Cognitive impairment following experimental febrile seizures is determined by sex and seizure duration

Sex differences in cholinergic signaling affect functional outcomes for theta-gamma coordination in hippocampal subcircuits following experimental febrile status epilepticus

OBJECTIVE

Sex determines cognitive outcome in animal models of early life seizure, where males exhibit impaired hippocampal-dependent learning and memory compared with females. The physiological underpinnings of this sex effect are unclear. Cholinergic signaling is essential for the generation of hippocampal oscillations, and supplementation of cholinergic precursors prior to status epilepticus in immature male rats prevents subsequent memory deficits. We hypothesized that there are sex differences in acetylcholine circuits and their response to experimental febrile status epilepticus (eFSE).

METHODS

eFSE was induced in male and female rat pups. We transversed the hippocampus of postnatal day >60 control (CTL) and eFSE rats with a 64-channel laminar silicon probe to assay cholinergic-dependent theta oscillations under urethane anesthesia. Local field potential properties were compared during (1) baseline sensory stimulation, (2) pharmacological stimulation via acetylcholine reuptake blockade, and (3) sensory stimulation after muscarinic acetylcholine receptor block (atropine).

RESULTS

In all groups, a baseline tail pinch could elicit theta oscillations via corticohippocampal synaptic input. Following atropine, a tail pinch response could no longer be elicited in CTL male, CTL female, or eFSE female rats. In contrast, induced slow theta power in eFSE males after atropine was not decreased to spontaneous levels. Analysis of oscillation bandwidths revealed sex differences in acetylcholine modulation of theta frequency and slow gamma frequency and power. This study also identified significant effects of both sex and eFSE on baseline theta-gamma comodulation, indicating a loss of coupling in eFSE males and a potential gain of function in eFSE females.

SIGNIFICANCE

There are differences in cholinergic modulation of theta and gamma signal coordination between male and female rats. These differences may underlie worse cognitive outcomes in males following eFSE. Promoting the efficacy of muscarinic acetylcholine signaling prior to or following early life seizures could elucidate a mechanism for the temporal discoordination of neural signals within and between hippocampus and neocortex and provide a novel therapeutic approach for improving cognitive outcomes.

CBD treatment following early life seizures alters orbitofrontal-striatal signaling during adulthood

Obsessive compulsive disorder (OCD) is a comorbid condition of epilepsy and often adds to the burden of epilepsy. Both OCD and epilepsy are disorders of hyperexcitable circuits. Fronto-striatal circuit dysfunction is implicated in OCD. Prior work in our laboratory has shown that in rat pups following a series of flurothyl-induced early life seizures (ELS) exhibit frontal-lobe dysfunction along with alterations in electrographic temporal coordination between the orbitofrontal cortex (OFC) and dorsomedial striatum (DMS), circuits implicated in OCD. Here, we studied the effects of ELS in male and female rat pups on OCD-like behaviors as adults using the marble burying test (MBT). Because cannabidiol (CBD) is an effective antiseizure medication and has shown efficacy in the treatment of individuals with OCD, we also randomized rats to CBD or vehicle treatment following ELS to determine if CBD had any effect on OCD-like behaviors. While the flurothyl model of ELS did not induce OCD-like behaviors, as measured in the MBT, ELS did alter neural signaling in structures implicated in OCD and CBD had sex-dependent effects of temporal coordination in a way which suggests it may have a beneficial effect on epilepsy-related OCD.

Do vaccines cause epilepsy? Review of cases in the National Vaccine Injury Compensation Program

OBJECTIVE

The National Childhood Vaccine Injury Act of 1986 created the National Vaccine Injury Compensation Program (VICP), a no-fault alternative to the traditional tort system. Since 1988, the total compensation paid exceeds $5 billion. Although epilepsy is one of the leading reasons for filing a claim, there has been no review of the process and validity of the legal outcomes given current medical information. The objectives were to review the evolution of the VICP program in regard to vaccine-related epilepsy and assess the rationale behind decisions made by the court.

