The role of cytokines and growth factors in seizures and their sequelae

Differential immunoreactivity of microglial and astrocytic marker protein in the hippocampus of the seizure resistant and sensitive gerbils

In the present study, we compared differences in ionized calcium-binding adapter molecule 1 (Iba-1) and glial fibrillary acidic protein (GFAP) immunoreactivities for microglia and astrocytes, respectively, in the hippocampus of the seizure-resistant (SR) and seizure-sensitive (SS) gerbils. The density of Iba-1 immunoreactive microglia in the hippocampal CA1 region (CA1) and dentate gyrus (DG) of the SS gerbil was higher than that in the SR gerbil, and many Iba-1 immunoreactive microglia in the SS gerbil were hypertrophied in morphology. In contrast, we could not find significant difference in the density of GFAP immunoreactive astrocytes between the SR and SS gerbils. This result indicates that Iba-1 immunoreactive microglia in CA1 and DG of the SS gerbil are activated compared to those in the SR gerbil.

Glutamate and neurotrophic factors in neuronal plasticity and disease

Glutamate's role as a neurotransmitter at synapses has been known for 40 years, but glutamate has since been shown to regulate neurogenesis, neurite outgrowth, synaptogenesis, and neuron survival in the developing and adult mammalian nervous system. Cell-surface glutamate receptors are coupled to Ca(2+) influx and release from endoplasmic reticulum stores, which causes rapid (kinase- and protease-mediated) and delayed (transcription-dependent) responses that change the structure and function of neurons. Neurotrophic factors and glutamate interact to regulate developmental and adult neuroplasticity. For example, glutamate stimulates the production of brain-derived neurotrophic factor (BDNF), which, in turn, modifies neuronal glutamate sensitivity, Ca(2+) homeostasis, and plasticity. Neurotrophic factors may modify glutamate signaling directly, by changing the expression of glutamate receptor subunits and Ca(2+)-regulating proteins, and also indirectly by inducing the production of antioxidant enzymes, energy-regulating proteins, and antiapoptotic Bcl-2 family members. Excessive activation of glutamate receptors, under conditions of oxidative and metabolic stress, may contribute to neuronal dysfunction and degeneration in diseases ranging from stroke and Alzheimer's disease to psychiatric disorders. By enhancing neurotrophic factor signaling, environmental factors such as exercise and dietary energy restriction, and chemicals such as antidepressants may optimize glutamatergic signaling and protect against neurological disorders.

Fgf-2 overexpression increases excitability and seizure susceptibility but decreases seizure-induced cell loss

Fibroblast growth factor 2 (FGF-2) has multiple, pleiotropic effects on the nervous system that include neurogenesis, neuroprotection and neuroplasticity. Thus, alteration in FGF-2 expression patterns may have a profound impact in brain function, both in normal physiology and in pathology. Here, we used FGF-2 transgenic mice (TgFGF2) to study the effects of endogenous FGF-2 overexpression on susceptibility to seizures and to the pathological consequences of seizures. TgFGF2 mice display increased FGF-2 expression in hippocampal pyramidal neurons and dentate granule cells. Increased density of glutamatergic synaptic vesicles was observed in the hippocampus of TgFGF2 mice, and electrophysiological data (input/output curves and patch-clamp recordings in CA1) confirmed an increase in excitatory inputs in CA1, suggesting the presence of a latent hyperexcitability. Indeed, TgFGF2 mice displayed increased susceptibility to kainate-induced seizures compared with wild-type (WT) littermates, in that latency to generalized seizure onset was reduced, whereas behavioral seizure scores and lethality were increased. Finally, WT and TgFGF2 mice with similar seizure scores were used for examining seizure-induced cellular consequences. Neurogenesis and mossy fiber sprouting were not significantly different between the two groups. In contrast, cell damage (assessed with Fluoro-Jade B, silver impregnation and anti-caspase 3 immunohistochemistry) was significantly lower in TgFGF2 mice, especially in the areas of overexpression (CA1 and CA3), indicating reduction of seizure-induced necrosis and apoptosis. These data suggest that FGF-2 may be implicated in seizure susceptibility and in seizure-induced plasticity, exerting different, and apparently contrasting effects: favoring ictogenesis but reducing seizure-induced cell death.

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.

Glia as a source of cytokines: implications for neuronal excitability and survival

In the last decade, preclinical studies have provided a better characterization of the homeostatic and maladaptive mechanisms occurring either during the process of epileptogenesis or after the permanent epileptic state has emerged. Experimental evidence supported by clinical observations highlighted the possibility that brain inflammation is a common factor contributing, or predisposing, to the occurrence of seizures and cell death, in various forms of epilepsy of different etiologies. Expression of proinflammatory cytokines, as a hallmark of brain inflammation, has been demonstrated in glia in various experimental models of seizures and in human epilepsies. Experimental studies in rodents with perturbed cytokine systems indicate that these inflammatory mediators can alter neuronal excitability and affect cell survival by activating transcriptional and posttranslational intracellular pathways. This paper will provide an overview on the current knowledge in this field to discuss mechanistic hypotheses into the study of pathogenesis of epilepsy and recognize new potential therapeutic options.

Role of brain inflammation in epileptogenesis

Inflammation is known to participate in the mediation of a growing number of acute and chronic neurological disorders. Even so, the involvement of inflammation in the pathogenesis of epilepsy and seizure-induced brain damage has only recently been appreciated. Inflammatory processes, including activation of microglia and astrocytes and production of proinflammatory cytokines and related molecules, have been described in human epilepsy patients as well as in experimental models of epilepsy. For many decades, a functional role for brain inflammation has been implied by the effective use of anti-inflammatory treatments, such as steroids, in treating intractable pediatric epilepsy of diverse causes. Conversely, common pediatric infectious or autoimmune diseases are often accompanied by seizures during the course of illness. In addition, genetic susceptibility to inflammation correlated with an increased risk of epilepsy. Mounting evidence thus supports the hypothesis that inflammation may contribute to epileptogenesis and cause neuronal injury in epilepsy. We provide an overview of the current knowledge that implicates brain inflammation as a common predisposing factor in epilepsy, particularly childhood epilepsy.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

A chronic histopathological and electrophysiological analysis of a rodent hypoxic-ischemic brain injury model and its use as a model of epilepsy

