Serum neuron-specific enolase is a marker for neuronal damage following status epilepticus in the rat

Fluid Biomarkers of Neuro-Glial Injury in Human Status Epilepticus: A Systematic Review

As per the latest ILAE definition, status epilepticus (SE) may lead to long-term irreversible consequences, such as neuronal death, neuronal injury, and alterations in neuronal networks. Consequently, there is growing interest in identifying biomarkers that can demonstrate and quantify the extent of neuronal and glial injury. Despite numerous studies conducted on animal models of status epilepticus, which clearly indicate seizure-induced neuronal and glial injury, as well as signs of atrophy and gliosis, evidence in humans remains limited to case reports and small case series. The implications of identifying such biomarkers in clinical practice are significant, including improved prognostic stratification of patients and the early identification of those at high risk of developing irreversible complications. Moreover, the clinical validation of these biomarkers could be crucial in promoting neuroprotective strategies in addition to antiseizure medications. In this study, we present a systematic review of research on biomarkers of neuro-glial injury in patients with status epilepticus.

The outcome of early life status epilepticus—lessons from laboratory animals

Status epilepticus (SE) is the most common neurologic emergency in children. Both clinical and laboratory studies have demonstrated that SE in early life can cause brain damage and permanent behavioral abnormalities, trigger epileptogenesis, and interfere with normal brain development. In experimental rodent models, the consequences of seizures are dependent upon age, the model used, and seizure duration. In studies involving neonatal and infantile animals, the model used, experimental design, conditions during the experiment, and manipulation of animals can significantly affect the course of the experiments as well as the results obtained. Standardization of laboratory approaches, harmonization of scientific methodology, and improvement in data collection can improve the comparability of data among laboratories.

Microglia and Status Epilepticus in the Immature Brain

Microglia are the resident immune cells of the Central Nervous System (CNS), which are activated due to brain damage, as part of the neuroinflammatory response. Microglia undergo morphological and biochemical modifications during activation, adopting a pro-inflammatory or an anti-inflammatory state. In the developing brain, status epilepticus (SE) promotes microglia activation that is associated with neuronal injury in some areas of the brain, such as the hippocampus, thalamus and amygdala. However, the timing of this activation, the anatomical pattern, and the morphological and biochemical characteristics of microglia in the immature brain are age-dependent and have not been fully characterized. Therefore, this review focuses on the response of microglia to SE and its relationship to neurodegeneration.

Neurological Complications Acquired During Pediatric Critical Illness: Exploratory "Mixed Graphical Modeling" Analysis Using Serum Biomarker Levels

OBJECTIVES

Neurologic complications, consisting of the acute development of a neurologic disorder, that is, not present at admission but develops during the course of illness, can be difficult to detect in the PICU due to sedation, neuromuscular blockade, and young age. We evaluated the direct relationships of serum biomarkers and clinical variables to the development of neurologic complications. Analysis was performed using mixed graphical models, a machine learning approach that allows inference of cause-effect associations from continuous and discrete data.

DESIGN

Secondary analysis of a previous prospective observational study.

SETTING

PICU, single quaternary-care center.

PATIENTS

Individuals admitted to the PICU, younger than18 years old, with intravascular access via an indwelling catheter.

INTERVENTIONS

None.

MEASUREMENTS

About 101 patients were included in this analysis. Serum (days 1-7) was analyzed for glial fibrillary acidic protein, ubiquitin C-terminal hydrolase-L1, and alpha-II spectrin breakdown product 150 utilizing enzyme-linked immunosorbent assays. Serum levels of neuron-specific enolase, myelin basic protein, and S100 calcium binding protein B used in these models were reported previously. Demographic data, use of selected clinical therapies, lengths of stay, and ancillary neurologic testing (head CT, brain MRI, and electroencephalogram) results were recorded. The Mixed Graphical Model-Fast-Causal Inference-Maximum algorithm was applied to the dataset.

MAIN RESULTS

About 13 of 101 patients developed a neurologic complication during their critical illness. The mixed graphical model identified peak levels of the neuronal biomarker neuron-specific enolase and ubiquitin C-terminal hydrolase-L1, and the astrocyte biomarker glial fibrillary acidic protein to be the direct causal determinants for the development of a neurologic complication; in contrast, clinical variables including age, sex, length of stay, and primary neurologic diagnosis were not direct causal determinants.

CONCLUSIONS

Graphical models that include biomarkers in addition to clinical data are promising methods to evaluate direct relationships in the development of neurologic complications in critically ill children. Future work is required to validate and refine these models further, to determine if they can be used to predict which patients are at risk for/or with early neurologic complications.

Increases in GFAP immunoreactive astrocytes in the cerebellar molecular layer of young adult CBA/J mice

Background

CBA/J mice are standard experimental animals in auditory studies, and age-related changes in auditory pathways are well documented. However, changes in locomotion-related brain regions have not been systematically explored.

Results

We showed an increase in immunoreactivity for glial fibrillary acidic protein (GFAP) in the cerebellar molecular layer associated with Purkinje cells in mice at 24 weeks of age but not in the younger mice. Increased GFAP immunoreactivity appeared in the form of clusters and distributed multifocally consistent with hyperplasia of astrocytes that were occasionally associated with Purkinje cell degeneration. Three out of 12 animals at 16 and 24 weeks of age exhibited pre-convulsive clinical signs. Two of these 3 animals also showed increased GFAP immunoreactivity in the cerebellum. Rotarod behavioral assessments indicated decreased performance at 24 weeks of age.

Conclusions

These results suggest minimal to mild reactive astrocytosis likely associated with Purkinje cell degeneration in the cerebellum at 24 weeks of age in CBA/J mice. These findings should be taken into consideration prior to using this mouse strain for studying neuroinflammation or aging.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42826-021-00100-5.