METHODS

Publicly available cases involving epilepsy claims in the VICP were searched through Westlaw and the US Court of Federal Claims websites. All published reports were reviewed for petitioner's theories supporting vaccine-induced epilepsy, respondent's counterarguments, the final decision regarding compensation, and the rationale underlying these decisions. The primary goal was to determine which factors went into decisions regarding whether vaccines caused epilepsy.

RESULTS

Since the first epilepsy case in 1989, there have been many changes in the program, including the removal of residual seizure disorder as a vaccine-related injury, publication of the Althen prongs, release of the acellular form of pertussis, and recognition that in genetic conditions the underlying genetic abnormality rather than the immunization causes epilepsy. We identified 532 unique cases with epilepsy: 105 with infantile spasms and 427 with epilepsy without infantile spasms. The petitioners' experts often espoused outdated, erroneous causation theories that lacked an acceptable medical or scientific foundation and were frequently criticized by the court.

SIGNIFICANCE

Despite the lack of epidemiological or mechanistic evidence indicating that childhood vaccines covered by the VICP result in or aggravate epilepsy, these cases continue to be adjudicated. After 35 years of intense litigation, it is time to reconsider whether epilepsy should continue to be a compensable vaccine-induced injury.

Impact of Respiratory Viruses and SARS-CoV-2 on Febrile Seizures in Saudi Children: Insights into Etiologies, Gender, and Familial Associations

BACKGROUND Childhood febrile seizures occur between 5 months and 6 years of age in children without a previous history of seizure and are associated with high temperature in the absence of intracranial infection. This retrospective study identified 71 children aged 6 months to 5 years with febrile seizures between 2017 and 2021 at a single center in Saudi Arabia and aimed to identify an association between common respiratory virus and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. MATERIAL AND METHODS Pediatric nasopharyngeal specimens were tested using a multiplex PCR respiratory panel detecting human coronaviruses (NL63, 229E, OC43, HKU1), influenza A/B, human adenovirus, parainfluenza viruses 1-4, respiratory syncytial virus, human metapneumovirus, rhinovirus/enterovirus, Middle East respiratory syndrome coronavirus, and, as of September 2021, SARS-CoV-2, confirmed using the Cepheid Xpert Xpress SARS-CoV2 RT-PCR kit. RESULTS In a cohort of 71 pediatric patients (median age, 19 months; 54.9% female), dominant pathogens included human rhinovirus/enterovirus (23.9%), influenza A/B (26.8%), and SARS-CoV-2 (14.1%). Concurrent infections were noted in 28.2%. Simple seizures occurred in 69%, and complex seizures in 31%. Females exhibited an 8.18-fold increased risk for complex seizures. Each additional fever day reduced complex seizure risk by 36%. Familial seizure history increased risk 8.76-fold. Human rhinovirus/enterovirus or parainfluenza infections inversely affected complex seizure likelihood compared with adenovirus. CONCLUSIONS In Saudi children with febrile seizures, distinct viral etiologies, sex, and familial links play pivotal roles. Given regional viral variations, region-tailored diagnostic and therapeutic strategies are paramount. A multicenter prospective cohort study is essential for comprehensive understanding.

Alterations in Rat Hippocampal Glutamatergic System Properties after Prolonged Febrile Seizures

