Antiepileptogenic and anticonvulsant activity of interleukin-1β in amygdala-kindled rats

Neuroinflammation in Pathogenesis of Audiogenic Epilepsy: Altered Proinflammatory Cytokine Levels in the Rats of Krushinsky-Molodkina Seizure-Prone Strain

Neuroinflammation plays an important role in epileptogenesis, however, most studies are performed using pharmacological models of epilepsy, while there are only few data available for non-invasive, including genetic, models. The levels of a number of pro-inflammatory cytokines were examined in the Krushinsky-Molodkina (KM) rat strain with high audiogenic epilepsy (AE) proneness (intense tonic seizure fit in response to loud sound) and in the control strain "0" (not predisposed to AE) using multiplex immunofluorescence magnetic assay (MILLIPLEX map Kit). Cytokine levels were determined in the dorsal striatum tissue and in the brain stem. Background levels of IL-1β, IL-6, and TNF-α in the dorsal striatum of the KM rats were significantly lower than in the rats "0" (by 32.31, 27.84, and 38.87%, respectively, p < 0.05, 0.05, and 0.01), whereas no inter-strain differences in the levels of these metabolites were detected in the brain stem in the "background" state. Four hours after sound exposure, the TNF-α level in the dorsal striatum of the KM rats was significantly lower (by 38.34%, p < 0.01) than in the "0" rats. In the KM rats, the dorsal striatal levels of IL-1β and IL-6 were significantly higher after the sound exposure and subsequent seizure fit, compared to the background (35.29 and 50.21% increase, p < 0.05, 0.01, respectively). In the background state the IL-2 level in the KM rats was not detected, whereas after audiogenic seizures its level was 14.01 pg/ml (significant difference, p < 0.01). In the KM rats the brain stem levels of IL-1β and TNF-α after audiogenic seizures were significantly lower than in the background (13.23 and 23.44% decrease, respectively, p < 0.05). In the rats of the "0" strain, the levels of cytokines in the dorsal striatum after the action of sound (which did not induce AE seizures) were not different from those of the background, while in the brain stem of the "0" strain the levels of IL-1β were lower than in the background (40.28%, p < 0.01). Thus, the differences between the background levels of cytokines and those after the action of sound were different in the rats with different proneness to AE. These data suggest involvement of the analyzed cytokines in pathophysiology of the seizure state, namely in AE seizures.

Modulating Expression of Endogenous Interleukin 1 Beta in the Acute Phase of the Pilocarpine Model of Epilepsy May Change Animal Survival

The pilocarpine-induced (PILO) model has helped elucidate the electrophysiological and molecular aspects related to mesial temporal lobe epilepsy. It has been suggested that the extensive cell death and edema observed in the brains of these animals could be induced by increased inflammatory responses, such as the rapid release of the inflammatory cytokine interleukin 1 beta (Il1b). In this study, we investigate the role of endogenous Il1b in the acute phase of the PILO model. Our aim is twofold. First, we want to determine whether it is feasible to silence Il1b in the central nervous system using a non-invasive procedure. Second, we aim to investigate the effect of silencing endogenous Il1b and its antagonist, Il1rn.We used RNA interference applied non-invasively to knockdown Il1b and its endogenous antagonist Il1rn. We found that knocking down Il1b prior to pilocarpine injection increased the mortality rate of treated animals. Furthermore, we observed that, when exposing the animals to more Il1b by silencing its endogenous antagonist Il1rn, there was a better response to status epilepticus with decreased animal mortality in the acute phase of the PILO model. Thus, we show the feasibility of using a novel, less invasive approach to study genes involved in the inflammatory response in the central nervous system. Furthermore, our results provide suggestive evidence that modulating endogenous Il1b improves animal survival in the acute phase of the PILO model and may have effects that extend into the chronic phase.

The Function of NF-Kappa B During Epilepsy, a Potential Therapeutic Target

The transcriptional regulator nuclear factor kappa B (NF-κB) modulates cellular biological activity by binding to promoter regions in the nucleus and transcribing various protein-coding genes. The NF-κB pathway plays a major role in the expressing genes related to inflammation, including chemokines, interleukins, and tumor necrosis factor. It also transcribes genes that can promote neuronal survival or apoptosis. Epilepsy is one of the most common brain disorders and it not only causes death worldwide but also affects the day-to-day life of affected individuals. While epilepsy has diverse treatment options, there remain patients who are not sensitive to the existing treatment methods. Recent studies have implicated the critical role of NF-κB in epilepsy. It is upregulated in neurons, glial cells, and endothelial cells, due to neuronal loss, glial cell proliferation, blood-brain barrier dysfunction, and hippocampal sclerosis through the glutamate and γ-aminobutyric acid imbalance, ion concentration changes, and other mechanisms. In this review, we summarize the functional changes caused by the upregulation of NF-κB in the central nervous system during different periods after seizures. This review is the first to deconvolute the complicated functions of NF-κB, and speculate that the regulation of NF-κB can be a safe and effective treatment strategy for epilepsy.

