Repetitive febrile seizures in rat pups cause long-lasting deficits in synaptic plasticity and NR2A tyrosine phosphorylation

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 The petitioners' experts often espoused outdated, erroneous causation theories that lacked an acceptable medical or scientific foundation and were frequently criticized by the court.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.

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.

Na+/K+- and Mg2+-ATPases and Their Interaction with AMPA, NMDA and D2 Dopamine Receptors in an Animal Model of Febrile Seizures

Febrile seizures (FS) are one of the most common seizure disorders in childhood which are classified into short and prolonged, depending on their duration. Short FS are usually considered as benign. However, epidemiological studies have shown an association between prolonged FS and temporal lobe epilepsy. The development of animal models of FS has been very useful to investigate the mechanisms and the consequences of FS. One of the most used, the "hair dryer model", has revealed that prolonged FS may lead to temporal lobe epilepsy by altering neuronal function. Several pieces of evidence suggest that Na⁺/ K⁺-ATPase and Mg²⁺-ATPase may play a role in this epileptogenic process. In this work, we found that hyperthermia-induced seizures (HIS) significantly increased the activity of Na⁺/ K⁺-ATPase and Mg²⁺-ATPase five and twenty days after hyperthermic insult, respectively. These effects were diminished in response to AMPA, D₂ dopamine A₁ and A_2A receptors activation, respectively. Furthermore, HIS also significantly increased the protein level of the AMPA subunit GluR1. Altogether, the increased Na⁺/ K⁺-ATPase and Mg²⁺-ATPase agree well with the presence of protective mechanisms. However, the reduction in ATPase activities in the presence of NMDA and AMPA suggest an increased propensity for epileptic events in adults.

Early Life Febrile Seizures Impair Hippocampal Synaptic Plasticity in Young Rats

Febrile seizures (FSs) in early life are significant risk factors of neurological disorders and cognitive impairment in later life. However, existing data about the impact of FSs on the developing brain are conflicting. We aimed to investigate morphological and functional changes in the hippocampus of young rats exposed to hyperthermia-induced seizures at postnatal day 10. We found that FSs led to a slight morphological disturbance. The cell numbers decreased by 10% in the CA1 and hilus but did not reduce in the CA3 or dentate gyrus areas. In contrast, functional impairments were robust. Long-term potentiation (LTP) in CA3-CA1 synapses was strongly reduced, which we attribute to the insufficient activity of N-methyl-D-aspartate receptors (NMDARs). Using whole-cell recordings, we found higher desensitization of NMDAR currents in the FS group. Since the desensitization of NMDARs depends on subunit composition, we analyzed NMDAR current decays and gene expression of subunits, which revealed no differences between control and FS rats. We suggest that an increased desensitization is due to insufficient activation of the glycine site of NMDARs, as the application of D-serine, the glycine site agonist, allows the restoration of LTP to a control value. Our results reveal a new molecular mechanism of FS impact on the developing brain.

Protective effects of maternal administration of curcumin and hesperidin in the rat offspring following repeated febrile seizure: Role of inflammation and TLR4

Neuroinflammation has a key role in seizure generation and perpetuation in the neonatal period, and toll-like receptor 4 (TLR4) pathway has a prominent role in neuroinflammatory diseases. Administration of antioxidants and targeting TLR4 in the embryonic period may protect rat offspring against the next incidence of febrile seizure and its harmful effects. Curcumin and hesperidin are natural compounds with anti-inflammatory and antioxidant properties and have an inhibitory action on TLR4 receptors. We evaluated the effect of maternal administration of curcumin and hesperidin on infantile febrile seizure and subsequent memory dysfunction in adulthood. Hyperthermia febrile seizure was induced on postnatal days 9-11 on male rat pups with 24 h intervals, in a Plexiglas box that was heated to ~45 °C by a heat lamp. We used enzyme-linked immunosorbent assay, Western blotting, malondialdehyde (MDA), and glutathione (GSH) assessment for evaluation of inflammatory cytokine levels, TLR4 protein expression, and oxidative responses in the hippocampal tissues. For assessing working memory and long-term potentiation, the double Y-maze test and Schaffer collateral-CA1 in vivo electrophysiological recording were performed, respectively Our results showed that curcumin and hesperidin decreased TNF-α, IL-10, and TLR4 protein expression and reversed memory dysfunction. However, they did not provoke a significant effect on GSH content or amplitude and slope of recorded fEPSPs in the hippocampus. In addition, curcumin, but not hesperidin, decreased interleukin-1β (IL-1β) and MDA levels. These findings imply that curcumin and hesperidin induced significant protective effects on febrile seizures, possibly via their anti-inflammatory and antioxidant properties and downregulation of TLR4.