Ischemic brain injury is one of the leading causes of epilepsy in the elderly, and there are currently no adult rodent models of global ischemia, unilateral hemispheric ischemia, or focal ischemia that report the occurrence of spontaneous motor seizures following ischemic brain injury. The rodent hypoxic-ischemic (H-I) model of brain injury in adult rats is a model of unilateral hemispheric ischemic injury. Recent studies have shown that an H-I injury in perinatal rats causes hippocampal mossy fiber sprouting and epilepsy. These experiments aimed to test the hypothesis that a unilateral H-I injury leading to severe neuronal loss in young-adult rats also causes mossy fiber sprouting and spontaneous motor seizures many months after the injury, and that the mossy fiber sprouting induced by the H-I injury forms new functional recurrent excitatory synapses. The right common carotid artery of 30-day old rats was permanently ligated, and the rats were placed into a chamber with 8% oxygen for 30 min. A quantitative stereologic analysis revealed that the ipsilateral hippocampus had significant hilar and CA1 pyramidal neuronal loss compared with the contralateral and sham-control hippocampi. The septal region from the ipsilateral and contralateral hippocampus had small but significantly increased amounts of Timm staining in the inner molecular layer compared with the sham-control hippocampi. Three of 20 lesioned animals (15%) were observed to have at least one spontaneous motor seizure 6-12 months after treatment. Approximately 50% of the ipsilateral and contralateral hippocampal slices displayed abnormal electrophysiological responses in the dentate gyrus, manifest as all-or-none bursts to hilar stimulation. This study suggests that H-I injury is associated with synaptic reorganization in the lesioned region of the hippocampus, and that new recurrent excitatory circuits can predispose the hippocampus to abnormal electrophysiological activity and spontaneous motor seizures.

High-level expression and purification of Tat-haFGF19-154

Human acidic fibroblast growth factor (haFGF) stimulates repair and regeneration of central and peripheral nerves after various injuries. However, it is unable to cross the blood-brain barrier (BBB). To produce a therapeutic haFGF with cell-permeable activity, we fused the haFGF(19-154) gene with Tat-PTD. After its construction by a single-step insertion of a polymerase chain reaction (PCR)-amplified coding sequence, the vector pTat-haFGF(19-154)-His was expressed in Escherichia coli BL21 (DE3) cells. The optimal expression level of the soluble fusion protein was up to 36.7% of the total cellular protein. The recombinant Tat-haFGF(19-154)-His was purified by a combination of Ni-NTA affinity, Sephadex G-25, and heparin affinity chromatography to 95% as detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The final yield was 171 mg/l culture. Purified Tat-haFGF(19-154)-His had distinct mitogenic activity in Balb/c 3T3 cells, as measured by methylthiazoletetrazolium (MTT) assay and its ED(50) was 3.931 x 10(-4) micromol/l. Tat-haFGF(19-154)-His protein intravenously injected at the dose of 10 mg/kg could be detected in the pallium and hippocampi.

Protective effects of interleukin-10 on the development of epileptiform activity evoked by transient episodes of hypoxia in rat hippocampal slices

The aim of the present work was to study the effects of interleukin-10 at concentrations of 1 and 10 ng/ml on the development of epileptiform discharges evoked in pyramidal neurons in field CA3 in rat hippocampal slices by transient episodes of hypoxia. Three 3-min episodes of hypoxia led to decreases in the generation threshold for evoked trains of population spikes and an increase in the number of population spikes per train in pyramidal neurons of field CA1. Interleukin-10 at a concentration of 1 ng/ml completely eliminated the development of epileptiform activity, while its protective effect was less marked at a concentration of 10 ng/ml. These effects of interleukin-10 on living hippocampal slices in in vitro conditions show that they may be associated with the functions of this cytokine as an intercellular mediator of the central nervous system itself rather than being mediated by the peripheral immune system. The results of these studies provide the first experimental evidence of the action of the anti-inflammatory cytokine interleukin-10 on the development of hypoxia-evoked epileptiform events in the hippocampus.

The cellular and behavioral consequences of interleukin-1 alpha penetration through the blood-brain barrier of neonatal rats: a critical period for efficacy

Proinflammatory cytokines circulating in the periphery of early postnatal animals exert marked influences on their subsequent cognitive and behavioral traits and are therefore implicated in developmental psychiatric diseases such as schizophrenia. Here we examined the relationship between the permeability of the blood-brain barrier to interleukin-1 alpha (IL-1 alpha) in neonatal and juvenile rats and their later behavioral performance. Following s.c. injection of IL-1 alpha into rat neonates, IL-1 alpha immunoreactivity was first detected in the choroid plexus, brain microvessels, and olfactory cortex, and later diffused to many brain regions such as neocortex and hippocampus. In agreement, IL-1 alpha administration to the periphery resulted in a marked increase in brain IL-1 alpha content of neonates. Repeatedly injecting IL-1 alpha to neonates triggered astrocyte proliferation and microglial activation, followed by behavioral abnormalities in startle response and putative prepulse inhibition at the adult stage. Analysis of covariance with a covariate of startle amplitude suggested that IL-1 alpha administration may influence prepulse inhibition. However, adult rats treated with IL-1 alpha as neonates exhibited normal learning ability as measured by contextual fear conditioning, two-way passive shock avoidance, and a radial maze task and had no apparent sign of structural abnormality in the brain. In comparison, when IL-1 alpha was administered to juveniles, the blood-brain barrier permeation was limited. The increases in brain IL-1 alpha content and immunoreactivity were less pronounced following IL-1 alpha administration and behavioral abnormalities were not manifested at the adult stage. During early development, therefore, circulating IL-1 alpha efficiently crosses the blood-brain barrier to induce inflammatory reactions in the brain and influences later behavioral traits.

Innate and adaptive immunity during epileptogenesis and spontaneous seizures: evidence from experimental models and human temporal lobe epilepsy

We investigated the activation of the IL-1 beta system and markers of adaptive immunity in rat brain during epileptogenesis using models of temporal lobe epilepsy (TLE). The same inflammatory markers were studied in rat chronic epileptic tissue and in human TLE with hippocampal sclerosis (HS). IL-1 beta was expressed by both activated microglia and astrocytes within 4 h from the onset of status epilepticus (SE) in forebrain areas recruited in epileptic activity; however, only astrocytes sustained inflammation during epileptogenesis. Activation of the IL-1 beta system during epileptogenesis was associated with neurodegeneration and blood-brain barrier breakdown. In rat and human chronic epileptic tissue, IL-1 beta and IL-1 receptor type 1 were broadly expressed by astrocytes, microglia and neurons. Granulocytes appeared transiently in rat brain during epileptogenesis while monocytes/macrophages were present in the hippocampus from 18 h after SE onset until chronic seizures develop, and they were found also in human TLE hippocampi. In rat and human epileptic tissue, only scarce B- and T-lymphocytes and NK cells were found mainly associated with microvessels. These data show that specific inflammatory pathways are chronically activated during epileptogenesis and they persist in chronic epileptic tissue, suggesting they may contribute to the etiopathogenesis of TLE.

