Early Postnatal Stress Confers Enduring Vulnerability to Limbic Epileptogenesis

Fluoxetine accelerates epileptogenesis and magnifies disease severity in a rat model of acquired epilepsy

OBJECTIVE

Many people with epilepsy experience comorbid anxiety and depression, and antidepressants remain a primary treatment for this. Emerging evidence suggests that these agents may modulate epileptogenesis to influence disease severity. Here, we assessed how treatment with the selective serotonin reuptake inhibitor (SSRI) antidepressant fluoxetine impacts epileptogenic, behavioral, and pathological sequelae following status epilepticus.

METHODS

Male Wistar rats received kainic acid to induce status epilepticus (SE) or vehicle (sham). Animals then received either fluoxetine (10 mg/kg/day) or vehicle for 8 weeks via subcutaneous osmotic pump. Video-electroencephalography was recorded continuously until behavioral testing at day 56, including assessments of anxiety- and depression-like behavior and spatial cognition. Postmortem immunocytochemistry studies examined mossy fiber sprouting.

RESULTS

Fluoxetine treatment significantly accelerated epileptogenesis following SE, reducing the average period to the first spontaneous seizure (from 32 days [vehicle] to 6 days [fluoxetine], p < .01). Also, fluoxetine exposure magnified the severity of the resultant epilepsy, increasing seizure frequency compared to vehicle (p < .01). Exposure to fluoxetine was associated with improved anxiety- and depression-like behaviors but significantly worsened cognition. Mossy fiber sprouting was more pronounced in fluoxetine-treated rats compared to vehicle (p < .0001).

SIGNIFICANCE

Our studies demonstrate that, using a model exhibiting spontaneous seizures, epileptogenesis is accelerated and magnified by fluoxetine, an effect that may be related to more severe pathological neuroplasticity. The differential influence of fluoxetine on behavior indicates that different circuitry and mechanisms are responsible for these comorbidities. These findings suggest that caution should be exercised when prescribing SSRI antidepressants to people at risk of developing epilepsy.

Effects of season, daytime, sex, and stress on the incidence, latency, frequency, severity, and duration of neonatal seizures in a rat model of birth asphyxia

Neonatal seizures are common in newborn infants after birth asphyxia. They occur more frequently in male than female neonates, but it is not known whether sex also affects seizure severity or duration. Furthermore, although stress and diurnal, ultradian, circadian, or multidien cycles are known to affect epileptic seizures in adults, their potential impact on neonatal seizures is not understood. This prompted us to examine the effects of season, daytime, sex, and stress on neonatal seizures in a rat model of birth asphyxia. Seizures monitored in 176 rat pups exposed to asphyxia on 40 experimental days performed over 3 years were evaluated. All rat pups exhibited seizures when exposed to asphyxia at postnatal day 11 (P11), which in terms of cortical development corresponds to term human babies. A first examination of these data indicated a seasonal variation, with the highest seizure severity in the spring. Sex and daytime did not affect seizure characteristics. However, when rat pups were subdivided into animals that were exposed to acute (short-term) stress after asphyxia (restraint and i.p. injection of vehicle) and animals that were not exposed to this stress, the seizures in stress-exposed rats were more severe but less frequent. Acute stress induced an increase in hippocampal microglia density in sham-exposed rat pups, which may have an additive effect on microglia activation induced by asphyxia. When seasonal data were separately analyzed for stress-exposed vs. non-stress-exposed rat pups, no significant seasonal variation was observed. This study illustrates that without a detailed analysis of all factors, the data would have erroneously indicated significant seasonal variability in the severity of neonatal seizures. Instead, the study demonstrates that even mild, short-lasting postnatal stress has a profound effect on asphyxia-induced seizures, most likely by increasing the activity of the hypothalamic-pituitary-adrenal axis. It will be interesting to examine how postnatal stress affects the treatment and adverse outcomes of birth asphyxia and neonatal seizures in the rat model used here.

Microglial activation and over pruning involved in developmental epilepsy

To understand the potential role of microglia in synaptic pruning following status epilepticus (SE), we examined the time course of expression of Iba-1, and immune and neuroinflammatory regulators, including CD86, CD206, and CX3CR1, and TLR4/NF-κB after SE induced by pilocarpine in rats. Behavioral tests, TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) staining, immunohistochemical staining, Western blotting, PCR, and fluorescence double staining assessments were performed. The expression of Iba-1 protein was lowest in the control group, and peaked after 2 days (p < 0.001). CD86 and CD206 mRNA levels increased gradually in the microglia of the epilepsy group after 12 hours, 1 day, 2 days, and 3 days; peak expression was on the second day. The expression of the chemokine receptor CX3CR1 in microglia increased to varying degrees after SE, and expression of the presynaptic protein synapsin decreased. The expression of TLR4/NF-κB in microglia positively correlated with Iba-1 protein expression. These findings indicate that the TLR4/NF-κB signaling pathway may be involved in the activation and polarization of microglia in epilepsy and in excess synaptic pruning, which could lead to an increase in brain injury.

