure peaks. Although research has proven AED chronotherapy, commonly known as differential dosing, to be safe, well tolerated, and highly effective in managing cyclic seizure patterns in selected childhood epilepsies, conventional, equally divided AED dosing remains the standard of care. Differential dosing is more often applied in the emergency management of acute seizure clustering resulting from drug resistance-a harmful epilepsy-related consequence that affects 30% of children. Moreover, drug resistance is a major risk factor in status epilepticus and sudden, unexpected death in epilepsy. Although these facts should promote the wider use of differential dosing in selected cases, a credible hypothesis is needed that defines the differential dosing strategy and application in cyclic epilepsy and for the greater purpose of preventing harmful outcomes.

Altered MT1 and MT2 melatonin receptors expression in the hippocampus of pilocarpine-induced epileptic rats

Clinical and experimental findings show that melatonin may be used as an adjuvant to the treatment of epilepsy-related complications by alleviates sleep disturbances, circadian alterations and attenuates seizures alone or in combination with AEDs. In addition, it has been observed that there is a circadian component on seizures, which cause changes in circadian system and in melatonin production. Nevertheless, the dynamic changes of the melatoninergic system, especially with regard to its membrane receptors (MT₁ and MT₂) in the natural course of TLE remain largely unknown. The aim of this study was to evaluate the 24-hour profile of MT₁ and MT₂ mRNA and protein expression in the hippocampus of rats submitted to the pilocarpine-induced epilepsy model analyzing the influence of the circadian rhythm in the expression pattern during the acute, silent, and chronic phases. Melatonin receptor MT₁ and MT₂ mRNA expression levels were increased in the hippocampus of rats few hours after SE, with MT₁ returning to normal levels and MT₂ reducing during the silent phase. During the chronic phase, mRNA expression levels of both receptors return to levels close to control, however, presenting a different daily profile, showing that there is a circadian change during the chronic phase. Also, during the acute and silent phase it was possible to verify MT₁ label only in CA2 hippocampal region with an increased expression only in the dark period of the acute phase. The MT₂ receptor was present in all hippocampal regions, however, it was reduced in the acute phase and it was found in astrocytes. In chronic animals, there is a reduction in the presence of both receptors especially in regions where there is a typical damage derived from epilepsy. Therefore, we conclude that SE induced by pilocarpine is able to change melatonin receptor MT₁ and MT₂ protein and mRNA expression levels in the hippocampus of rats few hours after SE as well as in silent and chronic phases.

A Realistic Seizure Prediction Study Based on Multiclass SVM

A patient-specific algorithm, for epileptic seizure prediction, based on multiclass support-vector machines (SVM) and using multi-channel high-dimensional feature sets, is presented. The feature sets, combined with multiclass classification and post-processing schemes aim at the generation of alarms and reduced influence of false positives. This study considers 216 patients from the European Epilepsy Database, and includes 185 patients with scalp EEG recordings and 31 with intracranial data. The strategy was tested over a total of 16,729.80[Formula: see text]h of inter-ictal data, including 1206 seizures. We found an overall sensitivity of 38.47% and a false positive rate per hour of 0.20. The performance of the method achieved statistical significance in 24 patients (11% of the patients). Despite the encouraging results previously reported in specific datasets, the prospective demonstration on long-term EEG recording has been limited. Our study presents a prospective analysis of a large heterogeneous, multicentric dataset. The statistical framework based on conservative assumptions, reflects a realistic approach compared to constrained datasets, and/or in-sample evaluations. The improvement of these results, with the definition of an appropriate set of features able to improve the distinction between the pre-ictal and nonpre-ictal states, hence minimizing the effect of confounding variables, remains a key aspect.

Temporal patterns of epileptiform discharges in genetic generalized epilepsies

OBJECTIVE

We sought to investigate the temporal patterns and sleep-wake cycle-related epileptiform discharges (EDs) in genetic generalized epilepsies (GGEs).

METHODS

We studied 24-hour ambulatory electroencephalography (EEG) recordings of patients with GGE, diagnosed and classified according to the International League against Epilepsy criteria. We manually coded the type of discharge, time of occurrence, duration, and arousal state of each ED. We employed mixed effects Poisson regression modeling to study the temporal distribution of epileptiform discharges. Additionally, we used multinomial regression analysis to explore the significance of the relationship between different states of arousal and types of epileptiform discharges.

RESULTS

We analyzed 6923 EDs from 105 abnormal 24-hour EEGs. Mixed effects Poisson regression analysis demonstrated significant changes in ED counts across time blocks. This distribution was largely influenced by the state of arousal. Generalized fragments (duration<2s) and focal discharges were more frequent during non-REM sleep while paroxysms (duration≥2s) were more frequent in wakefulness. Overall, 67% of epileptiform discharges occurred in non-REM sleep and only 33% occurred in wakefulness. Twenty-four patients (23%) had ED exclusively in sleep. Epileptiform discharges peaked from 23:00 through 07:00h.