[S2k guidelines: status epilepticus in adulthood : Guidelines of the German Society for Neurology]

This S2k guideline on diagnosis and treatment of status epilepticus (SE) in adults is based on the last published version from 2021. New definitions and evidence were included in the guideline and the clinical pathway. A seizures lasting longer than 5 minutes (or ≥ 2 seizures over more than 5 mins without intermittend recovery to the preictal neurological state. Initial diagnosis should include a cCT or, if possible, an MRI. The EEG is highly relevant for diagnosis and treatment-monitoring of non-convulsive SE and for the exclusion or diagnosis of psychogenic non-epileptic seizures. As the increasing evidence supports the relevance of inflammatory comorbidities (e.g. pneumonia) related clinical chemistry should be obtained and repeated over the course of a SE treatment, and antibiotic therapy initiated if indicated.Treatment is applied on four levels: 1. Initial SE: An adequate dose of benzodiazepine is given i.v., i.m., or i.n.; 2. Benzodiazepine-refractory SE: I.v. drugs of 1st choice are levetiracetam or valproate; 3. Refractory SE (RSE) or 4. Super-refractory SE (SRSE): I.v. propofol or midazolam alone or in combination or thiopental in anaesthetic doses are given. In focal non-convulsive RSE the induction of a therapeutic coma depends on the circumstances and is not mandatory. In SRSE the ketogenic diet should be given. I.v. ketamine or inhalative isoflorane can be considered. In selected cased electroconvulsive therapy or, if a resectable epileptogenic zone can be defined epilepsy surgery can be applied. I.v. allopregnanolone or systemic hypothermia should not be used.

Cerebrospinal fluid and blood biomarkers of status epilepticus

Status epilepticus is a condition resulting either from the failure of the mechanisms responsible for seizure termination or from the initiation of mechanisms that lead to abnormally prolonged seizures and require urgent administration of antiepileptic drugs. Refractory status epilepticus requires anesthetics drugs and may lead to brain injury with molecular and cellular alterations (eg, inflammation, and neuronal and astroglial injury) that could induce neurologic sequels and further development of epilepsy. Outcome scores based on demographic, clinical, and electroencephalography (EEG) condition are available, allowing prediction of the risk of mortality, but the severity of brain injury in survivors is poorly evaluated. New biomarkers are needed to predict with higher accuracy the outcome of patients admitted with status in an intensive care unit. Here, we summarize the findings of studies from patients and animal models of status epilepticus. Specific protein markers can be detected in the cerebrospinal fluid and the blood. One of the first described markers of neuronal death is the neuron-specific enolase. Gliosis resulting from inflammatory responses after status can be detected through the increase of S100-beta, or some cytokines, like the High Mobility Group Box 1. Other proteins, like progranulin may reflect the neuroprotective mechanisms resulting from the brain adaptation to excitotoxicity. These new biomarkers aim to prospectively identify the severity and development of disability, and subsequent epilepsy of patients with status. We discuss the advantages and disadvantages of each biomarker, by evaluating their brain specificity, stability in the fluids, and sensitivity to external interferences, such as hemolysis. Finally, we emphasize the need for further development and validation of such biomarkers in order to better assess patients with severe status epilepticus.

Treatment of early life status epilepticus: What can we learn from animal models?

Treatment of status epilepticus (SE) in infants and children is challenging. There is a recognition that a broad set of developmental processes need to be considered to fully appreciate the physiologic complexity of severe seizures, and seizure outcomes, in infants and children. The development and use of basic models to elucidate important mechanisms will help further our understanding of these processes. Here we review some of the key experimental models and consider several areas relevant to treatment that could lead to productive translational research. Terminating seizures quickly is essential. Understanding pharmacoresistance of SE as it relates to receptor trafficking will be critical to seizure termination. Once a severe seizure is terminated, how will the developing brain respond? Basic studies suggest that there are important acute and long‐term histopathologic, and pathophysiologic, consequences that, if left unaddressed, will produce long‐lasting deficits on the form and function of the central nervous system. To fully utilize the evidence that basic models produce, age‐ and development‐ and model‐specific frameworks have to be considered carefully. Studies have demonstrated that severe seizures can cause perturbations to developmental processes during critical periods of development that lead to life‐long deficits. Unfortunately, some of the drugs that are commonly used to treat seizures may also produce negative outcomes by enhancing Cl^‐‐mediated depolarization, or by accelerating programmed cell death. More research is needed to understand these phenomena and their relevance to the human condition, and to develop rational drugs that protect the developing brain from severe seizures to the fullest extent possible.

Ictal Interictal Continuum Patterns

PURPOSE OF REVIEW

To present data available on the epidemiology and significance of rhythmic and periodic patterns that lie on the ictal interictal continuum and propose an algorithm for the clinical approach to patients exhibiting these patterns.

RECENT FINDINGS

There is accumulating evidence on the prognostic implications of various rhythmic and periodic patterns in the critically ill population. These patterns are not only associated with increased seizure risk but have also been associated with worse outcome and increased long-term risk of epilepsy in recent studies. There is emerging evidence suggesting that certain EEG features as well as ancillary studies including serum, neuroimaging, and invasive multimodality monitory can assist in the risk stratification of neuronal injury associated with these patterns, allowing for a targeted approach to these patterns. We present a case illustrating the clinical nuances of these patterns. We propose an algorithm for a personalized and targeted approach to ictal interictal patterns based on risk stratification according to clinical, EEG, imaging, and invasive monitoring markers.

Jobelyn® Supplement Lowered Neuronal Degeneration: Significance of Altered p53 and ɤ-Enolase Protein Expressions in Prefrontal Cortex of Rat Exposed to Ethanol

BACKGROUND

Alcohol-induced neurodegeneration, a consequence of chronic ethanol exposure, is a neuroadaptation that drives the progression of alcohol use disorder (AUD). Unfortunately, conventional drugs for AUDs do not prevent neurodegeneration as part of their pharmacological repertoire. Multimodal neuroprotective therapeutic agents are hypothesized to have high therapeutic utility in the treatment of central nervous system. Interestingly, nutraceuticals by nature are multimodal in mechanisms of action.

PURPOSE

This study examined the neuroprotective potential of Jobelyn in prefrontal cortex (PFC) of a binge-alcohol rat model of AUD.

METHODS

Three groups of rats were fed thrice daily through an orogastric tube with 5 g/kg ethanol (25% w/v), 5 g/kg ethanol (25% w/v) plus Jobelyn (4 mg/kg body weight), and 5 g/kg of a nutritionally complete diet (50% v/v), respectively. Cytoarchitectural study of the PFC was done in slides stained with haematoxylin and eosin. Immunohistochemical analyses were performed with mice monoclonal anti-p53 and anti-neuron specific enolase (NSE) antibodies to detect the degree of apoptosis and necrosis in the PFC. In addition, the degree of tissue damage and the level of lipid peroxidation were evaluated.

RESULTS

Jobelyn supplementation significantly lowered the levels of histologic and biochemical indices of neurodegeneration, and caused an increased expression of p53 protein and a decreased expression of NSE immunoreactivity (NSE-IR).