Epileptic pilocarpine-treated rats exhibit aberrant hippocampal EPSP-spike potentiation but retain long-term potentiation

Hippocampal neuron plasticity is strongly associated with learning, memory, and cognition. In addition to modification of synaptic function and connectivity, the capacity of hippocampal neurons to undergo plasticity involves the ability to change nonsynaptic excitability. This includes altering the probability that EPSPs will generate action potentials (E‐S plasticity). Epilepsy is a prevalent neurological disorder commonly associated with neuronal hyperexcitability and cognitive dysfunction. We examined E‐S plasticity in chronically epileptic Sprague–Dawley rats 3–10 weeks after pilocarpine‐induced status epilepticus. CA1 neurons in hippocampal slices were assayed by whole‐cell current clamp to measure EPSPs evoked by Schaffer collateral stimulation. Using a weak spike‐timing‐dependent protocol to induce plasticity, we found robust E‐S potentiation in conjunction with weak long‐term potentiation (LTP) in saline‐treated rats. In pilocarpine‐treated rats, a similar degree of LTP was found, but E‐S potentiation was reduced. Additionally, the degree of E‐S potentiation was not correlated with the degree of LTP for either group, suggesting that they independently contribute to neuronal plasticity. E‐S potentiation also differed from LTP in that E‐S plasticity could be induced solely from action potentials generated by postsynaptic current injection. The calcium chelating agent BAPTA in the intracellular solution blocked LTP and E‐S potentiation, revealing the calcium dependence of both processes. These findings suggest that LTP and E‐S potentiation have overlapping but nonidentical mechanisms of inducing neuronal plasticity that may independently contribute to cognitive disruptions observed in the chronic epileptic state.

Sleep-Related Disorders in Children with Attention-Deficit Hyperactivity Disorder: Preliminary Results of a Full Sleep Assessment Study

BACKGROUND AND METHODS

We present the preliminary results of a prospective case-control sleep study in children with a diagnosis of attention-deficit hyperactivity disorder (ADHD). A deep sleep assessment including sleep questionnaires, sleep habits, a video-polysomnographic recording with full high-density electroencephalography (EEG) and cardiorespiratory polygraphy, multiple sleep latency test, and 1-week actigraphic recording were performed to verify whether children with ADHD may be classified into one of the following five phenotypes: (1) hypoarousal state, resembling narcolepsy, which may be considered a "primary" form of ADHD; (2) delayed sleep onset insomnia; (3) sleep-disordered breathing; (4) restless legs syndrome and/or periodic limb movements; and (5) sleep epilepsy and/or EEG interictal epileptiform discharges.

RESULTS

Fifteen consecutive outpatients with ADHD were recruited (two female, mean age 10.6 ± 2.2, age range 8-13.7 years) over 6 months. The narcolepsy-like sleep phenotype was observed in three children, the sleep onset insomnia phenotype was observed in one child, mild obstructive sleep apnea was observed in three children, sleep hyperkinesia and/or PLMs were observed in five children, while IEDs and or nocturnal epilepsy were observed in three children. Depending on the sleep phenotype, children received melatonin, iron supplementation, antiepileptic drugs, or stimulants.

CONCLUSIONS

Our study further highlights the need to design an efficient sleep diagnostic algorithm for children with ADHD, thereby more accurately identifying cases in which a full sleep assessment is indicated.

