Do seizures and epileptic activity worsen epilepsy and deteriorate cognitive function?

Statistical learning in epilepsy: Behavioral and anatomical mechanisms in the human brain

OBJECTIVE

Statistical learning, the fundamental cognitive ability of humans to extract regularities across experiences over time, engages the medial temporal lobe (MTL) in the healthy brain. This leads to the hypothesis that statistical learning (SL) may be impaired in patients with epilepsy (PWE) involving the temporal lobe, and that this impairment could contribute to their varied memory deficits. In turn, studies done in collaboration with PWE, that evaluate the necessity of MTL circuitry through disease and causal perturbations, provide an opportunity to advance basic understanding of SL.

METHODS

We implemented behavioral testing, volumetric analysis of the MTL substructures, and direct electrical brain stimulation to examine SL across a cohort of 61 PWE and 28 healthy controls.

RESULTS

We found that behavioral performance in an SL task was negatively associated with seizure frequency irrespective of seizure origin. The volume of hippocampal subfields CA1 and CA2/3 correlated with SL performance, suggesting a more specific role of the hippocampus. Transient direct electrical stimulation of the hippocampus disrupted SL. Furthermore, the relationship between SL and seizure frequency was selective, as behavioral performance in an episodic memory task was not impacted by seizure frequency.

SIGNIFICANCE

Overall, these results suggest that SL may be hippocampally dependent and that the SL task could serve as a clinically useful behavioral assay of seizure frequency that may complement existing approaches such as seizure diaries. Simple and short SL tasks may thus provide patient-centered endpoints for evaluating the efficacy of novel treatments in epilepsy.

Statistical learning in epilepsy: Behavioral, anatomical, and causal mechanisms in the human brain

Statistical learning, the fundamental cognitive ability of humans to extract regularities across experiences over time, engages the medial temporal lobe in the healthy brain. This leads to the hypothesis that statistical learning may be impaired in epilepsy patients, and that this impairment could contribute to their varied memory deficits. In turn, epilepsy patients provide a platform to advance basic understanding of statistical learning by helping to evaluate the necessity of medial temporal lobe circuitry through disease and causal perturbations. We implemented behavioral testing, volumetric analysis of the medial temporal lobe substructures, and direct electrical brain stimulation to examine statistical learning across a cohort of 61 epilepsy patients and 28 healthy controls. Behavioral performance in a statistical learning task was negatively associated with seizure frequency, irrespective of where seizures originated in the brain. The volume of hippocampal subfields CA1 and CA2/3 correlated with statistical learning performance, suggesting a more specific role of the hippocampus. Indeed, transient direct electrical stimulation of the hippocampus disrupted statistical learning. Furthermore, the relationship between statistical learning and seizure frequency was selective: behavioral performance in an episodic memory task was impacted by structural lesions in the medial temporal lobe and by antiseizure medications, but not by seizure frequency. Overall, these results suggest that statistical learning may be hippocampally dependent and that this task could serve as a clinically useful behavioral assay of seizure frequency distinct from existing neuropsychological tests. Simple and short statistical learning tasks may thus provide patient-centered endpoints for evaluating the efficacy of novel treatments in epilepsy.

Impairments of Long-Term Synaptic Plasticity in the Hippocampus of Young Rats during the Latent Phase of the Lithium-Pilocarpine Model of Temporal Lobe Epilepsy

Status epilepticus (SE) causes persistent abnormalities in the functioning of neuronal networks, often resulting in worsening epileptic seizures. Many details of cellular and molecular mechanisms of seizure-induced changes are still unknown. The lithium–pilocarpine model of epilepsy in rats reproduces many features of human temporal lobe epilepsy. In this work, using the lithium–pilocarpine model in three-week-old rats, we examined the morphological and electrophysiological changes in the hippocampus within a week following pilocarpine-induced seizures. We found that almost a third of the neurons in the hippocampus and dentate gyrus died on the first day, but this was not accompanied by impaired synaptic plasticity at that time. A diminished long-term potentiation (LTP) was observed following three days, and the negative effect of SE on plasticity increased one week later, being accompanied by astrogliosis. The attenuation of LTP was caused by the weakening of N-methyl-D-aspartate receptor (NMDAR)-dependent signaling. NMDAR-current was more than two-fold weaker during high-frequency stimulation in the post-SE rats than in the control group. Application of glial transmitter D-serine, a coagonist of NMDARs, allows the enhancement of the NMDAR-dependent current and the restoration of LTP. These results suggest that the disorder of neuron–astrocyte interactions plays a critical role in the impairment of synaptic plasticity.

Down-regulation of AMPA receptors and long-term potentiation during early epileptogenesis

Epilepsy is a brain disorder characterized by the occurrence of recurrent spontaneous seizures. Behavioral disorders and altered cognition are frequent comorbidities affecting the quality of life of people with epilepsy. These impairments are undoubtedly multifactorial and the specific mechanisms underlying these comorbidities are largely unknown. Long-lasting alterations in synaptic strength due to changes in expression, phosphorylation, or function of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptors (AMPARs) have been associated with alterations in neuronal synaptic plasticity. In particular, alterations in hippocampal long-term potentiation (LTP), a well-accepted model of learning and memory, have been associated with altered cognition in epilepsy. Here, we analyzed the effects of pilocarpine-induced status epilepticus (SE) on AMPARs to determine if alterations in AMPAR signaling might be one of the mechanisms contributing to altered cognition during epilepsy. We found alterations in the phosphorylation and plasma membrane expression of AMPARs. In addition, we detected altered expression of GRIP, a key scaffolding protein involved in the proper distribution of AMPARs at the neuronal cell surface. Interestingly, a functional analysis revealed that these molecular changes are linked to impaired LTP. Together, these observations suggest that seizure-induced alterations in the molecular machinery regulating AMPARs likely impact the neuron's ability to support synaptic plasticity that is required for learning and memory.

Leveraging electrophysiologic correlates of word encoding to map seizure onset zone in focal epilepsy: Task-dependent changes in epileptiform activity, spectral features, and functional connectivity

OBJECTIVE

Verbal memory dysfunction is common in focal, drug-resistant epilepsy (DRE). Unfortunately, surgical removal of seizure-generating brain tissue can be associated with further memory decline. Therefore, localization of both the circuits generating seizures and those underlying cognitive functions is critical in presurgical evaluations for patients who may be candidates for resective surgery. We used intracranial electroencephalographic (iEEG) recordings during a verbal memory task to investigate word encoding in focal epilepsy. We hypothesized that engagement in a memory task would exaggerate local iEEG feature differences between the seizure onset zone (SOZ) and neighboring tissue as compared to wakeful rest ("nontask").

METHODS

Ten participants undergoing presurgical iEEG evaluation for DRE performed a free recall verbal memory task. We evaluated three iEEG features in SOZ and non-SOZ electrodes during successful word encoding and compared them with nontask recordings: interictal epileptiform spike (IES) rates, power in band (PIB), and relative entropy (REN; a functional connectivity measure).