CONCLUSIONS

Jobelyn supplementation ameliorates neurodegeneration in the PFC of AUD rats by reducing the oxidative stress, reducing the NSE-IR, and by increasing the expression of cellular tumor antigen p53 in the cortical neurons.

Beneficial influence of physical exercise following status epilepticus in the immature brain of rats

Studies in adult animals have demonstrated a beneficial effect of physical exercise on epileptic insults. Although the effects of physical exercise on the mature nervous system are well documented, its influence on the developing nervous system subjected to injuries in childhood has been little explored. The purpose of our study was to investigate whether a physical exercise program applied during brain development could influence the hippocampal plasticity of rats submitted to status epilepticus (SE) induced by pilocarpine model at two different ages of the postnatal period. Male Wistar rats aged 18 (P18) and 28 (P28) days were randomly divided into four groups: Control (CTRL), Exercise (EX), SE (SE) and SE Exercise (SE/EX) (n=17 per group). After the aerobic exercise program, histological and behavioral (water maze) analyses were performed. Our results showed that only animals subjected to pilocarpine-induced SE at P28 presented spontaneous seizures during the observational period. A significant reduction in seizure frequency was observed in the SE/EX group compared to the SE group. In adulthood, animals submitted to early-life SE displayed impairment in long-term memory in the water maze task, while the exercise program reversed this deficit. Reduced mossy fiber sprouting in the dentate gyrus was noted in animals that presented spontaneous seizures (SE/EX vs SE). Exercise increased cell proliferation (Ki-67 staining) and anti-apoptotic response (bcl-2 staining) and reduced pro-apoptotic response (Bax staining) in animals of both ages of SE induction (P18/28). Exercise also modified the brain-derived neurotrophic factor (BDNF) levels in EX and SE/EX animals. Our findings indicate that in animals subjected to SE in the postnatal period a physical exercise program brings about beneficial effects on seizure frequency and hippocampal plasticity in later stages of life.

Molecular biomarkers of epileptogenesis

Epileptogenesis, a process leading to a reduced threshold for seizures after transient brain insults, as well as the mechanisms underlying the propensity to generate spontaneous epileptic seizures, are highly dynamic processes. Biomarkers--objective measures of biological processes--would be excellent tools for monitoring epileptogenesis and the dynamics of increased seizure propensity, as well as the potential to interfere, for example pharmacologically, with these key pathological aspects of epilepsy. Molecular biomarkers have revolutionized therapies, as well as response prediction and monitoring of therapies in other biomedical fields. However, high-impact molecular biomarkers are still not available in the context of epilepsy. Several factors, such as the large heterogeneity of epileptic syndromes and their underlying pathological patterns, as well as the limited availability of tissue samples, represent a particular challenge to the development of molecular biomarkers in epileptogenesis and epilepsy. However, substantial technical progress has been made recently with respect to biomarker characterization and monitoring by large throughput analysis on the genomic, mRNA, and proteomic levels, starting from minute amounts of brain tissue or body fluids, for example cerebrospinal fluid, blood, serum, or plasma. Given the substantial cellular- and network-level functional pathophysiology involved in epilepsy, it may be beneficial in the future to combine molecular analysis with other methods, such as imaging and electrophysiological biomarkers.

Behavioral impairments in rats with chronic epilepsy suggest comorbidity between epilepsy and attention deficit/hyperactivity disorder

Attention deficit/hyperactivity disorder (ADHD) is encountered among patients with epilepsy at a significantly higher rate than in the general population. Mechanisms of epilepsy-ADHD comorbidity remain largely unknown. We investigated whether a model of chronic epilepsy in rats produces signs of ADHD, and thus, whether it can be used for studying mechanisms of this comorbidity. Epilepsy was induced in male Wistar rats via pilocarpine status epilepticus. Half of the animals exhibited chronic ADHD-like abnormalities, particularly increased impulsivity and diminished attention in the lateralized reaction-time task. These impairments correlated with the suppressed noradrenergic transmission in locus coeruleus outputs. The other half of animals exhibited depressive behavior in the forced swimming test congruently with the diminished serotonergic transmission in raphe nucleus outputs. Attention deficit/hyperactivity disorder and depressive behavior appeared mutually exclusive. Therefore, the pilocarpine model of epilepsy affords a system for reproducing and studying mechanisms of comorbidity between epilepsy and both ADHD and/or depression.

When and how do seizures kill neurons, and is cell death relevant to epileptogenesis?

The effect of seizures on neuronal death and the role of seizure-induced neuronal death in acquired epileptogenesis have been debated for decades. Isolated brief seizures probably do not kill neurons; however, severe and repetitive seizures (i.e., status epilepticus) certainly do. Because status epilepticus both kills neurons and also leads to chronic epilepsy, neuronal death has been proposed to be an integral part of acquired epileptogenesis. Several studies, particularly in the immature brain, have suggested that neuronal death is not necessary for acquired epileptogenesis; however, the lack of neuronal death is difficult if not impossible to prove, and more recent studies have challenged this concept. Novel mechanisms of cell death, beyond the traditional concepts of necrosis and apoptosis, include autophagy, phagoptosis, necroptosis, and pyroptosis. The traditional proposal for why neuronal death may be necessary for epileptogenesis is based on the recapitulation of development hypothesis, where a loss of synaptic input from the dying neurons is considered a critical signal to induce axonal sprouting and synaptic-circuit reorganization. We propose a second hypothesis - the neuronal death pathway hypothesis, which states that the biochemical pathways causing programmed neurodegeneration, rather than neuronal death per se, are responsible for or contribute to epileptogenesis. The reprogramming of neuronal death pathways - if true - is proposed to derive from necroptosis or pyroptosis. The proposed new hypothesis may inform on why neuronal death seems closely linked to epileptogenesis, but may not always be.