TRPV1 promotes repetitive febrile seizures by pro-inflammatory cytokines in immature brain

Febrile seizure (FS) is the most common seizure disorder in children, and children with FS are regarded as a high risk for the eventual development of epilepsy. Brain inflammation may be implicated in the mechanism of FS. Transient receptor potential vanilloid 1 (TRPV1) is believed to act as a monitor and regulator of body temperature. The role of inflammation in synaptic plasticity mediation indicates that TRPV1 is relevant to several nervous system diseases, such as epilepsy. Here, we report a critical role for TRPV1 in a febrile seizure mouse model and reveal increased levels of pro-inflammatory factors in the immature brain. Animals were subjected to hyperthermia for 30 min, which generates seizures lasting approximately 20 min, and then were used for experiments. To invoke frequently repetitive febrile seizures, mice are exposed to hyperthermia for three times daily at an interval of 4h between every time induced seizure, and a total of 4 days to induce. Behavioral testing for febrile seizures revealed that a TRPV1 knock-out mouse model demonstrated a prolonged onset latency and a shortened duration and seizure grade of febrile seizure when compared with wild type (WT) mice. The expression levels of both TRPV1 mRNA and protein increased after a hyperthermia-induced febrile seizure in WT mice. Notably, TRPV1 activation resulted in a significant elevation in the expression of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α and HMGB1) in the hippocampus and cortex. These data indicate that the reduction of TRPV1 expression parallels a decreased susceptibility to febrile seizures. Thus, preventative strategies might be developed for use during febrile seizures.

Early life seizures: evidence for chronic deficits linked to autism and intellectual disability across species and models

Recent work in Exp Neurol by Lugo et al. (2014b) demonstrated chronic alterations in sociability, learning and memory following multiple early life seizures (ELS) in a mouse model. This work adds to the growing body of evidence supporting the detrimental nature of ELS on the developing brain to contribute to aspects of an autistic phenotype with intellectual disability. Review of the face validity of behavioral testing and the construct validity of the models used informs the predictive ability and thus the utility of these models to translate underlying molecular and cellular mechanisms into future human studies.

Origins of temporal lobe epilepsy: febrile seizures and febrile status epilepticus

Temporal lobe epilepsy (TLE) and hippocampal sclerosis (HS) commonly arise following early-life long seizures, and especially febrile status epilepticus (FSE). However, there are major gaps in our knowledge regarding the causal relationships of FSE, TLE, HS and cognitive disturbances that hamper diagnosis, biomarker development and prevention. The critical questions include: What is the true probability of developing TLE after FSE? Are there predictive markers for those at risk? A fundamental question is whether FSE is simply a marker of individuals who are destined to develop TLE, or if FSE contributes to the risk of developing TLE. If FSE does contribute to epileptogenesis, then does this happen only in the setting of a predisposed brain? These questions are addressed within this review, using information gleaned over the past two decades from clinical studies as well as animal models.

Cognitive performance and convulsion risk after experimentally-induced febrile-seizures in rat

Many reports indicated that small percentage of children with febrile seizures develop epilepsy and cognitive disorders later in adulthood. In addition, the neuronal network of the hippocampus was reported to be deranged in adult animals after being exposed to hyperthermia-induced seizures in their neonatal life. The aims of this study were to investigate (1) latency and probability of seizures, (2) spatial learning and memory, in adult rats after neonatal hyperthermia-induced febrile seizures (FS). Prolonged FS were elicited in 10-day old, male Sprague Dawleys (n=11/group) by exposure to heated air (48-52 °C) for 30 min; control rats were exposed to 30 °C air. After 1.5 months the animal's cognitive performance was assessed by 5 day trial in the Morris water maze. In another experiment the latency and probability of seizures were measured in response to pentylenetetrazole (PTZ) injections (increased doses ranged from 7 to 140 mg/kg; i.p.). In water maze, both groups showed improvements in escape latency and distance swam to reach the platform; effects were significantly greater in control versus hyperthermia-treated animals on days 3 and 4. Latency and probability of PTZ-induced seizures were shorter and higher respectively, in hyperthermia-treated animals compared to controls. We concluded that FS in neonatal rats leads to enhanced susceptibility for seizures, as well as cognitive deficits in adults.