Synaptic activity-induced global gene expression patterns in the dentate gyrus of adult behaving rats: induction of immunity-linked genes

Gene expression in adult neuronal circuits is dynamically modulated in response to synaptic activity. Persistent changes in synaptic strength, as seen during high-frequency stimulation (HFS)-induced long-term potentiation (LTP), require new gene expression. While modulation of many individual genes has been shown, an understanding of LTP as a complex dynamical response requires elucidation of the global gene expression signature and its impact on biologically meaningful gene sets. In this study, we demonstrate that LTP induction in the dentate gyrus of awake freely moving rats was associated with changes in the expression of genes linked to signal transduction, protein trafficking, cell structure and motility, and other processes consistent with the induction of mechanisms of synaptic reorganization and growth. Interestingly, the most significantly over-represented gene sets were related to immunity and defense, including T-cell-mediated immunity and major histocompatibility complex (MHC) class I-mediated immunity. Real-time PCR confirmed the upregulation of a panel of immune-linked genes including the rt1-a/ce family, and the MHC class II members cd74, rt1-Ba and rt1-Da. These genes were N-methyl-d-aspartate receptor-independent and not induced following HFS-LTP induction in anesthetized rats, indicating a gene response specific to behaving rats. Our data support recent assumptions that immunity-associated processes are functionally linked to adaptive neuronal responses in the brain, although the differential expression of immunity-linked genes could also be related to the HFS per se.

Postsynaptic currents prior to onset of epileptiform activity in rat microgyria

Structural malformations of the cortex, arising as a result of genetic mutation or injury during development are associated with dyslexia, epilepsy, and other neurological deficits. We have used a rat model of a microgyral malformation to examine mechanisms of epileptogenesis. Our previous studies showed that the frequency of miniature excitatory postsynaptic currents (mEPSCs) recorded in neocortical layer V pyramidal neurons is increased in malformed cortex at a time when field potential epileptiform events can be evoked. Here we show that the increase occurs at an age before onset of cortical epileptiform activity and at a time when the frequency of mEPSCs in control layer V pyramidal neurons is stable. An increase in the frequency of spontaneous (s)EPSCs in layer V pyramidal neurons of malformed cortex occurs earlier than that for mEPSCs, suggesting that there may additionally be alterations in intrinsic properties that increase the excitability of the cortical afferents. Frequencies of EPSC bursts and late evoked activity were also increased in malformed cortex. These results suggest that a hyperinnervation of layer V pyramidal neurons by excitatory afferents occurs as an active process likely contributing to subsequent development of field epileptiform events.

Expression of Adhesion Factors Induced by Epileptiform Activity in the Endothelium of the Isolated Guinea Pig Brain In Vitro

PURPOSE

Brain inflammation has been recently considered in the pathogenesis of focal epilepsies. Synthesis of pro-inflammatory mediators in the brain was described both in experimental models of seizures and in human postsurgical tissue. Inflammatory mediators may up-regulate endothelial adhesion molecules, therefore promoting adhesion and homing of leucocytes into the brain. In the present study, expression of inducible adhesion factors in brain endothelium was verified after pharmacological induction of seizure-like activity in specific brain areas of the in vitro isolated guinea pig brain.

METHODS

Experiments were performed in isolated guinea-pig brains maintained in vitro by arterial perfusion. In this preparation, brief application of the GABAa receptor-antagonist, bicuculline, consistently induced focal ictal discharges in the limbic region that secondarily diffuse to the neocortex, as verified by simultaneous electrophysiological recording of extracellular activity. At the end of the electrophysiological experiment (after 5 h in vitro), brains were fixed and immunostaining for adhesion molecules P-selectin and ICAM-1 and for Fos protein was evaluated.

RESULTS

Immunohistochemical analysis of isolated brains in which seizure-like activity was induced revealed expression of inducible adhesion factors P-selectin and ICAM-1 in the endothelium of small-medium size brain vessels. In particular, the expression of these molecules was consistently observed in all areas involved in epileptic seizure-like ictal activity (limbic cortices and neocortex), and was infrequently found in regions that generated interictal spiking (piriform cortex), suggesting a trigger role played by seizures for endothelial activation. An increase in Fos protein expression was evident in all analyzed limbic areas and in the neocortex, indicating a correlation between the areas of neuronal and endothelial activation. In control brains maintained in vitro for comparable times without induction of epileptiform activity, no immunoreactivity for Fos and adhesion molecules was observed.

CONCLUSIONS

Seizure-like activity in an in vitro isolated brain preparation induces the expression of adhesion molecules in the cerebral endothelium. These observations indicate that local endothelial activation may represent a crucial step for the development of an inflammatory response induced by seizures, and suggest a possible novel pathogenic mechanism during the process of epileptogenesis.

Neuroprotective effects of interleukin-10 and tumor necrosis factor-α against hypoxia-induced hyperexcitability in hippocampal slice neurons

In our previous experiments we have demonstrated that repeated exposures of rat hippocampal slices to brief episodes of hypoxia induce a sustained decrease in the threshold of stimulus-evoked epileptiform discharges in CA1 pyramidal neurons. The aim of this study was to investigate the comparative effects of interleukin-10 (IL-10) and tumor necrosis factor-alpha (TNF-alpha) on the hyperexcitability of CA1 pyramidal neurons induced by brief episodes of hypoxia in the rat hippocampal slices. The method of field potentials measurement in CA1 region of hippocampal slices have been described in our previous work [O. Godukhin, A. Savin, S. Kalemenev, S. Levin, Neuronal hyperexcitability induced by repeated brief episodes of hypoxia in rat hippocampal slices: involvement of ionotropic glutamate receptors and L-type Ca2+ channels, Neuropharmacology 42 (2002) 459-466]. The principal results of our work are summarized as follow. Pro-inflammatory cytokine TNF-alpha (0.8, 4 and 20 ng/ml) and anti-inflammatory cytokine IL-10 (1 and 10 ng/ml) significantly reduced the hyperexcitability in CA1 pyramidal neurons induced by brief episodes of hypoxia in the rat hippocampal slices. The neuroprotective effects of IL-10 and TNF-alpha against the hypoxia-induced hyperexcitability were mediated by anti-hypoxic actions of these cytokines through, possibly, mechanism of preconditioning.