Antagonism of the ghrelin receptor type 1a in the rat brain induces status epilepticus in an electrical kindling model of epilepsy

Studies have shown the anti-seizure properties of the ghrelin hormone in different models of epilepsy. Nevertheless, the role of the endogenous ghrelin is unknown in the electrical kindling model of epilepsy. In this study, we evaluated the effect of the antagonism of the ghrelin receptors in the brain of fully kindled rats. Adult male Wistar rats weighing 300 g were used. Animals were stereotaxically implanted with two uni-polar electrodes in the skull surface and a tri-polar electrode in the basolateral amygdala, and a guide cannula in the left lateral ventricle. Animals underwent a rapid kindling protocol. After showing three consecutive stages of five seizures, the animals were considered fully kindled. D-Lys-3-GHRP-6 (1, 50, and 100 μg/rat) was injected intracerebroventricularly (i.c.v.) in the kindled animals. Each rat was considered as its control and received a single dose of D-Lys-3-GHRP-6. Seizure parameters including after discharge duration (ADD), seizure stage (SS), stage four latency (S4L), and stage five duration (S5D) were recorded. The paired t test indicated a significant increase in seizure induction. D-Lys-3-GHRP-6 (1 μg/rat; i.c.v.) prolonged ADD in the kindled rats, significantly. D-Lys-3-GHRP-6 (50 and 100 μg/rat; i.c.v.) induced spontaneous seizures, which led to status epilepticus in the kindled rats. The results indicate that the antagonism of the ghrelin functional receptors prolongs seizures and induces status epilepticus in the kindling model of epilepsy, and propose that the endogenous ghrelin signaling has crucial antiepileptic properties.

Neuroinflammation and Proinflammatory Cytokines in Epileptogenesis

Increasing evidence corroborates the fundamental role of neuroinflammation in the development of epilepsy. Proinflammatory cytokines (PICs) are crucial contributors to the inflammatory reactions in the brain. It is evidenced that epileptic seizures are associated with elevated levels of PICs, particularly interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α), which underscores the impact of neuroinflammation and PICs on hyperexcitability of the brain and epileptogenesis. Since the pathophysiology of epilepsy is unknown, determining the possible roles of PICs in epileptogenesis could facilitate unraveling the pathophysiology of epilepsy. About one-third of epileptic patients are drug-resistant, and existing treatments only resolve symptoms and do not inhibit epileptogenesis; thus, treatment of epilepsy is still challenging. Accordingly, understanding the function of PICs in epilepsy could provide us with promising targets for the treatment of epilepsy, especially drug-resistant type. In this review, we outline the role of neuroinflammation and its primary mediators, including IL-1β, IL-1α, IL-6, IL-17, IL-18, TNF-α, and interferon-γ (IFN-γ) in the pathophysiology of epilepsy. Furthermore, we discuss the potential therapeutic targeting of PICs and cytokine receptors in the treatment of epilepsy.

Experimental chronic sleep fragmentation alters seizure susceptibility and brain levels of interleukins 1β and 6

Brain hyperexcitability in sleep apnea is believed to be provoked by hypoxemia, but sleep fragmentation can also play a significant role. Sleep fragmentation can trigger inflammatory mechanisms. The aim of this research was to investigate the effects of chronic sleep fragmentation on seizure susceptibility and brain cytokine profile. Chronic sleep fragmentation in male rats with implanted EEG electrodes was achieved by the treadmill method. Rats were randomized to: treadmill control (TC); activity control (AC) and sleep fragmentation (SF) group. Convulsive behavior was assessed 14 days later by seizure incidence, latency time and seizure severity during 30 min following lindane administration. The number and duration of EEG ictal periods were determined. Levels of IL-1β and IL-6 were measured in the animals' serum and brain structures (hippocampus, thalamus and cerebral cortex), in separate rat cohort that underwent the same fragmentation protocol except lindane administration. Incidence and severity of seizures were significantly increased, while latency was significantly decreased in SF+L compared with TC+L group. Seizure latency was also significantly decreased in SF+L compared to AC+L group. The number and duration of ictal periods were increased in the SF+L compared to the AC+L group. IL-1β was significantly increased in the thalamus, cortex and hippocampus in the SF compared to the AC and TC groups. IL-6 was statistically higher only in the cortex of SF animals, while in the thalamic or hippocampal tissue, no difference was observed between the groups. It could be concluded that fourteen-day sleep fragmentation increases seizure susceptibility in rats and modulates brain production of IL-1β and IL-6.