Focal epileptiform activity in the prefrontal cortex is associated with long-term attention and sociability deficits

There is a well-described association between childhood epilepsy and pervasive cognitive and behavioral deficits. Often these children not only have ictal EEG events, but also frequent interictal abnormalities. The precise role of these interictal discharges in cognition remains unclear. In order to understand the relationship between frequent epileptiform discharges during neurodevelopment and cognition later in life, we developed a model of frequent focal interictal spikes (IIS). Postnatal day (p) 21 rats received injections of bicuculline methiodine into the prefrontal cortex (PFC). Injections were repeated in order to achieve 5 consecutive days of transient inhibitory/excitatory imbalance resulting in IIS. Short-term plasticity (STP) and behavioral outcomes were studied in adulthood. IIS is associated with a significant increase in STP bilaterally in the PFC. IIS rats did not show working memory deficits, but rather showed marked inattentiveness without significant alterations in motivation, anxiety or hyperactivity. Rats also demonstrated significant deficits in social behavior. We conclude that GABAergic blockade during early-life and resultant focal IIS in the PFC disrupt neural networks and are associated with long-term consequences for behavior at a time when IIS are no longer present, and thus may have important implications for ADHD and autism spectrum disorder associated with childhood epilepsy.

Protective effect of the KCNQ activator flupirtine on a model of repetitive febrile seizures

Activation of KCNQ-channels has been shown to decrease or reduce the propagation of neuronal excitation in the immature central nervous system, and KCNQ activators represent a new class of anticonvulsant compounds. Their effectiveness has been demonstrated in many seizure models but not in repetitive febrile seizures (RFS) models. This study aimed to test whether the KCNQ channel activator flupirtine is also effective for RFS in rats. RFS were induced in Sprague-Dawley (SD) rats at postnatal day 10 (P10) in a warm water bath for eight consecutive days with or without the pre-administration of flupirtine or phenobarbital. As results, both drugs significantly increased the latency and decreased the rate of febrile seizures. Furthermore, seizures in the flupirtine group had a significantly shorter duration and were less severe compared with the phenobarbital group. The flupirtine-treated group showed less impairment in learning and memory and less obvious pathological changes in the brain following RFS compared with the phenobarbital-treated group. In summary, flupirtine appears to be effective in RFS prophylaxis and may merit further study as a candidate for the treatment of RFS in infants and children.

Long-term consequences of a prolonged febrile seizure in a dual pathology model

Clinical evidence suggests that febrile status epilepticus (SE) in children can lead to acute hippocampal injury and subsequent temporal lobe epilepsy. The contribution of febrile SE to the mechanisms underlying temporal lobe epilepsy are however poorly understood. A rat model of temporal lobe epilepsy following hyperthermic SE was previously established in our laboratory, wherein a focal cortical lesion induced at postnatal day 1 (P1), followed by a hyperthermic SE (more than 30 min) at P10, leads to hippocampal atrophy at P22 (dual pathology model) and spontaneous recurrent seizures (SRS) with mild visuospatial memory deficits in adult rats. The goal of this study was to identify the long term electrophysiological, anatomical and molecular changes in this model. Following hyperthermic SE, all cortically lesioned pups developed progressive SRS as adults, characterized by the onset of highly rhythmic activity in the hippocampus. A reduction of hippocampal volume on the side of the lesion preceded the SRS and was associated with a loss of hippocampal neurons, a marked decrease in pyramidal cell spine density, an increase in the hippocampal levels of NMDA receptor NR2A subunit, but no significant change in GABA receptors. These findings suggest that febrile SE in the abnormal brain leads to hippocampal injury that is followed by progressive network reorganization and molecular changes that contribute to the epileptogenesis as well as the observed memory deficits.

