Early life stress enhancement of limbic epileptogenesis in adult rats: mechanistic insights

Phytocannabinoids restore seizure-induced alterations in emotional behaviour in male rats

Epilepsy often presents with severe emotional comorbidities including anxiety and abnormal fear responses which impose a significant burden on, and reduce, quality of life in people living with the disease. Our lab has recently shown that kindled seizures lead to changes in emotional processing resulting from the downregulation of anandamide signalling within the amygdala. Phytocannabinoids derived from the Cannabis sativa plant have attracted a lot of interest as a new class of drugs with potential anticonvulsant effects. Among the wide number of compounds occurring in Cannabis sativa, Δ9- tetrahydrocannabinol (THC), the one responsible for its main psychoactive effects, and the nonpsychoactive cannabidiol (CBD) have been extensively examined under pre-clinical and clinical contexts to control seizures, however, neither have been assessed in the context of the management of emotional comorbidities associated with seizure activity. We used two behavioural procedures to assess anxiety- and fear-like responding in adult male Long-Evans rats: elevated plus maze and auditory fear conditioning. In agreement with previous reports, we found seizure-induced increases in anxiety- and fear-like responding. These effects were reversed by either CBD (vaporized) or THC (oral). We also found that antagonism of serotonin 1 A receptors prior to CBD exposure prevented its protective effects. Phytocannabinoids offer a novel and reliable opportunity to treat seizure induced comorbid emotional alterations.

Early life stress influences epilepsy outcomes in mice

Stress is a common seizure trigger that has been implicated in worsening epilepsy outcomes, which encompasses psychiatric and cognitive comorbidities and sudden unexpected death in epilepsy (SUDEP) risk. The neuroendocrine response to stress is mediated by the hypothalamic-pituitary-adrenal (HPA) axis and HPA axis dysfunction worsens epilepsy outcomes, increasing seizure burden, behavioral comorbidities, and risk for SUDEP in mice. Early life stress (ELS) reprograms the HPA axis into adulthood, impacting both the basal and stress-induced activity. Thus, we propose that ELS may influence epilepsy outcomes by influencing the function of the HPA axis. To test this hypothesis, we utilized the maternal separation paradigm and examined the impact on seizure susceptibility. We show that ELS exerts a sex dependent effect on seizure susceptibility in response to acute administration of the chemoconvulsant, kainic acid, which is associated with an altered relationship between seizure activity and HPA axis function. To further examine the impact of ELS on epilepsy outcomes, we utilized the intrahippocampal kainic acid model of chronic epilepsy in mice previously exposed to maternal separation. We find that the relationship between corticosterone levels and the extent of epileptiform activity is altered in mice subjected to ELS. We demonstrate that ELS impacts behavioral outcomes associated with chronic epilepsy in a sex-dependent manner, with females being more affected. We also observe reduced mortality (presumed SUDEP) in female mice subjected to ELS, consistent with previous findings suggesting a role for HPA axis dysfunction in SUDEP risk. These data demonstrate for the first time that ELS influences epilepsy outcomes and suggest that previous life experiences may impact the trajectory of epilepsy.

Early life stress influences epilepsy outcomes in mice

Stress is a common seizure trigger that has been implicated in worsening epilepsy outcomes. The neuroendocrine response to stress is mediated by the hypothalamic-pituitary-adrenal (HPA) axis and HPA axis dysfunction worsens epilepsy outcomes, increasing seizure burden, behavioral comorbidities, and risk for sudden unexpected death in epilepsy (SUDEP) in mice. Early life stress (ELS) reprograms the HPA axis into adulthood, impacting both the basal and stress-induced activity. Thus, we propose that ELS may influence epilepsy outcomes by influencing the function of the HPA axis. To test this hypothesis, we utilized the maternal separation paradigm and examined the impact on seizure susceptibility. We show that ELS exerts a sex dependent effect on seizure susceptibility in response to acute administration of the chemoconvulsant, kainic acid, which is associated with an altered relationship between seizure activity and HPA axis function. To further examine the impact of ELS on epilepsy outcomes, we utilized the intrahippocampal kainic acid model of chronic epilepsy in mice previously exposed to maternal separation. We find that the relationship between corticosterone levels and the extent of epileptiform activity is altered in mice subjected to ELS. We demonstrate that ELS impacts behavioral outcomes associated with chronic epilepsy in a sex-dependent manner, with females being more affected. We also observe reduced mortality (presumed SUDEP) in female mice subjected to ELS, consistent with previous findings suggesting a role for HPA axis dysfunction in SUDEP risk. These data demonstrate for the first time that ELS influences epilepsy outcomes and suggest that previous life experiences may impact the trajectory of epilepsy.

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.

Effects of attachment styles, childhood traumas, and alexithymia in Turkish patients with epilepsy and functional seizures

INTRODUCTION

In this cross-sectional study, we used self-report scales to compare childhood traumas, attachment styles, and alexithymia among patients with functional seizures (FS) to patients with epilepsy and healthy controls. We also investigated risk factors associated with FS.

MATERIAL AND METHODS

A total of 44 patients with epilepsy, 14 patients with FS, and 25 healthy controls were included. All participants were over the age of 18 and were referred to the Baskent University Adana Epilepsy and Video-EEG Center. The patients underwent neurological examinations, brain MRIs, and video-EEG evaluations. Epileptic seizures were classified based on video EEG. The control group consisted of healthy individuals without neurological or psychiatric illness and a history of epileptic seizures or syncope. Beck Depression Inventory (BDI), Childhood Trauma Questionnaire (CTQ), Adult Attachment Scale (AAS), and Toronto Alexithymia Scale-20 (TAS-20) were applied to all participants.

RESULTS

Patients with FS had lower educational levels, higher rates of unemployment and single-marital status. The FS group had higher depression, childhood trauma, and alexithymia scores than the other groups. Furthermore, FS patients had a higher prevalence of avoidant attachment. The alexithymia and childhood trauma scores were both correlated with depression. Through the logistic regression analysis, childhood trauma scores and alexithymia were significant risk factors for FS.

CONCLUSION

The use of video-EEG for diagnosing FS can reduce the risk of misdiagnosis and inappropriate antiepileptic treatment. Psychiatric comorbidities, childhood traumas, and alexithymia are prevalent in patients with FS. Therefore, implementing a multidisciplinary treatment approach that addresses the psychological, medical, and social aspects of FS can significantly improve outcomes.

Metyrapone abolishes spike-wave discharge seizures in genetic absence epilepsy rats from Strasbourg by reducing stress hormones

OBJECTIVE

Stress is one of the most commonly reported triggers for seizures in patients with epilepsy, although the mechanisms that mediate this effect are not established. The clinical evidence supporting this is derived from patients' subjective experience of stress, and how this influences their own seizures. Animal models can be used to explore this phenomenon in controlled environments, free from subjective bias. Here, we used genetic absence epilepsy rats from Strasbourg (GAERS), a genetic rat model of absence epilepsy, to explore the influence of stress and stress hormones on spontaneous seizures.

METHODS

Adult male GAERS (n = 38) and nonepileptic control (NEC) rats (n = 4) were used. First, rats were subjected to 30-min restraint stress to assess hypothalamic-pituitary-adrenal axis function. Next, we assessed the effects of 30-min noise stress, and cage tilt stress, on spike-wave discharge seizures in GAERS. We then performed pharmacological experiments to assess the direct effects of stress hormones on seizures, including corticosterone, metyrapone, and deoxycorticosterone.