RESULTS

We found a complex pattern of PIB and REN changes in SOZ and non-SOZ electrodes during successful word encoding compared to nontask. Successful word encoding was associated with a reduction in local electrographic functional connectivity (increased REN), which was most exaggerated in temporal lobe SOZ. The IES rates were reduced during task, but only in the non-SOZ electrodes. Compared with nontask, REN features during task yielded marginal improvements in SOZ classification.

SIGNIFICANCE

Previous studies have supported REN as a biomarker for epileptic brain. We show that REN differences between SOZ and non-SOZ are enhanced during a verbal memory task. We also show that IESs are reduced during task in non-SOZ, but not in SOZ. These findings support the hypothesis that SOZ and non-SOZ respond differently to task and warrant further exploration into the use of cognitive tasks to identify functioning memory circuits and localize SOZ.

Knockdown of Lingo-1 by short hairpin RNA promotes cognitive function recovery in a status convulsion model

The purpose of this study was to determine the dynamic changes of the Nogo-66 receptor 1 (NgR1) pathway during epileptogenesis and the potential beneficial of leucine-rich repeat and Ig-like domain-containing Nogo receptor interacting protein 1 (Lingo-1) inhibition on epilepsy rats. The hippocampal changes of the NgR1 pathway during epileptogenesis were determined by western blot analysis of multiple proteins, including neurite outgrowth inhibitor protein A (NogoA), myelin-associated glycoprotein (MAG), oligodendrocyte-myelin glycoprotein (OMgp), Lingo-1, ras homolog family member A (RhoA) and phosphorylated RhoA (p-RhoA). Lentivirus-mediated short hairpin RNA (shRNA) was used to knockdown the hippocampal expression of Lingo-1. Novel object recognition (NOR) test and Morris Water Maze (MWM) test were employed to determine the cognitive functions of rats. Hematoxylin and eosin (H&E) staining, protein expressions of RhoA, p-RhoA, and myelin basic protein (MBP), as well as convulsion susceptibility test were additionally performed. Our results showed that the NgR1 pathway was activated during epileptogenesis, characterized by up-regulation of NogoA, MAG, OMgp, and Lingo-1, which was especially significant at the chronic phase of epilepsy. The cognitive function, convulsion susceptibility and hippocampal neuronal survival of rats were impaired at the chronic phase of epileptogenesis but all improved by Lingo-1 inhibition; besides, the hippocampal protein expressions of p-RhoA and MBP were significantly decreased at the chronic phase of SC rats but increased after Lingo-1 inhibition. Our results demonstrated that Lingo-1 shRNA can improve epilepsy-induced cognitive impairment, which may be related with the pro-myelination and neuroprotection effects of Lingo-1 inhibition.

Implicit cognitive flexibility in self-limited focal epilepsy of childhood: An HD-EEG study

Self-limited focal epilepsy of childhood (SFEC) is often related to mild impairments in several neuropsychological domains, including cognitive flexibility, which is generally considered a process requiring volition and attention. However, recent evidence showed that it can be implicitly adjusted exploiting simple 'stimulus-response' associations as for example, the probability of the stimulus occurrence. Here, we evaluated the capability to implicitly extract environmental patterns of regularities and use them to flexibly adjust proactive control motor control. We tested 21 children with epilepsy (total IQ > 80; 13 with Childhood epilepsy with centro-temporal spikes, 8 with Panayiotopoulos syndrome (PS); 5-13 years old) compared to a healthy age-matched control group (32 participants). We used the Dynamic Temporal Prediction (DTP) task to investigate how behavioral performance is implicitly shaped by the manipulation of the stimulus occurrence probability over time. We recorded EEG to identify neural markers to differentiate the two groups. SFEC group showed a reduction in accuracy (p = .0013) and response speed (p < .001) as well as an absence of response adjustment (p = .65) in relation to the implicit changes in stimulus probability occurrence, in comparison to the control group. The epilepsy group performance in the DTP showed a significant correlation with the phonemic fluency (r = -0.50) and the Perseverations index of the CPT test (r = 0.53). Finally, children with SFEC did not show the modulation of the contingent negative variation (CNV) evoked potential. Overall, children with SFEC showed poor implicit flexibility compared to a control group. This pattern is individually related to high-level executive function, suggesting to extend neuropsychological assessment to the implicit domain.

Targeted Reducing of Tauopathy Alleviates Epileptic Seizures and Spatial Memory Impairment in an Optogenetically Inducible Mouse Model of Epilepsy

Intracellular deposition of hyperphosphorylated tau has been reported in the brain of epilepsy patients, but its contribution to epileptic seizures and the association with spatial cognitive functions remain unclear. Here, we found that repeated optogenetic stimulation of the excitatory neurons in ventral hippocampal CA1 subset could induce a controllable epileptic seizure in mice. Simultaneously, the mice showed spatial learning and memory deficits with a prominently elevated total tau and phospho-tau levels in the brain. Importantly, selective facilitating tau degradation by using a novel designed proteolysis-targeting chimera named C4 could effectively ameliorate the epileptic seizures with remarkable restoration of neuronal firing activities and improvement of spatial learning and memory functions. These results confirm that abnormal tau accumulation plays a pivotal role in the epileptic seizures and the epilepsy-associated spatial memory impairments, which provides new molecular target for the therapeutics.

Imidazodiazepine Anticonvulsant, KRM-II-81, Produces Novel, Non-diazepam-like Antiseizure Effects

The need for improved medications for the treatment of epilepsy and chronic pain is essential. Epileptic patients typically take multiple antiseizure drugs without complete seizure freedom, and chronic pain is not fully managed with current medications. A positive allosteric modulator (PAM) of α2/3-containing GABA_A receptors (5-(8-ethynyl-6-(pyridin-2-yl)-4H-benzo[f]imidazole[1,5-α][1,4]diazepin-3-yl) oxazole or KRM-II-81 (8) is a lead compound in a series of imidazodiazepines. We previously reported that KRM-II-81 produces broad-based anticonvulsant and antinociceptive efficacy in rodent models and provides a wider margin over motoric side effects than that of other GABA_A receptor PAMs. The present series of experiments was designed to fill key missing gaps in prior preclinical studies assessing whether KRM-II-81 could be further differentiated from nonselective GABA_A receptor PAMs using the anticonvulsant diazepam (DZP) as a comparator. In multiple chemical seizure provocation models in mice, KRM-II-81 was either equally or more efficacious than DZP. Most strikingly, KRM-II-81 but not DZP blocked the development of seizure sensitivity to the chemoconvulsants cocaine and pentylenetetrazol in seizure kindling models. These and predecessor data have placed KRM-II-81 into consideration for clinical development requiring the manufacture of kilogram amounts of good manufacturing practice material. We describe here a novel synthetic route amenable to kilogram quantity production. The new biological and chemical data provide key steps forward in the development of KRM-II-81 (8) as an improved treatment option for patients suffering from epilepsy.

