The Diathesis-Epilepsy Model: How Past Events Impact the Development of Epilepsy and Comorbidities

Persistent ∆FosB expression limits recurrent seizure activity and provides neuroprotection in the dentate gyrus of APP mice

Recurrent seizures lead to accumulation of the activity-dependent transcription factor ∆FosB in hippocampal dentate granule cells in both mouse models of epilepsy and mouse models of Alzheimer's disease (AD), which is also associated with increased incidence of seizures. In patients with AD and related mouse models, the degree of ∆FosB accumulation corresponds with increasing severity of cognitive deficits. We previously found that ∆FosB impairs spatial memory in mice by epigenetically regulating expression of target genes such as calbindin that are involved in synaptic plasticity. However, the suppression of calbindin in conditions of neuronal hyperexcitability has been demonstrated to provide neuroprotection to dentate granule cells, indicating that ∆FosB may act over long timescales to coordinate neuroprotective pathways. To test this hypothesis, we used viral-mediated expression of ∆JunD to interfere with ∆FosB signaling over the course of several months in transgenic mice expressing mutant human amyloid precursor protein (APP), which exhibit spontaneous seizures and develop AD-related neuropathology and cognitive deficits. Our results demonstrate that persistent ∆FosB activity acts through discrete modes of hippocampal target gene regulation to modulate neuronal excitability, limit recurrent seizure activity, and provide neuroprotection to hippocampal dentate granule cells in APP mice.

Stress and Epilepsy: Towards Understanding of Neurobiological Mechanisms for Better Management

Stress has been identified as a major contributor to human disease and is postulated to play a substantial role in epileptogenesis. In a significant proportion of individuals with epilepsy, sensitivity to stressful events contributes to dynamic symptomatic burden, notably seizure occurrence and frequency, and presence and severity of psychiatric comorbidities [anxiety, depression, posttraumatic stress disorder (PTSD)]. Here, we review this complex relationship between stress and epilepsy using clinical data and highlight key neurobiological mechanisms including the hypothalamic-pituitary-adrenal (HPA) axis dysfunction, altered neuroplasticity within limbic system structures, and alterations in neurochemical pathways such as brain-derived neurotrophic factor (BNDF) linking epilepsy and stress. We discuss current clinical management approaches of stress that help optimize seizure control and prevention, as well as psychiatric comorbidities associated with epilepsy. We propose that various shared mechanisms of stress and epilepsy present multiple avenues for the development of new symptomatic and preventative treatments, including disease modifying therapies aimed at reducing epileptogenesis. This would require close collaborations between clinicians and basic scientists to integrate data across multiple scales, from genetics to systems biology, from clinical observations to fundamental mechanistic insights. In future, advances in machine learning approaches and neuromodulation strategies will enable personalized and targeted interventions to manage and ultimately treat stress-related epileptogenesis.

Epileptogenic networks in drug-resistant epilepsy with amygdala enlargement: Assessment with stereo-EEG and 7 T MRI

OBJECTIVE

Amygdala enlargement is increasingly described in association with temporal lobe epilepsies. Its significance, however, remains uncertain both in terms of etiology and its link with psychiatric disorders and of its involvement in the epileptogenic zone. We assessed the epileptogenic networks underlying drug-resistant epilepsy with amygdala enlargement and investigated correlations between clinical features, epileptogenicity and morphovolumetric amygdala characteristics.

METHODS

We identified 12 consecutive patients suffering from drug-resistant epilepsy with visually suspected amygdala enlargement and available stereoelectroencephalographic recording. The epileptogenic zone was defined using the Connectivity Epileptogenicity Index. Morphovolumetric measurements were performed using automatic segmentation and co-registration on the 7TAMIbrain Amygdala atlas.

RESULTS

The epileptogenic zone involved the enlarged amygdala in all but three cases and corresponded to distributed, temporal-insular, temporal-insular-prefrontal or prefrontal-temporal networks in ten cases, while only two were temporo-mesial networks. Morphovolumetrically, amygdala enlargement was bilateral in 75% of patients. Most patients presented psychiatric comorbidities (anxiety, depression, posttraumatic stress disorder). The level of depression defined by screening questionnaire was positively correlated with the extent of amygdala enlargement.

CONCLUSIONS

Drug-resistant epilepsy with amygdala enlargement is heterogeneous; most cases implied "temporal plus" networks.

SIGNIFICANCE

The enlarged amygdala could reflect an interaction of stress-mediated limbic network alterations and mechanisms of epileptogenesis.