RESULTS

GAERS exhibited elevated baseline corticosterone levels, compared to NEC rats. Noise stress and cage tilt stress significantly enhanced seizure incidence (p < .05), but only during stress periods. Exogenous corticosterone administration also significantly increased seizure occurrence (p < .05). Metyrapone, an inhibitor of corticosterone synthesis, completely abolished seizures in GAERS, and seizures remained suppressed for >2 h. However, deoxycorticosterone, the precursor of corticosterone, increased seizures.

SIGNIFICANCE

These results suggest that GAERS exhibit elevations in stress hormones, and this may contribute to seizures. Inhibiting corticosterone synthesis with metyrapone prevents seizures in GAERS, and shows potential for repurposing this drug as a future antiseizure medication.

Antidepressant Drugs for Seizures and Epilepsy: Where do we Stand?

People with epilepsy (PWE) are more likely to develop depression and both these complex chronic diseases greatly affect health-related quality of life (QOL). This comorbidity contributes to the deterioration of the QOL further than increasing the severity of epilepsy worsening prognosis. Strong scientific evidence suggests the presence of shared pathogenic mechanisms. The correct identification and management of these factors are crucial in order to improve patients' QOL. This review article discusses recent original research on the most common pathogenic mechanisms of depression in PWE and highlights the effects of antidepressant drugs (ADs) against seizures in PWE and animal models of seizures and epilepsy. Newer ADs, such as selective serotonin reuptake inhibitors (SRRI) or serotonin-noradrenaline reuptake inhibitors (SNRI), particularly sertraline, citalopram, mirtazapine, reboxetine, paroxetine, fluoxetine, escitalopram, fluvoxamine, venlafaxine, duloxetine may lead to improvements in epilepsy severity whereas the use of older tricyclic antidepressant (TCAs) can increase the occurrence of seizures. Most of the data demonstrate the acute effects of ADs in animal models of epilepsy while there is a limited number of studies about the chronic antidepressant effects in epilepsy and epileptogenesis or on clinical efficacy. Much longer treatments are needed in order to validate the effectiveness of these new alternatives in the treatment and the development of epilepsy, while further clinical studies with appropriate protocols are warranted in order to understand the real potential contribution of these drugs in the management of PWE (besides their effects on mood).

The impact of early-life environment on absence epilepsy and neuropsychiatric comorbidities

This review discusses the long-term effects of early-life environment on epileptogenesis, epilepsy, and neuropsychiatric comorbidities with an emphasis on the absence epilepsy. The WAG/Rij rat strain is a well-validated genetic model of absence epilepsy with mild depression-like (dysthymia) comorbidity. Although pathologic phenotype in WAG/Rij rats is genetically determined, convincing evidence presented in this review suggests that the absence epilepsy and depression-like comorbidity in WAG/Rij rats may be governed by early-life events, such as prenatal drug exposure, early-life stress, neonatal maternal separation, neonatal handling, maternal care, environmental enrichment, neonatal sensory impairments, neonatal tactile stimulation, and maternal diet. The data, as presented here, indicate that some early environmental events can promote and accelerate the development of absence seizures and their neuropsychiatric comorbidities, while others may exert anti-epileptogenic and disease-modifying effects. The early environment can lead to phenotypic alterations in offspring due to epigenetic modifications of gene expression, which may have maladaptive consequences or represent a therapeutic value. Targeting DNA methylation with a maternal methyl-enriched diet during the perinatal period appears to be a new preventive epigenetic anti-absence therapy. A number of caveats related to the maternal methyl-enriched diet and prospects for future research are discussed.

Bidirectional Relations Among Depression, Migraine, and Epilepsy: Do They Have an Impact on Their Response to Treatment?

The evaluation and treatment of patients with epilepsy is not limited to the type of epilepsy, but it must incorporate the common comorbid neurologic, psychiatric, and medical disorders, as the latter can bare an impact on the course and response to treatment of the seizure disorder and vice versa. In this article we review the bidirectional relations among epilepsy and two of its most common comorbidities, mood disorders and migraine and examine the implications of these relations on the selection of therapies of these three disorders and their response to treatment. We also review the most salient common pathogenic mechanisms that may explain such relations.

Sex differences in the developing brain impact stress-induced epileptogenicity following hyperthermia-induced seizures

Febrile seizures (FS) are common, affecting 2-5% of children between the ages of 3 months and 6 years. Complex FS occur in 10% of patients with FS and are strongly associated with mesial temporal lobe epilepsy. Current research suggests that predisposing factors, such as genetic and anatomic abnormalities, may be necessary for complex FS to translate to mesial temporal lobe epilepsy. Sex hormones are known to influence seizure susceptibility and epileptogenesis, but whether sex-specific effects of early life stress play a role in epileptogenesis is unclear. Here, we investigate sex differences in the activity of the hypothalamic-pituitary-adrenal (HPA) axis following chronic stress and the underlying contributions of gonadal hormones to the susceptibility of hyperthermia-induced seizures (HS) in rat pups. Chronic stress consisted of daily injections of 40 mg/kg of corticosterone (CORT) subcutaneously from postnatal day (P) 1 to P9 in male and female rat pups followed by HS at P10. Body mass, plasma CORT levels, temperature threshold to HS, seizure characteristics, and electroencephalographic in vivo recordings were compared between CORT- and vehicle (VEH)-injected littermates during and after HS at P10. In juvenile rats (P18-P22), in vitro CA1 pyramidal cell recordings were recorded in males to investigate excitatory and inhibitory neuronal circuits. Results show that daily CORT injections increased basal plasma CORT levels before HS and significantly reduced weight gain and body temperature threshold of HS in both males and females. CORT also significantly lowered the generalized convulsions (GC) latency while increasing recovery time and the number of electrographic seizures (>10s), which had longer duration. Furthermore, sex-specific differences were found in response to chronic CORT injections. Compared to females, male pups had increased basal plasma CORT levels after HS, longer recovery time and a higher number of electrographic seizures (>10s), which also had longer duration. Sex-specific differences were also found at baseline conditions with lower latency to generalized convulsions and longer duration of electrographic seizures in males but not in females. In juvenile male rats, the amplitude of evoked excitatory postsynaptic potentials, as well as the amplitude of inhibitory postsynaptic currents, were significantly greater in CORT rats when compared to VEH littermates. These findings not only validate CORT injections as a stress model, but also show a sex difference in baseline conditions as well as a response to chronic CORT and an impact on seizure susceptibility, supporting a potential link between sustained early-life stress and complex FS. Overall, these effects also indicate a putatively less severe phenotype in female than male pups. Ultimately, studies investigating the biological underpinnings of sex differences as a determining factor in mental and neurologic problems are necessary to develop better diagnostic, preventative, and therapeutic approaches for all patients regardless of their sex.

The glucocorticoid receptor specific modulator CORT108297 reduces brain pathology following status epilepticus

OBJECTIVE

Glucocorticoid levels rise rapidly following status epilepticus and remain elevated for weeks after the injury. To determine whether glucocorticoid receptor activation contributes to the pathological sequelae of status epilepticus, mice were treated with a novel glucocorticoid receptor modulator, C108297.