Anterior cingulate cortex, but not amygdala, modulates the anxiogenesis induced by living with conspecifics subjected to chronic restraint stress in male mice

Cohabitation with a partner undergoing chronic restraint stress (CRE) induces anxiogenic-like behaviors through emotional contagion. We hypothesized that the anterior cingulate cortex (ACC) and the amygdala would be involved in the modulation of this emotional process. This study investigated the role of the ACC and amygdala in empathy-like behavior (e.g., anxiety-like responses) induced by living with a mouse subjected to CRE. Male Swiss mice were housed in pairs for 14 days and then allocated into two groups: cagemate stress (one animal of the pair was subjected to 14 days of restraint stress) and cagemate control (no animal experienced stress). Twenty-four hours after the last stress session, cagemates had their brains removed for recording FosB labeling in the ACC and amygdala (Exp.1). In experiments 2 and 3, 24 h after the last stress session, the cagemates received 0.1 μL of saline or cobalt chloride (CoCl₂ 1 mM) into the ACC or amygdala, and then exposed to the elevated plus-maze (EPM) for recording anxiety. Results showed a decrease of FosB labeling in the ACC without changing immunofluorescence in the amygdala of stress cagemate mice. Cohabitation with mice subjected to CRE provoked anxiogenic-like behaviors. Local inactivation of ACC (but not the amygdala) reversed the anxiogenic-like effects induced by cohabitation with a partner undergoing CRE. These results suggest the involvement of ACC, but not the amygdala, in anxiety induced by emotional contagion.

Sex differences in addiction-relevant behavioral outcomes in rodents following early life stress

In humans, exposure to early life stress (ELS) is an established risk factor for the development of substance use disorders (SUDs) during later life. Similarly, rodents exposed to ELS involving disrupted mother-infant interactions, such as maternal separation (MS) or adverse caregiving due to scarcity-adversity induced by limited bedding and nesting (LBN) conditions, also exhibit long-term alterations in alcohol and drug consumption. In both humans and rodents, there is a range of addiction-related behaviors that are associated with drug use and even predictive of subsequent SUDs. In rodents, these include increased anxiety-like behavior, impulsivity, and novelty-seeking, altered alcohol and drug intake patterns, as well as disrupted reward-related processes involving consummatory and social behaviors. Importantly, the expression of these behaviors often varies throughout the lifespan. Moreover, preclinical studies suggest that sex differences play a role in how exposure to ELS impacts reward and addiction-related phenotypes as well as underlying brain reward circuitry. Here, addiction-relevant behavioral outcomes and mesolimbic dopamine (DA) dysfunction resulting from ELS in the form of MS and LBN are discussed with a focus on age- and sex-dependent effects. Overall, these findings suggest that ELS may increase susceptibility for later life drug use and SUDs by interfering with the normal maturation of reward-related brain and behavioral function.

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.

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.

New Insights Into the Anticonvulsant Effects of Essential Oil From Melissa officinalis L. (Lemon Balm)

Melissa officinalis L. is used in traditional European and Iranian folk medicines to treat a plethora of neurological diseases including epilepsy. We utilized the in vitro and in vivo models of epilepsy to probe the anticonvulsant potentials of essential oil from M. officinalis (MO) to gain insight into the scientific basis for its applications in traditional medicine for the management of convulsive disorders. MO was evaluated for effects on maximal electroshock (MES) and pentylenetetrazole (PTZ) -induced seizures in mice, on 4–aminopyridine (4-AP)-brain slice model of epilepsy and sustained repetitive firing of current clamped neurons; and its ameliorative effects were examined on seizure severity, anxiety, depression, cognitive dysfunction, oxidative stress and neuronal cell loss in PTZ-kindled rats. MO reversibly blocked spontaneous ictal-like discharges in the 4-AP-brain slice model of epilepsy and secondary spikes from sustained repetitive firing, suggesting anticonvulsant effects and voltage-gated sodium channel blockade. MO protected mice from PTZ– and MES–induced seizures and mortality, and ameliorated seizure severity, fear-avoidance, depressive-like behavior, cognitive deficits, oxidative stress and neuronal cell loss in PTZ–kindled rats. The findings warrant further study for the potential use of MO and/or its constituent(s) as adjunctive therapy for epileptic patients.

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.