Brain hyperexcitability in sleep apnea is believed to be provoked by hypoxemia, but sleep fragmentation can also play a significant role. Sleep fragmentation can trigger inflammatory mechanisms. The aim of this research was to investigate the effects of chronic sleep fragmentation on seizure susceptibility and brain cytokine profile. Chronic sleep fragmentation in male rats with implanted EEG electrodes was achieved by the treadmill method. Rats were randomized to: treadmill control (TC); activity control (AC) and sleep fragmentation (SF) group. Convulsive behavior was assessed 14 days later by seizure incidence, latency time and seizure severity during 30 min following lindane administration. The number and duration of EEG ictal periods were determined. Levels of IL-1β and IL-6 were measured in the animals’ serum and brain structures (hippocampus, thalamus and cerebral cortex), in separate rat cohort that underwent the same fragmentation protocol except lindane administration. Incidence and severity of seizures were significantly increased, while latency was significantly decreased in SF+L compared with TC+L group. Seizure latency was also significantly decreased in SF+L compared to AC+L group. The number and duration of ictal periods were increased in the SF+L compared to the AC+L group. IL-1β was significantly increased in the thalamus, cortex and hippocampus in the SF compared to the AC and TC groups. IL-6 was statistically higher only in the cortex of SF animals, while in the thalamic or hippocampal tissue, no difference was observed between the groups. It could be concluded that fourteen-day sleep fragmentation increases seizure susceptibility in rats and modulates brain production of IL-1β and IL-6.

Transcranial direct current stimulation (tDCS) affects neuroinflammation parameters and behavioral seizure activity in pentylenetetrazole-induced kindling in rats

Despite the introduction of new antiepileptic drugs, about 30 % of patients with epilepsy are refractory to drug therapy. Thus, the search for non-pharmacological interventions such as transcranial direct current stimulation (tDCS) may be an alternative, either alone or in combination with low doses of anticonvulsants. This study evaluated the effect of anodal (a-tDCS) and cathodal tDCS (c-tDCS) on seizure behavior and neuroinflammation parameters. Rats were submitted to the kindling model induced by pentylenetetrazole (PTZ) using diazepam (DZP) as anticonvulsant standard. tDCS groups were submitted to 10 sessions of a-tDCS or c-tDCS or SHAM-tDCS. Every 3 days they received saline (SAL), low dose of DZP (alone or in combination with tDCS) or effective dose of DZP 30 min before administration of PTZ, totaling 16 days of protocol. Neither a-tDCS nor c-tDCS reduced the occurrence of clonic forelimb seizures (convulsive motor seizures - stage 3 by the adapted Racine scale we based on). Associated with DZP, c-tDCS (c-tDCS/DZP0.15) increased the latency to first clonic forelimb seizure on the 10th and 16th days. Hippocampal IL-1β levels were reduced by c-tDCS and c-tDCS/DZP0.15. In contrast, these treatments induced an increase in cortical IL-1β levels. Hippocampal TNF-α levels were not altered by c-tDCS or a-tDCS, but c-tDCS and c-tDCS/DZP0.15 increased those levels in cerebral cortex. Cortical NGF levels were increased by c-tDCS and c-tDCS/DZP0.15. a-tDCS/DZP0.15 reduced hippocampal BDNF levels and c-tDCS/DZP0.15 increased these levels in cerebral cortex. In conclusion, c-tDCS alone or in combination with a low dose of DZP showed to affect neuroinflammation, improving central neurotrophin levels and decreasing hippocampal IL-1β levels after PTZ-induced kindling without statistically significant effect on seizure behavior.

The role of UCH-L1, MMP-9, and GFAP as peripheral markers of different susceptibility to seizure development in a preclinical model of epilepsy

In our study, we assessed the potency of the brain-derived proteins ubiquitin carboxy-terminal hydrolase L1 (UCH-L1), matrix metalloproteinase 9 (MMP-9), glial fibrillary acidic protein (GFAP) and the immune activation indicators interleukin 1β (IL-1β) and interleukin 6 (IL-6) as peripheral biomarkers of different susceptibilities to kindling in a preclinical model. We observed increased plasma UCH-L1 levels in kindled vs. control animals. Furthermore, MMP-9 and IL-1β concentrations were the lowest in rats resistant to kindling. In summary, UCH-L1 is an indicator of neuronal loss and BBB disruption after seizure. MMP-9 and IL-1β may indicate resistance to kindling. UCH-L1, MMP-9 and IL-1β may have utility as peripheral biomarkers with translational potency in the clinic.