METHODS

Mice were treated with either C108297 or vehicle for 10 days beginning one day after pilocarpine-induced status epilepticus. Baseline and stress-induced glucocorticoid secretion were assessed to determine whether hypothalamic-pituitary-adrenal axis hyperreactivity could be controlled. Status epilepticus-induced pathology was assessed by quantifying ectopic hippocampal granule cell density, microglial density, astrocyte density and mossy cell loss. Neuronal network function was examined indirectly by determining the density of Fos immunoreactive neurons following restraint stress.

RESULTS

Treatment with C108297 attenuated corticosterone hypersecretion after status epilepticus. Treatment also decreased the density of hilar ectopic granule cells and reduced microglial proliferation. Mossy cell loss, on the other hand, was not prevented in treated mice. C108297 altered the cellular distribution of Fos protein but did not restore the normal pattern of expression.

INTERPRETATION

Results demonstrate that baseline corticosterone levels can be normalized with C108297, and implicate glucocorticoid signaling in the development of structural changes following status epilepticus. These findings support the further development of glucocorticoid receptor modulators as novel therapeutics for the prevention of brain pathology following status epilepticus.

Maternal behavior and the neonatal HPA axis in the Wistar Audiogenic Rat (WAR) strain: Early-life implications for a genetic animal model in epilepsy

Epileptogenesis is a multistage process and seizure susceptibility can be influenced by stress early in life. Wistar Audiogenic Rat (WAR) strain is an interesting model to study the association between stress and epilepsy, since it is naturally susceptible to seizures and present changes in the hypothalamus-pituitary-adrenal (HPA) axis activity. All these features are related to the pathogenic mechanisms usually associated with psychiatric comorbidities present in epilepsy. Therefore, the current study aimed to evaluate the neonate HPA axis function and maternal care under control and stress conditions in the WAR strain. Maternal behavior and neonate HPA axis were evaluated in Wistar and WAR strains under rest and after the presence of stressors. We observed that WAR pups present higher plasmatic corticosterone concentration as compared to Wistar pups. Although WAR dams do not show significant altered maternal behavior at rest, there is a higher latency to recover the litter in the pup retrieval test, while some did not recover all the litter. Wistar Audiogenic Rat dams presented similar behaviors to Wistar dams to a female intruder and maternal care with the pups in the maternal defense test. Taken together, these findings indicate that the WAR strain could show HPA axis disruption early in life and dams present altered maternal behavior under stressful events. Those alterations make the WAR strain an interesting model to evaluate vulnerability to epilepsy and its associated neuropsychiatric comorbidities.

Effect of titanium dioxide nanoparticles administered during pregnancy on depression-like behavior in forced swimming and tail suspension tests in offspring mice

INTRODUCTION

Applications of engineered nanoparticles are rapidly increasing. Titanium dioxide nanoparticles (TiO₂ NPs) are used in many products including those produced by pigment and cosmetic manufacturers. The objective of this study was to investigate the effects of maternal exposure during pregnancy to TiO₂ NPs on depressive-like behavior in the first and second generation offspring.

MATERIALS AND METHODS

Forty female albino mice were placed into four groups for 2 weeks. Fertile males were then added to each cage by a ratio of two males to five females. After detection of pregnancy, the mice were transferred to separate cages. The study groups were divided into four groups: the first group, served as control, did not receive any treatment; the second group received injections of normal saline; groups 3 and 4 received, respectively, 50 and 100 µl of TiO₂ NP solution injections subcutaneously on days 3, 7, 10, and 14 after mating. Behavioral tests were conducted on postnatal days 21 and 40.

FINDINGS

Subcutaneous injection of 50 and 100 µl of TiO₂ NPs significantly (p < 0.05) increased the immobility time in the forced swimming test and tail suspension test (TST). No significant difference was observed in measured variables between groups receiving 50 and 100 µl of TiO₂ NPs. No significant difference was also found between male and female offspring. Depression-like behavior increased in the second generation of mice in the forced swim test and TST.

CONCLUSION

Prenatal exposure of mothers to TiO₂ NPs would increase depression-like behavior in neonatal mice.

Evaluation of the HPA Axis' Response to Pharmacological Challenges in Experimental and Clinical Early-Life Stress-Associated Depression

Early-life stress (ELS) is associated with a higher risk of psychopathologies in adulthood, such as depression, which may be related to persistent changes in the hypothalamic-pituitary-adrenal (HPA) axis. This study aimed to evaluate the effects of ELS on the functioning of the HPA axis in clinical and experimental situations. Clinically, patients with current depressive episodes, with and without ELS, and healthy controls, composed the sample. Subjects took a capsule containing placebo, fludrocortisone, prednisolone, dexamethasone or spironolactone followed by an assessment of plasma cortisol the morning after. Experimentally, male Wistar rats were submitted to ELS protocol based on variable, unpredictable stressors from postnatal day (PND)1 to PND21. On PND65 animals were behaviorally evaluated through the forced-swimming test (FST). At PND68, pharmacological challenges started, using mifepristone, dexamethasone, spironolactone, or fludrocortisone, and corticosterone levels were determined 3 h after injections. Cortisol response of the patients did not differ significantly from healthy subjects, regardless of their ELS history, and it was lower after fludrocortisone, prednisolone, and dexamethasone compared with placebo, indicating the suppression of plasma cortisol by all these treatments. Animals exposed to ELS presented altered phenotype as indicated by an increased immobility time in the FST when compared with control, but no significant long-lasting effects of ELS were observed on the HPA axis response. Limitations on the way the volunteers were sampled may have contributed to the lack of ELS effects on the HPA axis, pointing out the need for further research to understand these complex phenomena.

Glucocorticoid-mediated mechanisms of hippocampal damage: Contribution of subgranular neurogenesis

A comprehensive overview of the interplay between glucocorticoids (GCs) and adult hippocampal neurogenesis (AHN) is presented, particularly, in the context of a diseased brain. The effectors of GCs in the dentate gyrus neurogenic niche of the hippocampal are reviewed, and the consequences of the GC signaling on the generation and integration of new neurons are discussed. Recent findings demonstrating how GC signaling mediates impairments of the AHN in various brain pathologies are overviewed. GC-mediated effects on the generation and integration of adult-born neurons in the hippocampal dentate gyrus depend on the nature, severity, and duration of the acting stress factor. GCs realize their effects on the AHN primarily via specific glucocorticoid and mineralocorticoid receptors. Disruption of the reciprocal regulation between the hypothalamic-pituitary-adrenal (HPA) axis and the generation of the adult-born granular neurons is currently considered to be a key mechanism implicating the AHN into the pathogenesis of numerous brain diseases, including those without a direct hippocampal damage. These alterations vary from reduced proliferation of stem and progenitor cells to increased cell death and abnormalities in morphology, connectivity, and localization of young neurons. Although the involvement of the mutual regulation between the HPA axis and the AHN in the pathogenesis of cognitive deficits and mood impairments is evident, several unresolved critical issues are stated. Understanding the details of GC-mediated mechanisms involved in the alterations in AHN could enable the identification of molecular targets for ameliorating pathology-induced imbalance in the HPA axis/AHN mutual regulation to conquer cognitive and psychiatric disturbances.