Sex-specific behavioral and structural alterations caused by early-life stress in C57BL/6 and BTBR mice

Lately, the development of various mental illnesses, such as depression, personality disorders, and autism spectrum disorders, is often associated with traumatic events in childhood. Nonetheless, the mechanism giving rise to this predisposition is still unknown. Because the development of a disease often depends on a combination of a genetic background and environment, we decided to evaluate the effect of early-life stress on BTBR mice, which have behavioral, neuroanatomical, and physiological features of autism spectrum disorders. As early-life stress, we used prolonged separation of pups from their mothers in the first 2 weeks of life (3 h once a day). We assessed effects of the early-life stress on juvenile (postnatal day 23) and adolescent (postnatal days 37-38) male and female mice of strains C57BL/6 (B6) and BTBR. We found that in both strains, the early-life stress did not lead to changes in the level of social behavior, which is an important characteristic of autism-related behavior. Nonetheless, the early-life stress resulted in increased locomotor activity in juvenile BTBR mice. In adolescent mice, the stress early in life caused a low level of anxiety in B6 males and BTBR females and increased exploratory activity in adolescent BTBR males and females. In addition, adolescent B6 male and female mice with a history of the early-life stress tended to have a thinner motor cortex as assessed by magnetic resonance imaging. As compared to B6 mice, BTBR mice showed reduced levels of social behavior and exploratory activity but their level of locomotor activity was higher. BTBR mice had smaller whole-brain, cortical, and dorsal hippocampal volumes; decreased motor cortex thickness; and increased ventral-hippocampus volume as compared to B6 mice, and these parameters correlated with the level of exploratory behavior of BTBR mice. Overall, the effects of early postnatal stress are sex- and strain-dependent.

Anxious Profile Influences Behavioral and Immunohistological Findings in the Pilocarpine Model of Epilepsy

Anxiety and epilepsy have a complex bidirectional relationship, where a depressive/anxious condition is a factor that can trigger seizures which in turn can aggravate the depressive/anxious condition. In addition, brain structures such as the hippocampus and amygdala might have a critical relevance in both epilepsy and anxiety. The aim of the present work was to investigate the influence of different anxious profiles to epileptogenesis. Initially, animals were screened through the elevated plus-maze anxiety test, and then seizure development was evaluated using the pilocarpine model of epilepsy. There were no differences in the susceptibility to status epilepticus, mortality rate or frequency of spontaneous recurrent seizures between animals characterized as anxious as compared to the non-anxious animals. Next, we evaluated immunohistological patterns related to seizures and anxiety in various related brain areas. Despite a decrease in the density of neuropeptide Y and parvalbumin expression in epileptic animals, those presenting greater neuropeptide Y immunoreactivity in various brain regions, also showed higher spontaneous recurrent seizures frequency. Differences on the anxious profile showed to interfere with some of these findings in some regions. In addition, animals that were injected with pilocarpine, but did not develop status epilepticus, had behavioral and neuroanatomical alterations as compared to control animals, indicating its importance as an additional tool for investigating the heterogeneity of the epileptogenic response after an initial insult. This study allowed to better understand the association between anxiety and temporal lobe epilepsy and might allow for therapeutic targets to be developed to minimize the negative impacts associated with it.

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.

Does Stress Trigger Seizures? Evidence from Experimental Models

This chapter describes the experimental evidence of stress modulation of epileptic seizures and the potential role of corticosteroids and neurosteroids in regulating stress-linked seizure vulnerability. Epilepsy is a chronic neurological disorder that is characterized by repeated seizures. There are many potential causes for epilepsy, including genetic predispositions, infections, brain injury, and neurotoxicity. Stress is a known precipitating factor for seizures in individuals suffering from epilepsy. Severe acute stress and persistent exposure to stress may increase susceptibility to seizures, thereby resulting in a higher frequency of seizures. This occurs through the stress-mediated release of cortisol, which has both excitatory and proconvulsant properties. Stress also causes the release of endogenous neurosteroids from central and adrenal sources. Neurosteroids such as allopregnanolone and THDOC, which are allosteric modulators of GABA-A receptors, are powerful anticonvulsants and neuroprotectants. Acute stress increases the release of neurosteroids, while chronic stress is associated with severe neurosteroid depletion and reduced inhibition in the brain. This diminished inhibition occurs largely as a result of neurosteroid deficiencies. Thus, exogenous administration of neurosteroids (neurosteroid replacement therapy) may offer neuroprotection in epilepsy. Synthetic neurosteroid could offer a rational approach to control neurosteroid-sensitive, stress-related epileptic seizures.

Chronic postnatal chemogenetic activation of forebrain excitatory neurons evokes persistent changes in mood behavior

Early adversity is a risk factor for the development of adult psychopathology. Common across multiple rodent models of early adversity is increased signaling via forebrain Gq-coupled neurotransmitter receptors. We addressed whether enhanced Gq-mediated signaling in forebrain excitatory neurons during postnatal life can evoke persistent mood-related behavioral changes. Excitatory hM3Dq DREADD-mediated chemogenetic activation of forebrain excitatory neurons during postnatal life (P2–14), but not in juvenile or adult windows, increased anxiety-, despair-, and schizophrenia-like behavior in adulthood. This was accompanied by an enhanced metabolic rate of cortical and hippocampal glutamatergic and GABAergic neurons. Furthermore, we observed reduced activity and plasticity-associated marker expression, and perturbed excitatory/inhibitory currents in the hippocampus. These results indicate that Gq-signaling-mediated activation of forebrain excitatory neurons during the critical postnatal window is sufficient to program altered mood-related behavior, as well as functional changes in forebrain glutamate and GABA systems, recapitulating aspects of the consequences of early adversity.

