Do epileptic seizures damage the brain?:

Functional definition of seizure provides new insight into post-traumatic epileptogenesis

Experimental animals’ seizures are often defined arbitrarily based on duration, which may lead to misjudgement of the syndrome and failure to develop a cure. We employed a functional definition of seizures based on the clinical practice of observing epileptiform electrocorticography and simultaneous ictal behaviour, and examined post-traumatic epilepsy induced in rats by rostral parasagittal fluid percussion injury and epilepsy patients evaluated with invasive monitoring. We showed previously that rostral parasagittal fluid percussion injury induces different types of chronic recurrent spontaneous partial seizures that worsen in frequency and duration over the months post injury. However, a remarkable feature of rostral parasagittal fluid percussion injury is the occurrence, in the early months post injury, of brief (<2 s) focal, recurrent and spontaneous epileptiform electrocorticography events (EEEs) that are never observed in sham-injured animals and have electrographic appearance similar to the onset of obvious chronic recurrent spontaneous partial seizures. Simultaneous epidural-electrocorticography and scalp-electroencephalography recordings in the rat demonstrated that these short EEEs are undetectable by scalp electrocorticography. Behavioural analysis performed blinded to the electrocorticography revealed that (i) brief EEEs lasting 0.8–2 s occur simultaneously with behavioural arrest; and (ii) while behavioural arrest is part of the rat's behavioural repertoire, the probability of behavioural arrest is greatly elevated during EEEs. Moreover, spectral analysis showed that EEEs lasting 0.8–2 s occurring during periods of active behaviour with dominant theta activity are immediately followed by loss of such theta activity. We thus conclude that EEEs lasting 0.8–2 s are ictal in the rat. We demonstrate that the assessment of the time course of fluid percussion injury-induced epileptogenesis is dramatically biased by the definition of seizure employed, with common duration-based arbitrary definitions resulting in artificially prolonged latencies for epileptogenesis. Finally, we present four human examples of electrocorticography capturing short (<2 s), stereotyped, neocortically generated EEEs that occurred in the same ictal sites as obvious complex partial seizures, were electrographically similar to rat EEEs and were not noted during scalp electroencephalography. When occurring in the motor cortex, these short EEEs were accompanied by ictal behaviour detectable with simultaneous surface electromyography. These data demonstrate that short (<2 s) focal recurrent spontaneous EEEs are seizures in both rats and humans, that they are undetectable by scalp electroencephalography, and that they are typically associated with subtle and easily missed behavioural correlates. These findings define the earliest identifiable markers of progressive post-traumatic epilepsy in the rat, with implications for mechanistic and prophylactic studies, and should prompt a re-evaluation of the concept of post-traumatic silent period in both animals and humans.

Pilocarpine vs. lithium-pilocarpine for induction of status epilepticus in mice: development of spontaneous seizures, behavioral alterations and neuronal damage

In recent years, the pilocarpine model of temporal lobe epilepsy has become the most popular and widely used rodent model of this common and difficult-to-treat type of epilepsy. In this model, the cholinomimetic convulsant pilocarpine is used to induce a status epilepticus, which is followed by hippocampal damage and development of spontaneous recurrent seizures. In rats, pilocarpine is either administered alone or in combination with lithium, which allows a conspicuous reduction of the pilocarpine dose required to induce status epilepticus and results in a higher percentage of animals developing status epilepticus. In mice, lithium has only rarely been used in association with pilocarpine, which prompted us to directly compare the pilocarpine and lithium-pilocarpine models in this species. In contrast to rats, pretreatment with lithium in mice did not potentiate the convulsant effect of pilocarpine. The sequence of behavioral changes observed in mice undergoing a status epilepticus was very similar for lithium-pilocarpine compared to pilocarpine administered alone. All mice that survived status epilepticus developed epilepsy with spontaneous recurrent seizures. Epileptic mice exhibited significant increases of anxiety-related behavior and impaired learning and memory. Neuronal damage resulting from status epilepticus was essentially similar in the lithium-pilocarpine and pilocarpine models and was characterized by severe neurodegeneration in the hippocampal formation, resembling hippocampal sclerosis in mesial temporal lobe epilepsy. Mice in which pilocarpine or lithium-pilocarpine did not induce status epilepticus but only single brief seizures did not show any significant differences in behavior, spatial learning or hippocampal histology from controls. Our data demonstrate that the syndromes produced by pilocarpine and lithium-pilocarpine in mice are behaviorally and neuropathologically indistinguishable, and that both models can be used to study the relationship between seizures, neuronal damage and psychopathology.

Neurons that fire together also conspire together: is normal sleep circuitry hijacked to generate epilepsy?

Brain circuits oscillate during sleep. The same circuits appear to generate pathological oscillations. In this review, we discuss recent advances in our understanding of how epilepsy co-opts normal, sleep-related circuits to generate seizures.

Preservation of mitochondrial integrity and energy metabolism during experimental status epilepticus leads to neuronal apoptotic cell death in the hippocampus of the rat

Status epilepticus results in mitochondrial damage or dysfunction and preferential neuronal cell loss in the hippocampus. Since a critical determinant of the eventual cell death fate resides in intracellular ATP concentration, we investigated whether mitochondrial integrity and level of energy metabolism are related with apoptotic cell death in specific hippocampal neuronal populations. A kainic acid (KA)-induced experimental temporal lobe status epilepticus model was used. Qualitative and quantitative analysis of DNA fragmentation, TUNEL immunohistochemistry, double immunofluorescence staining for activated caspase-3, electron microscopy or measurement of ATP level in the bilateral hippocampus was carried out 1, 3 or 7 days after microinjection unilaterally of a low dose of KA (0.5 nmol) into the CA3 hippocampal subfield. Characteristic biochemical (DNA fragmentation), histochemical (TUNEL or activated caspase-3 staining) or ultrastructural (electron microscopy) features of apoptotic cell death were presented bilaterally in the hippocampus 7 days after the elicitation of sustained hippocampal seizure activity by microinjection of KA into the unilateral CA3 subfield. At the same time, CA3 or CA1 subfield on either side manifested a maintained ATP level; alongside relatively intact mitochondria, rough endoplasmic reticulum, Golgi apparatus or cytoplasmic membrane in hippocampal neurons that exhibited ultrastructural features of apoptotic cell death. Our results demonstrated that preserved mitochondrial ultrastructural integrity and maintained energy metabolism during experimental temporal lobe status epilepticus is associated specifically with apoptotic, not necrotic, cell death in hippocampal CA3 or CA1 neurons.

Non-convulsive status epilepticus; the rate of occurrence in a general hospital

BACKGROUND

Non-convulsive status epilepticus (NCSE) has been increasingly recognized as a cause of impaired level of consciousness in the ICU and emergency rooms. The diagnosis can be easily missed without an electroencephalogram (EEG) given the paucity of overt clinical signs in this condition. Recently few published data estimated the prevalence to be between 3% and 8%.

OBJECTIVE

To assess the rate of occurrence of NCSE among patients with various degrees of impaired consciousness referred to the Neurophysiology Laboratory at Vancouver General Hospital.

