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The gut microbiome is emerging as a key regulator of brain function and behavior and is associated with symptoms of several neurological disorders. There is emerging evidence that alterations in the gut microbiota are seen in epilepsy and in response to seizure interventions. In this review, we highlight recent studies reporting that individuals with refractory epilepsy exhibit altered composition of the gut microbiota. We further discuss antibiotic treatment and infection as microbiome-related factors that influence seizure susceptibility in humans and animal models. In addition, we evaluate how the microbiome may mediate effects of the ketogenic diet, probiotic treatment, and anti-epileptic drugs on reducing both seizure frequency and severity. Finally, we assess the open questions in interrogating roles for the microbiome in epilepsy and address the prospect that continued research may uncover fundamental insights for understanding risk factors for epilepsy, as well as novel approaches for treating refractory epilepsy.

The term epilepsy refers to a diverse group of disorders of different origin, which are all characterized by the repeated occurrence of transitory and localized outbursts of electrical activity, known as seizures. Several forms of epilepsy have a clear neurodevelopmental origin, due to congenital brain malformations, altered neurotransmission, or defects in maturation and plasticity of neuronal networks. A role for serotonin (5-hydroxytryptamine, 5-HT) in epilepsy has long been proposed, and classical pharmacological studies provided contrasting evidences about the 5-HT receptor pathways involved in epilepsy, supporting both a pro- and an antiepileptic action of 5-HT. More recently, work performed on mice lacking genes involved in 5-HT neuron differentiation showed that an altered development of 5-HT circuits markedly affects neuronal activity in postnatal life, indicating a protective role of 5-HT against hyperexcitability. In this chapter, we will review the major developmental perturbations of 5-HT innervation affecting neuronal excitability and seizure susceptibility.

Few studies have reported the impact of intensive exercise on seizure susceptibility. Here, we present a case in which a patient developed drug-resistant focal epilepsy after craniotomy for a low-grade glioma. She had a marked reduction in seizure frequency after switching from moderate exercise to a high-intensity exercise program. Psychological benefits of exhaustive exercise included decreased suicide ideation, in part mediated by fewer seizures., Highlights • A case who started high-intensity exercise had a decline in seizure frequency. • In conjunction with diet, high intensity exercise increased urine ketones. • High-intensity exercise decreased suicide ideation and improved quality of life.

Environmental exposure early in development plays a role in susceptibility to disease in later life. Here, we demonstrate that prolonged febrile seizures induced by exposure of rat pups to a hyperthermic environment enhance seizure susceptibility not only in these hyperthermia-treated rats but also in their future offspring, even if the offspring never experience febrile seizures. This transgenerational transmission was intensity-dependent and was mainly from mothers to their offspring. The transmission was associated with DNA methylation. Thus, our study supports a “Lamarckian”-like mechanism of pathogenesis and the crucial role of epigenetic factors in neurological conditions., Highlights • FS induced enhanced seizure susceptibility was transgenerational transmitted. • The transgenerational transmission was FS-intensity dependent. • The transgenerational transmission was mainly from mothers to their offspring. • The transmission was associated with DNA methylation. Environmental experience during developmental period plays a critical role. Whether the enhanced seizure susceptibility induced by early life FS transmitted to their unaffected offspring and the underlie characteristic of this transgenerational transmission Here, we used a well-established FS models showed that prolonged febrile seizures enhance seizure susceptibility not only in these hyperthermia-treated rats but also in their future non-FS offspring. This transgenerational transmission was intensity-dependent and was mainly from mothers to their offspring, and was associated with DNA methylation.

Atypical febrile seizures are considered a risk factor for epilepsy onset and cognitive impairments later in life. Patients with temporal lobe epilepsy and a history of atypical febrile seizures often carry a cortical malformation. This association has led to the hypothesis that the presence of a cortical dysplasia exacerbates febrile seizures in infancy, in turn increasing the risk for neurological sequelae. The mechanisms linking these events are currently poorly understood. Potassium-chloride cotransporter KCC2 affects several aspects of neuronal circuit development and function, by modulating GABAergic transmission and excitatory synapse formation. Recent data suggest that KCC2 downregulation contributes to seizure generation in the epileptic adult brain, but its role in the developing brain is still controversial. In a rodent model of atypical febrile seizures, combining a cortical dysplasia and hyperthermia-induced seizures (LHS rats), we found a premature and sustained increase in KCC2 protein levels, accompanied by a negative shift of the reversal potential of GABA. In parallel, we observed a significant reduction in dendritic spine size and mEPSC amplitude in CA1 pyramidal neurons, accompanied by spatial memory deficits. To investigate whether KCC2 premature overexpression plays a role in seizure susceptibility and synaptic alterations, we reduced KCC2 expression selectively in hippocampal pyramidal neurons by in utero electroporation of shRNA. Remarkably, KCC2 shRNA-electroporated LHS rats show reduced hyperthermia-induced seizure susceptibility, while dendritic spine size deficits were rescued. Our findings demonstrate that KCC2 overexpression in a compromised developing brain increases febrile seizure susceptibility and contribute to dendritic spine alterations.