Stress and adversity in early childhood can have long-lasting effects, predisposing people to mental illness and mood disorders in adult life. The weeks immediately before and after birth are critical for establishing key networks of neurons in the brain. Therefore, any disruption to these neural circuits during this time can be detrimental to emotional development. However, it is still unclear which cellular mechanisms cause these lasting changes in behavior.

Studies in animals suggest that these long-term effects could result from abnormalities in a few signaling pathways in the brain. For example, it has been proposed that overstimulating the cells that activate circuits in the forebrain – also known as excitatory neurons – may contribute to the behavioral changes that persist into adulthood.

To test this theory, Pati et al. used genetic engineering to modulate a signaling pathway in male mice, which is known to stimulate excitatory neurons in the forebrain. The experiments showed that prolonged activation of excitatory neurons in the first two weeks after birth resulted in anxious and despair-like behaviors as the animals aged. The mice also displayed discrepancies in how they responded to certain external sensory information, which is a hallmark of schizophrenia-like behavior. However, engineering the same changes in adolescent and adult mice had no effect on their mood-related behaviors.

This animal study reinforces just how critical the first few weeks of life are for optimal brain development. It provides an insight into a possible mechanism of how disruption during this time could alter emotional behavior. The findings are also relevant to psychiatrists interested in the underlying causes of mental illness after early childhood adversity.

Maternal separation induces long-term oxidative stress alterations and increases anxiety-like behavior of male Balb/cJ mice

Early life stress (ELS) exposure is a well-known risk factor for the development of psychiatric conditions, including anxiety disorder. Preclinical studies show that maternal separation (MS), a classical model of ELS, causes hypothalamic-pituitary-adrenal (HPA) axis alterations, a key contributor to the stress response modulation. Given that HPA axis activation has been shown to induce oxidative stress, it is possible to hypothesize that oxidative stress mediates the relationship between chronic ELS exposure and the development of several disorders. Here, we investigate the effects of MS in the oxidative status [plasma and brain reduced glutathione, catalase and thiobarbituric acid reactive substances (TBARS)], metabolism (glucose, triglycerides and cholesterol) and anxiety-like behaviors in adult Balb/cJ mice. In short, we found that MS increased anxiety-like behaviors in the open field, light/dark test but not in the elevated-plus maze. Animals also presented increased circulating cholesterol, increased TBARS in the plasma and decreased catalase in the hippocampus. Our findings suggest that MS induces long-term alterations in oxidative stress and increased anxiety-like behaviors.

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.

Altered corticolimbic connectivity reveals sex-specific adolescent outcomes in a rat model of early life adversity

Exposure to early-life adversity (ELA) increases the risk for psychopathologies associated with amygdala-prefrontal cortex (PFC) circuits. While sex differences in vulnerability have been identified with a clear need for individualized intervention strategies, the neurobiological substrates of ELA-attributable differences remain unknown due to a paucity of translational investigations taking both development and sex into account. Male and female rats exposed to maternal separation ELA were analyzed with anterograde tracing from basolateral amygdala (BLA) to PFC to identify sex-specific innervation trajectories through juvenility (PD28) and adolescence (PD38;PD48). Resting-state functional connectivity (rsFC) was assessed longitudinally (PD28;PD48) in a separate cohort. All measures were related to anxiety-like behavior. ELA-exposed rats showed precocial maturation of BLA-PFC innervation, with females affected earlier than males. ELA also disrupted maturation of female rsFC, with enduring relationships between rsFC and anxiety-like behavior. This study is the first providing both anatomical and functional evidence for sex- and experience-dependent corticolimbic development.

Having a traumatic childhood increases the risk a person will develop anxiety disorders later in life. Early life adversity affects men and women differently, but scientists do not yet know why. Learning more could help scientists develop better ways to prevent or treat anxiety disorders in men and women who experienced childhood trauma.

Anxiety occurs when threat-detecting brain circuits turn on. These circuits begin working in infancy, and during childhood and adolescence, experiences shape the brain to hone the body’s responses to perceived threats. Two areas of the brain that are important hubs for anxiety-related brain circuits include the basolateral amygdala (BLA) and the prefrontal cortex (PFC).

Now, Honeycutt et al. show that rats that experience early life adversity develop stronger connections between the BLA and PFC, and these changes occur earlier in female rats. In the experiments, one group of rats was repeatedly separated from their mothers and littermates (an early life trauma), while a second group was not. Honeycutt et al. examined the connections between the BLA and PFC in the two groups at three different time periods during their development: the juvenile stage, early adolescence, and late adolescence.