Role of Endogenous Neural Stem Cells in Neurological Disease and Brain Repair

These examples show that stem-cell-based therapy of neuro-psychiatric disorders will not follow a single scheme, but rather include widely different approaches. This is in accordance with the notion that the impact of stem cell biology on neurology will be fundamental, providing a shift in perspective, rather than introducing just one novel therapeutic tool. Stem cell biology, much like genomics and proteomics, offers a "view from within" with an emphasis on a theoretical or real potential and thereby the inherent openness, which is central to the concept of stem cells. Thus, stem cell biology influences many other, more traditional therapeutic approaches, rather than introducing one distinct novel form of therapy. Substantial advances have been made i n neural stemcell research during the years. With the identification of stem and progenitor cells in the adult brain and the complex interaction of different stem cell compartments in the CNS--both, under physiological and pathological conditions--new questions arise: What is the lineage relationship between t he different progenitor cells in the CNS and how much lineage plasticity exists? What are the signals controlling proliferation and differentiation of neural stem cells and can these be utilized to allow repair of the CNS? Insights in these questions will help to better understand the role of stem cells during development and aging and the possible relation of impaired or disrupted stem cell function and their impact on both the development and treatment of neurological disease. A number o f studies have indicated a limited neuronal and glial regeneration certain pathological conditions. These fundamental observations have already changed our view on understanding neurological disease and the brain's capacity for endogenous repair. The following years will have to show how we can influence andmodulate endogenous repair nisms by increasing the cellular plasticity in the young and aged CNS.

Rasmussen's encephalitis: interleukin-10-dependent Tc2 cell polarization may explain its pathophysiology and clinical course

Little is known about the cellular immune dynamics and pathophysiology of Rasmussen's encephalitis (RE). We investigated transcriptional expression of pro- and anti-inflammatory cytokines and characterized the T-cell subset types present in temporal and frontal lobe specimens obtained from a child with RE. Interleukin (IL)-10 and macrophage scavenger receptor type I mRNA assessed by semiquantitative reverse transcription polymerase chain reaction was found in temporal but not in affected frontal lobe tissue. Messenger RNA specific to tumor necrosis factor alpha, IL-l, IL-4, IL-6, IL-12, IL-15, IL-18, transforming growth factor beta, CD-14, and inducible nitric oxide synthase was not detected in either temporal or frontal tissue with histopathologically manifest evidence of disease. Virtually all lymphocytic infiltrate consisted of CD3+ CD8+ T cells. We speculate that RE is a disease mediated by Tc2 polarization of the immune response and that its immunohistopathology, natural history, and clinical evolution (chronic, staircase progression) reflect the dual/pleiotropic actions of IL-10, which, depending on the state of activation of the immune system, may be either cytolytic or immunosuppressant.

Neurotrophins in the dentate gyrus

Since the discovery of nerve growth factor (NGF) in the 1950s and brain-derived neurotrophic factor (BDNF) in the 1980s, a great deal of evidence has mounted for the roles of neurotrophins (NGF; BDNF; neurotrophin-3, NT-3; and neurotrophin-4/5, NT-4/5) in development, physiology, and pathology. BDNF in particular has important roles in neural development and cell survival, as well as appearing essential to molecular mechanisms of synaptic plasticity and larger scale structural rearrangements of axons and dendrites. Basic activity-related changes in the central nervous system (CNS) are thought to depend on BDNF modulation of synaptic transmission. Pathologic levels of BDNF-dependent synaptic plasticity may contribute to conditions such as epilepsy and chronic pain sensitization, whereas application of the trophic properties of BDNF may lead to novel therapeutic options in neurodegenerative diseases and perhaps even in neuropsychiatric disorders. In this chapter, I review neurotrophin structure, signal transduction mechanisms, localization and regulation within the nervous system, and various potential roles in disease. Modulation of neurotrophin action holds significant potential for novel therapies for a variety of neurological and psychiatric disorders.

CRE-mediated transcription and COX-2 expression in the pilocarpine model of status epilepticus

Status epilepticus (SE) triggers neuronal death, reactive gliosis and remodeling of synaptic circuitry, thus leading to profound pathological alterations in CNS physiology. These processes are, in part, regulated by the rapid upregulation of both cytotoxic and cytoprotective genes. One pathway that may couple SE to transcriptionally dependent alterations in CNS physiology is the CREB (cAMP response element-binding protein)/CRE (cAMP response element) cascade. Here, we utilized the pilocarpine model of SE on a mouse strain transgenic for a CRE-reporter construct (beta-galactosidase) to begin to characterize how seizure activity regulates the activation state of the CREB/CRE pathway in both glia and neurons of the hippocampus. SE triggered a rapid (4-8 h post-SE) but transient increase in CRE-mediated gene expression in the neuronal sublayers. In contrast to neurons, SE induced a lasting increase (up to 20 days) in CRE-mediated transcription in both reactive astrocytes and microglia. CRE-mediated gene expression correlated with expression of the pro-inflammatory enzyme cyclooxygenase-2 (COX-2). To examine the role of CREB in SE-induced COX-2 expression, we generated a transgenic mouse strain that expresses A-CREB, a potent repressor of CREB-dependent transcription. In these animals, the capacity of SE to stimulate COX-2 expression was markedly attenuated, indicating that CREB is a key intermediate in SE-induced COX-2 expression. Collectively these data show that SE triggers two waves of CREB-mediated gene expression, a transient wave in neurons and a long-lasting wave in reactive glial cells, and that CREB couples SE to COX-2 expression.

Changes in brain interleukin-1β following the coadministration of norfloxacin with biphenylacetic acid in rats

We sought to determine the changes in brain interleukin-1beta (IL-1beta) following the coadministration of norfloxacin (25 mg/kg, i.p.) with biphenylacetic acid (100 mg/kg, p.o.) in rats. Norfloxacin provoked clonic convulsions in rats treated concomitantly with biphenylacetic acid, a major metabolite of the nonsteroidal anti-inflammatory drug fenbufen. Seizure activity was analyzed by EEG monitoring. Behavioral changes were also monitored. IL-1beta expressions in the prefrontal cortex and hippocampus at different time intervals were studied by reverse transcriptase-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). The epileptiform discharges appeared in all the rats, accompanied with limb twitching and clonic-tonic seizures after administration of norfloxacin coadministered with biphenylacetic acid. Norfloxacin plus biphenylacetic acid-induced convulsions rapidly and transiently enhanced IL-1beta mRNA in the prefrontal cortex and hippocampus. IL-1beta mRNA expression in the prefrontal cortex and hippocampus was detected as soon as 30 min after norfloxacin injection, and decayed to control levels by 6 h. ELISA analysis revealed significant increase of the IL-1beta protein in the prefrontal cortex and hippocampus at 2 h and 6 h. Administration of either norfloxacin or biphenylacetic acid alone did not elicit convulsions and increase in IL-1beta mRNA and protein expressions. The results suggest that the increased IL-1beta expressions in the prefrontal cortex and hippocampus induced by norfloxacin with biphenylacetic acid relate to seizure activities, and that these brain regions play pivotal roles in norfloxacin-induced convulsions.