Neuronal degeneration is observed in multiple regions outside the hippocampus after lithium pilocarpine-induced status epilepticus in the immature rat

Although hippocampal sclerosis is frequently identified as a possible epileptic focus in patients with temporal lobe epilepsy, neuronal loss has also been observed in additional structures, including areas outside the temporal lobe. The claim from several researchers using animal models of acquired epilepsy that the immature brain can develop epilepsy without evidence of hippocampal neuronal death raises the possibility that neuronal death in some of these other regions may also be important for epileptogenesis. The present study used the lithium pilocarpine model of acquired epilepsy in immature animals to assess which structures outside the hippocampus are injured acutely after status epilepticus. Sprague-Dawley rat pups were implanted with surface EEG electrodes, and status epilepticus was induced at 20 days of age with lithium pilocarpine. After 72 h, brain tissue from 12 animals was examined with Fluoro-Jade B, a histochemical marker for degenerating neurons. All animals that had confirmed status epilepticus demonstrated Fluoro-Jade B staining in areas outside the hippocampus. The most prominent staining was seen in the thalamus (mediodorsal, paratenial, reuniens, and ventral lateral geniculate nuclei), amygdala (ventral lateral, posteromedial, and basomedial nuclei), ventral premammillary nuclei of hypothalamus, and paralimbic cortices (perirhinal, entorhinal, and piriform) as well as parasubiculum and dorsal endopiriform nuclei. These results demonstrate that lithium pilocarpine-induced status epilepticus in the immature rat brain consistently results in neuronal injury in several distinct areas outside of the hippocampus. Many of these regions are similar to areas damaged in patients with temporal lobe epilepsy, thus suggesting a possible role in epileptogenesis.

IL-1β induction and IL-6 suppression are associated with aggravated neuronal damage in a lipopolysaccharide-pretreated kainic acid-induced rat pup seizure model

OBJECTIVES

Reportedly, hippocampal neuronal degeneration by kainic acid (KA)-induced seizures in rats <14 days old was enhanced by lipopolysaccharide (LPS). This study was to test the hypothesis that cytokines such as interleukin (IL)-1β, IL-6 and tumor necrosis factor-α are associated with aggravated neuronal damage.

MATERIALS AND METHODS

Sixty male Sprague-Dawley, 14-day-old rats were used. Experiments were conducted in saline, LPS + saline, saline + KA and LPS + KA groups. Intraperitoneal LPS injections (0.04 mg/kg) were administered 3 h prior to KA injection (3 mg/kg).

RESULTS

The LPS + KA group showed a tendency toward shorter latency to seizure onset (p = 0.086) and significantly longer seizure duration (p < 0.05) compared with the KA group. Induction of the proconvulsant cytokine IL-1β in rat pup brains was significantly greater in the LPS + KA group compared to the KA group (38.8 ± 5.5 vs. 9.2 ± 1.0 pg/µg; p < 0.05); however, IL-6 levels were higher in the KA group than in the LPS + KA group (108.7 ± 6.8 vs. 60.9 ± 4.7 pg/µg; p < 0.05). The difference in tumor necrosis factor-α between the LPS + KA group and the KA group was insignificant (12.1 ± 0.6 vs. 10.9 ± 2.3 pg/µg; p = 0.64).

CONCLUSIONS

Our results showed an increase in the proconvulsant cytokine IL-1β and a decrease in a potentially neuroprotective cytokine, IL-6, in rat pups treated with LPS + KA. These results warrant further investigation into the possible role of IL-1β induction and IL-6 suppression in LPS-promoted neuronal damage.

Lithium pilocarpine-induced status epilepticus in postnatal day 20 rats results in greater neuronal injury in ventral versus dorsal hippocampus

Many quantitative animal studies examining the possible relationship between hippocampal neuronal loss and the development of epilepsy have examined only the dorsal hippocampus. The ventral hippocampus, however, represents the more homologous structure to the anterior hippocampus in humans, which is the area associated with the maximal damage in patients with temporal lobe epilepsy. This study tested the hypothesis that the ventral hippocampus has greater neuronal injury than the dorsal hippocampus in an animal model of chemoconvulsant-status epilepticus at postnatal day 20. Status epilepticus was induced in postnatal day 20 Sprague-Dawley rat pups with the chemoconvulsant lithium-pilocarpine and brain tissue was examined with Fluoro-Jade B. Horizontal sections (n=7) favoring a visualization of the ventral hippocampus showed marked Fluoro-Jade B staining in CA1, CA3, and hilar region. Coronal sections favoring a visualization of the dorsal hippocampus did not consistently show as robust a staining pattern in these regions. In coronal sections where both the dorsal and ventral hippocampus could be viewed, greater staining was always seen in ventral versus dorsal hippocampus. Quantitative analysis of cell counts demonstrated a significant difference between ventral and dorsal hippocampus in CA1 and CA3, but not hilus. These results demonstrate that in ventral hippocampus, lithium pilocarpine-induced status epilepticus consistently results in hippocampal neuronal injury in postnatal day 20 rats. This study shows the importance of including the ventral hippocampus in any analysis of seizure-induced hippocampal neuronal injury, and raises concerns about the accuracy of studies quantifying hippocampal neuronal loss when only the dorsal hippocampus is examined.

Hypoxic-ischemic brain injury exacerbates neuronal apoptosis and precipitates spontaneous seizures in glucose transporter isoform 3 heterozygous null mice

We examined the effects of 45-min hypoxia (FiO(2) 0.08; Hx) vs. normoxia (FiO(2) 0.21; Nx) on the ipsilateral (Ipsi) and contralateral (Ctrl) sides of the brain in neuronal glucose transporter isoform 3 (Glut3) heterozygous null mice (glut3(+/-)) and their wild-type littermates (WT), undergoing unilateral carotid artery ligation. Glut3(+/-) mice, under Nx, demonstrated a compensatory increase in blood-brain barrier/glial Glut1 protein concentration and a concomitant increase in neuronal nitric oxide synthase (nNOS) enzyme activity and Bax protein, with a decrease in procaspase 3 protein (P < 0.05 each). After Hx, reoxygenation in FiO(2) of 0.21 led to no comparable adaptive up-regulation of the ipsilateral brain Glut3 or Glut1 protein at 4 hr and Glut1 at 24 hr in glut3(+/-) vs. WT. These brain Glut changes in glut3(+/-) but not WT mice were associated with an increase in proapoptotic Bax protein and caspase-3 enzyme activity (P < 0.01 each) and a decline in the antiapoptotic Bcl-2 and procaspase-3 proteins (P < 0.05 each). Glut3(+/-) mice after Hx demonstrated TUNEL-positive neurons with nuclear pyknosis in most ipsilateral (hypoxic-ischemia) brain regions. A subset (∼55%) of glut3(+/-) mice developed spontaneous seizures after hypoxic-ischemia, confirmed by electroencephalography, but the WT mice remained seizure-free. Pentylenetetrazole testing demonstrated an increased occurrence of longer lasting clinical seizures at a lower threshold in glut3(+/-) vs. WT mice, with no detectable differences in monamine neurotransmitters. We conclude that hypoxic-ischemic brain injury in glut3(+/-) mice exacerbates cellular apoptosis and necrosis and precipitates spontaneous seizures.