Effect of gabapentin on sleep patterns disturbed by epilepsy

For a long time, numerous sleep alterations induced by nocturnal epilepsy have been described. Such alterations include sleep fragmentation, decrement of sleep efficiency, increment of the wake time after sleep onset (WASO), increment of light sleep, and decrement of sleep depth. On the other hand, gabapentin (GBP), an antiepileptic drug analog of γ-aminobutyric acid (GABA) used as adjunctive and eventually, as a monotherapeutic treatment, induces a significant improvement in patients with both focal and secondarily generalized partial seizures. In experimental epilepsy models, this drug protects against pentylenetetrazol (PTZ)-induced convulsions. In consideration of such GBP properties, the aim of this work was to investigate its efficacy to protect against sleep disturbances provoked by convulsive seizures induced by the administration of PTZ. Nine-hour (9-hour) polygraphic studies were carried out in chronically implanted male adult Wistar rats separated into 4 different groups of 6 individuals. Control recordings in each group were done after saline administration. One group received a SC Subcutaneous (SC) injection of 50 mg/kg of PTZ alone while the other three groups were injected with either 15, 30, or 60 mg/kg IP Intraperitoneal (IP) of GBP 30 min prior to PTZ (50 mg/kg SC) administration. Animals displayed the whole range of electrophysiological and behavioral manifestations of the disease during the epileptic episodes induced by PTZ administration, and the states of vigilance were significantly altered. Insomnia occurred immediately after PTZ injection preceding the appearance of the first epileptic symptoms. Thus, both slow wave sleep (SWS) and rapid eye movement sleep (REM sleep) were completely inhibited during a relatively long period of time. The disturbing effects of epilepsy on sleep decreased when animals were under GBP treatment. Improvement of sleep was dependent on the administered dose of this antiepileptic drug.

Comparison of behavioral, neuroprotective, and proinflammatory cytokine modulating effects exercised by (+)-cis-EC and (-)-cis-EC stereoisomers in a PTZ-induced kindling test in mice

Epoxy-carvone (EC) has chiral centers that allow generation of stereoisomers, including (+)-cis-EC and (-)-cis-EC, whose effects in the kindling tests have never been studied. Accordingly, this study aims to comparatively investigate the effect of stereoisomers (+)-cis-epoxy-carvone and (-)-cis-epoxy-carvone on behavioral changes measured in scores, in the levels of cytokines (IL-1β, IL-6, and TNFα) and neuronal protection in the face of continuous treatment with pentylenetetrazol. Swiss mice were divided into five groups (n = 10), receiving vehicle, (+) - cis-EC, (-) - cis-EC (both at the dose of 30 mg/kg), and diazepam (4 mg/kg). Thirty minutes after the respective treatment was administered to the animals one subconvulsive dose of PTZ (35 mg/kg). Seven subconvulsives treatments were made on alternate days, in which each treatment several parameters were recorded. In the eighth treatment, the animals receiving the highest dose of PTZ (75 mg/kg) and were sacrificed for quantification of cytokines and histopathologic analysis. All drugs were administered by intraperitoneal route. In the kindling test, (+)-cis-EC and (-)-cis-EC reduced the average scores. The stereoisomer (+)-cis-EC decreased levels of proinflammatory cytokines IL-1β, IL-6, and TNFα, whereas comparatively (-)-cis-EC did not reduce IL-1β levels. Histopathological analysis of the mice hippocampi undergoing this methodology showed neural protection for treated with (+)-cis-EC. The results suggest that the anticonvulsant effect of (+)-cis-EC possibly takes place due to reduction of proinflammatory cytokines involved in the epileptogenic process, besides neuronal protection, yet further investigation of the mechanisms involved is required.

Interleukin-1 receptor (IL-1R) mediates epilepsy-induced sleep disruption

Background

Sleep disruptions are common in epilepsy patients. Our previous study demonstrates that homeostatic factors and circadian rhythm may mediate epilepsy-induced sleep disturbances when epilepsy occurs at different zeitgeber hours. The proinflammatory cytokine, interleukin-1 (IL-1), is a somnogenic cytokine and may also be involved in epileptogenesis; however, few studies emphasize the effect of IL-1 in epilepsy-induced sleep disruption. We herein hypothesized that IL-1 receptor type 1 (IL-1R1) mediates the pathogenesis of epilepsy and epilepsy-induced sleep disturbances. We determined the role of IL-1R1 by using IL-1R1 knockout (IL-1R1 −/− KO) mice.

Results

Our results elucidated the decrease of non-rapid eye movement (NREM) sleep during the light period in IL-1R −/− mice and confirmed the somnogenic role of IL-1R1. Rapid electrical amygdala kindling was performed to induce epilepsy at the particular zeitgeber time (ZT) point, ZT13. Our results demonstrated that seizure thresholds induced by kindling stimuli, such as the after-discharge threshold and successful kindling rates, were not altered in IL-1R −/− mice when compared to those obtained from the wildtype mice (IL-1R +/+ mice). This result suggests that IL-1R1 is not involved in kindling-induced epileptogenesis. During sleep, ZT13 kindling stimulation significantly enhanced NREM sleep during the subsequent 6 h (ZT13-18) in wildtype mice, and sleep returned to the baseline the following day. However, the kindling-induced sleep alteration was absent in the IL-1R −/− KO mice.

Conclusions

These results indicate that the IL-1 signal mediates epilepsy-induced sleep disturbance, but dose not participate in kindling-induced epileptogenesis.

Pharmacokinetic/pharmacodynamic considerations for epilepsy - depression comorbidities

INTRODUCTION

Epilepsy may be frequently associated with psychiatric disorders and its co-existence with depression usually results in the reduced quality of life of patients with epilepsy. Also, the efficacy of antiepileptic treatment in depressed patients with epilepsy may be significantly reduced.