Reduced expression of the glucocorticoid receptor in the hippocampus of patients with drug-resistant temporal lobe epilepsy and comorbid depression

Objective

Depressive disorders are common among about 50% of the patients with drug‐resistant temporal lobe epilepsy (TLE). The underlying etiology remains elusive, but hypothalamus‐pituitary‐adrenal (HPA) axis activation due to changes in glucocorticoid receptor (GR) protein expression could play an important role. Therefore, we set out to investigate expression of the GR in the hippocampus, an important brain region for HPA axis feedback, of patients with drug‐resistant TLE, with and without comorbid depression.

Methods

GR expression was studied using immunohistochemistry on hippocampal sections from well‐characterized TLE patients with depression (TLE + D, n = 14) and without depression (TLE − D, n = 12) who underwent surgery for drug‐resistant epilepsy, as well as on hippocampal sections from autopsy control cases (n = 9). Video–electroencephalography (EEG), magnetic resonance imaging (MRI), and psychiatric and memory assessments were performed prior to surgery.

Results

Abundant GR immunoreactivity was present in dentate gyrus granule cells and CA1 pyramidal cells of controls. In contrast, neuronal GR expression was lower in patients with TLE, particularly in the TLE + D group. Quantitative analysis showed a smaller GR+ area in TLE + D as compared to TLE − D patients and controls. Furthermore, the ratio between the number of GR+/NeuN+ cells was lower in patients with TLE + D as compared to TLE − D and correlated negatively with the depression severity based on psychiatric history. The expression of the GR was also lower in glial cells of TLE + D compared to TLE − D patients and correlated negatively to the severity of depression.

Significance

Reduced hippocampal GR expression may be involved in the etiology of depression in patients with TLE and could constitute a biological marker of depression in these patients.

Immune Challenges and Seizures: How Do Early Life Insults Influence Epileptogenesis?

The development of epilepsy, a process known as epileptogenesis, often occurs later in life following a prenatal or early postnatal insult such as cerebral ischemia, stroke, brain trauma, or infection. These insults share common pathophysiological pathways involving innate immune activation including neuroinflammation, which is proposed to play a critical role in epileptogenesis. This review provides a comprehensive overview of the latest preclinical evidence demonstrating that early life immune challenges influence neuronal hyperexcitability and predispose an individual to later life epilepsy. Here, we consider the range of brain insults that may promote the onset of chronic recurrent spontaneous seizures at adulthood, spanning intrauterine insults (e.g. maternal immune activation), perinatal injuries (e.g. hypoxic–ischemic injury, perinatal stroke), and insults sustained during early postnatal life—such as fever-induced febrile seizures, traumatic brain injuries, infections, and environmental stressors. Importantly, all of these insults represent, to some extent, an immune challenge, triggering innate immune activation and implicating both central and systemic inflammation as drivers of epileptogenesis. Increasing evidence suggests that pro-inflammatory cytokines such as interleukin-1 and subsequent signaling pathways are important mediators of seizure onset and recurrence, as well as neuronal network plasticity changes in this context. Our current understanding of how early life immune challenges prime microglia and astrocytes will be explored, as well as how developmental age is a critical determinant of seizure susceptibility. Finally, we will consider the paradoxical phenomenon of preconditioning, whereby these same insults may conversely provide neuroprotection. Together, an improved appreciation of the neuroinflammatory mechanisms underlying the long-term epilepsy risk following early life insults may provide insight into opportunities to develop novel immunological anti-epileptogenic therapeutic strategies.

Mechanisms of Psychiatric Comorbidities in Epilepsy

Psychiatric illnesses, including depression and anxiety, are highly comorbid with epilepsy (for review see Josephson and Jetté (Int Rev Psychiatry 29:409-424, 2017), Salpekar and Mula (Epilepsy Behav 98:293-297, 2019)). Psychiatric comorbidities negatively impact the quality of life of patients (Johnson et al., Epilepsia 45:544-550, 2004; Cramer et al., Epilepsy Behav 4:515-521, 2003) and present a significant challenge to treating patients with epilepsy (Hitiris et al., Epilepsy Res 75:192-196, 2007; Petrovski et al., Neurology 75:1015-1021, 2010; Fazel et al., Lancet 382:1646-1654, 2013) (for review see Kanner (Seizure 49:79-82, 2017)). It has long been acknowledged that there is an association between psychiatric illnesses and epilepsy. Hippocrates, in the fourth-fifth century B.C., considered epilepsy and melancholia to be closely related in which he writes that "melancholics ordinarily become epileptics, and epileptics, melancholics" (Lewis, J Ment Sci 80:1-42, 1934). The Babylonians also recognized the frequency of psychosis in patients with epilepsy (Reynolds and Kinnier Wilson, Epilepsia 49:1488-1490, 2008). Despite the fact that the relationship between psychiatric comorbidities and epilepsy has been recognized for thousands of years, psychiatric illnesses in people with epilepsy still commonly go undiagnosed and untreated (Hermann et al., Epilepsia 41(Suppl 2):S31-S41, 2000) and systematic research in this area is still lacking (Devinsky, Epilepsy Behav 4(Suppl 4):S2-S10, 2003). Thus, although it is clear that these are not new issues, there is a need for improvements in the screening and management of patients with psychiatric comorbidities in epilepsy (Lopez et al., Epilepsy Behav 98:302-305, 2019) and progress is needed to understand the underlying neurobiology contributing to these comorbid conditions. To that end, this chapter will raise awareness regarding the scope of the problem as it relates to comorbid psychiatric illnesses and epilepsy and review our current understanding of the potential mechanisms contributing to these comorbidities, focusing on both basic science and clinical research findings.

In Up to My Ears and Temporal Lobes: Effects of Early Life Stress on Epilepsy Development

Epilepsy and stress are each significant concerns in today's society, bearing heavy impacts on mental and physical health and overall quality of life. Unfortunately, the intersection between these is potentially even more concerning, as stress is a frequent trigger of seizures and may contribute to neural hyperexcitability. A growing body of research suggests a connection between early life stress (occurring in the prenatal or postnatal stage) and later development of epilepsy. While the larger part of this literature suggests that early life stress increases vulnerability for epilepsy development, there are a number of interacting factors influencing this relationship. These factors include developmental stage at which both stressor and seizure assessment occur, type of stressor, sex effects, and type of seizure (convulsive or non-convulsive). Additionally, a number of potential mechanisms have been identified, including activation of the hypothalamic-pituitary-adrenal axis, neuroinflammation, altered inhibitory/excitatory balance, and temporal lobe structures. Developing a clearer understanding of this relationship between early life stress and epilepsy, the factors that influence it, and underlying mechanisms that may serve as targets for intervention is crucial to improving quality of life for persons with epilepsy.

Size of Subcortical Band Heterotopia Influences the Susceptibility to Hyperthermia-Induced Seizures in a Rat Model

Studies conducted in human and rodent models have suggested that preexisting neurodevelopmental defects could predispose immature brains to febrile seizures (FS). However, the impact of the anatomical extent of preexisting cortical malformations on FS susceptibility was never assessed. Here, we induced hyperthermic seizures (HS) in rats with bilateral subcortical band heterotopia (SBH) and found variable degrees of HS susceptibility depending on inter-individual anatomical differences in size and extent of SBH. This indicates that an association exists between the overall extent or location of a cortical malformation, and the predisposition to FS. This also suggests that various predisposing factors and underlying causes may contribute to the etiology of complex FS.

Neurobiologic properties of mood disorders may have an impact on epilepsy: Should this motivate neurologists to screen for this psychiatric comorbidity in these patients?