Hippocampal Interictal Spikes during Sleep Impact Long-Term Memory Consolidation

OBJECTIVE

Non-rapid eye movement (NREM) sleep is supposed to play a key role in long-term memory consolidation transferring information from hippocampus to neocortex. However, sleep also activates epileptic activities in medial temporal regions. This study investigated whether interictal hippocampal spikes during sleep would impair long-term memory consolidation.

METHOD

We prospectively measured visual and verbal memory performance in 20 patients with epilepsy investigated with stereoelectroencephalography (SEEG) at immediate, 30-minute, and 1-week delays, and studied the correlations between interictal hippocampal spike frequency during waking and the first cycle of NREM sleep and memory performance, taking into account the number of seizures occurring during the consolidation period and other possible confounding factors, such as age and epilepsy duration.

RESULTS

Retention of verbal memory over 1 week was negatively correlated with hippocampal spike frequency during sleep, whereas no significant correlation was found with hippocampal interictal spikes during waking. No significant result was found for visual memory. Regression tree analysis showed that the number of seizures was the first factor that impaired the verbal memory retention between 30 minutes and 1 week. When the number of seizures was below 5, spike frequency during sleep higher than 13 minutes was associated with impaired memory retention over 1 week.

INTERPRETATION

Our results show that activation of interictal spikes in the hippocampus during sleep and seizures specifically impair long-term memory consolidation. We hypothesize that hippocampal interictal spikes during sleep interrupt hippocampal-neocortical transfer of information. ANN NEUROL 2020;87:976-987.

Glioma-Induced Alterations in Neuronal Activity and Neurovascular Coupling during Disease Progression

Diffusely infiltrating gliomas are known to cause alterations in cortical function, vascular disruption, and seizures. These neurological complications present major clinical challenges, yet their underlying mechanisms and causal relationships to disease progression are poorly characterized. Here, we follow glioma progression in awake Thy1-GCaMP6f mice using in vivo wide-field optical mapping to monitor alterations in both neuronal activity and functional hemodynamics. The bilateral synchrony of spontaneous neuronal activity gradually decreases in glioma-infiltrated cortical regions, while neurovascular coupling becomes progressively disrupted compared to uninvolved cortex. Over time, mice develop diverse patterns of high amplitude discharges and eventually generalized seizures that appear to originate at the tumors' infiltrative margins. Interictal and seizure events exhibit positive neurovascular coupling in uninfiltrated cortex; however, glioma-infiltrated regions exhibit disrupted hemodynamic responses driving seizure-evoked hypoxia. These results reveal a landscape of complex physiological interactions occurring during glioma progression and present new opportunities for exploring novel biomarkers and therapeutic targets.

Valproic Acid and Epilepsy: From Molecular Mechanisms to Clinical Evidences

After more than a century from its discovery, valproic acid (VPA) still represents one of the most efficient antiepi-leptic drugs (AEDs). Pre and post-synaptic effects of VPA depend on a very broad spectrum of actions, including the regu-lation of ionic currents and the facilitation of GABAergic over glutamatergic transmission. As a result, VPA indirectly mod-ulates neurotransmitter release and strengthens the threshold for seizure activity. However, even though participating to the anticonvulsant action, such mechanisms seem to have minor impact on epileptogenesis. Nonetheless, VPA has been reported to exert anti-epileptogenic effects. Epigenetic mechanisms, including histone deacetylases (HDACs), BDNF and GDNF modulation are pivotal to orientate neurons toward a neuroprotective status and promote dendritic spines organization. From such broad spectrum of actions comes constantly enlarging indications for VPA. It represents a drug of choice in child and adult with epilepsy, with either general or focal seizures, and is a consistent and safe IV option in generalized convulsive sta-tus epilepticus. Moreover, since VPA modulates DNA transcription through HDACs, recent evidences point to its use as an anti-nociceptive in migraine prophylaxis, and, even more interestingly, as a positive modulator of chemotherapy in cancer treatment. Furthermore, VPA-induced neuroprotection is under investigation for benefit in stroke and traumatic brain injury. Hence, VPA has still got its place in epilepsy, and yet deserves attention for its use far beyond neurological diseases. In this review, we aim to highlight, with a translational intent, the molecular basis and the clinical indications of VPA.

Effects of eplerenone on cerebral aldosterone levels and brain lesions in spontaneously hypertensive rats

Evidence indicates that renin-angiotensin-aldosterone system (RAS) inhibitors can protect the brain in Alzheimer's disease and Parkinson's disease. The current study evaluated the relationship between aldosterone and tissue damage in the brains of spontaneously hypertensive rats (SHRs) and whether the RAS inhibitor eplerenone can mitigate the damage seen in these rats. SHRs were randomly divided into eplerenone (n = 10) and SHR (n = 10) groups, and Wistar-Kyoto (WKY) rats (n = 10) were used as controls. Eplerenone 50 mg/kg/day was administered orally to the eplerenone group. Pathological changes to the hippocampal formation, plasma and encephalic aldosterone, and plasma potassium levels were compared among the groups. After 10 weeks, rats in the eplerenone and SHR groups showed higher systolic BP (p = .01) than the control group. Aldosterone levels in the brain were higher in the SHR group (0.20 ± 0.06 pg/ml) than in the eplerenone (0.14 ± 0.05 pg/ml, p = .044) or control (0.12 ± 0.07 pg/ml, p = .007) groups. Plasma aldosterone levels in the SHR group were 1.7 times higher than those in the control group (p = .006). Cerebral cortex was thinner in the SHR group (225.18 ± 15.43 μm) than in the eplerenone (240.38 ± 12.85 μm, p < .01) or control (244.72 ± 18.92 μm, p < .01) groups. Thickness did not differ between the latter two groups. The SHR group exhibited apoptotic cells in the hippocampal formation, which were rare in the eplerenone and control groups. Plasma potassium levels were higher in the eplerenone group than those in the other two groups (p < .05). Our results showed that eplerenone can alleviate brain damage (thinning of cortex and increased apoptosis) caused by aldosterone in a rat model of hypertension.

Antiepileptic drugs are not independently associated with cognitive dysfunction

OBJECTIVE

To test the hypothesis that individual antiepileptic drugs (AEDs) are not associated with cognitive impairment beyond other clinically relevant factors, we performed a cross-sectional study of patients admitted to an inpatient video-EEG monitoring unit.

METHODS

We prospectively enrolled patients admitted to an inpatient specialist epilepsy program between 2009 and 2016. Assessments included objective cognitive function, quality of life subscales for subjective cognitive function, and questionnaires for anxiety and depressive symptoms. Bayesian model averaging identified predictors of cognitive function. Bayesian model selection approach investigated effect of individual AEDs on cognition. Conventional frequentist analyses were also performed.