AREAS COVERED

Results of experimental studies indicate that antidepressants co-administered with antiepileptic drugs may either increase their anticonvulsant activity, remain neutral or decrease the protective action of antiepileptic drugs in models of seizures. Apart from purely pharmacodynamic interactions, pharmacokinetic mechanisms have been proven to contribute to the final outcome. We report on clinical data regarding the pharmacokinetic interactions of enzyme-inducing antiepileptic drugs with various antidepressants, whose plasma concentration may be significantly reduced. On the other hand, antidepressants (especially selective serotonin reuptake inhibitors) may influence the metabolism of antiepileptics, in many cases resulting in the elevation of plasma concentration of antiepileptic drugs.

EXPERT OPINION

The preclinical data may provide valuable clues on how to combine these two groups of drugs - antidepressant drugs neutral or potentiating the anticonvulsant action of antiepileptics are recommended in this regard. Avoidance of antidepressants clearly decreasing the convulsive threshold or decreasing the anticonvulsant efficacy of antiepileptic drugs (f.e. bupropion or mianserin) in patients with epilepsy is recommended.

The Pro-inflammatory Cytokine Interleukin-1β is a Key Regulatory Factor for the Postictal Suppression in Mice

AIMS

The postictal suppression (PS) is a common and important period following an epileptic seizure but has not been well studied. This study was designed to determine whether interleukin-1β (IL-1β) is involved in the PS.

METHODS

The effects of IL-1β on the PS were tested in three independent seizure models induced by hippocampal kindling, maximal electroshock seizure (MES), and 4-aminopyridine, respectively.

RESULTS

IL-1R1 knockout or IL-1RA enhanced the seizure refractory phenomenon without influencing the baseline seizure threshold in intermittent MES model. IL-1β attenuated the seizure refractory phenomenon without affecting the severity of the preceding seizures in hippocampal kindling model, while IL-1RA enhanced it. Besides, IL-1β reduced the postictal EEG suppression period, while IL-1RA prolonged it. And IL-1β showed no further effect on the postictal EEG suppression and seizure refractory phenomenon in IL-1R1 knockout mice. In addition, 30 min after intrahippocampal injection of 4-aminopyridine, IL-1β increased the incidence of SE, while IL-1RA prolonged the intervals between recurrent seizures.

CONCLUSIONS

This study provides the first direct evidence that IL-1β is key regulatory factor for the PS, and its receptor IL-1R1 may be a potential target for adjuvant treatment of postictal problems.

IL-1β: an important cytokine associated with febrile seizures?

Febrile seizures (FSs) are the most common convulsions in childhood. Studies have demonstrated a significant relationship between a history of prolonged FSs during early childhood and temporal sclerosis, which is responsible for intractable mesial temporal lobe epilepsy. It has been shown that interleukin-1β (IL-1β) is intrinsically involved in the febrile response in children and in the generation of FSs. We summarize the gene polymorphisms, changes of IL-1β levels and the putative role of IL-1β in the generation of FSs. IL-1β could play a role either in enhancing or in reducing neural excitability. If the enhancing and reducing effects are balanced, an FS does not occur. When the enhancing effect plays the leading role, an FS is generated. A mild imbalance can cause simple FSs while a severe imbalance can cause complex FSs and febrile status epilepticus. Therefore, anti-IL-1β therapy may help to treat FSs.

The role of interleukin-1β in the pentylenetetrazole-induced kindling of seizures, in the rat hippocampus

Because the contribution of inflammatory mediators to seizure disorders is unclear, we investigated the changes in the expression of interleukin-1β (IL-β) and its receptor - IL-1 receptor type 1 (IL-1R1), tumour necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in the rat hippocampus at different stages of pentylenetetrazole (PTZ)-induced kindling. The occurrence and progressive development of seizures were induced by repeated systemic administration of PTZ, a non-competitive antagonist of the γ-aminobutyric acid type A (GABAA) receptor at a subconvulsive dose of 30 mg/kg. We also examined the effects of continuous intracerebroventricular administration of IL-1β and lipopolysaccharide (LPS) in this model of epilepsy using subcutaneously implanted osmotic mini-pumps. We observed enhanced IL-1R1 expression in the dentate gyrus (DG) at different stages of kindling, whereas the elevated IL-1β level was distinctive to fully kindled seizures. We did not detect significant changes in the concentration of IL-6 or TNF-α throughout the kindling process. LPS accelerated transiently the process of kindling, while IL-1β showed a predisposition to delay kindling acquisition. Our study supports the concept of seizure-related modifications in brain cytokine production during epileptogenesis. Although some evidence indicates a proconvulsant property of IL-1β activity, it cannot be ruled out that the alterations in IL-1 system reflect the activation of endogenous protective mechanisms with respect to the kindling of seizures.