The experiments showed stronger connections between the BLA and PFC begin to appear earlier in juvenile traumatized female rats. But these changes did not appear in their male counterparts until adolescence. Lastly, the rats that developed these strengthened BLA-PFC connections also behaved more anxiously later in life. This may mean that the ideal timing for interventions may be different for males and females. More work is needed to see if these results translate to humans and then to find the best times and methods to help people who experienced childhood trauma.

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".

Febrile seizures and increased stress sensitivity in children: How it relates to seizure characteristics

BACKGROUND

Studies suggest that the relationship between seizures and stress starts early in life. However, evidence of long-term altered stress reactivity following early-life seizures is lacking. Our objectives were to assess alterations in stress hormone reactivity in children with past febrile seizures (FS) and investigate how these alterations relate to clinical characteristics.

METHOD

This case-control study compared a convenience sample of children with simple FS (n = 24), complex FS (n = 18), and matched healthy controls (n = 42). Stress was induced by electrode placement for an electroencephalography (EEG) exam. Salivary cortisol to stress, using three samples collected before and after the stressor, was compared between groups and sex. The relationship between stress reactivity and clinical characteristics (i.e., FS duration, age at first FS, time since the last FS) was investigated.

RESULTS

Cortisol reactivity to stress was significantly different depending on study groups, F(1, 78) = 6.415, p = 0.003, η²_p = 0.141, but not sex nor was there a significant interaction between group and sex (p ≥ 0.581). Participants with simple FS showed higher cortisol reactivity to stress (M = 14.936, Standard deviation (SD) = 26.852) compared with those with complex FS (M = -4.663, SD = 18.649, p = 0.015) and controls (M = -3.817, SD = 18.907, p = 0.003). There was no significant difference between participants with complex FS and controls (p > 0.999). Stress reactivity was not linked to clinical characteristics.

CONCLUSIONS

Children with past simple FS showed greater changes in salivary cortisol following stress, suggesting enhanced stress sensitivity. As similar results were not found in a population with complex FS, our study shows that stress alterations are not caused by seizure severity. Future studies are needed to investigate whether stress sensitivity may be premorbid to simple FS and may contribute to simple FS incidence.

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.

A Comprehensive Overview on Stress Neurobiology: Basic Concepts and Clinical Implications

Stress is recognized as an important issue in basic and clinical neuroscience research, based upon the founding historical studies by Walter Canon and Hans Selye in the past century, when the concept of stress emerged in a biological and adaptive perspective. A lot of research after that period has expanded the knowledge in the stress field. Since then, it was discovered that the response to stressful stimuli is elaborated and triggered by the, now known, stress system, which integrates a wide diversity of brain structures that, collectively, are able to detect events and interpret them as real or potential threats. However, different types of stressors engage different brain networks, requiring a fine-tuned functional neuroanatomical processing. This integration of information from the stressor itself may result in a rapid activation of the Sympathetic-Adreno-Medullar (SAM) axis and the Hypothalamus-Pituitary-Adrenal (HPA) axis, the two major components involved in the stress response. The complexity of the stress response is not restricted to neuroanatomy or to SAM and HPA axes mediators, but also diverge according to timing and duration of stressor exposure, as well as its short- and/or long-term consequences. The identification of neuronal circuits of stress, as well as their interaction with mediator molecules over time is critical, not only for understanding the physiological stress responses, but also to understand their implications on mental health.

Neurobiology and consequences of social isolation stress in animal model-A comprehensive review

The brain is a vital organ, susceptible to alterations under genetic influences and environmental experiences. Social isolation (SI) acts as a stressor which results in alterations in reactivity to stress, social behavior, function of neurochemical and neuroendocrine system, physiological, anatomical and behavioral changes in both animal and humans. During early stages of life, acute or chronic SIS has been proposed to show signs and symptoms of psychiatric and neurological disorders such as anxiety, depression, schizophrenia, epilepsy and memory loss. Exposure to social isolation stress induces a variety of endocrinological changes including the activation of hypothalamic-pituitary-adrenal (HPA) axis, culminating in the release of glucocorticoids (GCs), release of catecholamines, activation of the sympatho-adrenomedullary system, release of Oxytocin and vasopressin. In several regions of the central nervous system (CNS), SIS alters the level of neurotransmitter such as dopamine, serotonin, gamma aminobutyric acid (GABA), glutamate, nitrergic system and adrenaline as well as leads to alteration in receptor sensitivity of N-methyl-D-aspartate (NMDA) and opioid system. A change in the function of oxidative and nitrosative stress (O&NS) mediated mitochondrial dysfunction, inflammatory factors, neurotrophins and neurotrophicfactors (NTFs), early growth response transcription factor genes (Egr) and C-Fos expression are also involved as a pathophysiological consequences of SIS which induce neurological and psychiatric disorders.