Epilepsy and psychiatric comorbidities have a complex relation, which can be manifested by their relatively high comorbid occurrence and the existence of a bidirectional relation, whereby not only are people with epilepsy (PWE) at greater risk of developing psychiatric disorders, but patients with primary psychiatric disorders are at higher risk of developing epilepsy. The existence of common pathogenic mechanisms operant in primary psychiatric disorders and epilepsy has been postulated as one of the leading hypothesis to explain their close and very complex relation. The neurobiologic characteristics of mood disorders can be used as a model to test this hypothesis. In this manuscript, we highlight data that suggest how several neurobiologic aspects of mood disorders can facilitate the epileptogenic process in animal models and explain the increased risk of patients with primary mood disorders to develop epilepsy in general and treatment-resistant epilepsy in particular. It is our hope that the inclusion of these data in this Special Issue will motivate neurologists to screen common psychiatric comorbidities in PWE. This article is part of the Special Issue "Obstacles of Treatment of Psychiatric Comorbidities in Epilepsy".

The Relationship Between Epilepsy and Anxiety Disorders

PURPOSE OF REVIEW

The current review aims at providing an overview of relevant aspects of anxiety symptoms and anxiety disorders (AD) in adults patients with epilepsy (PWE).

RECENT FINDINGS

Firstly, the appropriate diagnosis of type of anxiety symptoms and AD in PWE will be presented. Anxiety symptoms are often peri-ictal and classified in relation to their temporal occurrence to seizures. Anxiety symptoms are of three types: preictal (preceding a seizure), ictal (presenting as part of the seizure symptoms and signs), and postictal (occurring within 72 h of a seizure). AD are diagnosed in the interictal period and occur independently of seizures. Four specific AD in PWE can be objectified: anticipatory anxiety of epileptic seizures (AAS), seizure phobia, epileptic social phobia, and epileptic panic disorder. Secondly, the bidirectional pathophysiological relationship between anxiety and epilepsy will be described. Anxiety is a trigger for seizures in some patients, and the notion of stress and arousal is essential to understand the relationship between anxiety and seizure. Moreover, seizures arising from the limbic network especially involving amygdala, which may express fear-related semiology, provide insight into the pathophysiology of AD comorbidities. Thirdly, the methods of screening for AD and anxiety symptoms will be detailed. Fourthly, the pharmacological and psychobehavioral management of anxiety symptoms and AD in PWE will be presented. Arousal-based approaches for preictal and ictal symptoms and anxiety-based approaches for postictal and interictal symptoms will be presented. Despite lack of evidence-based approaches, it is recognized that management of epilepsy is not only about controlling seizures, but also depends heavily on detecting, correctly diagnosing, and appropriately managing anxiety symptoms and AD comorbidities, in order to maximize quality of life. Improving self-control and self-efficacy is of fundamental importance in the management of PWE. Further rigorously designed studies focusing on anxiety symptoms and AD are essential to improve the overall care of PWE.

Hyperthermia-induced seizures followed by repetitive stress are associated with age-dependent changes in specific aspects of the mouse stress system

Stress is among the most frequently self-reported factors provoking epileptic seizures in children and adults. It is still unclear, however, why some people display stress-sensitive seizures and others do not. Recently, we showed that young epilepsy patients with stress-sensitive seizures exhibit a dysregulated hypothalamic-pituitary-adrenal (HPA)-axis. Most likely, this dysregulation gradually develops, and is triggered by stressors occurring early in life (early-life stress [ELS]). ELS may be particularly impactful when overlapping with the period of epileptogenesis. To examine this in a controlled and prospective manner, the present study investigated the effect of repetitive variable stressors or control treatment between postnatal day (PND) 12 and 24 in male mice exposed on PND10 to hyperthermia (HT)-induced prolonged seizures (control: normothermia). A number of peripheral and central indices of HPA-axis activity were evaluated at pre-adolescent and young adult age (ie, at PND25 and 90, respectively). At PND25 but not at PND90, body weight gain and absolute as well as relative (to body weight) thymus weight were reduced by ELS (vs control), whereas relative adrenal weight was enhanced, confirming the effectiveness of the stress treatment. Basal and stress-induced corticosterone levels were unaffected, though, by ELS at both ages. HT by itself did not affect any of these peripheral markers of HPA-axis activity, nor did it interact with ELS. However, centrally we did observe age-specific interaction effects of HT and ELS with regard to hippocampal glucocorticoid receptor mRNA expression, neurogenesis with the immature neurone marker doublecortin and the number of hilar (ectopic) granule cells using Prox1 staining. This lends some support to the notion that exposure to repetitive stress after HT-induced seizures may dysregulate central components of the stress system in an age-dependent manner. Such dysregulation could be one of the mechanisms conferring higher vulnerability of individuals with epilepsy to develop seizures in the face of stress.

Bidirectional relations among common psychiatric and neurologic comorbidities and epilepsy: Do they have an impact on the course of the seizure disorder?

The treatment of epilepsy is not limited to the achievement of a seizure‐free state. It must also incorporate the management of common psychiatric and neurologic comorbidities, affecting on average between 30 and 50% of patients with epilepsy, which have a significant impact on their lives at various levels, including quality of life and the prognosis of the seizure disorder. Mood and anxiety disorders are the most frequent psychiatric comorbidities, whereas stroke and migraine are among the more common neurologic comorbidities, migraine among the younger patients and stroke among the older patients. Not only do these psychiatric and neurologic comorbidities each have a bidirectional relation with epilepsy, but primary mood disorders have a bidirectional relation with these 2 neurologic disorders. Furthermore, depression and migraine have been each associated with a more severe epilepsy course, whereas depression has been associated with a more severe course of stroke and migraines. The purpose of this article is to review the clinical implications of the complex relations among epilepsy and these 3 comorbid disorders, and to identify any clinical and/or experimental evidence that may suggest that having more than one of these comorbid disorders may increase the risk of and course of epilepsy.

Common data elements (CDEs) for preclinical epilepsy research: Introduction to CDEs and description of core CDEs. A TASK3 report of the ILAE/AES joint translational task force

Common data elements (CDEs) are becoming more common as more areas of preclinical research have generated CDEs. Herein we provide an overview of the progress to date in generating CDEs for preclinical epilepsy research. Currently there are CDEs that have been developed for Physiology (in vivo), Behavior, Pharmacology, and Electroencephalography (EEG). Together the CDEs and methodologic considerations associated with these CDEs are laid out in consecutive manuscripts published in Epilepsia Open, each describing CDEs for their respective topic area. In addition to the overview of progress for the 4 subjects, core characteristics (Core CDEs) are described and explained. Data collection using a case report form (CRF) is described, and considerations that are involved in using the CDEs and CRFs are discussed.

Affective, neurocognitive and psychosocial disorders associated with traumatic brain injury and post-traumatic epilepsy

Survivors of traumatic brain injury (TBI) often develop chronic neurological, neurocognitive, psychological, and psychosocial deficits that can have a profound impact on an individual's wellbeing and quality of life. TBI is also a common cause of acquired epilepsy, which is itself associated with significant behavioral morbidity. This review considers the clinical and preclinical evidence that post-traumatic epilepsy (PTE) acts as a 'second-hit' insult to worsen chronic behavioral outcomes for brain-injured patients, across the domains of emotional, cognitive, and psychosocial functioning. Surprisingly, few well-designed studies have specifically examined the relationship between seizures and behavioral outcomes after TBI. The complex mechanisms underlying these comorbidities remain incompletely understood, although many of the biological processes that precipitate seizure occurrence and epileptogenesis may also contribute to the development of chronic behavioral deficits. Further, the relationship between PTE and behavioral dysfunction is increasingly recognized to be a bidirectional one, whereby premorbid conditions are a risk factor for PTE. Clinical studies in this arena are often challenged by the confounding effects of anti-seizure medications, while preclinical studies have rarely examined an adequately extended time course to fully capture the time course of epilepsy development after a TBI. To drive the field forward towards improved treatment strategies, it is imperative that both seizures and neurobehavioral outcomes are assessed in parallel after TBI, both in patient populations and preclinical models.