According to the World Health Organization, 50 million people worldwide have epilepsy. Traumatic brain injury (TBI) is estimated to cause 10%–20% of all of symptomatic epilepsies, and 5% of all epilepsies. Over the past 15 years, several laboratories have reported spontaneous seizures after inducing TBI in rats and mice. The TBI models in which spontaneous seizures are detected include fluid percussion injury, and controlled cortical impact models. Increased seizure susceptibility has also been described in a weight-drop model. Recent studies identified some genotypes that predispose to post-TBI epileptogenesis or comorbidogenesis. The use of post-TBI models in antiseizure drug-discovery is rare, but they have been used in more than 10 proof-of-concept preclinical antiepileptogenesis trials in an attempt to find treatments to alleviate the development of post-TBI epilepsy and comorbidities. Despite significant progress in modeling posttraumatic epileptogenesis, the animal models still represent only a few of the injury types and pathologies of patients with TBI destined to develop epilepsy. Also, experimental studies investigating posttraumatic epileptogenesis in young or old animals, as well as in females, are lacking. Endophenotyping human epileptogenic TBI is critical for the advancement of preclinical model development.

Kindling was first recognized in 1968 by Graham Goddard during experiments investigating whether learning in rats was disrupted by repeated hippocampal electrical stimulation. Goddard observed that repeated electrical stimulation of a variety of brain pathways unexpectedly evoked gradually evolving seizures and permanent progressive increases in seizure susceptibility that he described as “kindling,” and recognized as potentially significant for epilepsy.

Genetic Generalized Epilepsy (GGE) encompasses two well-studied syndrome specific epilepsies. Here we discuss recent advances in our understanding of mouse models of Generalized Epilepsy with Febrile Seizures plus (GEFS+) and Dravet syndrome. This disease spectrum includes individuals with a broad range of clinical features, from mildly to severely affected, and often associated with the same genetic mutation. Insight gained through the analyses of genetic mouse models have advanced our understanding of the mechanisms that transform monogenic lesions to cell-type specific, network, and whole brain dysfunction. Growing evidence suggests that while ion channel gene mutations are primarily linked to seizure genesis, structural changes are also evident and may contribute to epileptogenesis, including increased seizure susceptibility and disease severity.

There are reports of sex differences in epilepsy with respect to incidence, progression and severity of the disease, response to therapy, and occurrence of adverse drug effects. Thus, it is necessary to design sex-specific treatment strategies. Similarly, more animal studies are needed to determine the underlying mechanisms for sex differences in seizure susceptibility. Preclinical testing of antiepileptic drugs should include separate sex-specific testing to determine the effectiveness or possible adverse effects in males and females.

It is becoming increasingly clear that the genetic background of mice and rats, even in inbred strains, can have a profound influence on measures of seizure susceptibility and epilepsy. These differences can be capitalized upon through genetic mapping studies to reveal genes important for seizures and epilepsy. In this chapter, we discuss findings related to how this genetic heterogeneity has been (and can be) utilized in the epilepsy field to reveal novel insights into seizures and epilepsy. Moreover, we discuss how caution is needed with regard to rodent strain or even animal vendor choice, and how this can significantly influence seizure and epilepsy parameters in unexpected ways. This is particularly critical in decisions regarding the strain of choice used in generating mice with targeted deletions of genes.

We investigated the potential of 4-AP (50-100 microM) to induce seizure-like events (SLEs) in combined entorhinal cortex-hippocampal slices from Sprague Dawley rats which developed spontaneous limbic seizures following kainic acid induced status epilepticus. Slices from control rats (n=8) displayed SLEs in the entorhinal and perirhinal cortex upon application of 50 or 100 microM 4-AP. By contrast, 4-AP failed to induce SLEs in slices from chronic epileptic rats (n=13) except for one slice from one rat. This animal displayed only minor cell loss in layer III of the entorhinal cortex, in contrast to the other epileptic rats for which layer III neuronal loss was extensive. In all slices from epileptic rats, 4-AP induced recurrent epileptiform discharges similar to the interictal activity observed in control rats. Combined application of 4-AP (100 microM) and bicuculline methiodide (30 microM) induced frequent and prolonged recurrent epileptiform discharges in both control and chronic epileptic rats. 4-AP at 50-100 microM likely affects potassium channels containing Kv1.4, Kv1.5, Kv3.1 or Kv3.2 subunits. Real-time PCR revealed no significant downregulation of Kv1.4, Kv1.5, Kv3.1 or Kv3.2 in the subiculum, entorhinal and perirhinal cortex from chronic epileptic rats compared to controls. However, the expression of Kv3.4, responding to 4-AP in mM range, was significantly reduced. Using sub-unit-specific antibodies, the real-time PCR findings were confirmed by immunocytochemistry. We suggest that after chronic epilepsy, reorganization in the entorhinal cortex is accompanied by adaptations in homeostatic plasticity with anticonvulsant consequences.