RESULTS

A total of 331 patients met inclusion criteria. Mean age was 39.3 years and 61.9% of patients were women. A total of 45.0% of patients were prescribed AED polypharmacy, 25.1% AED monotherapy, and 29.9% no AED. Age, seizure frequency, and a diagnosis of concomitant epilepsy and psychogenic nonepileptic seizure were predictors of objective cognitive function. Depression, anxiety, and seizure frequency were predictors of subjective cognitive function. Individual AEDs were not independently associated with impaired cognitive function beyond other clinically relevant variables.

CONCLUSIONS

This study found that no AED was independently associated with cognitive dysfunction. Significant determinants of objective and subjective cognitive dysfunction included seizure frequency and depression, respectively. These findings suggest that optimizing therapy to prevent seizures is not likely to occur at the expense of cognitive function.

Crosstalk between the Ketogenic Diet and Epilepsy: From the Perspective of Gut Microbiota

Given the association between a range of neurological disorders and changes in the gut microbiota, interest in the gut microbiota has recently increased. In particular, the significant involvement of the autoimmune processes in the development of epilepsy, one of the most serious and widespread neurological diseases, has led to a suggested link with the gut microbiome. Because the constitution of the gut microbiome can be influenced by diet, dietary therapy has been shown to have a positive impact on a wide range of conditions via alteration of the gut microbiota. An example of one such diet is the ketogenic diet (KD), which promotes a diet that contains high levels of fat, adequate levels of protein, and low levels of carbohydrate. Due to the near-total elimination of carbohydrates from the individual's food in this ultra-high-fat diet, ketone bodies become an important source of energy. Although the ketogenic diet has proven successful in the treatment of refractory epilepsy and other illnesses, the underlying mechanisms of its neuroprotective effects have yet to be fully elucidated. Nevertheless, recent studies strongly indicate a role for the gut microbiota in the effective treatment of epilepsy with the ketogenic diet. The latest advances regarding the links between the ketogenic diet, gut microbiota, and epilepsy are reviewed in this article, with a particular focus on the role of the gut microbiota in the treatment outcome.

Epileptiform activity contralateral to unilateral hippocampal sclerosis does not cause the expression of brain damage markers

OBJECTIVE

Patients with epilepsy often ask if recurrent seizures harm their brain and aggravate their epileptic condition. This crucial question has not been specifically addressed by dedicated experiments. We analyze here if intense bilateral seizure activity induced by local injection of kainic acid (KA) in the right hippocampus produces brain damage in the left hippocampus.

METHODS

Adult guinea pigs were bilaterally implanted with hippocampal electrodes for continuous video-electroencephalography (EEG) monitoring. Unilateral injection of 1 μg KA in the dorsal CA1 area induced nonconvulsive status epilepticus (ncSE) characterized by bilateral hippocampal seizure discharges. This treatment resulted in selective unilateral sclerosis of the KA-injected hippocampus. Three days after KA injection, the animals were killed, and the brains were submitted to ex vivo magnetic resonance imaging (MRI) and were processed for immunohistochemical analysis.

RESULTS

During ncSE, epileptiform activity was recorded for 27.6 ± 19.1 hours in both the KA-injected and contralateral hippocampi. Enhanced T1-weighted MR signal due to gadolinium deposition, mean diffusivity reduction, neuronal loss, gliosis, and blood-brain barrier permeability changes was observed exclusively in the KA-injected hippocampus. Despite the presence of a clear unilateral hippocampal sclerosis at the site of KA injection, no structural alterations were detected by MR and immunostaining analysis performed in the hippocampus contralateral to KA injection 3 days and 2 months after ncSE induction. Fluoro-Jade and terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining at the same time points confirmed the absence of degenerating cells in the hippocampi contralateral to KA injection.

SIGNIFICANCE

We demonstrate that intense epileptiform activity during ncSE does not cause obvious brain damage in the hippocampus contralateral to unilateral hippocampal KA injection. These findings argue against the hypothesis that epileptiform activity per se contributes to focal brain injury in previously undamaged cortical regions.

From adagio to allegretto: The changing tempo of theta frequencies in epilepsy and its relation to interneuron function

Despite decades of research, our understanding of epilepsy, including how seizures are generated and propagate, is incomplete. However, there is growing recognition that epilepsy is more than just the occurrence of seizures, with patients often experiencing comorbid deficits in cognition that are poorly understood. In addition, the available therapies for treatment of epilepsy, from pharmaceutical treatment to surgical resection and seizure prevention devices, often exacerbate deficits in cognitive function. In this review, we discuss the hypothesis that seizure generation and cognitive deficits have a similar pathological source characterized by, but not limited to, deficits in theta oscillations and their influence on interneurons. We present a new framework that describes oscillatory states in epilepsy as alternating between hyper- and hypo-synchrony rather than solely the spontaneous transition to hyper-excitability characterized by the seizures. This framework suggests that as neural oscillations, specifically in the theta range, vary their tempo from a slowed almost adagio tempo during interictal periods to faster, more rhythmic allegretto tempo preictally, they impact the function of interneurons, modulating their ability to control seizures and their role in cognitive processing. This slow wave oscillatory framework may help explain why current therapies that work to reduce hyper-excitability do not completely eliminate seizures and often lead to exacerbated cognitive deficits.

Dietary Omega-3 Polyunsaturated Fatty Acid Deprivation Does Not Alter Seizure Thresholds but May Prevent the Anti-seizure Effects of Injected Docosahexaenoic Acid in Rats

Background: Brain concentrations of omega-3 docosahexaenoic acid (DHA, 22:6n-3) have been reported to positively correlate with seizure thresholds in rodent seizure models. It is not known whether brain DHA depletion, achieved by chronic dietary omega-3 polyunsaturated fatty acid (PUFA) deficiency, lowers seizure thresholds in rats.

Objective: The present study tested the hypothesis that lowering brain DHA concentration with chronic dietary n-3 PUFA deprivation in rats will reduce seizure thresholds, and that compared to injected oleic acid (OA), injected DHA will raise seizure thresholds in rats maintained on n-3 PUFA adequate and deficient diets.

Methods: Rats (60 days old) were surgically implanted with electrodes in the amygdala, and subsequently randomized to the AIN-93G diet containing adequate levels of n-3 PUFA derived from soybean oil or an n-3 PUFA-deficient diet derived from coconut and safflower oil. The rats were maintained on the diets for 37 weeks. Afterdischarge seizure thresholds (ADTs) were measured every 4–6 weeks by electrically stimulating the amygdala. Between weeks 35 and 37, ADTs were assessed within 1 h of subcutaneous OA or DHA injection (600 mg/kg). Seizure thresholds were also measured in a parallel group of non-implanted rats subjected to the maximal pentylenetetrazol (PTZ, 110 mg/kg) seizure test. PUFA composition was measured in the pyriform-amygdala complex of another group of non-implanted rats sacrificed at 16 and 32 weeks.