Post-traumatic stress disorder (PTSD) in patients with epilepsy

Anxiety and depression in epilepsy are strongly documented but post-traumatic stress disorder (PTSD) is underestimated and poorly known. We studied the links between psycho-traumagenic events (TE), onset of epilepsy, and severity of PTSD symptoms in patients with epilepsy. The study included 54 patients with epilepsy and 61 controls. We used validated questionnaires to screen for anxiety, depression, and PTSD symptoms and we conducted an interview to measure the prevalence of TE. We developed an original exploratory questionnaire to assess the presence of PTSD during interictal and peri-ictal periods. The results show that patients reported more exposure to a TE and presented significantly more severe PTSD symptoms than controls. Seventy-eight percent of patients (vs. 52% of controls) had been exposed to a TE, and 26% (vs. 7%) had a score above the diagnostic threshold of the PTSD scale. In addition, 18.6% of patients reported that their epilepsy began at the same time as they began to experience PTSD symptoms following a TE. Patients with high PTSD scores (above the threshold, n = 14) reported significantly more depression symptoms than patients without PTSD and reported PTSD symptoms both during the ictal and peri-ictal periods. Within the whole group of patients, anxiety (72%) and depression (33%) symptoms significantly correlated with PTSD symptoms reported by the scale. This study shows that patients with epilepsy have increased prevalence of self-reported PTSD symptoms. We describe the clinical picture specific to patients with epilepsy, which may include classical PTSD symptoms but also specific peri-ictal symptoms.

Genes Bound by ΔFosB in Different Conditions With Recurrent Seizures Regulate Similar Neuronal Functions

Seizure incidence is increased in Alzheimer’s disease (AD) patients and mouse models, and treatment with the antiseizure drug levetiracetam improves cognition. We reported that one mechanism by which seizures can exert persistent effects on cognition is through accumulation of ΔFosB, a transcription factor with a long half-life. Even the infrequent seizures that spontaneously occur in transgenic mice expressing human amyloid precursor protein (APP) lead to persistent increases in ΔFosB in the hippocampus, similar to what we observed in patients with AD or temporal lobe epilepsy. ΔFosB epigenetically regulates expression of target genes, however, whether ΔFosB targets the same genes when induced by seizures in different neurological conditions is not clear. We performed ChIP-sequencing to assess the repertoire of ΔFosB target genes in APP mice and in pilocarpine-treated wildtype mice (Pilo mice), a pharmacological model of epilepsy. These mouse models allowed us to compare AD, in which seizures occur in the context of high levels of amyloid beta, and epilepsy, in which recurrent seizures occur without AD-specific pathophysiology. Network profiling of genes bound by ΔFosB in APP mice, Pilo mice, and respective control mice revealed that functional domains modulated by ΔFosB in the hippocampus are expanded and diversified in APP and Pilo mice (vs. respective controls). Domains of interest in both disease contexts involved neuronal excitability and neurotransmission, neurogenesis, chromatin remodeling, and cellular stress and neuroinflammation. To assess the gene targets bound by ΔFosB regardless of seizure etiology, we focused on 442 genes with significant ΔFosB binding in both APP and Pilo mice (vs. respective controls). Functional analyses identified pathways that regulate membrane potential, glutamatergic signaling, calcium homeostasis, complement activation, neuron-glia population maintenance, and chromatin dynamics. RNA-sequencing and qPCR measurements in independent mice detected altered expression of several ΔFosB targets shared in APP and Pilo mice. Our findings indicate that seizure-induced ΔFosB can bind genes in patterns that depend on seizure etiology, but can bind other genes regardless of seizure etiology. Understanding the factors that underlie these differences, such as chromatin accessibility and/or abundance of co-factors, could reveal novel insights into the control of gene expression in disorders with recurrent seizures.

Caffeine Consumption During Pregnancy Accelerates the Development of Cognitive Deficits in Offspring in a Model of Tauopathy

Psychoactive drugs used during pregnancy can affect the development of the brain of offspring, directly triggering neurological disorders or increasing the risk for their occurrence. Caffeine is the most widely consumed psychoactive drug, including during pregnancy. In Wild type mice, early life exposure to caffeine renders offspring more susceptible to seizures. Here, we tested the long-term consequences of early life exposure to caffeine in THY-Tau22 transgenic mice, a model of Alzheimer’s disease-like Tau pathology. Caffeine exposed mutant offspring developed cognitive earlier than water treated mutants. Electrophysiological recordings of hippocampal CA1 pyramidal cells in vitro revealed that early life exposure to caffeine changed the way the glutamatergic and GABAergic drives were modified by the Tau pathology. We conclude that early-life exposure to caffeine affects the Tau phenotype and we suggest that caffeine exposure during pregnancy may constitute a risk-factor for early onset of Alzheimer’s disease-like pathology.