Multimodal early-life stress induces biological changes associated to psychopathologies

Evidences suggest the contributive role of early-life stress (ELS) to affective and anxiety disorders. Chronic exposure to the same stressor may generate habituation, while the exposure to different and repeated stressors gradually promotes maladaptive plasticity. Therefore, to further understand the effects of heterotypic stressors during early life period, male Wistar rat pups (P1-P21) were exposed to Multimodal ELS paradigm. Results indicate pups did not habituate to multimodal ELS and neonates respond to both physical and psychogenic stressors. Adult rats that underwent ELS protocol showed significant lower sucrose intake, decreased latency to immobility in the forced swim test and increased latency to light compartment in the light-dark test when compared to control group. Although it has been shown that ELS-induced changes in hippocampus can be used as biomarkers, multimodal ELS did not significantly alter BDNF, Tyrosine Kinase B (TrkB) receptor expression or neurogenesis in the hippocampus. Taken together, these findings indicate that multimodal ELS protocol can be an interesting experimental model for understanding long-term psychiatric disorders associated with stress. Indeed, our data with neurogenesis, BDNF and TrkB, and conflicting data from the literature, suggest that additional studies on synaptic plasticity/intracellular cascades would help to detect the underlying mechanisms.

Stress and Corticosteroids Aggravate Morphological Changes in the Dentate Gyrus after Early-Life Experimental Febrile Seizures in Mice

Stress is the most frequently self-reported seizure precipitant in patients with epilepsy. Moreover, a relation between ear stress and epilepsy has been suggested. Although ear stress and stress hormones are known to influence seizure threshold in rodents, effects on the development of epilepsy (epileptogenesis) are still unclear. Therefore, we studied the consequences of ear corticosteroid exposure for epileptogenesis, under highly controlled conditions in an animal model. Experimental febrile seizures (eFS) were elicited in 10-day-old mice by warm-air induced hyperthermia, while a control group was exposed to a normothermic condition. In the following 2 weeks, mice received either seven corticosterone or vehicle injections or were left undisturbed. Specific measures indicative for epileptogenesis were examined at 25 days of age and compared with vehicle injected or untreated mice. We examined structural [neurogenesis, dendritic morphology, and mossy fiber sprouting (MFS)] and functional (glutamatergic postsynaptic currents and long-term potentiation) plasticity in the dentate gyrus (DG). We found that differences in DG morphology induced by eFS were aggravated by repetitive (mildly stressful) vehicle injections and corticosterone exposure. In the injected groups, eFS were associated with decreases in neurogenesis, and increases in cell proliferation, dendritic length, and spine density. No group differences were found in MFS. Despite these changes in DG morphology, no effects of eFS were found on functional plasticity. We conclude that corticosterone exposure during early epileptogenesis elicited by eFS aggravates morphological, but not functional, changes in the DG, which partly supports the hypothesis that ear stress stimulates epileptogenesis.

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.

Can Neurochemical Changes of Mood Disorders Explain the Increase Risk of Epilepsy or its Worse Seizure Control?

The existence of a bidirectional relation between mood disorders and epilepsy has been suggested by six population-based studies. Furthermore, three studies have associated a higher risk of treatment-resistant epilepsy with a history of depression preceding the onset of epilepsy. Common pathogenic mechanisms operant in depression and epilepsy may provide a possible explanation of these observations. This article reviews some of the leading pathogenic mechanisms of depression with respect to potential proconvulsant properties that may provide explanations for these phenomena.

The Wistar Audiogenic Rat (WAR) strain and its contributions to epileptology and related comorbidities: History and perspectives

In the context of modeling epilepsy and neuropsychiatric comorbidities, we review the Wistar Audiogenic Rat (WAR), first introduced to the neuroscience international community more than 25years ago. The WAR strain is a genetically selected reflex model susceptible to audiogenic seizures (AS), acutely mimicking brainstem-dependent tonic-clonic seizures and chronically (by audiogenic kindling), temporal lobe epilepsy (TLE). Seminal neuroethological, electrophysiological, cellular, and molecular protocols support the WAR strain as a suitable and reliable animal model to study the complexity and emergent functions typical of epileptogenic networks. Furthermore, since epilepsy comorbidities have emerged as a hot topic in epilepsy research, we discuss the use of WARs in fields such as neuropsychiatry, memory and learning, neuroplasticity, neuroendocrinology, and cardio-respiratory autonomic regulation. Last, but not least, we propose that this strain be used in "omics" studies, as well as with the most advanced molecular and computational modeling techniques. Collectively, pioneering and recent findings reinforce the complexity associated with WAR alterations, consequent to the combination of their genetically-dependent background and seizure profile. To add to previous studies, we are currently developing more powerful behavioral, EEG, and molecular methods, combined with computational neuroscience/network modeling tools, to further increase the WAR strain's contributions to contemporary neuroscience in addition to increasing knowledge in a wide array of neuropsychiatric and other comorbidities, given shared neural networks. During the many years that the WAR strain has been studied, a constantly expanding network of multidisciplinary collaborators has generated a growing research and knowledge network. Our current and major wish is to make the WARs available internationally to share our knowledge and to facilitate the planning and execution of multi-institutional projects, eagerly needed to contribute to paradigm shifts in epileptology. This article is part of a Special Issue entitled "Genetic and Reflex Epilepsies, Audiogenic Seizures and Strains: From Experimental Models to the Clinic".

Psychiatric comorbidities in epilepsy: Should they be considered in the classification of epileptic disorders?

The prevalence of psychiatric comorbidities is relatively high in people with epilepsy (PWE), as one in three patients will have experienced a psychiatric disorder in the course of their life. The new definition of epilepsy recognizes these comorbidities as part of the seizure disorder, which need to be recognized and treated together with the actual epileptic seizures. Psychiatric comorbidities have a complex relation with epilepsy, being associated with a negative course of the seizure disorder, worse tolerance of pharmacotherapy with AEDs, development of iatrogenic psychiatric complications from pharmacologic and surgical treatments, and increased mortality risks. Given their negative impact at several levels of the lives of PWE, should psychiatric comorbidities be included in a classification of the epilepsies? This question is addressed in this article. This article is part of a Special Issue entitled "The new approach to classification: Rethinking cognition and behavior in epilepsy".

Early childhood trauma and hippocampal volumes in patients with epileptic and psychogenic seizures

OBJECTIVE

Exposure to early life childhood trauma has been implicated as resulting in a vulnerability to epileptic and psychogenic nonepileptic seizures (PNES), hippocampal atrophy, and psychiatric disorders. This study aimed to explore the relationships between childhood trauma, epilepsy, PNES, and hippocampal volume in patients admitted to a video-electroencephalogram monitoring (VEM) unit.