SIGNIFICANCE

There is a time-of-day dependency of ED with a significant influence exerted by the state of arousal. Our observations suggest that the generation of epileptiform discharges is not a random process but is the result of complex interactions among biological rhythms such as the sleep-wake cycle and the intrinsic circadian pacemaker. High density of ED in sleep suggests that 24-hour EEG recording with the capture of natural sleep may be more useful than routine EEG to diagnose GGE.

Functional State of the Heart during Spontaneous Nonconvulsive Seizure Activity at Various Times of the Day

Circadian peculiarities of HR regulation and functional capacities of the heart in WAG/Rij rats with genetically determined absence epilepsy are related to spike-wave activity of the brain. The number of spike-wave discharges (SWD) is maximum at night, early morning, and evening time and decreases to minimum at 08.00-16.00. At night, functional capacities of the heart are reduced and stress test at night induces ischemic changes in the myocardium at a lower functional load than in the daytime (low level of SWD activity). The decrease in the number of SWD and spike-wave index during the daytime contributes to the central mechanisms of autonomic regulation of the heart. However, these capacities are reduced against the background of increased seizure activity during nighttime.

Interictal spikes and epileptic seizures: their relationship and underlying rhythmicity

We report on a quantitative analysis of electrocorticography data from a study that acquired continuous ambulatory recordings in humans over extended periods of time. The objectives were to examine patterns of seizures and spontaneous interictal spikes, their relationship to each other, and the nature of periodic variation. The recorded data were originally acquired for the purpose of seizure prediction, and were subsequently analysed in further detail. A detection algorithm identified potential seizure activity and a template matched filter was used to locate spikes. Seizure events were confirmed manually and classified as either clinically correlated, electroencephalographically identical but not clinically correlated, or subclinical. We found that spike rate was significantly altered prior to seizure in 9 out of 15 subjects. Increased pre-ictal spike rate was linked to improved predictability; however, spike rate was also shown to decrease before seizure (in 6 out of the 9 subjects). The probability distribution of spikes and seizures were notably similar, i.e. at times of high seizure likelihood the probability of epileptic spiking also increased. Both spikes and seizures showed clear evidence of circadian regulation and, for some subjects, there were also longer term patterns visible over weeks to months. Patterns of spike and seizure occurrence were highly subject-specific. The pre-ictal decrease in spike rate is not consistent with spikes promoting seizures. However, the fact that spikes and seizures demonstrate similar probability distributions suggests they are not wholly independent processes. It is possible spikes actively inhibit seizures, or that a decreased spike rate is a secondary symptom of the brain approaching seizure. If spike rate is modulated by common regulatory factors as seizures then spikes may be useful biomarkers of cortical excitability.

Pilocarpine-induced epilepsy alters the expression and daily variation of the nuclear receptor RORα in the hippocampus of rats

It is widely known that there is an increase in the inflammatory responses and oxidative stress in temporal lobe epilepsy (TLE). Further, the seizures follow a circadian rhythmicity. Retinoic acid receptor-related orphan receptor alpha (RORα) is related to anti-inflammatory and antioxidant enzyme expression and is part of the machinery of the biological clock and circadian rhythms. However, the participation of RORα in this neurological disorder has not been studied. The aim of this study was to evaluate the RORα mRNA and protein content profiles in the hippocampus of rats submitted to a pilocarpine-induced epilepsy model at different time points throughout the 24-h light-dark cycle analyzing the influence of the circadian rhythm in the expression pattern during the acute, silent, and chronic phases of the experimental model. Real-time PCR and immunohistochemistry results showed that RORα mRNA and protein expressions were globally reduced in both acute and silent phases of the pilocarpine model. However, 60days after the pilocarpine-induced status epilepticus (chronic phase), the mRNA expression was similar to the control except for the time point 3h after the lights were turned off, and no differences were found in immunohistochemistry. Our results indicate that the status epilepticus induced by pilocarpine is able to change the expression and daily variation of RORα in the rat hippocampal area during the acute and silent phases. These findings enhance our understanding of the circadian pattern present in seizures as well as facilitate strategies for the treatment of seizures.

The changes of HRV in refractory epilepsy: The potential index to predict the onset of epilepsy in children

In this study, we examine the potential of heart rate variability (HRV) as an efficient tool for predicting the onset of epilepsy in children. We totally collected 53 seizures EEG and ECG data using Video - EEG - ECG monitoring system. We then separated the ECG data into three segments: ten-minute before onset of each seizure, five-minute before onset of each seizure, and five-minute from the onset of each seizure. After the HRV parameters in all segments were calculated, we compared the differences between pre-ictal period and ictal period. We found that the values of meanHR, LF and LF/HF were greater in onset period. And the values of meanRR and the HF were less in ictal period. And it presented the similar changes when seizures occurred in the daytime and seizures occurred in the nighttime. In brief, we found that the sympathetic nervous system was under a more active status during onset period. We speculated that the HRV parameters such as the LF, HF or LF/HF could have potential to predict the seizures in children with epilepsy.