METHOD

We conducted a retrospective analysis of 451 adult patients (>16 years of age) with a question of NCSE or with an unknown cause of impaired level of consciousness between the years 2002 and 2004. NCSE was defined according to the Young's criteria of electrographic status epilepticus. NCSE was categorized into focal and generalized epileptic activity based on the continuous EEG monitoring (CEEG). Further analysis of age, gender and etiology was performed.

RESULTS

Of 451 patients, EEG demonstrated electrographic status epilepticus with no overt clinical signs in 42 patients (9.3%). Median age was 61.8 years (range 21-94). According to etiology, 38.1% of patients with NCSE had hypoxic-anoxic injury, 19% had intracerebral hemorrhage (including trauma), 11.9% had the diagnosis of idiopathic or cryptogenic epilepsy, 7.1% had ischemic stroke, 4.8% were secondary to tumors and 4.8% to viral encephalitis.

CONCLUSION

The rate of occurrence of NCSE in patients with decreased level of consciousness was 9.3%. The cohort represented a group of patients who were comatose and required assisted ventilation or had altered level of consciousness. Hypoxic brain injury was the most responsible etiology of NCSE in the cohort studied.

Human herpes virus 6B: a possible role in epilepsy?

Human herpes virus 6 (HHV6) infection is nearly ubiquitous in childhood and may include central nervous system invasion. There are two variants, HHV6A and HHV6B. Usually asymptomatic, it is associated with the common, self-limited childhood illness roseola infantum and rarely with more severe syndromes. In patients with immune compromise, subsequent reactivation of viral activity may lead to severe limbic encephalitis. HHV6 has been identified as a possible etiologic agent in multiple sclerosis, myocarditis, and encephalitis. A preponderance of evidence supports an association between HHV6 and febrile seizures. An ongoing multicenter study is investigating possible links between HHV6 infection, febrile status epilepticus, and development of mesial temporal sclerosis (MTS). Investigation of temporal lobectomy specimens showed evidence of active HHV6B but not HHV6A replication in hippocampal astrocytes in about two-thirds of patients with MTS but not other causes of epilepsy. It has been suggested that HHV6B may cause "excitotoxicity" by interfering with astrocyte excitatory amino acid transport. Although conventional inflammatory changes are not found in most MTS specimens, inflammatory modulators may play a role in neuronal injury leading to MTS as well. If the link between early viral infection, complex or prolonged febrile seizures, and later development of intractable temporal lobe epilepsy is confirmed, new therapeutic approaches to a common intractable epilepsy syndrome may be possible.

Speech, language, and cognition in preschool children with epilepsy

We studied expressive and receptive language, oral motor ability, attention, memory, and intelligence in 20 6-year-old children with epilepsy (14 females, six males; mean age 6y 5mo, range 6y-6y 11mo) without learning disability, cerebral palsy (CP), and/or autism, and in 30 reference children without epilepsy (18 females, 12 males; mean age 6y 5mo, range 6y-6y 11mo). Ten children had partial, six primarily generalized, and four unclassified epilepsy. Fourteen were having monotherapy and six were taking two or more antiepileptic drugs; 13 children were free from seizures 3 months before the assessment. Results show no statistically significant difference between the groups concerning Verbal IQ, expressive and receptive grammar, and receptive vocabulary. The children with epilepsy had a significantly lower Performance IQ and lower scores in tests of oral motor ability, articulation, emerging literacy, auditory attention, short-term memory, and rapid word retrieval. Parent ratings revealed no significant difference in communicative ability. Polytherapy and early onset of epilepsy influenced some results. Preschool children with epilepsy without learning disability, CP, and/or autism may have receptive verbal ability within the normal range but visuoperceptual, auditory attentional, and speech-language difficulties that could affect school achievement. Careful testing of children with epilepsy who appear to be functioning within the normal range is needed because this may reveal specific impairments that require appropriate professional input.

Neuropsychiatric morbidity in focal epilepsy

BACKGROUND

Previous work has identified elevated prevalence rates for psychiatric disorders in individuals with medically refractory focal epilepsy, particularly temporal lobe epilepsy. Many studies were undertaken before the advent of video electroencephalogram monitoring (VEM) and magnetic resonance imaging (MRI).

AIMS

To investigate which characteristics of the focal epilepsy syndromes are associated with the presence of depression or psychosis.

METHOD

Three hundred and nineteen individuals with focal epilepsy admitted for VEM were seen over an 11-year period. The lifetime history of depression and psychosis, epileptic site, laterality and type of lesion were determined by clinical assessment, VEM and MRI scan.

RESULTS

There was a significant association between the prevalence of depressive symptoms and non-lesional focal epilepsy. There were no significant differences in prevalence of neuropsychiatric disorders between the groups with temporal lobe epilepsy and those with extratemporal lobe epilepsy.

CONCLUSIONS

These findings contrast with previous findings in smaller cohorts. The association between non-lesional focal epilepsy and depression may be due to the effects of a more diffuse epileptogenic area.

Diffusion tensor analysis of temporal and extra-temporal lobe tracts in temporal lobe epilepsy

OBJECTIVE

To determine whether the major temporal lobe white matter tracts in patients with temporal lobe epilepsy manifest abnormal water diffusion properties.

METHODS

Diffusion tensor MRI measurements were obtained from tractography for uncinate, arcuate, inferior longitudinal fasciculi and corticospinal tract in 13 children with left temporal lobe epilepsy and normal conventional MRI, and the data were compared to measurements in 12 age-matched normal volunteers. The relationship between tensor parameters and duration of epilepsy was also determined.

RESULTS

All four tracts in the affected left hemisphere showed lower mean anisotropy, planar and linear indices, but higher spherical index in patients versus controls. Diffusion changes in the left uncinate and arcuate fasciculus correlated significantly with duration of epilepsy. Arcuate fasciculus showed a reversal of the normal left-right asymmetry. Various diffusion abnormalities were also seen in the four tracts studied in the right hemisphere.

CONCLUSION

Our findings indicate abnormal water diffusion in temporal lobe and extra-temporal lobe tracts with robust changes in the direction perpendicular to the axons. Diffusion abnormalities associated with duration of epilepsy suggest progressive changes in ipsilateral uncinate and arcuate fasciculus due to chronic seizure activity. Finally, our results in arcuate fasciculus are consistent with language reorganization to the contralateral right hemisphere.

Decreased hippocampal volume on MRI is associated with increased extracellular glutamate in epilepsy patients

PURPOSE

Temporal lobe epilepsy (TLE) is associated with smaller hippocampal volume and with elevated extracellular (EC) glutamate levels. We investigated the relationship between the hippocampal volume and glutamate in refractory TLE patients.

METHODS

We used quantitative MRI volumetrics to measure the hippocampal volume and zero-flow microdialysis to measure the interictal glutamate, glutamine, and GABA levels in the epileptogenic hippocampus of 17 patients with medication-resistant epilepsy undergoing intracranial EEG evaluation. The relationships between hippocampal volume, neurochemical levels, and relevant clinical factors were examined.