METHODS

One hundred thirty-one patients were recruited from the Royal Melbourne Hospital VEM unit. The diagnostic breakdown of this group was: temporal lobe epilepsy (TLE) (32), other epilepsy syndromes (35), PNES (47), other nonepileptic syndromes (5), both epilepsy and PNES (6), and uncertain diagnosis (6). All patients completed a questionnaire assessing exposure to childhood trauma, the Childhood Trauma Questionnaire (CTQ), as well as questionnaires assessing psychiatric symptomatology (SCL-90-R), Anxiety and Depression (HADS), quality of life (QOLIE-98) and cognition (NUCOG). Volumetric coronal T1 MRI scans were available for 84 patients. Hippocampal volumes were manually traced by a blinded operator.

RESULTS

The prevalence of childhood trauma in patients with PNES was higher than in patients with other diagnoses (p=0.005), and the group with PNES overall scored significantly higher on the CTQ (p=0.002). No association was found between CTQ scores and hippocampal volumes; however, patients with a history of sexual abuse were found to have smaller left hippocampal volumes than patients who had not (p=0.043). Patients reporting having experienced childhood trauma scored lower on measures of quality of life and higher on measures of psychiatric symptomatology.

SIGNIFICANCE

Patients with PNES report having experienced significantly more childhood trauma than those with epileptic seizures, and in both groups there was a relationship between a history of having experienced sexual abuse and reduced left hippocampal volume. Patients with PNES and those with epilepsy who have a history of childhood trauma have overall worse quality of life and more psychiatric symptomatology.

Common Mechanisms Underlying Epileptogenesis and the Comorbidities of Epilepsy

The importance of comorbidities in determining the quality of life of individuals with epilepsy and their families has received increasing attention in the past decade. Along with it has come a recognition that in some individuals, certain comorbidities may have preexisted, and may have contributed to their developing epilepsy. Many mechanisms are capable of interconnecting different dysfunctions that manifest as distinct disorders, often diagnosed and managed by different specialists. We review the human data from the perspective of epidemiology as well as insights gathered from neurodiagnostic and endocrine studies. Animal studies are reviewed to refine our mechanistic understanding of the connections, because they permit the narrowing of variables, which is not possible when studying humans.

Positive and negative early life experiences differentially modulate long term survival and amyloid protein levels in a mouse model of Alzheimer's disease

Stress has been implicated as a risk factor for the severity and progression of sporadic Alzheimer's disease (AD). Early life experiences determine stress responsivity in later life, and modulate age-dependent cognitive decline. Therefore, we examined whether early life experiences influence AD outcome in a bigenic mouse model which progressively develops combined tau and amyloid pathology (biAT mice).Mice were subjected to either early life stress (ELS) or to 'positive' early handling (EH) postnatally (from day 2 to 9). In biAT mice, ELS significantly compromised long term survival, in contrast to EH which increased life expectancy. In 4 month old mice, ELS-reared biAT mice displayed increased hippocampal Aβ levels, while these levels were reduced in EH-reared biAT mice. No effects of ELS or EH were observed on the brain levels of APP, protein tau, or PSD-95. Dendritic morphology was moderately affected after ELS and EH in the amygdala and medial prefrontal cortex, while object recognition memory and open field performance were not affected. We conclude that despite the strong transgenic background, early life experiences significantly modulate the life expectancy of biAT mice. Parallel changes in hippocampal Aβ levels were evident, without affecting cognition of young adult biAT mice.

Rapid Amygdala Kindling Causes Motor Seizure and Comorbidity of Anxiety- and Depression-Like Behaviors in Rats

Amygdala kindling is a model of temporal lobe epilepsy (TLE) with convulsion. The rapid amygdala kindling has an advantage on quick development of motor seizures and for antiepileptic drugs screening. The rapid amygdala kindling causes epileptogenesis accompanied by an anxiolytic response in early isolation of rat pups or depressive behavior in immature rats. However, the effect of rapid amygdala kindling on comorbidity of anxiety- and depression-like behaviors is unexplored in adult rats with normal breeding. In the present study, 40 amygdala stimulations given within 2 days were applied in adult Wistar rats. Afterdischarge (AD) and seizure stage were recorded throughout the amygdala kindling. Anxiety-like behaviors were evaluated by the elevated plus maze (EPM) test and open field (OF) test, whereas depression-like behaviors were assessed by the forced swim (FS) and sucrose consumption (SC) tests. A tonic-clonic convulsion was provoked in the kindle group. Rapid amygdala kindling resulted in a significantly lower frequency entering an open area of either open arms of the EPM or the central zone of an OF, lower sucrose intake, and longer immobility of the FS test in the kindle group. Our results suggest that rapid amygdala kindling elicited severe motor seizures comorbid with anxiety- and depression-like behaviors.

Induced adverse effects of prenatal exposure to silver nanoparticles on neurobehavioral development of offspring of mice

Steadily increased use of silver nanoparticles (Ag-NPs), has increased the amount of its exposure to humans and animals. Current scarce knowledge about the influences of prenatal exposure to Ag-NPs on postnatal outcomes, motivated us to investigate whether being exposed to it during pregnancy has any effects on neurobehavioral development of the adult offspring. Thirty virgin female NMRI mice were mated and treated subcutaneously once every three days from gestation day 3 until delivery, by 0, 0.2 and 2 mg/kg of bodyweight (BW) of Ag-NPs. Behavioral functions of adult offspring including spatial memory, passive avoidance learning, stress, anxiety-like behaviors and locomotor activities were assessed by commonly used neurobehavioral paradigms and the results were compared according to treatment and sex. Prenatal exposure to Ag-NPs significantly impaired their cognitive behavior in the Morris water maze. Although no evidence was observed indicating more anxiety-like behaviors in the treated offspring in the elevated plus maze, the number of defecations and leanings in the open field assay and number of passages in the light-dark box were greater in groups prenatally treated by Ag-NPs. Most of the impairments were more apparent in the offspring which had been prenatally exposed to high doses of Ag-NPs, particularly female ones. The present study indicated that the exposure of pregnant animals to Ag-NPs may lead to various neurobehavioral disorders in their offspring. Thus, more attention should be paid to avoid exposure to Ag-NPs, especially from pregnant females.

The interplay of early-life stress, nutrition, and immune activation programs adult hippocampal structure and function

Early-life adversity increases the vulnerability to develop psychopathologies and cognitive decline later in life. This association is supported by clinical and preclinical studies. Remarkably, experiences of stress during this sensitive period, in the form of abuse or neglect but also early malnutrition or an early immune challenge elicit very similar long-term effects on brain structure and function. During early-life, both exogenous factors like nutrition and maternal care, as well as endogenous modulators, including stress hormones and mediator of immunological activity affect brain development. The interplay of these key elements and their underlying molecular mechanisms are not fully understood. We discuss here the hypothesis that exposure to early-life adversity (specifically stress, under/malnutrition and infection) leads to life-long alterations in hippocampal-related cognitive functions, at least partly via changes in hippocampal neurogenesis. We further discuss how these different key elements of the early-life environment interact and affect one another and suggest that it is a synergistic action of these elements that shapes cognition throughout life. Finally, we consider different intervention studies aiming to prevent these early-life adversity induced consequences. The emerging evidence for the intriguing interplay of stress, nutrition, and immune activity in the early-life programming calls for a more in depth understanding of the interaction of these elements and the underlying mechanisms. This knowledge will help to develop intervention strategies that will converge on a more complete set of changes induced by early-life adversity.