Enhanced susceptibility to stress and seizures in GAD65 deficient mice

Reduced gamma-aminobutyric acid (GABA) inhibition has been implicated in both anxiety and epilepsy. GAD65^-/- (NOD/LtJ) mice have significantly decreased basal GABA levels in the brain and a lowered threshold for seizure generation. One fifth of GAD65 ^-/- mice experienced stress-induced seizures upon exposure to an open field at 4 weeks of age. In each successive week until 8 weeks of age, the latency to seizures decreased with prior seizure experience. 100% of GAD65^-/- mice exhibited stress-induced seizures by the end of 8 weeks. GAD65^-/- mice also exhibited marked impairment in open field exploratory behavior and deficits in spatial learning acquisition on a Barnes maze. Anxiety-like behavior in an open field was observed prior to seizure onset and was predictive of subsequent seizures. Immunohistochemical characterization of interneuron subtypes in GAD65^-/- mice showed a selective decrease in GABA and neuropeptide Y (NPY) levels and no change in calbindin (CLB) or calretinin (CLR) immunoreactivity in the hippocampus. Stem cells from the medial ganglionic eminence (MGE) were injected into the hippocampal hilus to restore GABAergic interneurons. One week after transplantation, MGE-transplanted mice demonstrated significant seizure resistance compared to sham surgical controls. The percent area of GFP⁺ MGE graft in the hippocampus correlated significantly with the increase in seizure latency. Our data indicate that impaired GABAergic neurotransmission can cause anxiety-like behavior and stress-induced seizures that can be rescued by MGE stem cell transplantation.

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.

Stress and Seizures: Space, Time and Hippocampal Circuits

Stress is a major trigger of seizures in people with epilepsy. Exposure to stress results in the release of several stress mediators throughout the brain, including the hippocampus, a region sensitive to stress and prone to seizures. Stress mediators interact with their respective receptors to produce distinct effects on the excitability of hippocampal neurons and networks. Crucially, these stress mediators and their actions exhibit unique spatiotemporal profiles, generating a complex combinatorial output with time- and space-dependent effects on hippocampal network excitability and seizure generation.

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.

Current psychiatric disorders in patients with epilepsy are predicted by maltreatment experiences during childhood

PURPOSE

Childhood maltreatment has been shown to be a risk factor for the development of psychiatric disorders. Although the prevalence of psychiatric disorders is high in epilepsy patients, it is unknown if childhood maltreatment experiences are elevated compared to the normal population and if early maltreatment is a risk factor for current psychiatric comorbidities in epilepsy patients. This is the main purpose of this study.

METHODS

Structured interviews were used to assess current Axis I diagnoses in 120 epilepsy patients from a tertiary Epilepsy Center (34 TLE patients, 86 non-TLE patients). Childhood maltreatment in the family and peer victimization were assessed with validated questionnaires. Patients' maltreatment scores were compared with those of a representative matched control group. Logistic regression analysis was conducted to assess the potential impact of childhood maltreatment on current psychiatric comorbidity in epilepsy patients.

RESULTS

Compared to a matched control group, epilepsy patients had higher emotional and sexual maltreatment scores. Patients with a current psychiatric diagnosis reported more family and peer maltreatment than patients without a psychiatric disorder. Family maltreatment scores predicted the likelihood of a current psychiatric disorder. TLE patients did not differ from non-TLE patients according to maltreatment experiences and rates of current psychiatric disorders.

CONCLUSION

Our findings suggest that in epilepsy patients emotional and sexual childhood maltreatment is experienced more often than in the normal population and that early maltreatment is a general risk factor for psychiatric comorbidities in this group.

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.

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.

Environmental enrichment imparts disease-modifying and transgenerational effects on genetically-determined epilepsy and anxiety

INTRODUCTION

The absence epilepsies are presumed to be caused by genetic factors, but the influence of environmental exposures on epilepsy development and severity, and whether this influence is transmitted to subsequent generations, is not well known. We assessed the effects of environmental enrichment on epilepsy and anxiety outcomes in multiple generations of GAERS - a genetic rat model of absence epilepsy that manifests comorbid elevated anxiety-like behaviour.

METHODS

GAERS were exposed to environmental enrichment or standard housing beginning either prior to, or after epilepsy onset, and underwent EEG recordings and anxiety testing. Then, we exposed male GAERS to early enrichment or standard housing and generated F1 progeny, which also underwent EEG recordings. Hippocampal CRH mRNA expression and DNA methylation were assessed using RT-PCR and pyrosequencing, respectively.