RESULTS

Increased EC glutamate in the epileptogenic hippocampus was significantly related to smaller ipsilateral (R(2)= 0.75, p < 0.0001), but not contralateral hippocampal volume when controlled for glutamine and GABA levels, and for clinical factors known to influence hippocampal volume. Glutamate in the atrophic hippocampus was significantly higher (p = 0.008, n = 9), with the threshold for hippocampal atrophy estimated as 5 microM. GABA and glutamine levels in the atrophic and nonatrophic hippocampus were comparable. Decreased hippocampal volume was related to higher seizure frequency (p = 0.008), but not to disease duration or febrile seizure history. None of these clinical factors were related to the neurochemical levels.

CONCLUSIONS

We provide evidence for a significant association between increased EC glutamate and decreased ipsilateral epileptogenic hippocampal volume in TLE. Future work will be needed to determine whether the increase in glutamate has a causal relationship with hippocampal atrophy, or whether another, yet unknown factor results in both. This work has implications for the understanding and treatment of epilepsy as well as other neurodegenerative disorders associated with hippocampal atrophy.

Neuroprotection in epilepsy

Neuroprotection following status epilepticus should encompass not only the prevention of neuronal death, but also preservation of neuronal and network function. This is critical because these aims are not necessarily equivalent; prevention of neuronal loss, for example, does not inevitably prevent epileptogenesis. There are endogenous neuroprotective mechanisms that can serve dichotomous roles (e.g. ERK 1/2 activation can result in either neuroprotection or promote neuronal death). The roles of potential endogenous mechanisms can depend upon the pattern and timing of their activation. The simplest exogenous neuroprotective mechanism is to halt seizure activity. Other approaches consist of early NMDA receptor antagonism or later inhibition of apoptotic pathways. The problem with the latter approach is that calcium accumulation results in the activation of a number of downstream pathways, the importance of which varies from region to region and in a cell-type specific manner. Neuroprotection in epilepsy is not a straightforward concept, and we need to be clear about our eventual objectives (e.g. preventing cognitive decline). There are numerous possible approaches to neuroprotection, and the efficacy of these depends upon their timing, the specific aims and even the method of status epilepticus induction.

Neuropathology in Drosophila mutants with increased seizure susceptibility

Genetic factors are known to contribute to seizure susceptibility, although the long-term effects of these predisposing factors on neuronal viability remain unclear. To examine the consequences of genetic factors conferring increased seizure susceptibility, we surveyed a class of Drosophila mutants that exhibit seizures and paralysis following mechanical stimulation. These bang-sensitive seizure mutants exhibit shortened life spans and age-dependent neurodegeneration. Because the increased seizure susceptibility in these mutants likely results from altered metabolism and since the Na(+)/K(+) ATPase consumes the majority of ATP in neurons, we examined the effect of ATPalpha mutations in combination with bang-sensitive mutations. We found that double mutants exhibit strikingly reduced life spans and age-dependent uncoordination and inactivity. These results emphasize the importance of proper cellular metabolism in maintaining both the activity and viability of neurons.

10-year research update review: psychiatric problems in children with epilepsy

OBJECTIVE

To critically review literature published from 1996 to 2007 on psychopathology in children with epilepsy (CWE).

METHOD

Using Ovid, we searched Medline and PsychInfo databases for original studies on epidemiology, risk factors, clinical characteristics, treatment, and outcome of psychopathology in CWE, ages 0 to 18 years, using the terms "psychopathology," "emotional and behavioral problems," and "mental health problems." We selectively present the findings of studies that are clinically relevant to mental health professionals.

RESULTS

Psychopathology occurs in 37% to 77% of CWE, and attention, internalizing, and thought problems may be specific to epilepsy. Cognitive and linguistic deficits, as well as family factors, have moderating effects on psychopathology in CWE. The association of epilepsy-related variables, including antiepileptic drugs, with psychopathology is inconsistent in cognitively normal CWE. Children with symptomatic epilepsy and devastating epilepsy syndromes have high rates of global developmental delay, hyperactivity, and autistic symptoms. The treatment of psychopathology in CWE integrates standard psychiatric practices.

CONCLUSIONS

Epilepsy is a neuropsychiatric disorder characterized by seizures, psychopathology, cognitive, and linguistic problems. Improved early identification of CWE at risk for psychopathology, evidence-based psychiatric treatment, and multidisciplinary management strategies would advance clinical practice in this highly complex field of pediatric neuropsychiatry.

Magnetic resonance spectroscopy in animal models of epilepsy

The noninvasive localization of the epileptogenic zone continues to be a challenge in many patients that present as candidates for possible epilepsy surgery. Magnetic resonance imaging (MRI) techniques provide accurate anatomical definition, but despite their high resolution, these techniques fail to visualize the pathological neocortical and hippocampal changes in a sizable number of patients with focal pathologies. Further, visualized lesions on MRI may not all produce seizures. One of the keys to the understanding of the epileptogenic zone lies in the recognition of the metabolic alterations that occur in the setting of epileptic seizures. Magnetic resonance spectroscopy (MRS) is a valuable tool that can be used to study the metabolic changes seen in both acute and chronic animal models of epilepsy. Such study allows for the identification of epileptic tissue with high sensitivity and specificity. We present here a review of the use of MRS in animal models of epilepsy.

Pyruvate protects against kainate-induced epileptic brain damage in rats

Although the majority of epileptic seizures can be effectively controlled with antiepileptic drugs and/or surgery, a significant number progress to status epilepticus of sufficient duration to cause permanent brain damage. Combined treatment with antiepileptic drugs and neuroprotective agents, however, may help protect these individuals from permanent brain damage. Since toxicity induced by endogenous zinc contributes to epileptic brain injury, and since pyruvate is effective in reducing zinc-triggered neuronal death in cortical culture as well as ischemic neuronal death in vivo, we examined whether systemic pyruvate administration reduces seizure-induced brain damage. Na pyruvate (500 mg/kg) or osmolarity-matched saline (265 mg/kg NaCl, i.p.) were given to adult SD rats 30 or 150 min after 10 mg/kg kainite injection (i.p.), and there was no significant difference in the time course or severity of seizures between these groups. Zinc accumulation in neuronal cell bodies in the hippocampus, however, was much lower in the pyruvate than in the saline group. There was a close correlation between zinc accumulation and cell death, as assessed by acid-fuchsin and TUNEL staining. Pyruvate treatment markedly reduced neuronal death in the hippocampus, neocortex and thalamus. Pyruvate increased HSP-70 expression in hippocampal neurons. These results suggest that pyruvate, a natural glucose metabolite, may be useful as adjunct treatment in status epilepticus to reduce permanent brain damage.

Nonconvulsive seizures: developing a rational approach to the diagnosis and management in the critically ill population

Originally described in patients with chronic epilepsy, nonconvulsive seizures (NCSs) are being recognized with increasing frequency, both in ambulatory patients with cognitive change, and even more so in the critically ill. In fact, the majority of seizures that occur in the critically ill are nonconvulsive and can only be diagnosed with EEG monitoring. The semiology of NCSs and the associated EEG findings are quite variable. There are a number of periodic, rhythmic or stimulation-related EEG patterns in the critically ill of unclear significance and even less clear treatment implications. The field struggles to develop useful diagnostic criteria for NCSs, to standardize nomenclature for the numerous equivocal patterns, and to devise studies that will help determine which patterns should be treated and how aggressively. This review surveys the evidence for and against NCSs causing neuronal injury, and attempts to develop a rational approach to the diagnosis and management of these seizures, particularly in the encephalopathic population.