Rhythm and blues: animal models of epilepsy and depression comorbidity

Clinical evidence shows a strong, bidirectional comorbidity between depression and epilepsy that is associated with decreased quality of life and responsivity to pharmacotherapies. At present, the neurobiological underpinnings of this comorbidity remain hazy. To complicate matters, anticonvulsant drugs can cause mood disturbances, while antidepressant drugs can lower seizure threshold, making it difficult to treat patients suffering from both depression and epilepsy. Animal models have been created to untangle the mechanisms behind the relationship between these disorders and to serve as screening tools for new therapies targeted to treat both simultaneously. These animal models are based on chemical interventions (e.g. pentylenetetrazol, kainic acid, pilocarpine), electrical stimulations (e.g. kindling, electroshock), and genetic/selective breeding paradigms (e.g. genetically epilepsy-prone rats (GEPRs), genetic absence epilepsy rat from Strasbourg (GAERS), WAG/Rij rats, swim lo-active rats (SwLo)). Studies on these animal models point to some potential mechanisms that could explain epilepsy and depression comorbidity, such as various components of the dopaminergic, noradrenergic, serotonergic, and GABAergic systems, as well as key brain regions, like the amygdala and hippocampus. These models have also been used to screen possible therapies. The purpose of the present review is to highlight the importance of animal models in research on comorbid epilepsy and depression and to explore the contributions of these models to our understanding of the mechanisms and potential treatments for these disorders.

Understanding the basic mechanisms underlying seizures in mesial temporal lobe epilepsy and possible therapeutic targets: a review

Despite years of research, epilepsy remains a poorly understood disorder. In the past several years, work has been conducted on a variety of projects with the goal of better understanding the pathogenesis and progression of mesial temporal lobe epilepsy (MTLE), in particular, and how to exploit those properties to generate innovative therapies for treatment of refractory epilepsies. This review seeks to give an overview of common morphological and biochemical changes associated with epilepsy and proposed treatments to address those changes. Furthering the understanding of ictogenesis and epileptogenesis remains an important goal for scientists seeking to find more effective treatments for MTLE.

Neuromodulatory role of endogenous interleukin-1β in acute seizures: possible contribution of cyclooxygenase-2

The function of endogenous interleukin-1β (IL-1β) signaling in acute seizure activity was examined using transgenic mice harboring targeted deletions in the genes for either IL-1β (Il1b) or its signaling receptor (Il1r1). Acute epileptic seizure activity was modeled using two mechanistically distinct chemoconvulsants, kainic acid (KA) and pentylenetetrazole (PTZ). KA-induced seizure activity was more severe in homozygous null (-/-) Il1b mice compared to their wild-type (+/+) littermate controls, as indicated by an increase in the incidence of sustained generalized convulsive seizure activity. In the PTZ seizure model, the incidence of acute convulsive seizures was increased in both Il1b and Il1r1-/- mice compared to their respective +/+ littermate controls. Interestingly, the selective cyclooxygenase (COX)-2 inhibitor, rofecoxib, mimicked the effect of IL-1β deficiency on PTZ-induced convulsions in Il1r1+/+ but not -/- mice. Together, these results suggest that endogenous IL-1β possesses anticonvulsive properties that may be mediated by arachidonic acid metabolites derived from the catalytic action of COX-2.

Cytokines and epilepsy

Epilepsy is a common chronic neurological disorder affecting approximately 8 out of 1000 people. Its pathophysiology, however, has remained elusive in many regards. Consequently, adequate seizure control is still lacking in about one third of patients. Cytokines are soluble mediators of cell communication that are critical in immune regulation. In recent years, studies have shown that epileptic seizures can induce the production of cytokines, which in turn influence the pathogenesis and course of epilepsies. At the time of this review, the focus is mostly on interleukin-1beta (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor alpha (TNFα). In this review, we summarize the current knowledge regarding these cytokines and their potential roles in epilepsy. The focus concentrates on their expression and influence on induced seizures in animal models of epilepsy, as well as findings in human studies. Both proconvulsive and anticonvulsive effects have been reported for each of these molecules. One possible explanation for this phenomenon is that cytokines play dichotomous roles through multiple pathways, each of which is dependent on free concentration and available receptors. Furthermore, the immune-mediated leakage in the blood-brain-barrier also plays an important role in epileptogenesis. Nonetheless, these observations demonstrate the multifarious nature of cytokine networks and the complex relationship between the immune system and epilepsy. Future studies are warranted to further clarify the influence of the immune system on epilepsy and vice versa.

The role of interleukin-1 in seizures and epilepsy: a critical review

Interleukin-1 (IL-1) has a multitude of functions in the central nervous system. Some of them involve mechanisms that are related to epileptogenesis. The role of IL-1 in seizures and epilepsy has been investigated in both patients and animal models. This review aims to synthesize, based on the currently available literature, the consensus role of IL-1 in epilepsy. Three lines of evidence suggest a role for IL-1: brain tissue from epilepsy patients and brain tissue from animal models shows increased IL-1 expression after seizures, and IL-1 has proconvulsive properties when applied exogeneously. However, opposing results have been published as well. More research is needed to fully establish the role of IL-1 in seizure generation and epilepsy, and to explore possible new treatment strategies that are based on interference with intracellular signaling cascades that are initiated when IL-1 binds to its receptor.