Epileptogenesis after prolonged febrile seizures: mechanisms, biomarkers and therapeutic opportunities

Epidemiological and recent prospective analyses of long febrile seizures (FS) and febrile status epilepticus (FSE) support the idea that in some children, such seizures can provoke temporal lobe epilepsy (TLE). Because of the high prevalence of these seizures, if epilepsy was to arise as their direct consequence, this would constitute a significant clinical problem. Here we discuss these issues, and describe the use of animal models of prolonged FS and of FSE to address the following questions: Are long FS epileptogenic? What governs this epileptogenesis? What are the mechanisms? Are there any predictive biomarkers of the epileptogenic process, and can these be utilized, together with information about the mechanisms of epileptogenesis, for eventual prevention of the TLE that results from long FS and FSE.

Long-lasting modulation of synaptic plasticity in rat hippocampus after early-life complex febrile seizures

A small fraction of children with febrile seizures appears to develop cognitive impairments. Recent studies in a rat model of hyperthermia-induced febrile seizures indicate that prolonged febrile seizures early in life have long-lasting effects on the hippocampus and induce cognitive deficits. However, data on network plasticity and the nature of cognitive deficits are conflicting. We examined three specific measures of hippocampal plasticity in adult rats with a prior history of experimental febrile seizures: (i) activity-dependent synaptic plasticity (long-term potentiation and depression) by electrophysiological recordings of Schaffer collateral/commissural-evoked field excitatory synaptic potentials in CA1 of acute hippocampal slices; (ii) Morris water maze spatial learning and memory; and (iii) hippocampal mossy fiber plasticity by Timm histochemistry and quantification of terminal sprouting in CA3 and the dentate gyrus. We found enhanced hippocampal CA1 long-term potentiation and reduced long-term depression but normal spatial learning and memory in adult rats that were subjected to experimental febrile seizures on postnatal day 10. Furthermore, rats with experimental febrile seizures showed modest but significant sprouting of mossy fiber collaterals into the inner molecular layer of the dentate gyrus in adulthood. We conclude that enhanced CA1 long-term potentiation and mild mossy fiber sprouting occur after experimental febrile seizures, without affecting spatial learning and memory in the Morris water maze. These long-term functional and structural alterations in hippocampal plasticity are likely to play a role in the enhanced seizure susceptibility in this model of prolonged human febrile seizures but do not correlate with overt cognitive deficits.

Characterization of developing rat cortical neurons after epileptiform discharges

The developing brain undergoes major reorganization in response to early environmental changes. The elevated excitation that allows the neonatal brain to develop quickly also makes it highly vulnerable to age-specific seizures that can cause lifelong cognitive and neurological disability. However, it is not yet clear how seizures interfere with the developmental program and how epileptogenesis actualize. Here, by using an in vitro model, we report a global abnormal status of cortical cells after epileptiform activity was induced: more NR2B is targeted on the neuronal surface with less NR2A. Dendrotoxicity including dendritic beading, distortion and simplification of dendritic branching patterns were observed. Early-life seizure-like insults also exert effects on the excitatory synaptic size and interactions between PSD-95 and NR2A or NR2B receptor subunits. Our findings support an abnormal development or, worse, cellular degeneration that resembles immature cells, which may enlighten better understanding of the pathological mechanism of early-life seizures and its related injury.

Novel etiological and therapeutic strategies for neurodiseases: mechanisms and consequences of febrile seizures: lessons from animal models

Febrile seizures (FS) are the most common type of convulsive events in infancy and childhood. Genetic and environmental elements have been suggested to contribute to FS. FS can be divided into simple and complex types, the former being benign, whereas it is controversial whether complex FS have an association with the development of temporal lobe epilepsy (TLE) in later life. In the hippocampus of TLE patients, several structural and functional alterations take place that render the region an epileptic foci. Thus, it is important to clarify the cellular and molecular changes in the hippocampus after FS and to determine whether they are epileptogenic. To achieve this goal, human studies are too limited because the sample tissues are only available from adult patients in the advanced and drug-resistant stages of the disease, masking the underlying etiology. These facts have inspired researchers to take advantage of well-established animal models of FS to answer the following questions: 1) How does hyperthermia induce FS? 2) Do FS induce neuroanatomical changes? 3) Do FS induce neurophysiological changes? 4) Do FS affect the behavior in later life? Here we introduce and discuss accumulating reports to answer these questions.