Do NMDA receptor antagonist models of schizophrenia predict the clinical efficacy of antipsychotic drugs?

N-methyl-D-aspartate (NMDA) receptor antagonists, such as ketamine and phencyclidine, induce perceptual abnormalities, psychosis-like symptoms, and mood changes in healthy humans and patients with schizophrenia. The similarity between NMDA receptor antagonist-induced psychosis and schizophrenia has led to the widespread use of the drugs to provide models to aid the development of novel treatments for the disorder. This review investigates the predictive validity of NMDA receptor antagonist models based on a range of novel treatments that have now reached clinical trials. Furthermore, it considers the extent to which the different hypotheses that have been proposed to account for the psychotomimetic effects of NMDA receptor antagonist have been validated by the results of these trials. Finally, the review discusses some of the caveats associated with use of the models and some suggestions as to how a greater use of translational markers might ensure progress in understanding the relationship between the models and schizophrenia.

In nonconvulsive status epilepticus (NCSE), treat to burst-suppression: pro and con

Dr. Jordan (PRO) argues that when refractory NCSE is combined with acute brain injury, it produces synergistically compounded brain damage that is time dependent. Treating to EEG burst-suppression is the most rapid and effective method for stopping NCSE. The risks of burst-suppression are common to many intensive care interventions and can be minimized with expert management. Dr. Hirsch (CON) argues that treating with coma-inducing medication is highly risky and has a high mortality rate, often due to iatrogenic complications. It remains unclear if nonconvulsive seizures cause permanent neuronal injury. Nonconvulsive seizures should be diagnosed and treated as quickly as possible,but with non-coma-inducing treatments in most cases [corrected]

Opposing Modifications in Intrinsic Currents and Synaptic Inputs in Post-Traumatic Mossy Cells: Evidence for Single-Cell Homeostasis in a Hyperexcitable Network

Recent experimental and modeling results demonstrated that surviving mossy cells in the dentate gyrus play key roles in the generation of network hyperexcitability. Here we examined if mossy cells exhibit long-term plasticity in the posttraumatic, hyperexcitable dentate gyrus. Mossy cells 1 wk after fluid percussion head injury did not show alterations in their current-firing frequency ( I-F) and current-membrane voltage ( I-V) relationships. In spite of the unchanged I-F and I-V curves, mossy cells showed extensive modifications in Na+, K+ and h-currents, indicating the coordinated nature of these opposing modifications. Computational experiments in a realistic large-scale model of the dentate gyrus demonstrated that individually, these perturbations could significantly affect network activity. Synaptic inputs also displayed systematic, opposing modifications. Miniature excitatory postsynaptic current (EPSC) amplitudes were decreased, whereas miniature inhibitory postsynaptic current (IPSC) amplitudes were increased as expected from a homeostatic response to network hyperexcitability. In addition, opposing alterations in miniature and spontaneous synaptic event frequencies and amplitudes were observed for both EPSCs and IPSCs. Despite extensive changes in synaptic inputs, cannabinoid-mediated depolarization-induced suppression of inhibition was not altered in posttraumatic mossy cells. These data demonstrate that many intrinsic and synaptic properties of mossy cells undergo highly specific, long-term alterations after traumatic brain injury. The systematic nature of such extensive and opposing alterations suggests that single-cell properties are significantly influenced by homeostatic mechanisms in hyperexcitable circuits.

A pathogenetic hypothesis of Unverricht–Lundborg disease onset and progression

Unverricht-Lundborg disease (EPM1), the most common progressive myoclonic epilepsy, is associated with a defect of cystatin B (CSTB), a protease inhibitor. We used CSTB knockout mice to test the hypothesis that EPM1 onset is related to a latent hyperexcitability and that progression depends on higher susceptibility to seizure-induced cell damage. Hippocampal slices prepared from CSTB-deficient mice were hyperexcitable, as they responded to afferent stimuli in CA1 with multiple population spikes and kainate perfusion provoked the appearance of epileptic-like activity earlier than in WT mice. This hyperexcitability may depend on loss of inhibition, because the density of GABA-immunoreactive cells was reduced in the hippocampus of CSTB knockouts. In vivo, CSTB-deficient mice treated with kainate displayed increased susceptibility to seizures, with shorter latency to seizure onset and increased seizure severity compared with WT littermates. Furthermore, a greater degree of neuronal damage was observed in CSTB-deficient than in WT mice after seizures of identical grade, indicating increased susceptibility to seizure-induced cell death.

Synaptic responses in superficial layers of medial entorhinal cortex from rats with kainate-induced epilepsy

Mesial temporal lobe epilepsy patients often display shrinkage of the entorhinal cortex, which has been attributed to neuronal loss in medial entorhinal cortex layer III (MEC-III). MEC-III neuronal loss is reproduced in chronic epileptic rats after kainate-induced (KA) status epilepticus. Here we examined, in vitro, functional changes in superficial entorhinal cortex layers. Alterations in superficial layer circuitry were suggested by showing that presubiculum, parasubiculum and deep MEC stimulation evoked 100-300 Hz field potential transients and prolonged EPSPs (superimposed on IPSPs) in superficial MEC which were partially blocked by APV (in contrast to control) and fully blocked by CNQX. Contrary to controls, bicuculline (5 and 30 microM) had minor effects on evoked field potentials in KA rats. GAD65/67 in situ hybridization revealed preserved interneurons in MEC-III. In conclusion, hyperexcitability in superficial MEC neurons is not due to loss of GABAergic interneurons and probably results from alterations in synaptic connectivity within superficial MEC.

Topological Determinants of Epileptogenesis in Large-Scale Structural and Functional Models of the Dentate Gyrus Derived From Experimental Data

In temporal lobe epilepsy, changes in synaptic and intrinsic properties occur on a background of altered network architecture resulting from cell loss and axonal sprouting. Although modeling studies using idealized networks indicated the general importance of network topology in epilepsy, it is unknown whether structural changes that actually take place during epileptogenesis result in hyperexcitability. To answer this question, we built a 1:1 scale structural model of the rat dentate gyrus from published in vivo and in vitro cell type–specific connectivity data. This virtual dentate gyrus in control condition displayed globally and locally well connected (“small world”) architecture. The average number of synapses between any two neurons in this network of over one million cells was less than three, similar to that measured for the orders of magnitude smaller C. elegans nervous system. To study how network architecture changes during epileptogenesis, long-distance projecting hilar cells were gradually removed in the structural model, causing massive reductions in the number of total connections. However, as long as even a few hilar cells survived, global connectivity in the network was effectively maintained and, as a result of the spatially restricted sprouting of granule cell axons, local connectivity increased. Simulations of activity in a functional dentate network model, consisting of over 50,000 multicompartmental single-cell models of major glutamatergic and GABAergic cell types, revealed that the survival of even a small fraction of hilar cells was enough to sustain networkwide hyperexcitability. These data indicate new roles for fractionally surviving long-distance projecting hilar cells observed in specimens from epilepsy patients.