Febrile seizures during early childhood may result in central nervous system developmental disorders. However, the specific mechanisms behind the impact of febrile seizures on the developing brain are not well understood. To address this gap in knowledge, we employed a hyperthermic model of febrile seizures in 10-day-old rats and tracked their development over two months. Our objective was to determine the degree to which the properties of the hippocampal glutamatergic system are modified. We analyzed whether pyramidal glutamatergic neurons in the hippocampus die after febrile seizures. Our findings indicate that there is a reduction in the number of neurons in various regions of the hippocampus in the first two days after seizures. The CA1 field showed the greatest susceptibility, and the reduction in the number of neurons in post-FS rats in this area appeared to be long-lasting. Electrophysiological studies indicate that febrile seizures cause a reduction in glutamatergic transmission, leading to decreased local field potential amplitude. This impairment could be attributable to diminished glutamate release probability as evidenced by decreases in the frequency of miniature excitatory postsynaptic currents and increases in the paired-pulse ratio of synaptic responses. We also found higher threshold current causing hind limb extension in the maximal electroshock seizure threshold test of rats 2 months after febrile seizures compared to the control animals. Our research suggests that febrile seizures can impair glutamatergic transmission, which may protect against future seizures.

Spatial learning impairments and discoordination of entorhinal-hippocampal circuit coding following prolonged febrile seizures

How the development and function of neural circuits governing learning and memory are affected by insults in early life remains poorly understood. The goal of this study was to identify putative changes in cortico-hippocampal signaling mechanisms that could lead to learning and memory deficits in a clinically relevant developmental pathophysiological rodent model, Febrile status epilepticus (FSE). FSE in both pediatric cases and the experimental animal model, is associated with enduring physiological alterations of the hippocampal circuit and cognitive impairment. Here, we deconstruct hippocampal circuit throughput by inducing slow theta oscillations in rats under urethane anesthesia and isolating the dendritic compartments of CA1 and dentate gyrus subfields, their reception of medial and lateral entorhinal cortex inputs, and the efficacy of signal propagation to each somatic cell layer. We identify FSE-induced theta-gamma decoupling at cortical synaptic input pathways and altered signal phase coherence along the CA1 and dentate gyrus somatodendritic axes. Moreover, increased DG synaptic activity levels are predictive of poor cognitive outcomes. We propose that these alterations in cortico-hippocampal coordination interfere with the ability of hippocampal dendrites to receive, decode and propagate neocortical inputs. If this frequency-specific syntax is necessary for cortico-hippocampal coordination and spatial learning and memory, its loss could be a mechanism for FSE cognitive comorbidities.

Inhibitory dysfunction may cause prospective memory impairment in temporal lobe epilepsy (TLE) patients: an event-related potential study

Introduction

Prospective memory (PM) is the ability to remember future intentions, and PM function is closely related to independence in daily life, particularly in patients with temporal lobe epilepsy (TLE). As PM involves various cognitive components of attention, working memory, inhibition and other executive functions, this study investigated how TLE may affect PM components and the underlying neural mechanisms.

Methods

Sixty-four subjects were recruited, including 20 refractory TLE patients, 18 well-controlled TLE patients and 26 age-matched healthy controls. A set of neuropsychological tests was administered to assess specific brain functions. An event-related potential (ERP) task was used to further explore how PM and its components would be differentially affected in the two TLE types.

Results

Our findings revealed that: (1) refractory TLE patients scored lower than the healthy controls in the digit span, Verbal Fluency Test and Symbol Digit Modalities Test; (2) refractory TLE patients exhibited impaired PM performance and reduced prospective positivity amplitudes over the frontal, central and parietal regions in ERP experiments when compared to the healthy controls; and (3) decreased P3 amplitudes in the nogo trials were observed over the frontal-central sites in refractory but not in well-controlled TLE patients.

Discussion

To our knowledge, this is the first ERP study on PM that has specifically identified PM impairment in refractory but not in well-controlled TLE patients. Our finding of double dissociation in PM components suggests that inhibition dysfunction may be the main reason for PM deficit in refractory TLE patients. The present results have clinical implications for neuropsychological rehabilitation in TLE patients.