A molecular study of hippocampus in dogs with convulsion during canine distemper virus encephalitis

In this study, we have investigated the expression of the nuclear transcription factor (c-Fos, NFkB), growth factors (nerve growth factor--NGF, brain-derived neurotrophic factor--BDNF), peptides (enkephalin, galanin) and glutamate transporter (AA 504-523 rat EAAC1) in 6 dogs sacrificed immediately after seizure attack during encephalomyelitis due to canine distemper virus (CDV) (as assessed by clinical examination, RT-PCR and viral RNA detection either in blood or brain tissue and CDV immunohistochemistry in brain slices). In all these CDV affected dogs, the observed neurological signs included untreatable seizures, leading to cluster seizure activity and status epilepticus. In the inter-ictal phase abnormal mentation, postural and gait deficits and sometimes involuntary movements such as myoclonus were recorded. The same investigation was carried out in 5 control dogs affected by different disorders, all characterized by the absence of seizures. Brains were dissected out immediately after euthanasia and fixed; sections collected from the dorsal hippocampus were processed for immunohistochemistry. By comparing hippocampus sections obtained from dog with and without seizure, the following regulations were observed. A strong up-regulation of glutamate transporter throughout the cell layers was found together with the onset of nuclear Fos and NFkB-IR in the pyramidal cell layer X. Among the investigated peptides, we observed a slight increase in enkephalinergic fibers and a strong up-regulation of mu-opioid receptors, whereas galanin-IR seemed to be weaker. Finally, both NGF and BDNF expression was strongly up-regulated. BDNF-IR was mainly localized in the apical dendrite in pyramidal neurons. To our knowledge, these data offer the first indication that molecular events described in experimental kindling also occur during spontaneous pathology in animal species sharing close similarities to human neuropathology.

Effects of second generation tetracyclines on penicillin-epilepsy-induced hippocampal neuronal loss and motor incoordination in rats

Epileptic seizures cause pathological changes such as sclerosis and pyramidal neuronal loss in the hippocampus. Experimentally, epilepsy can be induced by application of various chemicals directly to the cerebral cortex. In this study, epilepsy was induced in rats by intracortical application of 500 IU penicillin G, and the effect of minocycline and doxycycline on the resulting motor incoordination (rotarod) and hippocampal neuronal loss in CA1, CA2 and CA3 fields (optical fractionator method) were investigated. The rotarod performance was reduced in the epilepsy group to 285.1+/-6.9 s (P<0.05 vs. sham-300 s). Minocycline and doxycycline increased this performance to 297.4+/-1.0 s and 296.9+/-1.2 s respectively. No significant difference was detected between minocycline and doxycycline. The present results also showed that the number of neurons (x10(3)) in the sham group was 150+/-9. In the penicillin-epileptic rats, the number was decreased to 105+/-7 (P<0.01). Minocycline, but not doxycycline (125+/-8), significantly increased the number to 131+/-3 (P<0.05). In conclusion, the second generation tetracycline minocycline decreased the loss of hippocampal neurons and motor incoordination in penicillin-epileptic rats. Minocycline could protect against a variety of neurological insults including epilepsy.

Ameliorative effect of pioglitazone on seizure responses in genetically epilepsy-susceptible EL mice

Pioglitazone, a peroxisome proliferator-activated receptor-gamma agonist, delayed the development of seizure responses and mildly shortened the duration of convulsion of genetically epileptic EL mice. mRNA levels of IL-1beta, IL-6 and TNF-alpha before seizure and mRNA levels of IL-6 and TNF-alpha after seizure were decreased in the brains of the mice with pioglitazone. These results suggest that pioglitazone may have ameliorative effects on epileptic seizure responses partly through the reduction of inflammatory responses in the brain.

Leukemia inhibitory factor is a key regulator of astrocytic, microglial and neuronal responses in a low-dose pilocarpine injury model

Insult to the central nervous system (CNS) induces many changes, including altered neurotransmitter expression, activation of astrocytes and microglia, neurogenesis and cell death. Cytokines and growth factors are candidates to be involved in astrocyte and microglial activation, and the up-regulation of glial fibrillary acidic protein (GFAP) is associated with brain damage. One of these candidates is leukemia inhibitory factor (LIF), a pro-inflammatory cytokine that is induced in astrocytes by brain damage or seizure. LIF also regulates expression of both neuropeptide Y (NPY) and galanin following peripheral nerve injury. To test the hypothesis that LIF regulates astrocyte, microglial and neuropeptide responses to a mild insult, we used a low-dose pilocarpine model to induce a brief seizure in LIF knock-out (KO) mice. Compared to wild type mice, the LIF KO mouse displays reduced astrocyte and microglial activation in the hippocampus. In addition, LIF KO mice display dramatically altered NPY, but not galanin, expression in response to injury. Thus, LIF is required for normal glial responses to brain damage, and, as in the periphery, LIF regulates NPY expression in the CNS.

Causal links between brain cytokines and experimental febrile convulsions in the rat

PURPOSE

Despite the prevalence of febrile convulsions (FCs), their pathophysiology has remained elusive. We tested the hypothesis that components of the immune response, particularly the proinflammatory cytokine interleukin-1beta (IL-1beta) and its naturally occurring antagonist interleukin-1 receptor antagonist (IL-1ra) may play a role in the genesis of FC.

METHODS

Postnatal day 14 rats were treated with lipopolysaccharide (LPS; 200 microg/kg, i.p.) followed by a subconvulsant dose of kainic acid (1.75 mg/kg, i.p.). Brains were harvested at and 2 h after onset of FCs to measure brain levels of IL-1beta and IL-1ra. Separate groups of animals were given intracerebroventricular (ICV) injections of IL-1beta, or IL-1ra in an attempt to establish a causal relation between the IL-1beta/IL-1ra system and FCs.

RESULTS

Animals with FCs showed increased IL-1beta in the hypothalamus and hippocampus but not in the cortex compared with noFC animals that also received LPS and kainic acid. This increase was first detected in the hippocampus at onset of FCs. No detectable difference in IL-1ra was found in brain regions examined in either group. When animals were treated with IL-1beta ICV, a dose-dependant increase was noted in the proportion of animals that experienced FCs, whereas increasing doses of IL-1ra, given to separate groups of animals, were anticonvulsant.

CONCLUSIONS

Our results suggest that excessive amounts of IL-1beta may influence the genesis of FCs. This may occur by overproduction of IL-1beta, or by alteration in the IL-1beta/IL-1ra ratio in the brain after an immune challenge.