Hippocampal seizures cause depolymerization of filamentous actin in neurons independent of acute morphological changes

Seizures may exert pathophysiological effects on dendritic spines, but the molecular mechanisms mediating these effects are poorly understood. Actin represents a major structural protein of dendritic spines, and actin filaments (F-actin) can be depolymerized by the regulatory molecule, cofilin, leading to structural or functional changes in spines in response to normal physiological activity. To investigate mechanisms by which pathophysiological stimuli may affect dendritic spine structure and function, we examined changes in F-actin and cofilin in hippocampus due to 4-aminopyridine (4-AP)-induced seizures/epileptiform activity in vivo and in vitro and investigated possible structural correlates of these changes in actin dynamics. Within an hour of induction, seizure activity caused both a significant decrease in F-actin labeling, indicating depolymerization of F-actin, and a corresponding decrease in phosphorylated cofilin, signifying an increase in cofilin activity. However, 4-AP seizures had no overt short-term structural effects on dendritic spine density. By comparison, high potassium caused a more dramatic decrease in cofilin and an immediate dendritic beading and loss of dendritic spines. These findings indicate that activation of cofilin and depolymerization of F-actin represent mechanisms by which seizures may exert pathophysiological modulation of dendritic spines. In addition to affecting non-structural functions of spines, the degree to which overt structural changes occur with actin depolymerization is dependent on the severity and type of the pathophysiological stimulus.

Pentylenetetrazol kindling in rats: Is neurodegeneration associated with manifestations of convulsive activity?

Structural changes in neurons and measures of oxidative stress were studied in the hippocampus of rats tolerant (ST) and sensitive (SS) to developing clonic-tonic seizures in conditions of pentylenetetrazol kindling. Sequences of 11 injections of pentylenetetrazol significantly decreased the number of normal neurons in hippocampal field CA1 in SS rats, this effect being seen in both hippocampal field CA1 and the dentate fascia in ST rats. Decreases in the numbers of normal neurons were accompanied by increases in the numbers of damaged cells in field CA4 in rats of both groups. After 21 injections, decreases in the numbers of normal neurons were seen in field CA1 in both SS and ST rats, while the numbers of damaged neurons were significantly greater than control only in ST rats in fields CA1 and CA4. The glutathione level was significantly lower in the hippocampus in both groups of rats than in controls. Thus, rats " tolerant" to developing convulsions show signs of oxidative stress and neurodegenerative changes in the hippocampus. This suggests that oxidative neuron damage leading to neurodegeneration in the pentylenetetrazol kindling model is not directly associated with convulsive activity.

Prosopagnosia following nonconvulsive status epilepticus associated with a left fusiform gyrus malformation

A 67-year-old, right-handed woman became unable to recognize familiar faces following a period of nonconvulsive status epilepticus. Neuropsychological assessment revealed a relatively selective impairment of familiar face recognition in the absence of low-level visual deficits or widespread cognitive impairment. MRI scanning demonstrated an isolated lesion, probably a venous angioma, involving the left fusiform gyrus, mirror-symmetrical to the site typically linked to prosopagnosia. Potential explanations for the patient's prosopagnosia include seizure-related damage to a left fusiform region required for fully competent face recognition and damage to the contralateral fusiform gyrus via interhemispheric connections. Focal neuropsychological deficits in patients with refractory partial epilepsy who develop nonconvulsive status epilepticus may be underdiagnosed.

Cognitive effects of seizures

We aimed to review recent prospective and cross-sectional studies regarding the gradual and chronic effects of (cumulative) seizures on cognition. In contrast with the increasing evidence of structural changes in the brain associated with repeated seizures, its functional repercussions remain unclear. Methodological difficulties of cross-sectional and prospective studies are addressed. It appears that all but one of the prospective studies available on children are limited to measures of intelligence. Most studies revealed no significant adverse effects, although there appears to be a subgroup of about 10-25% of children that shows a clinically significant intellectual decline. Children with generalized symptomatic epilepsies, frequent seizures, high antiepileptic drug use, and early onset of epilepsy appear at risk, although psychosocial factors may also play an important role. Five of the six prospective studies on adults report evidence of a mild decline in cognition in patients with a (longstanding) history of pharmacoresistant epilepsy. The adverse effect on cognitive abilities, memory in particular, seems somewhat more robust than that on measures of intelligence. A significant association between cognitive decline and seizure related variables is rarely substantiated in prospective research and cross-sectional studies show contradicting results. Taken together, the data suggest a mild but measurable decline of intellectual performance in children and adults. Decline of specific cognitive abilities in children is impossible to evaluate given the very little data available. In adults, memory appears to be the most vulnerable cognitive function. Due to many confounding variables, the effect of seizures per se is difficult to estimate, but appears limited.

Repeated brief epileptic seizures by pentylenetetrazole cause neurodegeneration and promote neurogenesis in discrete brain regions of freely moving adult rats

Recurrent epileptic seizures are known to provoke various forms of cellular reorganization in the brains of humans and experimental animals. However, little is known about the mechanism of neuronal cell death resulting from epileptic seizures elicited by GABA antagonists. In the present study, we explored the effect on the central nervous systems of freely moving adult rats, of repeated brief epileptic seizures induced by systemic injection of pentylenetetrazole, a GABA-A receptor antagonist. Starting with minor convulsions, repeated epileptic seizures elicited a progressive increase in seizure severity, culminating in the fully kindled state. Histological examination showed that the epileptic seizures caused overt neuronal cell death in the limbic system, including the hippocampus and amygdala, and its adjoining cortex. During the recurrent epileptic seizures, neurogenesis occurred in the subgranular zone of the hippocampus, the subventricular zone of the lateral ventricle, and the amygdala. This type of pentylenetetrazole-induced neurogenesis was seen at an early stage of epileptogenesis in some regions in which massive cell loss was not evident. This suggests that neurogenesis is not a secondary consequence of neuronal cell death, but rather an independent effect of recurrent epileptic seizures.

Predicting seizure frequency after epilepsy surgery

OBJECTIVE

To identify clinical features related to seizure frequency after epilepsy surgery in patients with recurrent seizures.

BACKGROUND

No studies have examined the differences between patients who have rare seizures and patients who experience frequent seizures after epilepsy surgery. Since seizure frequency correlates with morbidity and quality of life, it is desirable to know which preoperative clinical features predict postoperative seizure frequency.

METHODS

Patients with recurrent seizures were placed in two categories: rare postoperative seizures (< or =2 per year) and frequent postoperative seizures (> or =12 per year) using seizure frequency in the second postoperative year. Variables included preoperative seizure frequency, age of first risk, age at first seizure, epilepsy duration, age at surgery, history of febrile convulsions, tonic-clonic seizures, status epilepticus, or family history, IQ, magnetic resonance imaging (MRI), and positron emission tomography (PET). Variables were analyzed using non-parametric tests to assess relationship to postoperative seizure frequency.

RESULTS

Of 475 patients who had epilepsy surgery, 111 had rare or frequent seizures in the second postoperative year. After anterior temporal lobectomy (ATL), age of first risk< or =5 years and presence of mesial temporal sclerosis on MRI were associated with rare seizures (66% of patients), whereas lack of these risk factors was associated with frequent seizures (75% of patients) (p<0.03). For non-ATL operations, preoperative seizure frequency of > or =20 seizures per month was associated with frequent postoperative seizures (p=0.03). No other variables influenced outcome.