Results: Dietary n-3 PUFA deprivation did not significantly alter amygdaloid seizure thresholds or latency to PTZ-induced seizures. Acute injection of OA did not alter amygdaloid ADTs of rats on the n-3 PUFA adequate or deficient diets, whereas acute injection of DHA significantly increased amygdaloid ADTs in rats on the n-3 PUFA adequate control diet as compared to rats on the n-3 PUFA deficient diet (P < 0.05). Pyriform-amygdala DHA percent composition did not significantly differ between the groups, while n-6 docosapentaenoic acid, a marker of n-3 PUFA deficiency, was significantly increased by 2.9-fold at 32 weeks.

Conclusion: Chronic dietary n-3 PUFA deficiency does not alter seizure thresholds in rats, but may prevent the anti-seizure effects of DHA.

Contemporary scope of inborn errors of metabolism involving epilepsy or seizures

Many inborn errors of metabolism may present with epilepsy or seizures, however, current scope of these diseases is unknown. Due to available precision medicine approaches in many inborn errors of metabolism and sophisticated traditional diagnostics, this group of disorders is of special relevance to clinicians. Besides, as current treatment is challenging and unsuccessful in more than 30% of all epilepsy patients, these diseases may provide valuable models for ictogenesis and epileptogenesis studies and potentially pave the ways to identification of novel treatments. The aim of this study was to elucidate genetic architecture of inborn errors of metabolism involving epilepsy or seizures and to evaluate their diagnostic approaches. After extensive search, 880 human genes were identified with a considerable part, 373 genes (42%), associated with inborn errors of metabolism. The most numerous group comprised disorders of energy metabolism (115, 31% of all inborn errors of metabolism). A substantial number of these diseases (26%, 97/373) have established specific treatments, therefore timely diagnosis comes as an obligation. Highly heterogenous, overlapping and non-specific phenotypes in most of inborn errors of metabolism presenting with epilepsy or seizures usually preclude phenotype-driven diagnostics. Besides, as traditional diagnostics involves a range of specialized metabolic tests with low diagnostic yields and is generally inefficient and lengthy, next-generation sequencing-based methods were proposed as a cost-efficient one-step way to shorten "diagnostic odyssey". Extensive list of 373 epilepsy- or seizures-associated inborn errors of metabolism genes may be of value in development of gene panels and as a tool for variants' filtration.

Preventing cognitive impairment in children with epilepsy

PURPOSE OF REVIEW

Cognitive impairments are common in children with epilepsy. They may already be present before the onset of epilepsy or occur - and even progress - during its course. Many variables contribute to cognitive dysfunction. Those that can be targeted to prevent (further) cognitive impairment will be highlighted in this review.

RECENT FINDINGS

Ideally, but not yet realistically, epileptogenesis is prevented to avert seizures and cognitive impairments in high-risk patients. New and targeted treatments of progressive epileptogenic disorders and precision medicine approaches in genetic epilepsies are increasingly applied. Cognitive outcome benefits from early diagnosis and treatment of epileptic encephalopathy. Ongoing seizures may cause permanent and progressive changes in brain structure and connectivity, suggesting that early seizure control optimizes eventual cognitive functioning. Frequent interictal epileptiform discharges justify treatment in children with cognitive impairments that are otherwise unexplained. Cognitive adverse effects of antiepileptic drugs should be closely monitored and balanced against potential benefits. Finally, early surgical treatment in selected candidates will improve their cognitive outcome.

SUMMARY

Although important determinants of intellectual functioning - including the child's genetic and environmental background and the epileptogenic pathology - may not be modifiable, several variables that contribute to cognitive impairment can be targeted to improve outcome. Early etiological diagnosis, personalized therapies, presurgical evaluation, and strict control of seizures - or in some patients interictal discharges - can prevent (further) cognitive impairments.

Within the Brain: The Renin Angiotensin System

For many years, modulators of the renin angiotensin system (RAS) have been trusted by clinicians for the control of essential hypertension. It was recently demonstrated that these modulators have other pleiotropic properties independent of their hypotensive effects, such as enhancement of cognition. Within the brain, different components of the RAS have been extensively studied in the context of neuroprotection and cognition. Interestingly, a crosstalk between the RAS and other systems such as cholinergic, dopaminergic and adrenergic systems have been demonstrated. In this review, the preclinical and clinical evidence for the impact of RAS modulators on cognitive impairment of multiple etiologies will be discussed. In addition, the expression and function of different receptor subtypes within the RAS such as: Angiotensin II type I receptor (AT1R), Angiotensin II type II receptor (AT2R), Angiotensin IV receptor (AT4R), Mas receptor (MasR), and Mas-related-G protein-coupled receptor (MrgD), on different cell types within the brain will be presented. We aim to direct the attention of the scientific community to the plethora of evidence on the importance of the RAS on cognition and to the different disease conditions in which these agents can be beneficial.

Comparing the Antiseizure and Neuroprotective Efficacy of LY293558, Diazepam, Caramiphen, and LY293558-Caramiphen Combination against Soman in a Rat Model Relevant to the Pediatric Population

The currently Food and Drug Administration-approved anticonvulsant for the treatment of status epilepticus (SE) induced by nerve agents is the benzodiazepine diazepam; however, diazepam does not appear to offer neuroprotective benefits. This is of particular concern with respect to the protection of children because, in the developing brain, synaptic transmission mediated via GABA_A receptors, the target of diazepam, is weak. In the present study, we exposed 21-day-old male rats to 1.2 × LD₅₀ soman and compared the antiseizure, antilethality, and neuroprotective efficacy of diazepam (10 mg/kg), LY293558 (an AMPA/GluK1 receptor antagonist; 15 mg/kg), caramiphen (CRM, an antimuscarinic with NMDA receptor-antagonistic properties; 50 mg/kg), and LY293558 (15 mg/kg) + CRM (50 mg/kg), administered 1 hour after exposure. Diazepam, LY293558, and LY293558 + CRM, but not CRM alone, terminated SE; LY293558 + CRM treatment acted significantly faster and produced a survival rate greater than 85%. Thirty days after soman exposure, neurodegeneration in limbic regions was most severe in the CRM-treated group, minimal to severe-depending on the region-in the diazepam group, absent to moderate in the LY293558-treated group, and totally absent in the LY293558 + CRM group. Amygdala and hippocampal atrophy, a severe reduction in spontaneous inhibitory activity in the basolateral amygdala, and increased anxiety-like behavior in the open-field and acoustic startle response tests were present in the diazepam and CRM groups, whereas the LY293558 and LY293558 + CRM groups did not differ from controls. The combined administration of LY293558 and CRM, by blocking mainly AMPA, GluK1, and NMDA receptors, is a very effective anticonvulsant and neuroprotective therapy against soman in young rats.

[Cognitive impairment. The effects of seizures?]