Hyper-excitability and epilepsy generated by chronic early-life stress

Epilepsy is more prevalent in populations with high measures of stress, but the neurobiological mechanisms are unclear. Stress is a common precipitant of seizures in individuals with epilepsy, and may provoke seizures by several mechanisms including changes in neurotransmitter and hormone levels within the brain. Importantly, stress during sensitive periods early in life contributes to ‘brain programming’, influencing neuronal function and brain networks. However, it is unclear if early-life stress influences limbic excitability and promotes epilepsy. Here we used an established, naturalistic model of chronic early-life stress (CES), and employed chronic cortical and limbic video-EEGs combined with molecular and cellular techniques to probe the contributions of stress to age-specific epilepsies and network hyperexcitability and identify the underlying mechanisms.

In control male rats, EEGs obtained throughout development were normal and no seizures were observed. EEGs demonstrated epileptic spikes and spike series in the majority of rats experiencing CES, and 57% of CES rats developed seizures: Behavioral events resembling the human age-specific epilepsy infantile spasms occurred in 11/23 (48%), accompanied by EEG spikes and/or electrodecrements, and two additional rats (9%) developed limbic seizures that involved the amygdala. Probing for stress-dependent, endogenous convulsant molecules within amygdala, we examined the expression of the pro-convulsant neuropeptide corticotropin-releasing hormone (CRH), and found a significant increase of amygdalar--but not cortical--CRH expression in adolescent CES rats.

In conclusion, CES of limited duration has long-lasting effects on brain excitability and may promote age-specific seizures and epilepsy. Whereas the mechanisms involved require further study, these findings provide important insights into environmental contributions to early-life seizures.

Reduction of epileptic spike-wave activity in WAG/Rij rats fostered by Wistar dams

In WAG/Rij rat genetic model of absence epilepsy, the first spike-wave discharges (EEG hallmark of absence epilepsy) are known to appear after puberty, and their incidence increases with age. WAG/Rij rats are known to have a genetic predisposition to absence epilepsy, and further development of epilepsy might be influenced by epigenetic factors. This preliminary study examined the effect of early postnatal factors on the incidence of epileptic spike-wave discharges in adulthood. The newborn WAG/Rij rats were fostered by Wistar dams (from birth throughout the weaning age), and their EEG was examined continuously from 5 to 13 months of age. It was found that the number and duration of absence seizures was reduced in WAG/Rij rats adopted by Wistar dams as compared with the age-matched control WAG/Rij rats nursed by their own mothers. These data indicate that natural (epigenetic) factors, such as maternal care during suckling period, affect development of seizure activity in genetically prone subjects. It is suggested that improvement of primarily care-giving environment in subjects with genetic predisposition to absence epilepsy is a way to reduce epileptic activity in later life.

Early life status epilepticus and stress have distinct and sex-specific effects on learning, subsequent seizure outcomes, including anticonvulsant response to phenobarbital

AIMS

Neonatal status epilepticus (SE) is often associated with adverse cognitive and epilepsy outcomes. We investigate the effects of three episodes of kainic acid-induced SE (3KA-SE) and maternal separation in immature rats on subsequent learning, seizure susceptibility, and consequences, and the anticonvulsant effects of phenobarbital, according to sex, type, and age at early life (EL) event.

METHODS

3KA-SE or maternal separation was induced on postnatal days (PN) 4-6 or 14-16. Rats were tested on Barnes maze (PN16-19), or lithium-pilocarpine SE (PN19) or flurothyl seizures (PN32). The anticonvulsant effects of phenobarbital (20 or 40 mg/kg/rat, intraperitoneally) pretreatment were tested on flurothyl seizures. FluoroJadeB staining assessed hippocampal injury.

RESULTS

3KA-SE or separation on PN4-6 caused more transient learning delays in males and did not alter lithium-pilocarpine SE latencies, but aggravated its outcomes in females. Anticonvulsant effects of phenobarbital were preserved and potentiated in specific groups depending on sex, type, and age at EL event.

CONCLUSIONS

Early life 3KA-SE and maternal separation cause more but transient cognitive deficits in males but aggravate the consequences of subsequent lithium-pilocarpine SE in females. In contrast, on flurothyl seizures, EL events showed either beneficial or no effect, depending on gender, type, and age at EL events.

Interaction between sex and early-life stress: influence on epileptogenesis and epilepsy comorbidities

Epilepsy is a common brain disorder which is characterised by recurring seizures. In addition to suffering from the constant stress of living with this neurological condition, patients also frequently experience comorbid psychiatric and cognitive disorders which significantly impact their quality of life. There is growing appreciation that stress, in particular occurring in early life, can negatively impact brain development, creating an enduring vulnerability to develop epilepsy. This aligns with the solid connections between early life environments and the development of psychiatric conditions, promoting the possibility that adverse early life events could represent a common risk factor for the later development of both epilepsy and comorbid psychiatric disorders. The influence of sex has been little studied, but recent research points to potential important interactions, particularly with regard to effects mediated by HPA axis programming. Understanding these interactions, and the underlying molecular mechanisms, will provide important new insights into the causation of both epilepsy and of psychiatric disorders, and potentially open up novel avenues for treatment.

Early life stress in epilepsy: a seizure precipitant and risk factor for epileptogenesis

Stress can influence epilepsy in multiple ways. A relation between stress and seizures is often experienced by patients with epilepsy. Numerous questionnaire and diary studies have shown that stress is the most often reported seizure-precipitating factor in epilepsy. Acute stress can provoke epileptic seizures, and chronic stress increases seizure frequency. In addition to its effects on seizure susceptibility in patients with epilepsy, stress might also increase the risk of epilepsy development, especially when the stressors are severe, prolonged, or experienced early in life. Although the latter has not been fully resolved in humans, various preclinical epilepsy models have shown increased seizure susceptibility in naïve rodents after prenatal and early postnatal stress exposure. In the current review, we first provide an overview of the effects of stress on the brain. Thereafter, we discuss human as well as preclinical studies evaluating the relation between stress, epileptic seizures, and epileptogenesis, focusing on the epileptogenic effects of early life stress. Increased knowledge on the interaction between early life stress, seizures, and epileptogenesis could improve patient care and provide a basis for new treatment strategies for epilepsy.

Is depression associated with an increased risk of treatment-resistant epilepsy? Research strategies to investigate this question

Persons with epilepsy (PWE) have a higher risk of developing depressive disorders (DDs), and people with primary DD have an increased risk of developing epilepsy. Furthermore, a lifetime history of DD has been associated with a worse response of the seizure disorder to pharmacotherapy and epilepsy surgery. The first part of this article reviews the literature of this problem with the intention of highlighting the neurobiologic pathogenic mechanisms operant in DD with a potential to facilitate the epileptogenic process and/or cortical hyperexcitability in humans and experimental animal studies of depression. They include the following: (i) a hyperactive hypothalamic-pituitary-adrenal axis and the associated structural and functional abnormalities of limbic structures, (ii) increased glutamatergic activity and decreased GABAergic and serotonergic activity, and (iii) immunologic disturbances. In the second part of this article, we suggest research strategies to test the hypothesis of whether depression worsens the course of epilepsy and identify the pathogenic mechanisms operant in this process.