Facilitation of spike-wave discharge activity by lipopolysaccharides in Wistar Albino Glaxo/Rijswijk rats

In normal rats the proinflammatory cytokines like interleukin-1beta, interleukin-6, which are induced by bacterial lipopolysaccharides, are able to control thalamo-cortical excitability by exerting strong effects on physiological synchronization such as sleep and on pathological synchronization like that in epileptic discharges. To investigate whether proinflammatory cytokines or lipopolysaccharides could modulate absence seizures resulting from a very different generator mechanism than the already investigated bicuculline-, kindling- and kainate-induced seizures, we used a genetically epileptic Wistar Albino Glaxo/Rijswijk rat strain, which is spontaneously generating high voltage spike-wave discharges. Wistar Albino Glaxo/Rijswijk rats responded with an increase of the number of spike-wave discharges to lipopolysaccharide injection (from 10 microg/kg to 350 microg/kg). Repetitive administration of 350 microg/kg lipopolysaccharides daily for 5 days increased the number of spike-wave discharges on the first, second and third days but the number of spike-wave discharges returned to the control value on day 5, at the 5th injection of lipopolysaccharides, showing a tolerance to lipopolysaccharides. The lipopolysaccharide-induced increase in spike-wave discharges was not directly correlated with the elevation of the core body temperature, as it is in febrile seizures, although lipopolysaccharide induced prostaglandin and is clearly pyrogenic at the doses used. Indomethacin, the prostaglandin synthesis inhibitor, efficiently blocked lipopolysaccharide-induced enhancement of spike-wave discharge genesis suggesting that the spike-wave discharge facilitating effect of lipopolysaccharides involves induction of cyclooxygenase 2 and subsequent synthesis and actions of prostaglandin E2. Low dose (40 mg/kg, i.p.) of competitive N-methyl-d-aspartate receptor antagonist 2-amino-5-phosphonopentanoic acid, and low dose of lipopolysaccharide (20 microg/kg) showed a synergistic interaction to increase the number of spike-wave discharges, whereas at supramaximal doses of lipopolysaccharide and the N-methyl-D-aspartate antagonist no synergy was present. The data reveal a functional connection between absence epileptic activity and lipopolysaccharide induction of prostaglandin synthesis and prostaglandin action and suggest some common cellular targets in epilepsy and lipopolysaccharide-induced inflammation.

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.

Prolonged seizures and cellular injury: understanding the connection

Status epilepticus (SE)-induced neuronal death is morphologically necrotic and is initiated by excessive glutamate release, which activates postsynaptic N-methyl-D-aspartate (NMDA) receptors and triggers receptor-mediated calcium influx (excitotoxicity). This results in activation of intracellular proteases and neuronal nitric oxide synthase, with generation of free radicals, and damage to cellular membranes, structural proteins, and essential enzymes. Programmed cell death mechanisms, such as p53 activation, activation of cell death-promoting Bcl-2 family members, and endonuclease-induced DNA laddering, occur in SE-induced neuronal death. Caspase-independent excitotoxic mechanisms, such as NMDA-induced calpain I activation, with activation and translocation of the cell death-promoting Bcl-2 family member Bid from cytoplasm to mitochondria, and subsequent translocation of apoptosis-inducing factor and endonuclease G to nuclei (which cause large-scale and internucleosomal DNA cleavage, respectively), may be triggered by SE. Poly(ADP-ribose) polymerase-1 (PARP-1) activation and cysteinyl cathepsin and DNase II release from lysosomes may occur following SE as well, but these events await future investigation. In the future, rational combinations of central nervous system-penetrable neuroprotective agents, based on our knowledge of excitotoxic mechanisms, may be useful in refractory human SE.

Epilepsy and apoptosis pathways

Epilepsy is a common, chronic neurologic disorder characterized by recurrent unprovoked seizures. Experimental modeling and clinical neuroimaging of patients has shown that certain seizures are capable of causing neuronal death. Such brain injury may contribute to epileptogenesis, impairments in cognitive function or the epilepsy phenotype. Research into cell death after seizures has identified the induction of the molecular machinery of apoptosis. Here, the authors review the clinical and experimental evidence for apoptotic cell death pathway function in the wake of seizure activity. We summarize work showing intrinsic (mitochondrial) and extrinsic (death receptor) apoptotic pathway function after seizures, activation of the caspase and Bcl-2 families of cell death modulators and the acute and chronic neuropathologic impact of intervening in these molecular cascades. Finally, we describe evolving data on nonlethal roles for these proteins in neuronal restructuring and cell excitability that have implications for shaping the epilepsy phenotype. This review highlights the work to date on apoptosis pathway signaling during seizure-induced neuronal death and epileptogenesis, and speculates on how emerging roles in brain remodeling and excitability have enriched the number of therapeutic strategies for protection against seizure-damage and epileptogenesis.

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

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

Status epilepticus induces time-dependent neuronal and astrocytic expression of interleukin-1 receptor type I in the rat limbic system

Interleukin-1beta is rapidly synthesized by glia after the induction of seizures. Recent evidence shows that endogenous IL-1beta has proconvulsant actions mediated by interleukin-1 receptor type I. This receptor also mediates interleukin-1beta effects on neuronal susceptibility to neurotoxic insults. In this study, we investigated the basal and seizure-induced expression of interleukin-1 receptor type I in rat forebrain to identify the cells targeted by interleukin-1beta during epileptic activity. Self-sustained limbic status epilepticus was induced in rats by electrical stimulation of the ventral hippocampus. Interleukin-1 receptor type I immunoreactivity was barely detectable in neurons in control brain tissue. During status epilepticus, interleukin-1 receptor type I was induced in the hippocampal neurons firstly, and several hours later in astrocytes localized in limbic and extralimbic areas. Neuronal interleukin-1 receptor type I expression in the hippocampus outlasted the duration of spontaneous electroencephalographic seizure and was not observed in degenerating neurons. Astrocytic expression occurred transiently, between six and 18 h after the induction of status epilepticus and was invariably found in regions of neuronal damage. These time-dependent, cell- and region-specific changes in interleukin-1 receptor type I expression during status epilepticus suggest that interleukin-1 receptor type I in neurons mediates interleukin-1beta-induced fast changes in hippocampal excitability while interleukin-1 receptor type I receptors in astrocytes may mediate interleukin-1beta effects on neuronal survival in hostile conditions.