This review discusses articles on cognitive impairments developing after one or more convulsive seizures. Cognitive disorders seem to be frequent complications of epilepsy. According to recent clinical studies, the intensity of cognitive declines depends on a frequency and severity of seizures. However, presence of an epileptic focus does not always indicate an increase in cognitive impairments. An effect of a single convulsive seizure on cognitive functions at this stage is uncertain. According to some data, cognitive impairments after a single generalized seizures develop only in specific clinical syndromes, on the other hand, they are influenced by the emotional state of the subject. This problem remains relevant today. Further work is needed in this direction.

Seizure activity per se does not induce tissue damage markers in human neocortical focal epilepsy

OBJECTIVE

The contribution of recurring seizures to the progression of epileptogenesis is debated. Seizure-induced brain damage is not conclusively demonstrated either in humans or in animal models of epilepsy. We evaluated the expression of brain injury biomarkers on postsurgical brain tissue obtained from 20 patients with frequent seizures and a long history of drug-resistant focal epilepsy.

METHODS

The expression patterns of specific glial, neuronal, and inflammatory molecules were evaluated by immunohistochemistry in the core of type II focal cortical dysplasias (FCD-II), at the FCD boundary (perilesion), and in the adjacent normal-appearing area included in the epileptogenic region. We also analyzed surgical specimens from cryptogenic patients not presenting structural alterations at imaging.

RESULTS

Astroglial and microglial activation, reduced neuronal density, perivascular CD3-positive T-lymphocyte clustering, and fibrinogen extravasation were demonstrated in the core of FCD-II lesions. No pathological immunoreactivity was observed outside the FCD-II or in cryptogenetic specimens, where the occurrence of interictal and ictal epileptiform activity was confirmed by either stereo-electroencephalography or intraoperative electrocorticography.

INTERPRETATION

Recurrent seizures do not induce the expression of brain damage markers in nonlesional epileptogenic cortex studied in postsurgical tissue from cryptogenic and FCD patients. This evidence argues against the hypothesis that epileptiform activity per se contributes to focal brain injury, at least in the neocortical epilepsies considered here. Ann Neurol 2017;82:331-341.

Analytic information processing style in epilepsy patients

Relevant to the study of epileptogenesis is learning processing, given the pivotal role that neuroplasticity assumes in both mechanisms. Recently, evoked potential analyses showed a link between analytic cognitive style and altered neural excitability in both migraine and healthy subjects, regardless of cognitive impairment or psychological disorders. In this study we evaluated analytic/global and visual/auditory perceptual dimensions of cognitive style in patients with epilepsy. Twenty-five cryptogenic temporal lobe epilepsy (TLE) patients matched with 25 idiopathic generalized epilepsy (IGE) sufferers and 25 healthy volunteers were recruited and participated in three cognitive style tests: "Sternberg-Wagner Self-Assessment Inventory", the C. Cornoldi test series called AMOS, and the Mariani Learning style Questionnaire. Our results demonstrate a significant association between analytic cognitive style and both IGE and TLE and respectively a predominant auditory and visual analytic style (ANOVA: p values <0,0001). These findings should encourage further research to investigate information processing style and its neurophysiological correlates in epilepsy.

Clinical studies and anti-inflammatory mechanisms of treatments

In this exciting era, we are coming closer and closer to bringing an anti-inflammatory therapy to the clinic for the purpose of seizure prevention, modification, and/or suppression. At present, it is unclear what this approach might entail, and what form it will take. Irrespective of the therapy that ultimately reaches the clinic, there will be some commonalities with regard to clinical trials. A number of animal models have now been used to identify inflammation as a major underlying mechanism of both chronic seizures and the epileptogenic process. These models have demonstrated that specific anti-inflammatory treatments can be effective at both suppressing chronic seizures and interfering with the process of epileptogenesis. Some of these have already been evaluated in early phase clinical trials. It can be expected that there will soon be more clinical trials of both "conventional, broad spectrum" anti-inflammatory agents and novel new approaches to utilizing specific anti-inflammatory therapies with drugs or other therapeutic interventions. A summary of some of those approaches appears below, as well as a discussion of the issues facing clinical trials in this new domain.

Epilepsy in ring chromosome 20 syndrome

OBJECTIVE

Ring chromosome 20 syndrome is characterized by severe, drug resistant childhood onset epilepsy, often accompanied by cognitive impairment. We characterized the electro-clinical phenotype and the long-term course of epilepsy in a large series.

METHODS

We reviewed the electro-clinical phenotype of 25 patients (aged 8-59 years), and assessed the relationship between epilepsy severity and clinical and/or genetic variables. We also searched for reports of patients diagnosed with r(20) syndrome in the literature, included those whose clinical information was sufficiently accurate, and compared their clinical features with the ones of our patients.

RESULTS

Epilepsy exhibited an age dependent course. When seizure onset occurred in childhood (21 patients), terrifying hallucinations associated with focal motor seizures, often sleep-related (8 patients), or dyscognitive seizures (13 patients), were prominent features, often evolving into epileptic encephalopathy associated with non-convulsive status epilepticus (11 patients). In the long-term, progressive stabilization of drug resistant epilepsy associated with non-convulsive status epilepticus, focal seizures with motor and autonomic features, and eyelid myoclonia were noticed. Epilepsy onset in adolescence (3 patients) was accompanied by a milder developmental course, dyscognitive seizures and non-convulsive status epilepticus, and no cognitive decline. Only three older patients became seizure free (>5 years) We found statistically significant correlations between age at epilepsy onset and cognitive level. Although in the study cohort the relationship between r(20) ratio, age at epilepsy onset and cognitive level was non-statistically significant, it reached significance evaluating the larger cohort of patients previously published.

SIGNIFICANCE

In ring(20) syndrome, epilepsy has an age dependent course and a worse outcome when age at seizure onset is earlier. The r(20) ratio and severity of cognitive impairment appear to be directly related to each other and inversely correlated with the age at epilepsy onset.

Psychosocial aspects of epilepsy: a wider approach

SUMMARY

Epilepsy is one of the most serious neurological conditions and has an impact not only on the affected individual but also on the family and, indirectly, on the community. A global approach to the individual must take into account cognitive problems, psychiatric comorbidities and all psychosocial complications that often accompany epilepsy. We discuss psychosocial issues in epilepsy with special focus on the relationship between stigma and psychiatric comorbidities. Social barriers to optimal care and health outcomes for people with epilepsy result in huge disparities, and the public health system needs to invest in awareness programmes to increase public knowledge and reduce stigma in order to minimise such disparities.

DECLARATIONS OF INTEREST

J.W.S. receives research support from the Dr Marvin Weil Epilepsy Research Fund, Eisai, GlaxoSmithKline, the World Health Organization and the EU's FP7 programme, and has been consulted by, and has received fees for lectures from, GlaxoSmithKline, Eisai, Lundbeck, Teva and UCB.