CONCLUSIONS

Some preoperative clinical features correlate with postoperative seizure frequency in patients with recurrent seizures after epilepsy surgery. This has implications for the surgical decision making process and early postoperative management.

Models of epilepsy in the developing and adult brain: implications for neuroprotection

Repeated seizures cause a sequence of molecular and cellular changes in both the developing and adult brain, which may lead to intractable epilepsy. This article reviews this sequence of neuronal alterations, with emphasis on the kindling model. At each step, the opportunity exists for strategic intervention to prevent or reduce the downstream consequences of epileptogenesis and seizure-induced adverse plasticity. The concept of seizure-induced brain damage must be expanded to include behavioral and cognitive deficits, as well as structural neuronal damage and increased predisposition to seizures.

Neuropathology in Drosophila membrane excitability mutants

Mutations affecting ion channels and neuronal membrane excitability have been identified in Drosophila as well as in other organisms and characterized for their acute effects on behavior and neuronal function. However, the long-term effect of these perturbations on the maintenance of neuronal viability has not been studied in detail. Here we perform an initial survey of mutations affecting Na+ channels and K+ channels in Drosophila to investigate their effects on life span and neuronal viability as a function of age. We find that mutations that decrease membrane excitability as well as those that increase excitability can trigger neurodegeneration to varying degrees. Results of double-mutant interactions with dominant Na+/K+ ATPase mutations, which themselves cause severe neurodegeneration, suggest that excitotoxicity owing to hyperexcitability is insufficient to explain the resultant phenotype. Although the exact mechanisms remain unclear, our results suggest that there is an important link between maintenance of proper neuronal signaling and maintenance of long-term neuronal viability. Disruption of these signaling mechanisms in any of a variety of ways increases the incidence of neurodegeneration.

Involvement of extracellular regulated kinase and p38 kinase in hippocampal seizure tolerance

The mechanisms underlying brain seizure tolerance, a phenomenon in which brief periods of seizures protect brain against the lethal effects of subsequent sustained seizures, are poorly understood. Because brain seizure tolerance and brain ischemia tolerance likely share certain common mechanisms, the recent evidence that activation of extracellular regulated kinase (ERK) and p38 kinase pathways plays a critical role in ischemic preconditioning suggests that a similar mechanism may underlie brain seizure tolerance. We investigated the hypothesis in a rat kainic acid preparation of seizure preconditioning and tolerance, which was established by induction of one episode of priming epileptic status lasting for 20 min on the first day and another episode of sustained epileptic status lasting for 2 hr on the second day. We observed that acute seizures lead to a rapid activation of ERK and p38 in the hippocampal CA3 area, the brain region most susceptible to the lethal effects of epileptic status. Pretreatment with the ERK inhibitor PD98059 and the p38 inhibitor SB203580 selectively reduces seizure-elicited activation of ERK and p38, respectively, and significantly reduces priming seizure-induced protection of CA3 neurons. These findings indicate that, similar to brain ischemia tolerance, brain seizure tolerance also involves the ERK and p38 signaling pathways.

Effects of defective herpes simplex vectors expressing neurotrophic factors on the proliferation and differentiation of nervous cells in vivo

Neurotrophic factors (NTFs) are known to govern the processes involved in central nervous system cell proliferation and differentiation. Thus, they represent very attractive candidates for use in the study and therapy of neurological disorders. We constructed recombinant herpesvirus-based-vectors capable of expressing fibroblast growth factor-2 (FGF-2) and ciliary neurotrophic factor (CNTF) alone or in combinations. In vitro, vectors expressing FGF-2 and CNTF together, but not those expressing either NTF alone, caused proliferation of O-2A progenitors. Furthermore, based on double-labeling experiments performed using markers for neurons (MAP-2), oligodendrocytes (CNPase) and astrocytes (GFAP), most of the new cells were identified as astrocytes, but many expressed neuronal or oligodendrocytic markers. In vivo, vectors have been injected in the rat hippocampus. At 1 month after inoculation, a highly significant increase in BrdU-positive cells was observed in the dentate gyrus of animals injected with the vector expressing FGF-2 and CNTF together, but not in those injected with vectors expressing the single NTFs. Furthermore, double-labeling experiments confirmed in vitro data, that is, most of the new cells identified as astrocytes, some as neurons or oligodendrocytes. These data show the feasibility of the vector approach to induce proliferation and differentiation of neurons and/or oligodendrocytes in vivo.

Atypical language representation in epilepsy: implications for injury-induced reorganization of brain function

This review addresses language function and reorganization associated with various forms of epilepsy. Longstanding epilepsy, particularly types with onset early in life, may be associated with changes in the representation of language function in the brain. As a result of this reorganization, language function may be relatively spared despite injury to areas of the brain that normally subserve these functions. We examine the changes seen in language function in two types of epilepsy: hemispheric epilepsy of childhood and focal epilepsies. Findings from behavioral studies, intracarotid amytal testing, intraoperative cortical testing, and more recent functional imaging studies are reviewed. Studying changes in the representation of language function seen in some forms of epilepsy provides information about brain plasticity with implications for other neurologic diseases, as well as for the neuroscientific understanding of how and when functional reorganization may occur.

Drug Resistance in Epilepsy: Putative Neurobiologic and Clinical Mechanisms

Drug-resistant epilepsy with uncontrolled severe seizures despite state-of-the-art medical treatment continues to be a major clinical problem for up to one in three patients with epilepsy. Although drug resistance may emerge or remit in the course of epilepsy or its treatment, in most patients, drug resistance seems to be continuous and to occur de novo. Unfortunately, current antiepileptic drugs (AEDs) do not seem to prevent or to reverse drug resistance in most patients, but add-on therapy with novel AEDs is able to exert a modest seizure reduction in as many as 50% of patients in short-term clinical trials, and a few become seizure free during the trial. It is not known why and how epilepsy becomes drug resistant, while other patients with seemingly identical seizure types can achieve seizure control with medication. Several putative mechanisms underlying drug resistance in epilepsy have been identified in recent years. Based on experimental and clinical studies, two major neurobiologic theories have been put forward: (a) removal of AEDs from the epileptogenic tissue through excessive expression of multidrug transporters, and (b) reduced drug-target sensitivity in epileptogenic brain tissue. On the clinical side, genetic and clinical features and structural brain lesions have been associated with drug resistance in epilepsy. In this article, we review the laboratory and clinical evidence to date supporting the drug-transport and the drug-target hypotheses and provide directions for future research, to define more clearly the role of these hypotheses in the clinical spectrum of drug-resistant epilepsy.