Tonic–clonic seizures induce division of neuronal progenitor cells with concomitant changes in expression of neurotrophic factors in the brain of pilocarpine–treated mice

Epileptic seizures cause severe and long-lasting events on the architecture of the brain, including neuronal cell death, accompanied neurogenesis, reactive gliosis, and mossy fiber sprouting. However, it remains uncertain whether these functional and anatomical alterations are associated with the development of hyperexcitability, or as inhibitory processes. Neurotrophic factors are probable mediators of these pathophysiological events. The present study was designed to clarify the role of various neurotrophic factors on the pilocarpine model of seizures. At 4 h following pilocarpine-induced seizures, expression of NGF, BDNF, HB-EGF, and FGF-2 increased only in the mice manifesting tonic-clonic convulsions and not in mice without seizures. NT-3 expression decreased in pilocarpine-treated mice experiencing seizures, tonic-clonic or not, compared to mice with no seizures. Neuronal cell damage, which was evident by Fluoro-Jade B staining, was observed within 24 h in the mice exhibiting tonic-clonic seizures, followed by an increase in the number of BrdU-positive cells and glial cells, which were evident after 2 days. None of these pathophysiological changes occurred in the mice which showed no seizures, although they were injected with pilocarpine, nor in the activated epilepsy-prone EL mice, which experienced repeated severe seizures. Together, these results suggest that neuronal damage occurring in the brain of the mice manifesting tonic-clonic seizures is accompanied by neurogenesis. This sequence of events may be regulated through changes in expression of neurotrophic factors such as NGF, BDNF, HB-FGF, and NT-3.

The Role of Glial Adenosine Receptors in Neural Resilience and the Neurobiology of Mood Disorders

Adenosine receptors were classified into A1- and A2-receptors in the laboratory of Bernd Hamprecht more than 25 years ago. Adenosine receptors are instrumental to the neurotrophic effects of glia cells. Both microglia and astrocytes release after stimulation via adenosine receptors factors that are important for neuronal survival and growth. Neuronal resilience is now considered as of pivotal importance in the neurobiology of mood disorders and their treatment. Both sleep deprivation and electroconvulsive therapy, two effective therapeutic measures in mood disorders, are associated with an increase of adenosine and upregulation of adenosine A1-receptors in the brain. Parameters closely related to adenosine receptor activation such as cerebral metabolic rate and delta power in the sleep EEG provide indirect evidence that adenosinergic signaling may be associated with the therapeutic response to these measures. Thus, neurotrophic effects evoked by adenosine receptors might be important in the mechanism of action of ECT and perhaps also sleep deprivation.

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

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

Effects of HI 6, diazepam and atropine on soman-induced IL-1 beta protein in rat brain

The current treatment for soman-intoxication is the oxime HI 6 together with the anticholinergic drug atropine. This antidote combination is known to have effects on seizures, respiratory system, blood pressure and animal survival in experiments. However, the inflammatory responses following soman-intoxication leading to neuronal damage have not been fully evaluated. In this paper we focus on the cytokine IL-1beta induction in the rat brain after soman-intoxication (1.0 x LD50 and 1.1 x LD50) and during antidote treatment. We analyzed the IL-1beta levels in rat brain to determine the effects of time of antidote HI 6 and atropine; the effects of different combinations of HI 6 and atropine; and also the effects of antidotes diazepam and atropine following soman-intoxication. We observed that the initiation of the antidote combination of HI 6 and atropine following soman-intoxication was crucial for successful treatment. The study also demonstrated that atropine alone was more effective against IL-1beta up-regulation after soman-intoxication within the 2-h time frame, than the combination of the HI 6 and atropine, the therapy of choice in many countries. Furthermore, treatment with a combination of diazepam and atropine maintained IL-1beta levels at normal when administered at the onset of the seizures following soman exposure. Soman-intoxicated groups without seizures did not have an elevated cytokine level. This corroborates our earlier studies where soman-intoxicated animals with seizures had high levels of IL-1beta, while animals without seizures had normal values. Our results show that both time and the antidote regime are crucial to the success of treatment.

The effects of vagus nerve stimulation on pro- and anti-inflammatory cytokines in humans: a preliminary report

OBJECTIVE

Vagus nerve stimulation (VNS) is a novel therapy in resistant epilepsy, and is undergoing clinical trials in resistant depression. The mechanism of action of VNS is assumed to be due to modulation of deep brain structures via its afferent connections. As the vagus nerve has potentially important immunological actions that may have relevance to its therapeutic effects, we hypothesised that an additional mechanism may occur via vagally mediated actions on cytokine synthesis.

METHODS

Patients (n=10) with resistant depression were studied in the weeks prior to, and 3 months following, implantation of a vagus nerve stimulator. No medication changes were made during the course of the study. High-sensitivity ELISA kits were used to measure plasma IL-1 beta, IL-6, TNF-alpha, IL-10 and TGF-beta concentrations. C-reactive protein (CRP) was measured using a high sensitivity immunonephelometry assay.

RESULTS

There were highly significant increases in the plasma levels of IL-6, TNF-alpha and TGF-beta. Increases seen with IL-10 and IL-1 beta were not significant. Plasma CRP levels were unchanged.

CONCLUSION

VNS is associated with marked peripheral increases in pro- and anti-inflammatory circulating cytokines. Such changes are unlikely to be non-specific inflammatory reactions, reflected by CRP levels. In view of gathering evidence supporting a role for the immune system in modulating affect, as well as seizure activity, these effects of VNS may be therapeutically relevant.

Inflammation and epilepsy

In recent years, increasing evidence has indicated that immune and inflammatory reactions occur in brain in various central nervous system (CNS) diseases. Furthermore, inflammatory processes, such as the production of proinflammatory cytokines and related molecules, have been described in brain after seizures induced in experimental models and in clinical cases of epilepsy. Although little is known about the role of inflammation in epilepsy, it has been hypothesized that activation of the innate immune system and associated inflammatory reactions in brain may mediate some of the molecular and structural changes occurring during and after seizure activity. Whether the innate immune response that takes place in epileptic tissue is beneficial or noxious to the CNS is still an open and intriguing question that should be addressed by further investigations.

Epilepsy and the immune system: is there a link?

The concept that the immune system plays a role in the epileptogenic process of some epileptic syndromes was first proposed more than 20 years ago. Since then, numerous studies have reported on the existence of a variety of immunological alterations in epileptic patients, on the observation of favourable responses of refractory epilepsy syndromes to immunomodulatory treatment, and on the association of certain well-known immune-mediated disease states with epilepsy. This review comprehensively recapitulates the currently available evidence supporting or arguing against the possible involvement of the immune system in the pathogenesis of certain types of epilepsy. It is concluded that an abundance of facts is in support of this concept and that further studies should be directed at substantiating the pathogenic significance of (auto)immune responses in certain types of epilepsy. Current progress in the functional and molecular immunological research techniques will indisputably contribute to the elucidation of this link.