COPYRIGHT AND USAGE

© The Royal College of Psychiatrists 2016. This is an open access article distributed under the terms of the Creative Commons Non-Commercial, No Derivatives (CC BY-NC-ND) license.

Whole-brain analytic measures of network communication reveal increased structure-function correlation in right temporal lobe epilepsy

The in vivo structure-function relationship is key to understanding brain network reorganization due to pathologies. This relationship is likely to be particularly complex in brain network diseases such as temporal lobe epilepsy, in which disturbed large-scale systems are involved in both transient electrical events and long-lasting functional and structural impairments. Herein, we estimated this relationship by analyzing the correlation between structural connectivity and functional connectivity in terms of analytical network communication parameters. As such, we targeted the gradual topological structure-function reorganization caused by the pathology not only at the whole brain scale but also both in core and peripheral regions of the brain. We acquired diffusion (dMRI) and resting-state fMRI (rsfMRI) data in seven right-lateralized TLE (rTLE) patients and fourteen healthy controls and analyzed the structure-function relationship by using analytical network communication metrics derived from the structural connectome. In rTLE patients, we found a widespread hypercorrelated functional network. Network communication analysis revealed greater unspecific branching of the shortest path (search information) in the structural connectome and a higher global correlation between the structural and functional connectivity for the patient group. We also found evidence for a preserved structural rich-club in the patient group. In sum, global augmentation of structure-function correlation might be linked to a smaller functional repertoire in rTLE patients, while sparing the central core of the brain which may represent a pathway that facilitates the spread of seizures.

Assessment of Treatment Side Effects and Quality of Life in People with Epilepsy

Epilepsy impairs quality of life in physical, psychological, cognitive, social, and occupational domains. In people who are not seizure free, depression and adverse medication effects have a predominant role in determining quality of life. The assessment of these factors and other comorbidities is essential for maximizing quality of life in epilepsy. There are multiple tools available to assess medication effects and quality of life in a structured format. Such tools can provide superior assessments and allow clinicians to have a greater impact on their patients' quality of life.

The enigma of the latent period in the development of symptomatic acquired epilepsy - Traditional view versus new concepts

A widely accepted hypothesis holds that there is a seizure-free, pre-epileptic state, termed the "latent period", between a brain insult, such as traumatic brain injury or stroke, and the onset of symptomatic epilepsy, during which a cascade of structural, molecular, and functional alterations gradually mediates the process of epileptogenesis. This review, based on recent data from both animal models and patients with different types of brain injury, proposes that epileptogenesis and often subclinical epilepsy can start immediately after brain injury without any appreciable latent period. Even though the latent period has traditionally been the cornerstone concept representing epileptogenesis, we suggest that the evidence for the existence of a latent period is spotty both for animal models and human epilepsy. Knowing whether a latent period exists or not is important for our understanding of epileptogenesis and for the discovery and the trial design of antiepileptogenic agents. The development of antiepileptogenic treatments to prevent epilepsy in patients at risk from a brain insult is a major unmet clinical need.

Validation of diagnostic tests for depressive disorder in drug-resistant mesial temporal lobe epilepsy

PURPOSE

This study aimed to evaluate the diagnostic accuracy of the Hamilton Rating Scale for Depression (HRSD), the Beck Depression Inventory (BDI), the Hospital Anxiety and Depression Scale (HADS), and the Hospital Anxiety and Depression Scale-Depression subscale (HADS-D) as diagnostic tests for depressive disorder in drug-resistant mesial temporal lobe epilepsy with hippocampal sclerosis (MTLE-HS).

METHODS

One hundred three patients with drug-resistant MTLE-HS were enrolled. All patients underwent a neurological examination, interictal and ictal video-electroencephalogram (V-EEG) analyses, and magnetic resonance imaging (MRI). Psychiatric interviews were based on DSM-IV-TR criteria and ILAE Commission of Psychobiology classification as a gold standard; HRSD, BDI, HADS, and HADS-D were used as psychometric diagnostic tests, and receiver operating characteristic (ROC) curves were used to determine the optimal threshold scores.

RESULTS

For all the scales, the areas under the curve (AUCs) were approximately 0.8, and they were able to identify depression in this sample. A threshold of ≥9 on the HRSD and a threshold of ≥8 on the HADS-D showed a sensitivity of 70% and specificity of 80%. A threshold of ≥19 on the BDI and HADS-D total showed a sensitivity of 55% and a specificity of approximately 90%. The instruments showed a negative predictive value of approximately 87% and a positive predictive value of approximately 65% for the BDI and HADS total and approximately 60% for the HRSD and HADS-D.

CONCLUSIONS

HRSD≥9 and HADS-D≥8 had the best balance between sensitivity (approximately 70%) and specificity (approximately 80%). However, with these thresholds, these diagnostic tests do not appear useful in identifying depressive disorder in this population with epilepsy, and their specificity (approximately 80%) and PPV (approximately 55%) were lower than those of the other scales. We believe that the BDI and HADS total are valid diagnostic tests for depressive disorder in patients with MTLE-HS, as both scales showed acceptable (though not high) specificity and PPV for this type of study.

Reactive astrogliosis causes the development of spontaneous seizures

Epilepsy is one of the most common chronic neurologic diseases, yet approximately one-third of affected patients do not respond to anticonvulsive drugs that target neurons or neuronal circuits. Reactive astrocytes are commonly found in putative epileptic foci and have been hypothesized to be disease contributors because they lose essential homeostatic capabilities. However, since brain pathology induces astrocytes to become reactive, it is difficult to distinguish whether astrogliosis is a cause or a consequence of epileptogenesis. We now present a mouse model of genetically induced, widespread chronic astrogliosis after conditional deletion of β1-integrin (Itgβ1). In these mice, astrogliosis occurs in the absence of other pathologies and without BBB breach or significant inflammation. Electroencephalography with simultaneous video recording revealed that these mice develop spontaneous seizures during the first six postnatal weeks of life and brain slices show neuronal hyperexcitability. This was not observed in mice with neuronal-targeted β1-integrin deletion, supporting the hypothesis that astrogliosis is sufficient to induce epileptic seizures. Whole-cell patch-clamp recordings from astrocytes further suggest that the heightened excitability was associated with impaired astrocytic glutamate uptake. Moreover, the relative expression of the cation-chloride cotransporters (CCC) NKCC1 (Slc12a2) and KCC2 (Slc12a5), which are responsible for establishing the neuronal Cl(-) gradient that governs GABAergic inhibition were altered and the NKCC1 inhibitor bumetanide eliminated seizures in a subgroup of mice. These data suggest that a shift in the relative expression of neuronal NKCC1 and KCC2, similar to that observed in immature neurons during development, may contribute to astrogliosis-associated seizures.