The long-term neurodevelopmental outcomes of febrile seizures and underlying mechanisms

Febrile seizures (FSs) are convulsions caused by a sudden increase in body temperature during a fever. FSs are one of the commonest presentations in young children, occurring in up to 4% of children between the ages of about 6 months and 5 years old. FSs not only endanger children's health, cause panic and anxiety to families, but also have many adverse consequences. Both clinical and animal studies show that FSs have detrimental effects on neurodevelopment, that cause attention deficit hyperactivity disorder (ADHD), increased susceptibility to epilepsy, hippocampal sclerosis and cognitive decline during adulthood. However, the mechanisms of FSs in developmental abnormalities and disease occurrence during adulthood have not been determined. This article provides an overview of the association of FSs with neurodevelopmental outcomes, outlining both the underlying mechanisms and the possible appropriate clinical biomarkers, from histological changes to cellular molecular mechanisms. The hippocampus is the brain region most significantly altered after FSs, but the motor cortex and subcortical white matter may also be involved in the development disorders induced by FSs. The occurrence of multiple diseases after FSs may share common mechanisms, and the long-term role of inflammation and γ-aminobutyric acid (GABA) system are currently well studied.

Warming Up to the Notion That Febrile Seizures Can Be Associated With Cognitive Impairment

Cognitive Impairment Following Experimental Febrile Seizures Is Determined by Sex and Seizure Duration

Kloc ML, Marchand DH, Holmes GL, Pressman RD, Barry JM. Epilepsy Behav. 2022;126:108430. doi:10.1016/j.yebeh.2021.108430

Background:

Febrile seizures are the most common type of seizures in children. While in most children the outcome is favorable, children with febrile status epilepticus may exhibit modest cognitive impairment. Whether children with other forms of complex febrile seizure, such as repetitive febrile seizures within the same illness are at risk of cognitive deficits is not known. In this study, we used a well-established model of experimental febrile seizures in rat pups to compare the effects of febrile status epilepticus and recurrent febrile seizures on subsequent spatial cognition and anxiety.

Methods:

Male and female rat pups were subjected to hyperthermic seizures at postnatal day 10 and were divided into groups of rats with continuous seizures for ≥40 min or recurrent febrile seizures. They were then tested as adults in the active avoidance and spatial accuracy tests to assess spatial learning and memory and the elevated plus maze to measure anxiety.

Results:

Febrile status epilepticus rats demonstrated impaired spatial cognition in active avoidance and spatial accuracy and exhibited reduced anxiety-like behavior in the elevated plus maze. Rats with recurrent febrile seizures did not differ significantly from the controls on any measures. There were also significant sex-related differences with females with FSE performing far better than males with FSE in active avoidance but demonstrating a navigational learning impairment relative to CTL females in spatial accuracy. However, once learned, females with FSE performed the spatial accuracy task as well as CTL females.

Conclusion:

There is a duration-dependent effect of febrile seizures on subsequent cognitive and behavioral outcomes. Febrile status epilepticus resulted in spatial cognitive deficits and reduced anxiety-related behaviors whereas rats with recurrent febrile seizures did not differ from controls. Sex had a remarkable effect on spatial cognitive outcome where males with FSE fared worse than females with FSE. The results demonstrate that sex should be considered as a biological variable in studies evaluating the effects of seizures on the developing brain.

Seizure duration predicts postictal electroencephalographic recovery after electroconvulsive therapy-induced seizures

OBJECTIVE

We aim to provide a quantitative description of the relation between seizure duration and the postictal state using features extracted from the postictal electroencephalogram (EEG).

METHODS

Thirty patients with major depressive disorder treated with electroconvulsive therapy (ECT) were studied with continuous EEG before, during, and after ECT-induced seizures. EEG recovery was quantified as the spectral difference between postictal and baseline EEG using the temporal brain symmetry index (BSI). The postictal temporal EEG evolution was modeled with a single exponential. The parameters of the model, including the time constant τ, describe the change and speed of postictal EEG recovery. The change from baseline EEG at t = 60 minutes post-seizure (ΔBSI) was calculated from the exponential fit. Postictal clinical reorientation time (ROT) was clinically established. A multivariate generalized multi-level Bayesian model was estimated with seizure duration and ROT as predictors of τ and ΔBSI.