Quantitative post-mortem study of the hippocampus in chronic epilepsy: seizures do not inevitably cause neuronal loss

Hippocampal sclerosis describes a pattern of neuronal loss and gliosis involving the medial temporal structures most often encountered in patients with epilepsy. It is still a matter for debate as to whether this lesion is acquired during the course of the patient's seizure history or is present at the outset. Early febrile seizures, episodes of status epilepticus as well as repetitive brief seizures may all contribute to the evolution of hippocampal sclerosis. In addition, genetic factors and developmental abnormalities of the hippocampus may both increase vulnerability to seizures and hippocampal injury. Recent human studies have addressed neuropathological changes in young adults and children undergoing surgery for refractory seizures with hippocampal sclerosis. Post-mortem examination, however, provides the opportunity to evaluate the effect of a lifetime of seizures on both left and right hippocampi, and the presence of any co-existing malformation. Post-mortem stereological analysis of 28 patients with poorly controlled seizures has confirmed a subgroup with absence of significant hippocampal neuronal loss despite decades of generalized seizures, including status epilepticus. The presence of granule cell dispersion correlated to the severity of hippocampal neuronal loss. Furthermore, in patients with confirmed hippocampal sclerosis at post-mortem examination, stereological assessment of the neocortex failed to confirm significant white matter neuronal heterotopia that might indicate an underlying developmental abnormality. In conclusion, seizures do not invariably lead to hippocampal injury and white matter heterotopia is not invariably associated with hippocampal sclerosis.

Febrile seizures and risk of schizophrenia

BACKGROUND

Febrile seizure is a benign condition for most children, but experiments in animals and neuroimaging studies in humans suggest that some febrile seizures may damage the hippocampus, a brain area of possible importance in schizophrenia.

METHODS

A population-based cohort of all children born in Denmark between January 1977 and December 1986 was followed until December 2001 by using data from nationwide registries.

RESULTS

We followed 558,958 persons including 16,429 with a history of febrile seizures for 2.8 million person-years and identified 952 persons who were diagnosed with schizophrenia. A history of febrile seizures was associated with a 44% increased risk of schizophrenia [relative risk (RR)=1.44; 95% confidence interval (CI), 1.07-1.95] after adjusting for confounding factors. The association between febrile seizures and schizophrenia remained virtually unchanged when restricting the analyses to people with no history of epilepsy. A history of both febrile seizures and epilepsy was associated with a 204% increased risk of schizophrenia (RR=3.04; 95% CI, 1.36-6.79) as compared with people with no such history.

CONCLUSIONS

We found a slightly increased risk of schizophrenia among persons with a history of febrile seizures. The association may be due to a damaging effect of prolonged febrile seizures on the developing brain, shared etiological factors, or confounding by unmeasured factors.

Susceptibility of immature and adult brains to seizure effects

The extent that status epilepticus (SE), but also brief seizures, affects neuronal structure and function has been the subject of much clinical and experimental research. There is a reliance on findings from animal research because there have been few prospective clinical studies. This review suggests that the features of seizure-induced injury in the immature brain compared with the adult brain are different and that duration of seizures (SE versus brief), number of seizures, cause of seizures, presence of pre-existing abnormalities, and genetics affect the injury. Increased awareness of age-specific injuries from seizure has promoted research to determine the circumstances under which seizures may produce permanent detrimental effects. Together with recent advances in functional neuroimaging, genomic investigation, and prospective human data, these studies are likely to substantially increase our knowledge of seizure-induced injury, leading to the development of improved algorithms for prevention and treatment of epilepsy.

The effects of brain-derived neurotrophic factor (BDNF) administration on kindling induction, Trk expression and seizure-related morphological changes

Brain-derived neurotrophic factor (BDNF) is a member of the neurotrophin family that mediates synaptic plasticity and excitability in the CNS. Recent evidence has shown that increased BDNF levels can lead to hyperexcitability and epileptiform activities, while suppression of BDNF function in transgenic mice or by antagonist administration retards the development of seizures. However, several groups, including our own, have reported that increasing BDNF levels by continuous intrahippocampal infusion inhibits epileptogenesis. It is possible that the continuous administration of BDNF produces a down-regulation of its high-affinity TrkB receptor, leading to a decrease of neuronal responsiveness to BDNF. If so, then animals should respond differently to bolus injections of BDNF, which presumably do not alter Trk expression, compared with continuous infusion. To test this hypothesis, we compared the effects of intrahippocampal BDNF continuous infusion and bolus injections on kindling induction. We showed that continuous infusion of BDNF inhibited the development of behavioral seizures and decreased the level of phosphorylated Trks or TrkB receptors. In contrast, multiple bolus microinjections of BDNF accelerated kindling development and did not affect the level of phosphorylated Trks or TrkB receptors. Our results indicate that different administration protocols yield opposite effects of BDNF on neuronal excitability, epileptogenesis and Trk expression. Unlike nerve growth factor and neurotrophin-3, which affect mossy fiber sprouting, we found that BDNF administration had no effect on the mossy fiber system in naive or kindled rats. Such results suggest that the effects of BDNF on epileptogenesis are not modulated by its effect on sprouting, but rather by its effects on excitability.

Basic mechanisms of partial epilepsies

PURPOSE OF REVIEW

Partial epilepsies are characterized by cell loss with consequences for neuronal organization, excitability, mnestic and cognitive functions and present with pharmaco-resistance and difficulties in clinical management. While mesial temporal lobe epilepsies present frequently with cell loss and neuronal reorganization, neocortical epilepsies frequently involve developmental alterations.

RECENT FINDINGS

There is increasing evidence that nerve cells in epileptic tissue become more vulnerable to excitotoxic cell death due to impairment of mitochondrial functions and that free radical formation is critically involved in these processes. Whether and to what extent such alterations contribute to pharmaco-resistance is unclear. However, at least three mechanisms may contribute to pharmaco-resistance: changes in target molecules for antiepileptic drugs, upregulation of drug transporters, and potentially reorganization processes in inhibitory networks. Upregulation of drug transporters also seems to be involved in pharmaco-resistance of developmental alterations underlying focal epilepsies. Recent data from the literature suggest that transgenic models for disturbances of cortical development may be useful models for the study of these variable forms of partial epilepsies.

SUMMARY

The data suggest that improvement of therapy could result from free radical scavenging and from manipulation of drug transport into the affected tissue. New models of developmental epilepsies may help us to understand mechanisms underlying increased vulnerability to seizures as well as improving strategies for treatment.

Febrile seizures and mesial temporal sclerosis

PURPOSE OF REVIEW

The sequence of febrile seizures followed by intractable temporal lobe epilepsy is rarely seen from a population perspective. However, several studies have shown a significant relationship between a history of prolonged febrile seizures in early childhood and mesial temporal sclerosis. The interpretation of these observations remains quite controversial. One possibility is that the early febrile seizure damages the hippocampus and is therefore a cause of mesial temporal sclerosis. Another possibility is that the child has a prolonged febrile seizure because the hippocampus was previously damaged by a prenatal or perinatal insult or by genetic predisposition.

RECENT FINDINGS

Imaging studies have shown that prolonged and focal febrile seizures can produce acute hippocampal injury that evolves to hippocampal atrophy, and that complex febrile seizures can originate in the temporal lobes in some children. Several lines of evidence now indicate that genetic predisposition is an important causal factor of febrile seizures and mesial temporal sclerosis. From recent clinical and molecular genetic studies, it appears that the relationship between febrile seizures and later epilepsy is frequently genetic, and there are several syndrome-specific genes for febrile seizures.