Thalamic abnormalities in children with continuous spike-wave during slow-wave sleep: An F-18-fluorodeoxyglucose positron emission tomography perspective

OBJECTIVE

Thalamic injury has been implicated in the development of continuous spike-wave during slow-wave sleep (CSWS) in children with epilepsy. We studied thalamic abnormalities in children with CSWS using F-18-fluorodeoxyglucose (FDG)-positron emission tomography (PET) imaging.

METHODS

Twenty-three patients (12 male; mean age 9 years) with CSWS and normal thalami on brain magnetic resonance imaging (MRI) underwent FDG-PET. Thalamic glucose metabolism, represented by standardized uptake value normalized to whole brain (nSUV, RT for right thalamus and LT for left thalamus), and its asymmetry--absolute asymmetry index (AAI): ¦(RT-LT)¦*100/[(RT+LT)/2]--was calculated. These values were compared with those from 10 normal healthy controls (five female; mean age 11.1 years).

RESULTS

Thalamic glucose metabolism was abnormal in 18 patients (78.3%). Thalamic nSUV was decreased (n = 6) or increased (n = 1) bilaterally in seven children without any asymmetry. Abnormal thalamic symmetry [AAI = 3.7-31.5% (0.8-3.3% in controls)] was seen in 11 children. Of these, six children had a unilateral thalamic metabolic abnormality (increased metabolism, n = 3 and decreased metabolism, n = 3), whereas 5 of 14 children had abnormal asymmetry index with bilaterally normal (n = 4) or increased (n = 1) thalamic metabolism. No clear association of thalamic metabolic abnormalities was seen with the stage of evolution of CSWS (prodromal, acute, or residual) or with the cortical FDG abnormalities.

SIGNIFICANCE

Functional thalamic abnormalities, both unilateral and bilateral, are frequently seen in patients with CSWS. FDG-PET is a sensitive and quantifiable modality to detect these changes.

Catamenial epilepsy: Update on prevalence, pathophysiology and treatment from the findings of the NIH Progesterone Treatment Trial

PURPOSE

To extend our knowledge and practical application of the concept of catamenial epilepsy.

METHODS

The review focuses on the impact of the NIH Progesterone Trial on our understanding of the pathophysiology and treatment of catamenial epilepsy.

RESULTS

Catamenial epilepsy refers to the cyclic exacerbation of seizures in relation to the menstrual cycle. An interaction between seizures and the menstrual cycle is suggested by variations in seizure frequency according to the day, phase and ovulatory status of the menstrual cycle. There are three commonly recognized patterns: perimenstrual (C1: Day -3 to +3), peri-ovulatory (C2: Day 10 to 3) and entire luteal phase in anovulatory cycles (C3: Day 10 to 3). Pathophysiological determinants include 1) the neuroactive properties of reproductive steroids, 2) the variation of neuroactive steroid levels across the menstrual cycle and 3) the differential susceptibility of epileptic substrates to neuroactive steroid effects. Perimenstrual seizure exacerbation may result from the premenstrual withdrawal of progesterone which is accompanied by withdrawal of allopregnanolone, a potent positive allosteric modulator of the GABAA receptor, and changes in the subunit composition of the GABAA receptor to the α4 subtype which is insensitive to benzodiazepine and GABA. Bioidentical progesterone supplement is no better than placebo in the treatment of women with focal onset epilepsy overall but shows superior efficacy in women whose seizures show robust perimenstrual exacerbation.

CONCLUSION

There is sound evidence for the existence of catamenial epilepsy and class 3 evidence for adjunctive progesterone treatment of the perimenstrually exacerbated subtype.

BMAL1 controls the diurnal rhythm and set point for electrical seizure threshold in mice

The epilepsies are a heterogeneous group of neurological diseases defined by the occurrence of unprovoked seizures which, in many cases, are correlated with diurnal rhythms. In order to gain insight into the biological mechanisms controlling this phenomenon, we characterized time-of-day effects on electrical seizure threshold in mice. Male C57BL/6J wild-type mice were maintained on a 14/10 h light/dark cycle, from birth until 6 weeks of age for seizure testing. Seizure thresholds were measured using a step-wise paradigm involving a single daily electrical stimulus. Results showed that the current required to elicit both generalized and maximal seizures was significantly higher in mice tested during the dark phase of the diurnal cycle compared to mice tested during the light phase. This rhythm was absent in BMAL1 knockout (KO) mice. BMAL1 KO also exhibited significantly reduced seizure thresholds at all times tested, compared to C57BL/6J mice. Results document a significant influence of time-of-day on electrical seizure threshold in mice and suggest that this effect is under the control of genes that are known to regulate circadian behaviors. Furthermore, low seizure thresholds in BMAL1 KO mice suggest that BMAL1 itself is directly involved in controlling neuronal excitability.