The role of cytokines in the pathophysiology of epilepsy

Recent findings in experimental models and in the clinical setting highlight the possibility that inflammatory processes in the brain contribute to the etiopathogenesis of seizures and to the establishment of a chronic epileptic focus. Prototypical inflammatory cytokines such as IL-1 beta, TNF-alpha and IL-6 have been shown to be overexpressed in experimental models of seizures in brain areas of seizure generation and propagation, prominently by glia and to a lesser extent by neurons. Cytokines receptors are also upregulated, and the related intracellular signalling is activated, in both cell populations highlighting autocrine and paracrine actions of cytokines in the brain. Cytokines have been shown to profoundly affect seizures in rodents; in particular, IL-1 beta is endowed of proconvulsant activity in a large variety of seizure models. The recent demonstration of functional interactions between cytokines and classical neurotransmitters such as glutamate and GABA, suggest the possibility that these interactions underlie the cytokine-mediated changes in neuronal excitability, thus promoting seizure phenomena and the associated neuropathology. These findings point out at novel glio-neuronal communications in diseased conditions and highlight potential new targets for therapeutic intervention.

Interleukin Converting Enzyme inhibition impairs kindling epileptogenesis in rats by blocking astrocytic IL-1beta production

An enhanced production of IL-1beta in glia is a typical feature of epileptogenic tissue in experimental models and in human drug-refractory epilepsy. We show here that the selective inhibition of Interleukin Converting Enzyme (ICE), which cleaves the biologically active form of IL-1beta using VX-765, blocks kindling development in rats by preventing IL-1beta increase in forebrain astrocytes, without interfering with glia activation. The average afterdischarge duration was not altered significantly by VX-765. Up to 24 h after kindling completion and drug washout, kindled seizures could not be evoked in treated rats. VX-765 did not affect seizures or afterdischarge duration in fully kindled rats. These data indicate an antiepileptogenic effect mediated by ICE inhibition and suggest that specific anti-IL-1beta pharmacological strategies can be envisaged to interfere with epileptogenic mechanisms.

The type 1 interleukin 1 receptor is not required for the death of murine hippocampal dentate granule cells and microglia activation

Alterations in inflammatory process, neuronal death, and glia response have been observed under manipulation of interleukin-1 (IL-1) and subsequent signaling through the type 1 IL-1 receptor (IL-1R1). To investigate the influence of IL-1R1 activation in the pathophysiology of a chemical-induced injury to the murine hippocampus, we examined the level and pattern of neuronal death and neuroinflammation in male weanling mice exposed to trimethyltin hydroxide (2.0 mg TMT/kg, i.p.). Dentate granule cell death occurred at 6 h post-TMT as detected by active caspase 3 immunostaining and presence of lectin positive microglia. The severity of neuronal death and microglia response increased by 12-24 h with elevations in mRNA levels for TNFalpha and IL-1alpha. In IL-1R1 null (IL-1R1-/-) mice, the pattern and severity of neuronal death at 24 or 72 h post-TMT was similar as compared to wildtype (WT) mice. In both groups, mRNA levels for TNFalpha and MIP-1alpha were elevated, no significant change was seen in either IL-1alpha or IL-1beta, and the early activation of microglia, including their ability to progress to a phagocytic phenotype, was maintained. Compared to WT mice, IL-1R1-/- mice displayed a limited glial fibrillary acidic protein (GFAP) astrocytic response, as well as a preferential induction in mRNA levels of Fas signaling components. Cumulatively, these results indicate that IL-1R1 activation is not necessary for TMT-induced death of dentate granule neurons or local activation of microglia; however, IL-1R1 signaling is involved in mediating the structural response of astrocytes to injury and may regulate apoptotic mechanisms via Fas signaling components.

Intra-amygdala all-trans retinoic acid inhibits amygdala-kindled seizures in rats

Amygdala plays an important role in induction and control of limbic seizures. There is a network of gap junctional communications in basolateral amygdala (BLA) as well. We compared the effect of intra-BLA infusion of the typical gap junction (GJ) blocker carbenoxolone (CBX), with the effect of putative GJ blocker all-trans retinoic acid (ATRA), on the afterdischarge (AD) recorded from BLA in amygdala-kindled rats. Both CBX and ATRA showed a rapid anti-seizure effect. Conversely, intra-BLA infusion of the known GJ opener, trimethylamine (TMA), enhanced seizure susceptibility by prolonging the duration of AD and generalized behavioral seizures. ATRA administered intra-BLA prevented the proconvulsant effect of TMA. The reduction of gap junctional conductance might be involved in the observed anticonvulsant effect of ATRA.