Proteomic profiling of the epileptic dentate gyrus

The development of epilepsy is often associated with marked changes in central nervous system cell structure and function. Along these lines, reactive gliosis and granule cell axonal sprouting within the dentate gyrus of the hippocampus are commonly observed in individuals with temporal lobe epilepsy (TLE). Here we used the pilocarpine model of TLE in mice to screen the proteome and phosphoproteome of the dentate gyrus to identify molecular events that are altered as part of the pathogenic process. Using a two-dimensional gel electrophoresis-based approach, followed by liquid chromatography-tandem mass spectrometry, 24 differentially expressed proteins, including 9 phosphoproteins, were identified. Functionally, these proteins were organized into several classes, including synaptic physiology, cell structure, cell stress, metabolism and energetics. The altered expression of three proteins involved in synaptic physiology, actin, profilin 1 and α-synuclein was validated by secondary methods. Interestingly, marked changes in protein expression were detected in the supragranular cell region, an area where robust mossy fibers sprouting occurs. Together, these data provide new molecular insights into the altered protein profile of the epileptogenic dentate gyrus and point to potential pathophysiologic mechanisms underlying epileptogenesis.

Do single seizures cause neuronal death in the human hippocampus?

The question of whether repeated single seizures cause neuronal death in the adult human brain is of great clinical importance and might have broad therapeutic implications. Reviewed here are recent studies on the effects of repeated single seizures (in the absence of status epilepticus) on hippocampal volume and on neuronal death markers in blood and in surgically ablated hippocampi.

Acute neuroprotection to pilocarpine-induced seizures is not sustained after traumatic brain injury in the developing rat

Following CNS injury there is a period of vulnerability when cells will not easily tolerate a secondary insult. However recent studies have shown that following traumatic brain injury (TBI), as well as hypoxic-ischemic injuries, the CNS may experience a period of protection termed "preconditioning." While there is literature characterizing the properties of vulnerability and preconditioning in the adult rodent, there is an absence of comparable literature in the developing rat. To determine if there is a window of vulnerability in the developing rat, post-natal day 19 animals were subjected to a severe lateral fluid percussion injury followed by pilocarpine (Pc)-induced status epilepticus at 1, 6 or 24 h post TBI. During the first 24 h after TBI, the dorsal hippocampus exhibited less status epilepticus-induced cell death than that normally seen following Pc administration alone. Instead of producing a state of hippocampal vulnerability to activation, TBI produced a state of neuroprotection. However, in a second group of animals evaluated 20 weeks post injury, double-injured animals were statistically indistinguishable in terms of seizure threshold, mossy fiber sprouting and cell survival when compared to those treated with Pc alone. TBI, therefore, produced a temporary state of neuroprotection from seizure-induced cell death in the developing rat; however, this ultimately conferred no long-term protection from altered hippocampal circuit rearrangements, enhanced excitability or later convulsive seizures.

Inflammation in rat pups subjected to short hyperthermic seizures enhances brain long-term excitability

Inflammatory processes in response to infection are involved in the pathophysiological mechanisms of febrile seizures (FS). Prolonged FS may promote the development of temporal lobe epilepsy. It has been shown in rats that prolonged hyperthermic seizures (HS) are followed by long-term modification of brain excitability. To examine whether short FS results in modification of brain excitability, we induced an inflammatory response in combination with short HS.

METHODS

HS were induced in rat pups at either P11 or P16 using a heating lamp with a continuous monitoring of the core temperature. Rat pups were maintained at the temperature seizure threshold during 5 min. In order to induce an inflammatory response, lipopolysaccharide (LPS, Eschericha coli 055:B5) was injected i.p. at 5 microg/kg or 50 microg/kg, 2h prior seizure induction. After 1 month, pentylenetetrazol threshold (PTZth) was used to assess the change of brain excitability. Histological studies were performed 24h after the FS (Fluorojade-B) and after the PTZth (cresyl violet).

RESULTS

The temperature thresholds to induce the seizures were not different among the groups. The PTZth was not significantly different between sham and FS only groups, and decreased dose-dependently when LPS was combined to FS. Histological studies suggested the absence of cell injury.

CONCLUSION

Lower PTZth obtained by using LPS in combination with HS in rat pups suggests a change in brain excitability. Our model with only 5 min of HS in combination with LPS suggests that an inflammatory response could, in part, explain long-term change in brain excitability following short FS.

Immunocytochemistry of neuron specific enolase (NSE) in the rat brain after single and repeated epileptic seizures

The aim of this study was to investigate neuron-specific enolase (NSE) immunoreactivity of the different brain regions after pentylenetetrazol (PTZ)- induced epileptic seizures in rats. Light microscopic examinations provided evidences for changes of neuronal activity after single and repeated seizures. The number of NSE (+) cells was well correlated with Nissl staining. The results suggest that NSE immunoreactivity may be a valuable marker for determination of the number of metabolically active neurons in different brain regions after single and repeated experimental seizures.

Age- and region-dependent patterns of Ca2+ accumulations following status epilepticus

Elevated Ca(2+) concentrations have been implicated in cell death mechanisms following seizures, however, the age and brain region of intracellular Ca(2+) accumulations [Ca(2+)](i), may influence whether or not they are toxic. Therefore, we examined regional accumulations of (45)Ca(2+) by autoradiography from rats of several developmental stages (P14, P21, P30 and P60) at 5, 14, and 24h after status epilepticus. To determine whether the uptake was intracellular, Ca(2+) was also assessed in hippocampal slices with the dye indicator, Fura 2AM at P14. Control animals accumulated low homogeneous levels of (45)Ca(2+); however, highly specific and age-dependent patterns of (45)Ca(2+) uptake were observed at 5h. (45)Ca(2+) accumulations were predominant in dorsal hippocampal regions, CA1/CA2/CA3a, in P14 and P21 rats and in CA3a and CA3c neurons of P30 and P60 rats. Selective midline and amygdala nuclei were marked at P14 but not at P21 and limbic accumulations recurred with maturation that were extensive at P30 and even more so at P60. At 14 h, P14 and P21 rats had no persistent accumulations whereas P30 and P60 rats showed persistent uptake patterns within selective amygdala, thalamic and hypothalamic nuclei, and other limbic cortical regions that continued to differ at these ages. For example, piriform cortex accumulation was highest at P60. Fura 2AM imaging at P14 confirmed that Ca(2+) rises were intracellular and occurred in both vulnerable and invulnerable regions of the hippocampus, such as CA2 pyramidal and dentate granule cells. Silver impregnation showed predominant CA1 injury at P20 and P30 but CA3 injury at P60 whereas little or no injury was found in extrahippocampal structures at P14 and P20 but was modest at P30 and maximal at P60. Thus, at young ages there was an apparent dissociation between high (45)Ca(2+) accumulations and neurotoxicity whereas in adults a closer relationship was observed, particularly in the extrahippocampal structures.