SUMMARY

Mesial temporal sclerosis probably has different causes. A number of retrospective studies showed that complex febrile seizures are a causative factor for the later development of mesial temporal sclerosis and temporal lobe epilepsy. However, contradictory results have come from several prospective and retrospective studies. The association between febrile seizures and temporal lobe epilepsy probably results from complex interactions between several genetic and environmental factors.

Safety of Diastat, a rectal gel formulation of diazepam for acute seizure treatment

Diazepam rectal gel (Diastat) is the only medication approved by the US FDA for the management of selected, refractory patients with epilepsy, on stable regimens of antiepilepsy drugs, who require intermittent use of diazepam to control bouts of increased seizure activity. An analysis of the safety of diazepam rectal gel reveals that this formulation has certain advantages over intravenous diazepam administration: most notably a very low incidence of respiratory depression, low potential for abuse and the opportunity for out-of-hospital use by non-professional caregivers. Sedation is the most common adverse effect of rectal diazepam treatment, occurring in approximately one-quarter of patients, although drug-induced somnolence is difficult to distinguish from normal post-ictal sedation. Overdosage of diazepam rectal gel is rarely associated with serious clinical consequences, and overdoses of up to 330% of the maximum recommended dosage have been reported without any respiratory or cardiac depression. Under-administration may be a serious safety issue because of morbidity that may result if seizures are not terminated. Chronic administration may cause tachyphylaxis and should be avoided.

Therapy for neurobehavioral disorders in epilepsy

Neurobehavioral disorders commonly affect patients with epilepsy. In addition to the behavioral changes during and immediately after seizures, the epileptogenic disorder of function often extends further into the postictal and interictal period. Cognitive impairments commonly affect attention, memory, mental speed, and language, as well as executive and social functions. Reducing seizure frequency and the antiepileptic drug burden can reduce these problems. Attentional deficits may respond to therapies for attention-deficit/hyperactivity disorder, but apart from patients with this comorbid disorder, their efficacy is unproven in other epilepsy patients. No effective therapies are established for other cognitive problems, but pragmatic, compensatory strategies can be helpful. Behavioral disorders include fatigue, depression, anxiety, and psychosis. Many of these disorders usually respond well to pharmacotherapy, which can be supplemented by psychotherapy. Cognitive and behavioral disorders can be the greatest cause of morbidity and impaired quality of life, often overshadowing seizures. Yet these problems often go unrecognized and, even when identified, are often undertreated or untreated.

Neonatal seizures: diagnosis, pharmacologic interventions, and outcomes

Neonatal seizures are difficult to detect, diagnose, and manage. Infants with a history of seizures often have long-term neurologic sequelae. Controversy exists as to whether neonatal seizures themselves cause damage to the developing brain, and thus, subsequent sequelae; or if these sequelae are due primarily to the underlying cause of the seizures. Treatment of seizures involves identifying and treating the underlying etiology of the seizure and appropriate use of pharmacologic interventions. To provide the context for pharmacological management of seizures in newborns, this article examines the pathophysiology and etiology of seizures and discusses pharmacological agents and issues, short- and long-term outcomes, clinical implications, and directions for future research. Understanding pharmacological issues within this context provides a comprehensive foundation for decision making and management of neonatal seizures.

Strain differences affect the induction of status epilepticus and seizure-induced morphological changes

Genetic deficits have been discovered in human epilepsy, which lead to alteration of the balance between excitation and inhibition, and ultimately result in seizures. Rodents show similar genetic determinants of seizure induction. To test whether seizure-prone phenotypes exhibit increased seizure-related morphological changes, we compared two standard rat strains (Long-Evans hooded and Wistar) and two specially bred strains following status epilepticus. The special strains, namely the kindling-prone (FAST) and kindling-resistant (SLOW) strains, were selectively bred based on their amygdala kindling rate. Although the Wistar and Long-Evans hooded strains experienced similar amounts of seizure activity, Wistar rats showed greater mossy fiber sprouting and hilar neuronal loss than Long-Evans hooded rats. The mossy fiber system was affected differently in FAST and SLOW rats. FAST animals showed more mossy fiber granules in the naïve state, but were more resistant to seizure-induced mossy fiber sprouting than SLOW rats. These properties of the FAST strain are consistent with those observed in juvenile animals, further supporting the hypothesis that the FAST strain shares circuit properties similar to those seen in immature animals. Furthermore, the extent of mossy fiber sprouting was not well correlated with sensitivity to status epilepticus, but was positively correlated with the frequency of spontaneous recurrent seizures in the FAST rats only, suggesting a possible role for axonal sprouting in the development of spontaneous seizures in these animals. We conclude that genetic factors clearly affect seizure development and related morphological changes in both standard laboratory strains and the selectively bred seizure-prone and seizure-resistant strains.

Single unprovoked seizures

Unprovoked seizures are common, affecting approximately 4% of the population by age 80. Only approximately 30% to 40% of patients with a first seizure will have a second unprovoked seizure (ie, epilepsy). Treatment with antiepileptic drugs (AEDs) should not be initiated unless the diagnosis of a seizure is firm. Decisions regarding treatment of single unprovoked seizures must balance seizure recurrence risk, the potential impact of a recurrent seizure, the likelihood of adverse effects of treatment, and patient preference. Risk factors for seizure recurrence include a history of remote neurologic insult, epileptiform abnormalities on electroencephalogram, focal structural lesion on neuroimaging, and family history of epilepsy. Adult patients with these risk factors have a recurrence risk of 60% to 70% and usually should be treated with an AED to prevent seizure recurrence. Without risk factors, the recurrence risk is 20% to 30%, and treatment depends on individual risk-to-benefit ratios and patient preference. Treatment of a first unprovoked seizure is often not necessary in childhood, especially if the seizure is part of a benign self-limited syndrome, such as benign Rolandic epilepsy of childhood. Treatment with an AED reduces the risk of seizure recurrence after a single unprovoked seizure. This must be balanced against the risk of adverse effects of AEDs. Treatment of the first seizure does not appear to affect the long-term prognosis of epilepsy. The choice of an AED should be guided by the seizure type and likely epilepsy syndrome diagnosis. Monotherapy is preferable. Standard AED options include phenytoin, carbamazepine, valproate, and phenobarbital. The newer AED, including gabapentin, lamotrigine, topiramate, oxcarbazepine, levetiracetam, and zonisamide, have good efficacy, favorable pharmacokinetic profiles, and often fewer adverse effects, supporting their use early in treatment. Not all of the newer AEDs are approved for use as monotherapy. Patients with single seizures should be counseled about seizure first aid and general safety measures, including precautions regarding swimming alone, engaging in high-risk activities, driving, possible seizure precipitation by photic stimuli (in generalized epilepsy), sleep deprivation, and alcohol.

Persistent severe amnesia due to seizure recurrence after unilateral temporal lobectomy

Anterograde amnesia is a severely disabling state which has been reported as a consequence of bilateral mesiotemporal lesions in humans. In the present paper, recurrent epileptic seizures after temporal lobectomy are described as a rare cause of severe amnesia in two patients. Diffusion-weighted MRI in one patient showed cytotoxic edema during a nonconvulsive status epilepticus and subsequent progressive hippocampal atrophy within the following month. In the other patient, repeated conventional MRI revealed no structural abnormalities in the contralateral temporal lobe.