N-methyl-D-aspartate, hyperpolarization-activated cation current (Ih) and gamma-aminobutyric acid conductances govern the risk of epileptogenesis following febrile seizures in rat hippocampus

Febrile seizures are the most common types of seizure in children, and are generally considered to be benign. However, febrile seizures in children with dysgenesis have been associated with the development of temporal lobe epilepsy. We have previously shown in a rat model of dysgenesis (cortical freeze lesion) and hyperthermia-induced seizures that 86% of these animals developed recurrent seizures in adulthood. The cellular changes underlying the increased risk of epileptogenesis in this model are not known. Using whole cell patch-clamp recordings from CA1 hippocampal pyramidal cells, we found a more pronounced increase in excitability in rats with both hyperthermic seizures and dysgenesis than in rats with hyperthermic seizures alone or dysgenesis alone. The change was found to be secondary to an increase in N-methyl-D-aspartate (NMDA) receptor-mediated excitatory postsynaptic currents (EPSCs). Inversely, hyperpolarization-activated cation current was more pronounced in naïve rats with hyperthermic seizures than in rats with dysgenesis and hyperthermic seizures or with dysgenesis alone. The increase in GABAA-mediated inhibition observed was comparable in rats with or without dysgenesis after hyperthermic seizures, whereas no changes were observed in rats with dysgenesis alone. Our work indicates that in this two-hit model, changes in NMDA receptor-mediated EPSCs may facilitate epileptogenesis following febrile seizures. Changes in the hyperpolarization-activated cation currents may represent a protective reaction and act by damping the NMDA receptor-mediated hyperexcitability, rather than converting inhibition into excitation. These findings provide a new hypothesis of cellular changes following hyperthermic seizures in predisposed individuals, and may help in the design of therapeutic strategies to prevent epileptogenesis following prolonged febrile seizures.

The long-term effects of febrile seizures on the hippocampal neuronal plasticity - clinical and experimental evidence

Febrile seizures are the most common seizure disorder in childhood, but their long-term effects on the developing brains especially neuronal injury and neurocognitive function remain unresolved. Recent epidemiological studies reassure that most febrile seizures do not adversely affect global intelligence and hippocampal function, such as memory. However, there are concerns regarding those children who experience febrile seizures during the first postnatal year, having prior developmental delay and pre- or peri-natal events. Magnetic resonance imaging (MRI) studies confirmed that prolonged and focal FS can occasionally produce acute hippocampal injury that evolves into atrophy. Animal studies have revealed that the exposure of hippocampal neurons to experimental febrile seizures early in life, particularly prolonged or frequently repetitive FS, or together with brain malformation, may lead to sustained dysfunction of these cells, in spite of the absence of neuronal damage. Genetic studies suggest that the relationship between febrile seizures and subsequent epilepsy and neurocognitive dysfunction is sometimes genetic, but there are complex interactions with genetic or environmental modifiers. Therefore, there is a small group of children in whom febrile seizures-induced hippocampal injury might occur. Identification of the target population for subsequent mesial temporal sclerosis is important for prevention and early intervention.