Effects of early-life LiCl-pilocarpine-induced status epilepticus on memory and anxiety in adult rats are associated with mossy fiber sprouting and elevated CSF S100B protein

PURPOSE

This study investigated putative correlations among behavioral changes and: (1) neuronal loss, (2) hippocampal mossy fiber sprouting, and (3) reactive astrogliosis in adult rats submitted to early-life LiCl-pilocarpine-induced status epilepticus (SE).

METHODS

Rats (P15) received LiCl (3 mEq/kg, i.p.) 12-18 h prior pilocarpine (60 mg/kg; s.c.). At adulthood, animals were submitted to behavioral tasks and after the completion of tasks biochemical and histological analysis were performed.

RESULTS

In SE group, it was observed an increased number of degenerating neurons in the CA1 subfield and in the hilus of animals 24 h after SE. At adulthood, SE group presented an aversive memory deficit in an inhibitory avoidance task and the animals that presented lower latency to the step down showed a higher score for mossy fiber sprouting. In the light-dark exploration task, SE rats returned less and spent less time in the light compartment and present an increased number of risk assessment behavior (RA). There was a negative correlation between the time spent in the light compartment and the score for mossy fiber sprouting and a positive correlation between score for mossy fiber sprouting and number of RA. LiCl-pilocarpine-treated animals showed higher levels of S100B immunocontent in the CSF as well as a positive correlation between the score for sprouting and the GFAP immunocontent in the CA1 subfield, suggesting an astrocytic response to neuronal injury.

CONCLUSIONS

We showed that LiCl-pilocarpine-induced SE during development produced long-lasting behavioral abnormalities, which might be associated with mossy fiber sprouting and elevated CSF S100B levels at adulthood.

Inflammation exacerbates seizure-induced injury in the immature brain

We examined the hypothesis that the introduction of an inflammatory agent would augment status epilepticus (SE)-induced neuronal injury in the developing rat brain in the absence of an increase in body temperature. Postnatal day 7 (P7) and P14 rat pups were injected with an exogenous provocative agent of inflammation, lipopolysaccharide (LPS), 2 h prior to limbic SE induced by either lithium-pilocarpine (LiPC) or kainic acid. Core temperature was recorded during the SE and neuronal injury was assessed 24 h later using profile cell counts in defined areas of the hippocampus. While LPS by itself did not produce any discernible cell injury at either age, it exacerbated hippocampal damage induced by seizures. In the LiPC model, this effect was highly selective for the CA1 subfield, and there was no concomitant rise in body temperature. Our findings show that inflammation increases the vulnerability of immature hippocampus to seizure-induced neuronal injury and suggest that inflammation might be an important factor aggravating the long-term outcomes of seizures occurring early in life.

Do seizures affect the developing brain? Lessons from the laboratory

Laboratory models of prolonged seizures and status epilepticus in developing animals demonstrate age- and model-dependent propensity for brain injury. Even in models without overt brain injury, plasticity, which leads to epileptogenicity as well as to behavioral and cognitive effects, has been demonstrated. Brief, recurrent seizures in the neonatal period not only appear to exhibit plasticity that can be anatomically and physiologically meaningful but also seem to produce cognitive deficits. Translation of these findings into clinical practice is limited by the effects chronic therapy may have on brain development. There is little evidence that available treatments can effectively alter epileptogenesis. However, it is widely agreed that prolonged seizures and status epilepticus can carry negative consequences. Preventing epileptogenesis remains an important goal to modify the development of comorbidities, and it represents an area of research in need of much progress. For now, prevention of prolonged seizures with early intervention is important and is the most effective available option to minimize the potential short- and long-term adverse effects of prolonged seizures and optimize patient outcomes.

Advances in the management of seizures and status epilepticus in critically ill patients

Seizures and status epilepticus are common in critically ill patients. They can be difficult to recognize because most are non-convulsive and require electroencephalogram monitoring to detect; hence, they are currently underdiagnosed. Early recognition and treatment are essential to obtain maximal response to first-line treatment and to prevent neurologic and systemic sequelae. Anti-seizure medication should be combined with management of the underlying cause and reversal of factors that can lower the seizure threshold, including many medications, fever, hypoxia, and metabolic imbalances. This article discusses specific treatments and specific situations, such as hepatic and renal failure patients and organ transplant patients.

Inflammation contributes to seizure-induced hippocampal injury in the neonatal rat brain

OBJECTIVE

The extent of neuronal injury in the hippocampus produced by experimental status epilepticus (SE) is age dependent and is not readily demonstrable in many models of neonatal seizures. Neonatal seizures often occur in clinical settings that include an inflammatory component. We examined the potential contributory role of pre-existing inflammation as an important variable in mediating neuronal injury.

MATERIALS AND METHODS

Postnatal day 7 (P7) and P14 rat pups were injected with lipopolysaccharide (LPS), 2 h prior to SE induced by lithium-pilocarpine (LiPC). Neuronal injury was assessed by well-described histologic methods.

RESULTS

While LPS by itself did not produce any discernible cell injury at either age, this treatment exacerbated hippocampal damage induced by LiPC-SE. The effect was highly selective for the CA1 subfield.

CONCLUSIONS

Inflammation can contribute substantially to the vulnerability of immature hippocampus to seizure-induced neuronal injury. The combined effects of inflammation and prolonged seizures in early life may impact long-term outcomes of neonatal seizures.