Novel antiseizure drug mechanisms

The amount of new knowledge being generated regarding brain mechanisms in general, and epileptic mechanisms in particular, is enormous. Anticonvulsant drugs are ineffective in approximately a third of people with epilepsy. To our knowledge, strategies for preventing epilepsy after an initial insult are nonexistent. In this review, we briefly examine some recent novel concepts for preventing seizures, which might lead to enhanced anticonvulsant drug therapy. We start with some known seizure mechanisms that have yet to yield widely used anticonvulsant drugs, including potassium channels, chloride cotransporters, extracellular space constriction, gap junctions and magnesium. Pharmacoresistance is then discussed, focusing on the upregulation of drug-resistance proteins (a concept with significant therapeutic appeal) and the drug-target hypothesis. Two further areas that hold great promise for future therapeutics are sex hormones and inflammatory processes. The genetics of epilepsy are currently being elaborated, providing potential novel anticonvulsant targets. Prevention being better than a cure, we discuss epileptogenesis and its treatment. Given the astounding progress of neuroscience research, one hopes for many new therapeutics for our intractable epileptic patients.

The role of inflammation in CNS injury and disease

For many years, the central nervous system (CNS) was considered to be 'immune privileged', neither susceptible to nor contributing to inflammation. It is now appreciated that the CNS does exhibit features of inflammation, and in response to injury, infection or disease, resident CNS cells generate inflammatory mediators, including proinflammatory cytokines, prostaglandins, free radicals and complement, which in turn induce chemokines and adhesion molecules, recruit immune cells, and activate glial cells. Much of the key evidence demonstrating that inflammation and inflammatory mediators contribute to acute, chronic and psychiatric CNS disorders is summarised in this review. However, inflammatory mediators may have dual roles, with detrimental acute effects but beneficial effects in long-term repair and recovery, leading to complications in their application as novel therapies. These may be avoided in acute diseases in which treatment administration might be relatively short-term. Targeting interleukin (IL)-1 is a promising novel therapy for stroke and traumatic brain injury, the naturally occurring antagonist (IL-1ra) being well tolerated by rheumatoid arthritis patients. Chronic disorders represent a greater therapeutic challenge, a problem highlighted in Alzheimer's disease (AD); significant data suggested that anti-inflammatory agents might reduce the probability of developing AD, or slow its progression, but prospective clinical trials of nonsteroidal anti-inflammatory drugs or cyclooxygenase inhibitors have been disappointing. The complex interplay between inflammatory mediators, ageing, genetic background, and environmental factors may ultimately regulate the outcome of acute CNS injury and progression of chronic neurodegeneration, and be critical for development of effective therapies for CNS diseases.

Epileptogenesis-related genes revisited

The main goal of this study was to identify common features in the molecular response to epileptogenic stimuli across different animal models of epileptogenesis. Therefore, we compared the currently available literature on the global analysis of gene expression following epileptogenic insult to search for (i) highly represented functional gene classes (GO terms) within data sets, and (ii) individual genes that appear in several data sets, and therefore, might be of particular importance for the development of epilepsy due to different etiologies. We focused on two well-described models of brain insult that induce the development of spontaneous seizures in experimental animals: status epilepticus and traumatic brain injury. Additionally, a few papers describing gene expression in rat and human epileptic tissue were included for comparison. Our analysis revealed that epileptogenic insults induce significant changes in gene expression within a subset of pre-defined GO terms, that is, in groups of functionally linked genes. We also found individual genes for which expression changed across different models of epileptogenesis. Alterations in gene expression appear time-specific and underlie a number of processes that are linked with epileptogenesis, such as cell death and survival, neuronal plasticity, or immune response. Particularly, our analysis highlighted alterations in gene expression in glial cells as well as in genes involved in the immune response, which suggests the importance of gliosis and immune reaction in epileptogenesis.

Brain inflammation in epilepsy: experimental and clinical evidence

Inflammatory reactions occur in the brain in various CNS diseases, including autoimmune, neurodegenerative, and epileptic disorders. Proinflammatory and antiinflammatory cytokines and related molecules have been described in CNS and plasma, in experimental models of seizures and in clinical cases of epilepsy. Inflammation involves both the innate and the adaptive immune systems and shares molecules and pathways also activated by systemic infection. Experimental studies in rodents show that inflammatory reactions in the brain can enhance neuronal excitability, impair cell survival, and increase the permeability of the blood-brain barrier to blood-borne molecules and cells. Moreover, some antiinflammatory treatments reduce seizures in experimental models and, in some instances, in clinical cases of epilepsy. However, inflammatory reactions in brain also can be beneficial, depending on the tissue microenvironment, the inflammatory mediators produced in injured tissue, the functional status of the target cells, and the length of time the tissue is exposed to inflammation. We provide an overview of the current knowledge in this field and attempt to bridge experimental and clinical evidence to discuss critically the possibility that inflammation may be a common factor contributing, or predisposing, to the occurrence of seizures and cell death, in various forms of epilepsy of different etiologies. The elucidation of this aspect may open new perspectives for the pharmacologic treatment of seizures.