RESULTS

Early environmental enrichment delayed the onset of epilepsy in GAERS, and resulted in fewer seizures in adulthood, compared with standard housed GAERS. Enrichment also reduced the frequency of seizures when initiated in adulthood. Anxiety levels were reduced by enrichment, and these anti-epileptogenic and anxiolytic effects were heritable into the next generation. We also found reduced expression of CRH mRNA in GAERS exposed to enrichment, but this was not due to changes in DNA methylation.

CONCLUSIONS

Environmental enrichment produces disease-modifying effects on genetically determined absence epilepsy and anxiety, and these beneficial effects are transferable to the subsequent generation. Reduced CRH expression was associated with these phenotypic improvements. Environmental stimulation holds promise as a naturalistic therapy for genetically determined epilepsy which may benefit subsequent generations.

Maternal separation prior to neonatal hypoxia-ischemia: Impact on emotional aspects of behavior and markers of synaptic plasticity in hippocampus

Exposure to early-life stress is associated with long-term alterations in brain and behavior, and may aggravate the outcome of neurological insults. This study aimed at investigating the possible interaction between maternal separation, a model of early stress, and subsequent neonatal hypoxia-ischemia on emotional behavior and markers of synaptic plasticity in hippocampus. Therefore, rat pups (N=60) were maternally separated for a prolonged (MS 180min) or a brief (MS 15min) period during the first six postnatal days, while a control group was left undisturbed. Hypoxia-ischemia was applied to a subgroup of each rearing condition on postnatal day 7. Emotional behavior was examined at three months of age and included assessments of anxiety (elevated plus maze), depression-like behavior (forced swimming) and spontaneous exploration (open field). Synaptic plasticity was evaluated based on BDNF and synaptophysin expression in CA3 and dentate gyrus hippocampal regions. We found that neonatal hypoxia-ischemia caused increased levels of anxiety, depression-like behavior and locomotor activity (ambulation). Higher anxiety levels were also seen in maternally separated rats (MS180min) compared to non-maternally separated rats, but prolonged maternal separation prior to HI did not potentiate the HI-associated effect. No differences among the three rearing conditions were found regarding depression-like behavior or ambulation. Immunohistochemical evaluation of synaptophysin revealed that both prolonged maternal separation (MS180min) and neonatal hypoxia-ischemia significantly reduced its expression in the CA3 and dentate gyrus. Decreases in synaptophysin expression in these areas were not exacerbated in rats that were maternally separated for a prolonged period prior to HI. Regarding BDNF expression, we found a significant decrease in immunoreactivity only in the hypoxic-ischemic rats that were subjected to the prolonged maternal separation paradigm. The above findings suggest that early-life stress prior to neonatal hypoxia-ischemia leads to significant alterations in synaptic plasticity of the dorsal hippocampus during adulthood, but does not exacerbate HI-related changes in emotional behavior.

NMDA receptor antagonists attenuate the proconvulsant effect of juvenile social isolation in male mice

Experiencing psychosocial stress in early life, such as social isolation stress (SIS), is known to have negative enduring effects on the development of the brain and behavior. In addition to anxiety and depressive-like behaviors, we previously showed that juvenile SIS increases susceptibility to pentylenetetrazole (PTZ)-induced seizures in mice through enhancing the nitrergic system activity in the hippocampus. In this study, we investigated the possible involvement of N-methyl-D-aspartate (NMDA) receptors in proconvulsant effects of juvenile SIS. Applying 4 weeks of SIS to juvenile male mice at postnatal day 21-23, we observed an increased susceptibility to PTZ as well as anxiety and depressive-like behaviors in adult mice. Intraperitoneal (i.p.) administration of NMDA receptor antagonists, MK-801 (0.05 mg/kg) and ketamine (0.5mg/kg), reversed the proconvulsant effects of SIS in Isolated (and not social) housed animals. Co-administration of non-effective doses of nitric oxide synthase (NOS) inhibitors, 7NI (25mg/kg) and L-NAME (10mg/kg), with NMDA receptor antagonists, MK-801 (0.01 mg/kg) and ketamine (0.1mg/kg) attenuated the proconvulsant effects of juvenile SIS only in isolated housed mice. Also, using real time RT-PCR, we showed that hippocampal upregulation of NR2B subunit of NMDA receptor may play a critical role in proconvulsant effects of juvenile SIS by dysregulation of NMDA/NO pathway. In conclusion, results of present study revealed that experiencing SIS during adolescence predisposes the co-occurrence of seizure disorders with psychiatric comorbidities and also, alteration of NMDA receptor structure and function in hippocampus plays a role in proconvulsant effects of juvenile SIS through enhancing the NMDA/NO pathway.