Lateral fluid percussion injury in the developing rat causes an acute, mild behavioral dysfunction in the absence of significant cell death

Lateral fluid percussion injury (LFP), a model of mild-moderate concussion, leads to the temporary loss of the capacity for experience-dependent plasticity in developing rats. To determine if this injury-induced loss in capacity for plasticity is due to cell death, we conducted stereological measurements within the cerebral cortex and CA3 of the hippocampus 2 weeks following mild, moderate or severe LFP in the post-natal day 19 (P19) rat. Results indicated that there was no significant change in the absolute number of neurons, regardless of injury severity, in either the ipsilateral cortex (sham = 10.6 +/- 1.7, mild = 11.5 +/- 2.1, moderate = 10.0 +/- 1.0, severe = 10.9 +/- 1.3 million neurons) or CA3 region of the hippocampus (sham = 251 +/- 38, mild = 289 +/- 2, moderate = 245 +/- 48, severe = 255 +/- 62 thousand neurons). Even though there was no evidence of a significant degree of injury-induced cell death, animals exhibited cognitive deficits as revealed in a Morris water maze task (MWM). The MWM results indicated that regardless of injury severity, P19-injured rats exhibited a significant increase in escape latency compared to age-matched shams (injury by day; P < 0.001) and a significant increase in the number of trials needed to reach criterion (P < 0.05). Analysis of a probe trial one week post-MWM training, however, indicated that there was no deficit in storage or recall of the learned behavior as analyzed by platform hits (sham = 2.9 +/- 0.37, mild = 2.0 +/- 0.40, moderate = 1 +/- 0, severe = 2.8 +/- 0.62) or percent time spent in, or immediately surrounding, the platform area (sham = 13.5 +/- 1.71, mild = 10.8 +/- 2.32, moderate = 12.7 +/- 0, severe = 13.5 +/- 1.69). Taken together, these results indicate that while LFP in P19-injured animals does not lead to significant cell death, it does generate acute, mild deficits in MWM performance.

Status Epilepticus in 12-day-old Rats Leads to Temporal Lobe Neurodegeneration and Volume Reduction: A Histologic and MRI Study

PURPOSE

Whether status epilepticus (SE) in early infancy, rather than the underlying illness, leads to temporal lobe neurodegeneration and volume reduction remains controversial.

METHODS

SE was induced with LiCl-pilocarpine in P12 rats. To assess acute neuronal damage, brains (five controls, five with SE) were investigated at 8 h after SE by using silver and Fluoro-Jade B staining. Some brains from the early phase were processed for electron microscopy. To assess chronic changes, brains from nine controls and 13 rats with SE at P12 were analyzed after 3 months by using histology and magnetic resonance imaging (MRI).

RESULTS

MRI analysis of the temporal lobe of adult animals with SE at P12 indicated that 23% of the rats had hippocampal, 15% had amygdaloid, and 31% had perirhinal volume reduction. Histologic analysis of sections from the MR-imaged brains correlated with the MRI data. Analysis of neurodegeneration 8 h after SE by using both silver and Fluoro-Jade B staining revealed degenerating neurons located in the same temporal lobe regions as the volume reduction in chronic samples. Electron microscopic analysis revealed irreversible ultrastructural alterations. As with the chronic histologic and MRI findings, interanimal variability was seen in the distribution and severity of acute damage.

CONCLUSIONS

Our data indicate that SE at P12 can cause acute neurodegeneration in the hippocampus as well as in the adjacent temporal lobe. It is likely that acute neuronal death contributes to volume reduction in temporal lobe regions that is detected with MRI in a subpopulation of animals in adulthood.

Hippocampal Sclerosis in Children with Lesional Epilepsy Is Influenced by Age at Seizure Onset

PURPOSE

Hippocampal sclerosis (HS) is the most common lesion underlying drug-resistant temporal lobe epilepsy. Whether HS is a developmental or acquired pathology remains unclear. Whereas HS has been causally linked to prolonged febrile convulsions in childhood, evidence also exists that it may coexist with extrahippocampal abnormalities, the concept of "dual pathology." The aims of this study were to address whether hippocampal abnormality consistent with HS (a) occurs in children with lesional extrahippocampal epilepsy, (b) is more commonly seen in association with developmental rather than acquired extrahippocampal pathologies, and (c) whether any effect of age at seizure onset is found on the occurrence of HS in lesional extrahippocampal epilepsy.

METHODS

Clinical and histopathologic data of patients having resective surgery for extrahippocampal epilepsy that included the hippocampus were investigated.

RESULTS

Twenty-nine children were retrospectively included in this study, and 21 (72%) of 29 were found to have a hippocampal abnormality consistent with HS. No relation was noted between developmental or acquired extrahippocampal pathologies and the presence of hippocampal abnormality. Children with normal hippocampi on visual histologic assessment had a significantly younger age at seizure onset (p < 0.001). Duration of epilepsy was not correlated with the presence of hippocampal abnormality.

CONCLUSIONS

Hippocampal abnormalities are seen in similar proportions with both acquired and developmental extra-hippocampal pathologies, suggesting that these abnormalities are the result of seizures from the focus that is remote from the hippocampus. In addition, children who have their initial seizure at an early age are less likely to develop seizure-induced hippocampal injury.

Perinatal seizures preferentially protect CA1 neurons from seizure-induced damage in prepubescent rats

Neonatal seizures may increase neuronal vulnerability later in life. Therefore, status epilepticus was induced with kainate (KA) during the first and second postnatal (P) weeks to determine whether early seizures shift the window of neuronal vulnerability to a younger age. KA was injected (i.p.) once (1x KA) on P13, P20 or P30 or three times (3 x KA), once on P6 and P9, and then either on P13, P20 or P30. After 1x KA, onset to behavioral seizures increased with age. Electroencephalography (EEG) showed interictal events appeared with maturation. After 3 x KA, spike number, frequency, spike amplitude, and high-frequency synchronous events and duration were increased at P13 when compared to age-matched controls. In contrast, P20 and P30 rats had decreases in EEG parameters relative to P20 and P30 rats with 1x KA despite that these animals had the same history of perinatal seizures on P6 and P9. In P13 rats with 1x KA, silver impregnation, hematoxylin/eosin and TUNEL methods showed no significant hippocampal injury and damage was minimal with 3 x KA. In contrast, P20 and P30 rats with 1x KA had robust eosinophilic or TUNEL positive labeling and preferential accumulation of silver ions within inner layer CA1 neurons. After 3 x KA, the CA1 but not CA3 of P20 and P30 rats was preferentially protected following 3 or 6 days. Although paradoxical changes occur in the EEG with maturation, the results indicate that early perinatal seizures do not significantly shift the window of hippocampal vulnerability to an earlier age but induce a tolerance that leads to long-term neuroprotection that differentially affects endogenous properties of CA1 versus CA3 neurons.