Effects of Single Cage Housing on Stress, Cognitive, and Seizure Parameters in the Rat and Mouse Pilocarpine Models of Epilepsy

Many experimental approaches require housing rodents in individual cages, including in epilepsy research. However, rats and mice are social animals; and individual housing constitutes a stressful situation. The goal of the present study was to determine the effects of individual housing as compared to conditions maintaining social contact on stress markers and epilepsy. Control male mice socially housed during pretest and then transferred to individual cages for six weeks displayed anhedonia, increased anxiety and biological markers of stress as compared to pretest values or mice kept socially housed during six weeks. Pilocarpine (pilo)-treated mice housed together showed increased levels of anhedonia, anxiety and stress markers as well as decreased cognitive performance as compared to the control group. The differences were more significant in pilo-treated mice housed individually. Anxiety correlated linearly with cognitive performance and stress markers independently of the experimental conditions. In the male rat pilo model, seizures were sixteen times more frequent in singly housed animals as compared to animals kept in pairs. Daily interactions with an experimenter in otherwise singly housed animals was sufficient to produce results identical to those found in animals kept in pairs. We propose that social isolation produces a severe phenotype in terms of stress and seizure frequency as compared to animals maintaining social contact (at least in these two models), a factor that needs to be taken into account for data interpretation, in particular for preclinical studies.

Epilepsy as a Network Disorder (1): What can we learn from other network disorders such as autistic spectrum disorder and mood disorders?

Epilepsy is a neurologic condition which often occurs with other neurologic and psychiatric disorders. The relation between epilepsy and these conditions is complex. Some population-based studies have identified a bidirectional relation, whereby not only patients with epilepsy are at increased risk of suffering from some of these neurologic and psychiatric disorders (migraine, stroke, dementia, autism, depression, anxiety disorders, Attention deficit hyperactivity disorder (ADHD), and psychosis), but also patients with these conditions are at increased risk of suffering from epilepsy. The existence of common pathogenic mechanisms has been postulated as a potential explanation of this phenomenon. To reassess the relationships between neurological and psychiatric conditions in general, and specifically autism, depression, Alzheimer's disease, schizophrenia, and epilepsy, a recent meeting brought together basic researchers and clinician scientists entitled "Epilepsy as a Network Disorder." This was the fourth in a series of conferences, the "Fourth International Halifax Conference and Retreat". This manuscript summarizes the proceedings on potential relations between Epilepsy on the one hand and autism and depression on the other. A companion manuscript provides a summary of the proceedings about the relation between epilepsy and Alzheimer's disease and schizophrenia, closed by the role of translational research in clarifying these relationships. The review of the topics in these two manuscripts will provide a better understanding of the mechanisms operant in some of the common neurologic and psychiatric comorbidities of epilepsy.

Low β2 Main Peak Frequency in the Electroencephalogram Signs Vulnerability to Depression

Objective: After an intense and repeated stress some rats become vulnerable to depression. This state is characterized by persistent low serum BDNF concentration. Our objective was to determine whether electrophysiological markers can sign vulnerability to depression. Methods: Forty-three Sprague Dawley rats were recorded with supradural electrodes above hippocampus and connected to wireless EEG transmitters. Twenty-nine animals experienced four daily social defeats (SD) followed by 1 month recovery. After SD, 14 rats had persistent low serum BDNF level and were considered as vulnerable (V) while the 15 others were considered as non-vulnerable (NV). EEG signals were analyzed during active waking before SD (Baseline), just after SD (Post-Stress) and 1 month after SD (Recovery). Results: We found that V animals are characterized by higher high θ and α spectral relative powers and lower β2 main peak frequency before SD. These differences are maintained at Post-Stress and Recovery for α spectral relative powers and β2 main peak frequency. Using ROC analysis, we show that low β2 main peak frequency assessed during Baseline is a good predictor of the future state of vulnerability to depression. Conclusion: Given the straightforwardness of EEG recordings, these results open the way to prospective studies in humans aiming to identify population at-risk for depression.

Diagnosing and treating depression in epilepsy

At least one third of patients with active epilepsy suffer from significant impairment of their emotional well-being. A targeted examination for possible depression (irrespective of any social, financial or personal burdens) can identify patients who may benefit from medical attention and therapeutic support. Reliable screening instruments such as the Neurological Disorders Depression Inventory for Epilepsy (NDDI-E) are suitable for the timely identification of patients needing help. Neurologists should be capable of managing mild to moderate comorbid depression but referral to mental health specialists is mandatory in severe and difficult-to-treat depression, or if the patient is acutely suicidal. In terms of the therapeutic approach, it is essential first to optimize seizure control and minimize unwanted antiepileptic drug-related side effects. Psychotherapy for depression in epilepsy (including online self-treatment programs) is underutilized although it has proven effective in ten well-controlled trials. In contrast, the effectiveness of antidepressant drugs for depression in epilepsy is unknown. However, if modern antidepressants are used (e.g. SSRI, SNRI, NaSSA), concerns about an aggravation of seizures and or problematic interactions with antiepileptic drugs seem unwarranted. Epilepsy-related stress ("burden of epilepsy") explains depression in many patients but acute and temporary seizure-related states of depression or suicidality have also been reported. Limbic encephalitits may cause isolated mood alteration without any recognizable psychoetiological background indicating a possible role of neuroinflammation. This review will argue that, overall, a bio-psycho-social model best captures the currently available evidence relating to the etiology and treatment of depression as a comorbidity of epilepsy.