Fighting with Spirits: Migration Trauma, Acculturative Stress, and New Sibling Transition-A Clinical Case Study of an 8-Year-Old Girl with Absence Epilepsy

In this article, we discuss the impact of migration and acculturation processes on the cultural, personal identity, and mental health of children who immigrate to a Western, multicultural environment, and the challenges clinicians in such environments face, when confronted with non-Western idioms of distress and healing practices. We do that by presenting a challenging clinical case of an 8-year-old girl who presented with very disorganized behavior, which matches a culturally accepted construct of spirit possession, in the context of migration trauma, acculturative stress, and new sibling transition. We identify cultural conflict in school and bullying as major mediators between acculturative stress and mental distress. We also aim at identifying vulnerability, risk and protective factors, and the importance of cultural coping resources. We explore in depth the patient's cultural background and the family's belief system and culturally shaped narratives, in order to arrive at a cultural formulation, which focuses on the significance of idioms of distress in shaping psychopathology and influencing the personal and interpersonal course of trauma- and stress-related disorders. We also call attention to the finding that in children, idioms of distress may manifest themselves in a somatic manner. We argue, together with other researchers, that spirit possession deserves more interest as an idiom of distress and a culture-specific response to traumatizing events. We finally emphasize the importance of an anti-reductionist clinical stance, that is able to use different levels of understanding processes of distress and healing, and seeks to reconciliate cultural divides and integrate different explanatory frameworks and help-seeking practices.

Experiencing neonatal maternal separation increased the seizure threshold in adult male mice: Involvement of the opioid system

Experiencing early-life stress has been considered as a potent risk factor for the development of many of brain disorders, including seizures. Intervening mechanisms through which neonatal maternal separation (MS) alters the seizure susceptibility in adulthood have not been well studied. In the current study, by applying 180 min of MS stress (PND 2-14), we determined the seizure susceptibility and considered the role of the opioid system. Maternal separation increased the seizure threshold, and administration of anticonvulsant/proconvulsant doses of morphine (1 and 30 mg/kg, respectively) reversed the impact of MS. Using tail flick and hot plate tests, we exposed animals to 30 min Restraint stress (RS) and found that MS decreased the pain threshold, suggesting the hyporesponsiveness of the opioid system. These results supported the abnormal seizure activity observed in the MS mice and suggested that abnormalities in the opioid system following MS alter seizure susceptibility in later life.

The relevance of neuropsychiatric symptoms and cognitive problems in new-onset epilepsy - Current knowledge and understanding

Neurobehavioral and cognition problems are highly prevalent in epilepsy, but most research studies to date have not adequately addressed the precise nature of the relationship between these comorbidities and seizures. To address this complex issue and to facilitate collaborative, innovative research in the rising field of neurobehavioral comorbidities and cognition disturbances in new-onset epilepsy, international epilepsy experts met at the 3rd Halifax International Epilepsy Conference & Retreat at White Point, South Shore, Nova Scotia, Canada from September 18 to 20, 2014. This Conference Proceedings provides a summary of the conference proceedings. Specifically, the following topics are discussed: (i) role of comorbidities in epilepsy diagnosis and management, (ii) role of antiepileptic medications in understanding the relationship between epilepsy and neurobehavioral and cognition problems, and (iii) animal data and diagnostic approaches. Evidence to date, though limited, strongly suggests a bidirectional relationship between epilepsy and cognitive and psychiatric comorbidities. In fact, it is likely that seizures and neurobehavioral problems represent different symptoms of a common etiology or network-wide disturbance. As a reflection of this shared network, psychiatric comorbidities and/or cognition problems may actually precede the seizure occurrence and likely get often missed if not screened.

Association of Tag SNPs and Rare CNVs of the MIR155HG/miR-155 Gene with Epilepsy in the Chinese Han Population

BACKGROUND

miR-155 likely acts as an important modulator in the inflammatory mechanism of epilepsy, and this study investigated its association with epilepsy from the perspective of molecular genetics.

METHODS

This study enrolled 249 epileptic patients and 289 healthy individuals of the Chinese Han population; 4 tag single-nucleotide polymorphisms (SNPs: rs969885, rs12483428, rs987195, and rs4817027) of the MIR155HG/miR-155 gene were selected, and their association with epilepsy was investigated. Additionally, this study determined the copy numbers of the MIR155HG/miR-155 gene.

RESULTS

The TCA haplotype (rs12483428-rs987195-rs4817027) and the AA genotype at rs4817027 conferred higher vulnerability to epilepsy in males. Stratification by age of onset revealed that the CC haplotype (rs969885-rs987195) was a genetic susceptibility factor for early-onset epilepsy. Further stratification by drug-resistant status indicated the CC haplotype (rs969885-rs987195) and the AA genotype at rs4817027 were genetic susceptibility factors for drug-resistant epilepsy (DRE) but the CG haplotype (rs987195-rs969885) was a genetically protective factor against DRE. Besides, 3 epileptic patients with copy number variants of the MIR155HG/miR-155 gene were observed.

CONCLUSIONS

This study first demonstrates the association of MIR155HG/miR-155 tag SNPs with epilepsy and shows that rare CNVs were found exclusively in epileptic patients, clarifying the genetic role of miR-155 in epilepsy.