Seizures, not hippocampal neuronal death, provoke neurogenesis in a mouse rapid electrical amygdala kindling model of seizures

PURPOSE

Proliferation of neural precursors adjacent to the granule cell layer of the dentate gyrus has been identified in previous epilepsy models. Convincingly demonstrating that seizure activity is the stimulant for neurogenesis, rather than neuronal death or other insults inherent to seizure models, is difficult. To address this we derived a rapid electrical amygdala kindling model in mice known to be resistant to seizure-induced neuronal death as an experimental model of focal seizures and to analyze subsequent neurogenesis.

METHODS

Mice were implanted with bipolar electrodes in the left amygdala and given electrical stimulation (3 s, 100 Hz, 1 ms monophasic square wave pulses every 5 min, 40 in total) while being observed and graded for the development of seizures. Neurogenesis in the hippocampus was assessed by counting bromodeoxyuridine-immunoreactive cells co-labeled for astrocyte (glial fibrillary acidic protein) and neuronal nuclear markers.

RESULTS

Bromodeoxyuridine-reactive cell numbers were three-fold higher in stimulated mice compared with controls at 1 week in the subgranular region and at three weeks extensive co-labeling with neuronal nuclear was noted in cells which had migrated into the body of the granule cell layer, while mice receiving stimulation but failing to kindle did not differ significantly from controls. No increase in neuronal death was detected by terminal deoxynucleotidyl transferase-mediated digoxigenin-11-dUTP nick end labeling, Fluorojade or fluorescent examination of hematoxylin and eosin-stained sections in any inter-group comparison.

CONCLUSIONS

We propose that this kindling paradigm, not previously applied to mice, demonstrates more convincingly than previously the surge in neurogenesis in response to seizures, and the effects of seizures alone in regard to neuronal injury and regeneration.

Continuous electroencephalogram monitoring in critically ill patients

The past few years have witnessed remarkable advances in continuous EEG monitoring (cEEG). The indications and applications for cEEG are broadening, including detection of nonconvulsive seizures, spell characterization, and prognostication. Seizures are common in the critically ill, are usually nonconvulsive, and can easily be missed without cEEG. Interpretation and clinical management of the complex periodic and rhythmic EEG patterns commonly identified in these patients require further study. With the use of quantitative analysis techniques, cEEG can detect cerebral ischemia very early, before permanent neuronal injury occurs. This article reviews the indications and recent advances in cEEG in critically ill patients. Continuous brain monitoring with cEEG is rapidly becoming the standard of care in critically ill patients with neurologic impairment.

Changes of cortical interhemispheric responses after status epilepticus in immature rats

PURPOSE

To study cortical excitability after status epilepticus induced in two age groups of immature rats.

METHODS

Lithium-pilocarpine status epilepticus was elicited in 12- (SE12) or 25-day-old (SE25) rats. Control siblings received saline instead of pilocarpine. Interhemispheric responses were elicited by stimulation of sensorimotor region of cerebral cortex 3, 6, 9, 13, or 26 days after status. Single biphasic pulses with intensities from 0.2 to 4 mA were used for stimulation; eight responses were always averaged. Amplitude of the first positive and negative waves (i.e., monosynaptic transcallosal responses) was measured and used for construction of input-output (I/O) curves. FluoroJade B was used to visualize degenerating neurons 24 h after status in both age groups.

RESULTS

No significant changes were found at short intervals, but only a tendency to lower amplitudes 3 days after status in SE12 group. Marked changes appeared 26 days after status. The younger group exhibited lower amplitudes than did control rats, whereas SE25 animals generated responses with higher amplitude than did controls (i.e., the I/O curve was steeper. FluoroJade B-positive neurons were scarce in SE12 rats, whereas a substantial number of positive neurons was found in SE25 animals. The positive neurons exhibited characteristics of interneurons, and their distribution in cortical layers differed in the two groups.

CONCLUSIONS

Status epilepticus resulted in neuronal death in both SE12 and SE25 animals. Changes in transcallosal evoked potentials were opposite in the two age groups. Augmented amplitude of responses in SE25 rats may indicate an increased cortical excitability.

Which EEG Patterns Warrant Treatment in the Critically Ill? Reviewing the Evidence for Treatment of Periodic Epileptiform Discharges and Related Patterns

Continuous electroencephalographic monitoring in critically ill patients has improved detection of nonconvulsive seizures and periodic discharges, but when and how aggressively to treat these electrographic patterns is unclear. A review of the literature was conducted to understand the nature of periodic discharges and the strength of the data on which management recommendations have been based. Periodic discharges are seen from a wide variety of etiologies, and the discharges themselves are electrographically heterogeneous. This spectrum suggests a need to consider these phenomena along a continuum between interictal and ictal, but more important clinically is the need to consider the likelihood of neuronal injury from each type of discharge in a given clinical setting. Recommendations for treatment are given, and a modification to current criteria for the diagnosis of nonconvulsive seizures is suggested.

Neuropathology of seizures in the immature rabbit

Acute morphologic changes of brain due to chemically induced seizures are studied in developing rabbits. Accordingly, rabbits of postnatal days 6 and 7 (p6-7) and p10-12 are injected with a single dose of 1-6 mg/kg kainic acid (KA) intraperitoneally (i.p.) or injected with a single dose of 200-300 mg/kg pilocarpine subcutaneously (s.c.). Many animals developed seizures of varying severity and length. Histologic examination of brain 2 days following injection showed that KA-induced seizures did not cause neuronal death. Pilocarpine-induced seizures resulted in neuronal death mainly involving the CA1 region of hippocampus. In the p6-7 group, only a small number of brains were involved, lesions were mild and limited to CA1. In the p10-12 group, majority of the brains were damaged, lesions were relatively severe, and in some brains extended beyond the CA1 region involving the subiculum, CA3, cortex, and amygdala. Measurements of physiologic parameters indicate that these changes were not secondary to hypoxemia during seizures. However, there was hypotension and hyperthermia, both of which may contribute to brain damage during seizures. The findings suggest that pilocarpine-induced seizures during the second postnatal week in rabbits is a useful model to study the morphologic changes of brain due to seizure in the developing animal and also to assess the systemic physiologic alterations during seizures.