RESULTS

EEG features of 290 seizures and postictal states were used for analyses. The model faithfully described the dynamics of the postictal EEG in nearly all patients. Seizure duration was associated with the recovery time constant, τ, and ΔBSI. ROT was associated with τ, but not with ΔBSI.

CONCLUSIONS

Longer seizures are associated with slower postictal EEG recovery and more enduring EEG changes compared to baseline.

SIGNIFICANCE

Quantitative EEG allows objective assessment of the postictal state.

Optogenetic modulation of hippocampal oscillations ameliorates spatial cognition and hippocampal dysrhythmia following early-life seizures

There is increasing human and animal evidence that brain oscillations play a critical role in the development of spatial cognition. In rat pups, disruption of hippocampal rhythms via optogenetic stimulation during the critical period for memory development impairs spatial cognition. Early-life seizures are associated with long-term deficits in spatial cognition and aberrant hippocampal oscillatory activity. Here we asked whether modulation of hippocampal rhythms following early-life seizures can reverse or improve hippocampal connectivity and spatial cognition. We used optogenetic stimulation of the medial septum to induce physiological 7 Hz theta oscillations in the hippocampus during the critical period of spatial cognition following early-life seizures. Optogenetic stimulation of the medial septum in control and rats subjected to early-life seizures resulted in precisely regulated frequency-matched hippocampal oscillations. Rat pups receiving active blue light stimulation performed better than the rats receiving inert yellow light in a test of spatial cognition. The improvement in spatial cognition in these rats was associated with a faster theta frequency and higher theta power, coherence and phase locking value in the hippocampus than rats with early-life seizures receiving inert yellow light. These findings indicate that following early life seizures, modification of hippocampal rhythms may be a potential novel therapeutic modality.

The cognitive functions and seizure outcomes of patients with low-grade epilepsy-associated neuroepithelial tumors

PURPOSE

The aim of the study was to evaluate the cognitive functions and seizure outcomes of patients with low-grade epilepsy-associated neuroepithelial tumors (LEATs).

METHODS

We retrospectively reviewed the clinical data of patients who underwent preoperative neuropsychological evaluations and subsequent epilepsy surgery for LEATs. The neuropsychological results of full-scaled intelligence quotient (FSIQ) and full-scaled memory quotient (FSMQ) were analyzed, as well as the postoperative seizure outcomes.

RESULTS

Of the 138 patients included in the study, 59 patients (40.4%) were female and 47 (36.6%) patients were children. Preoperatively, 138 patients received FSIQ assessments and 30 patients (21.7%) had an intellectual deficit (FSIQ < 80 scores); 124 patients received FSMQ assessments and 32 patients (25.8%) had a memory deficit (FSMQ < 80 scores). Younger age at seizure onset (OR 0.93; P = 0.035) and discordant ictal electroencephalography (EEG) findings (OR 5.26; P = 0.001) were found to predict intellectual deficits, while abnormal hippocampus (OR 2.36; P = 0.051) as well as discordant ictal EEG findings (OR 4.03; P = 0.007) tended to cause memory deficits. During postoperative follow-up, 123 patients (90.7%) were followed up at least 12 months, and among them, 105 patients (85.4%) got seizure-free (Engel class I), while 18 patients (14.6%) were not (Engel class II-IV); longer duration of epilepsy (OR 1.01; P < 0.001) and discordant interictal EEG findings (OR 5.91; P = 0.005) were found to be related to poor seizure outcomes in patients with LEATs.

CONCLUSION

Cognitive deficits commonly occur in patients with LEATs, especially in patients with early or childhood seizures. Early surgical intervention, however, could prevent most of patients from repeated seizure onsets and thus cognitive impairments.