A single early-life seizure impairs short-term memory but does not alter spatial learning, recognition memory, or anxiety

The impact of a single seizure on cognition remains controversial. We hypothesized that a single early-life seizure (sELS) on rat Postnatal Day (P) 7 would alter only hippocampus-dependent learning and memory in mature (P60) rats. The Morris water maze, the novel object and novel place recognition tasks, and contextual fear conditioning were used to assess learning and memory associated with hippocampus/prefrontal cortex, perirhinal/hippocampal cortex, and amygdala function, respectively. The elevated plus maze and open-field test were used to assess anxiety associated with the septum. We report that sELS impaired hippocampus-dependent short-term memory, but not spatial learning or recall. sELS did not disrupt performance in the novel object and novel place recognition tasks. Contextual fear conditioning performance suggested intact amydgala function. sELS did not change anxiety levels as measured by the elevated plus maze or open-field test. Our data suggest that the long-term cognitive impact of sELS is limited largely to the hippocampus/prefrontal cortex.

Involvement of the cAMP-dependent pathway in the reduction of epileptiform bursting caused by somatostatin in the mouse hippocampus

The cyclic AMP pathway is major signal transduction system involved in hippocampal neurotransmission. Recently, the peptide somatostatin-14 (SRIF) has emerged as a key signal that, by activating its receptors, inhibits epileptiform bursting in the mouse hippocampus. Little is known on transduction mechanisms, which may mediate SRIF function in native cell/tissues. Using a well-established model of epileptiform activity induced by Mg(2+)-free medium with 4-aminopyridine [0 Mg(2+)/4-aminopyridine (4-AP)] in mouse hippocampal slices, we demonstrated that protein kinase A (PKA)-related signaling is upregulated by hippocampal bursting and that treatment with SRIF normalizes this upregulation. We also demonstrated that the SRIF-induced inhibition of PKA impairs phosphorylation of the NMDA receptor subunit NR1. Extracellular recordings of the 0 Mg(2+)/4-AP-induced hippocampal discharge from the CA3 region demonstrated that treating slices with compounds, which interfere with PKA activity, prevent SRIF inhibition of epileptiform bursting. Our results suggest that SRIF modulation of hippocampal activity may involve PKA-related signaling.

Fever, febrile seizures and epilepsy

Seizures induced by fever (febrile seizures) are the most common type of pathological brain activity in infants and children. These febrile seizures and their potential contribution to the mechanisms of limbic (temporal lobe) epilepsy have been a topic of major clinical and scientific interest. Key questions include the mechanisms by which fever generates seizures, the effects of long febrile seizures on neuronal function and the potential contribution of these seizures to epilepsy. This review builds on recent advances derived from animal models and summarizes our current knowledge of the mechanisms underlying febrile seizures and of changes in neuronal gene expression and function that facilitate the enduring effects of prolonged febrile seizures on neuronal and network excitability. The review also discusses the relevance of these findings to the general mechanisms of epileptogenesis during development and points out gaps in our knowledge, including the relationship of animal models to human febrile seizures and epilepsy.

A single episode of neonatal seizures permanently alters glutamatergic synapses

OBJECTIVE

The contribution of seizures to cognitive changes remains controversial. We tested the hypothesis that a single episode of neonatal seizures (sNS) on rat postnatal day (P) 7 permanently impairs hippocampal-dependent function in mature (P60) rats because of long-lasting changes at the synaptic level.

METHODS

sNS was induced with subcutaneously injected kainate on P7. Learning, memory, mossy fiber sprouting, spine density, hippocampal synaptic plasticity, and glutamate receptor expression and subcellular distribution were measured at P60.

RESULTS

sNS selectively impaired working memory in a hippocampal-dependent radial arm water-maze task without inducing mossy fiber sprouting or altering spine density. sNS impaired CA1 hippocampal long-term potentiation and enhanced long-term depression. Subcellular fractionation and cross-linking, used to determine whether glutamate receptor trafficking underlies the alterations of memory and synaptic plasticity, demonstrated that sNS induced a selective reduction in the membrane pool of glutamate receptor 1 subunits. sNS induced a decrease in the total amount of N-methyl-D-aspartate receptor 2A and an increase in the primary subsynaptic scaffold, PSD-95.

INTERPRETATION

These molecular consequences are consistent with the alterations in plasticity and memory caused by sNS at the synaptic level. Our data demonstrate the cognitive impact of sNS and associate memory deficits with specific alterations in glutamatergic synaptic function.