Cognitive dysfunction in patients with epilepsy: focus on clinical variables

ABSTRACT 

A variety of factors can affect cognitive functions in patients with epilepsy, with the majority of cognitive problems having a multifactorial origin. In routine clinical practice, it can be difficult to dissect out the contribution of all of the different variables, because they are often interlinked together. In this article, all of the major variables implicated in cognitive dysfunction in epilepsy are discussed. In general terms, it is widely accepted that cognitive dysfunction in epilepsy can be trait dependent or state dependent. The former is a permanent condition due to the underlying brain damage or disorder, while the latter is a potentially reversible condition due to modifiable factors, such as antiepileptic drugs, seizure frequency and pattern and psychiatric comorbidity. Neuropsychological deficits also represent an important sequela in epilepsy surgery. Visual naming and visual memory loss have been clearly associated with temporal lobe surgery. It seems that the laterality of resection is not a major determinant, while the extension of resection is relevant for visual naming.

Negative BOLD in default-mode structures measured with EEG-MREG is larger in temporal than extra-temporal epileptic spikes

Introduction: EEG-fMRI detects BOLD changes associated with epileptic interictal discharges (IED) and can identify epileptogenic networks in epilepsy patients. Besides positive BOLD changes, negative BOLD changes have sometimes been observed in the default-mode network, particularly using group analysis. A new fast fMRI sequence called MREG (Magnetic Resonance Encephalography) shows increased sensitivity to detect IED-related BOLD changes compared to the conventional EPI sequence, including frequent occurrence of negative BOLD responses in the DMN. The present study quantifies the concordance between the DMN and negative BOLD related to IEDs of temporal and extra-temporal origin.

Methods: Focal epilepsy patients underwent simultaneous EEG-MREG. Areas of overlap were calculated between DMN regions, defined as precuneus, posterior cingulate, bilateral inferior parietal and mesial prefrontal cortices according to a standardized atlas, and significant negative BOLD changes revealed by an event-related analysis based on the timings of IED seen on EEG. Correlation between IED number/lobe of origin and the overlap were calculated.

Results: 15 patients were analyzed, some showing IED over more than one location resulting in 30 different IED types. The average overlap between negative BOLD and DMN was significantly larger in temporal (23.7 ± 19.6 cm³) than extra-temporal IEDs (7.4 ± 5.1 cm³, p = 0.008). There was no significant correlation between the number of IEDs and the overlap between DMN structures and negative BOLD areas.

Discussion: MREG results in an increased sensitivity to detect negative BOLD responses related to focal IED in single patients, with responses often occurring in DMN regions. In patients with high overlap with the DMN, this suggests that epileptic IEDs may be associated with a brief decrease in attention and cognitive ability. Interestingly this observation was not dependent on the frequency of IED but more common in IED of temporal origin.

Clinical risk factors associated with anti-epileptic drug responsiveness in canine epilepsy

The nature and occurrence of remission, and conversely, pharmacoresistance following epilepsy treatment is still not fully understood in human or veterinary medicine. As such, predicting which patients will have good or poor treatment outcomes is imprecise, impeding patient management. In the present study, we use a naturally occurring animal model of pharmacoresistant epilepsy to investigate clinical risk factors associated with treatment outcome. Dogs with idiopathic epilepsy, for which no underlying cause was identified, were treated at a canine epilepsy clinic and monitored following discharge from a small animal referral hospital. Clinical data was gained via standardised owner questionnaires and longitudinal follow up data was gained via telephone interview with the dogs’ owners. At follow up, 14% of treated dogs were in seizure-free remission. Dogs that did not achieve remission were more likely to be male, and to have previously experienced cluster seizures. Seizure frequency or the total number of seizures prior to treatment were not significant predictors of pharmacoresistance, demonstrating that seizure density, that is, the temporal pattern of seizure activity, is a more influential predictor of pharmacoresistance. These results are in line with clinical studies of human epilepsy, and experimental rodent models of epilepsy, that patients experiencing episodes of high seizure density (cluster seizures), not just a high seizure frequency pre-treatment, are at an increased risk of drug-refractoriness. These data provide further evidence that the dog could be a useful naturally occurring epilepsy model in the study of pharmacoresistant epilepsy.

Dynamic expression patterns of ATF3 and p53 in the hippocampus of a pentylenetetrazole-induced kindling model

Epilepsy is a common and often deleterious neurological condition. Emerging evidence has demonstrated the roles of innate immunity and the associated inflammatory processes in epilepsy. In a previous study, we found that Toll-like receptors (TLRs) are upregulated and promote mossy fiber sprouting (MFS) in an epileptic model. As downstream effectors of TLRs, the activating transcription factor 3 (ATF3) and p53 proteins were shown to be involved in neurite outgrowth. In the present study, we hypothesized that ATF3 and p53 participate in the process of epilepsy and can affect MFS. To investigate this hypothesis, we examined the expression of ATF3 and p53 in hippocampal tissues of rats kindled by pentylenetetrazole (PTZ) using immunofluorescence, immunohistochemistry and western blotting. MFS was evaluated by Timm staining in the hippocampus. Results from these experiments revealed that expression of ATF3 and p53 is significantly higher (p<0.05) in the CA3 area of the hippocampus in the PTZ-treated group compared to the control group. ATF3 expression gradually increased from 3 days to 4 weeks, peaked at 4 weeks and decreased slightly at 6 weeks in the PTZ group, while the expression of p53 was maintained at similar levels at different time-points following PTZ treatment. No obvious difference in the expression of these proteins was observed between the PTZ and the control group in the dentate gyrus (DG) area (p>0.05). The degree of MFS in the PTZ group peaked at 4 weeks and was maintained at a high level until 6 weeks post-PTZ treatment. In conclusion, ATF3 and p53 may be involved in the occurrence of seizure and play critical roles in MFS in the PTZ kindling model.

Animal models of epilepsy: use and limitations

Epilepsy is a chronic neurological condition characterized by recurrent seizures that affects millions of people worldwide. Comprehension of the complex mechanisms underlying epileptogenesis and seizure generation in temporal lobe epilepsy and other forms of epilepsy cannot be fully acquired in clinical studies with humans. As a result, the use of appropriate animal models is essential. Some of these models replicate the natural history of symptomatic focal epilepsy with an initial epileptogenic insult, which is followed by an apparent latent period and by a subsequent period of chronic spontaneous seizures. Seizures are a combination of electrical and behavioral events that are able to induce chemical, molecular, and anatomic alterations. In this review, we summarize the most frequently used models of chronic epilepsy and models of acute seizures induced by chemoconvulsants, traumatic brain injury, and electrical or sound stimuli. Genetic models of absence seizures and models of seizures and status epilepticus in the immature brain were also examined. Major uses and limitations were highlighted, and neuropathological, behavioral, and neurophysiological similarities and differences between the model and the human equivalent were considered. The quest for seizure mechanisms can provide insights into overall brain functions and consciousness, and animal models of epilepsy will continue to promote the progress of both epilepsy and neurophysiology research.