The claustrum has widespread anatomical connections, and it could play a role in generalization of seizures. A productive approach has been to examine the involvement of the claustrum in kindling, in which a permanent state of seizure susceptibility develops after repeated application of initially subconvulsant electrical stimulation. Studies from my laboratory have revealed a high susceptibility of the claustrum to kindling, although some anomalous features remain to be investigated further. Lesions of the claustrum can disrupt epileptogenesis and established seizures, consistent with the structure’s hypothesized role in generalization. I also report data on the seizure susceptibility of the nucleus submedius of thalamus, a structure that receives a dense projection from the anterior claustrum. Collectively the data support the hypothesis that the claustrum is part of a network of structures that promote seizure generalization, although many questions remain.

C57BL/6 (B6) and DBA/2 (D2) inbred strains of mice are well known for their difference in seizure susceptibility and have been used together for over 60 years as a model to study epilepsy. The relative resistance of B6 mice to a wide variety of experimentally induced seizures has been studied in relation to the susceptibility of D2 mice in many ways, including direct comparisons of brain anatomy, chemistry, and physiology. Such comparisons have so far failed to provide a comprehensive understanding of the mechanisms responsible for the remarkable strain differences in seizure susceptibility. On the other hand, genetic studies involving quantitative trait loci (QTL) mapping have been more successful in probing the mechanisms underlying this animal model. Currently, it is known that important genetic influences in the model emanate from the telomeric region of chromosome 1 and mid-chromosome 4 and quantitative trait genes (QTG) at these loci have been identified provisionally as Kcnj10 and Mpdz, respectively. Other QTLs in the model have also been identified and work is ongoing to translate them into QTGs, as well as to translate QTGs into clinical studies on epilepsy patients. The recent success in translating provisionally identified Kcnj10 seizure QTG on chromosome 1 into a susceptibility allele for common forms of human epilepsy underscores the potential power of this research strategy. Future work on B6 and D2 mice will allow the model to be exploited further and continue to advance our understanding of the biological mechanisms of seizure susceptibility and epilepsy in humans and aid in the development of new treatments.

Epilepsy is characterized by intermittent (aperiodical, sporadic), paroxysmal (abrupt onset and offset), hypersynchronous (simultaneous activation of a considerable neural mass) electrical activity, which may remain localized or spread and severely disrupt the brain's normal operation. Epileptic seizures and interictal spikes are typical manifestations of such activity, and are reminiscent of crises in nonlinear systems. It is only recently that prediction and control of epileptic seizures have been the subject of intensive interdisciplinary research. Within this context, we investigate epilepsy from the point of view of pathology of the dynamics of the electrical activity of the brain. Three critical aspects of the dynamics of epileptic seizures are discussed in this article: a) seizures are preceded by a long-term (on the order of minutes to hours) entrainment (synchronization of dynamics) of brain sites by the epileptogenic focus/zone; b) seizures typically reset the aforementioned dynamical entrainment and lead to the disentrainment (desynchronization of dynamics) of the focus from the rest of the brain; c) seizures may occur due to a failure of global or local internal feedback loops in the brain, normally responsible for keeping the spatial correlations/interactions within strict limits (time-wise and space-wise), and thus being able to support the brain's fast multi-processing and multi-task function. These aspects, taken together, constitute the basis for a dynamical interpretation of ictogenesis that may lead to the detection of seizure susceptibility periods, long-term prediction of seizures, epileptogenic focus localization, and potentially to the development of innovative treatments for epilepsy through timely interventions (e.g., electrical stimulation and/or in situ drug delivery) to control (ideally suppress) seizure occurrence. Preliminary evidence from dynamical analysis of EEG from patients with focal epilepsy and patients in status epilepticus, as well as from rodent and simulation models of epilepsy, supports the feasibility of these goals.

Publisher Summary The majority of human seizures occurs early in life, and many developmental seizures occur only during discrete windows of development. The immature brain differs from the adult brain in its susceptibility to seizures, seizure characteristics, and responses to antiepileptic drugs. Despite the lack of significant injury in the immature brain, in experimental models, evidence suggests that neonatal seizures may adversely alter the function of surviving neurons and neuronal circuitry to chronically lower seizure thresholds or promote epileptogenesis. Animal studies indicate that early postnatal development is a critical window during which synaptogenesis and neuronal plasticity are at the peak. The expression of glutamate transporters is also developmentally regulated and may play a role in the enhanced excitability of the immature brain. The developmental regulation of voltage-gated channels in axons and at presynaptic terminals may be particularly critical in the generation of seizure activity through their influence on neurotransmitter release. Developmental changes in factors that regulate neuronal excitability can alter seizure susceptibility, and seizures can alter the normal pattern of brain development.