Lipopolysaccharide-induced Febrile Convulsions in the Rat: Short-term Sequelae

PURPOSE

Febrile convulsions (FCs) occur in children as a result of fever. The mechanisms involved in the genesis of FCs and their long-term consequences on brain development remain unclear. We have developed a model of FC, by using fever as a parameter, to test the hypothesis that fever can lower seizure threshold and to examine the neurologic sequelae of FCs.

METHODS

Fourteen-day-old rat pups equipped with body-temperature telemetry devices exhibited approximately 1.5 degrees C fevers after lipopolysaccharide (Escherichia coli, 200 microg/kg). During such fevers, concurrently administered doses of kainic acid that are normally subconvulsant were used to induce convulsions with fever. Animals were then killed at varying times for pathological and immunohistochemical studies.

RESULTS

The pairing of lipopolysaccharide and subconvulsant kainic acid resulted in convulsions in approximately 50% of febrile animals, with very low mortality. To study the neural correlates of these FCs, we used fos immunohistochemistry and found that animals with FCs had fos-positive immunoreactivity in brain regions involved in seizures. After a period of 72 h, we also examined brains for pathologic changes and found no differences among our groups.

CONCLUSIONS

Our data indicate that a neuroimmune challenge and its accompanying fever reduce the seizure threshold. Furthermore, the FCs induced by fever in this model do not have short-term adverse effects on the brain. In addition, this model, by incorporating physiologic fever, may be useful for examining the role of fever and its constituent mediators in the genesis of FCs.

Brain-derived neurotrophic factor

Since the purification of BDNF in 1982, a great deal of evidence has mounted for its central roles in brain development, physiology, and pathology. Aside from its importance in neural development and cell survival, BDNF appears essential to molecular mechanisms of synaptic plasticity. Basic activity-related changes in the central nervous system are thought to depend on BDNF modification of synaptic transmission, especially in the hippocampus and neocortex. Pathologic levels of BDNF-dependent synaptic plasticity may contribute to conditions such as epilepsy and chronic pain sensitization, whereas application of the trophic properties of BDNF may lead to novel therapeutic options in neurodegenerative diseases and perhaps even in neuropsychiatric disorders.

Kindling and status epilepticus models of epilepsy: rewiring the brain

This review focuses on the remodeling of brain circuitry associated with epilepsy, particularly in excitatory glutamate and inhibitory GABA systems, including alterations in synaptic efficacy, growth of new connections, and loss of existing connections. From recent studies on the kindling and status epilepticus models, which have been used most extensively to investigate temporal lobe epilepsy, it is now clear that the brain reorganizes itself in response to excess neural activation, such as seizure activity. The contributing factors to this reorganization include activation of glutamate receptors, second messengers, immediate early genes, transcription factors, neurotrophic factors, axon guidance molecules, protein synthesis, neurogenesis, and synaptogenesis. Some of the resulting changes may, in turn, contribute to the permanent alterations in seizure susceptibility. There is increasing evidence that neurogenesis and synaptogenesis can appear not only in the mossy fiber pathway in the hippocampus but also in other limbic structures. Neuronal loss, induced by prolonged seizure activity, may also contribute to circuit restructuring, particularly in the status epilepticus model. However, it is unlikely that any one structure, plastic system, neurotrophin, or downstream effector pathway is uniquely critical for epileptogenesis. The sensitivity of neural systems to the modulation of inhibition makes a disinhibition hypothesis compelling for both the triggering stage of the epileptic response and the long-term changes that promote the epileptic state. Loss of selective types of interneurons, alteration of GABA receptor configuration, and/or decrease in dendritic inhibition could contribute to the development of spontaneous seizures.

Innate immune reaction in response to seizures: implications for the neuropathology associated with epilepsy

In the present study, the expression of pro-inflammatory transcripts was assessed across the brain of mice having undertaken pilocarpine-induced seizures. Pilocarpine-induced marked neurodegeneration and demyelination in multiple regions of the forebrain. The pattern of genes encoding toll-like receptor type 2 (TLR2) and I kappa B alpha (index of NF-kappa B activation) was associated with the neurodegenerating areas, but this was not the case for the mRNA encoding other inflammatory proteins. Scattered tumor necrosis factor-alpha (TNF-alpha)-expressing cells were found across brain, whereas the signals for monocyte-chemoattractant protein-1 and microsomal prostaglandin mPGES E synthase were robust in thalamus and cerebral cortex and weak in the hippocampus and amygdala. TLR2 and TNF-alpha transcripts were expressed mainly in microglia/macrophages. Cyclooxygenase-2 was induced specifically in the hippocampus and piriform cortex. A low increase in interleukin-12 mRNA was detected in the brain, but the signal for interferon gamma (IFN-gamma) remained undetectable. Although pro-inflammatory markers were induced in a different manner across the CNS, their patterns were not characteristic of those caused by other inflammatory challenges, such as endotoxin. These data suggest a different mechanism involved in regulating the innate immune reaction in response to seizures and could have direct implications for the neuropathology associated with epilepsy.

β-Hydroxy-butyrate alters the extracellular content of S100B in astrocyte cultures

Astrocytes have a variety of roles in maintaining neural tissue physiology, including energetic support, uptake and metabolism of glutamate and secretion of neurotrophic factors. Glutamate toxicity has been implicated in neurodegenerative disorders associated with conditions related to energy failure, and to elevation of glutamate extracellular levels in brain. Glucose is the main energetic substrate for brain cells but, in some circumstances, the ketone bodies are used as a supplementary source and have been suggested to be neuroprotective agents against seizure disorders. Here, we investigate some possible biochemical changes in astrocyte cultures induced by beta-hydroxy-butyrate, the predominant blood ketone body. Its effect upon S100B secretion, astrocyte morphology and glutamate uptake was particularly investigated. S100B, a calcium-binding protein expressed and secreted by astrocytes, has neurotrophic activity and a possible role in epileptogenesis. Cell morphology was investigated by phase-contrast microscopy and immunocytochemistry for actin, GFAP and S100B. Our data show that beta-hydroxy-butyrate induces dramatic changes in astrocyte morphology and, independent of this, causes changes in the extracellular content of S100B. We observed an increment in S100B 1 h after beta-hydroxy-butyrate addition and a decrease 24 h later. No changes were observed in glutamate uptake. These astrocytic modifications may be associated with reduced neuronal excitability observed in the ketogenic condition.

Differences in the regulation of BDNF and NGF synthesis in cultured neonatal rat astrocytes

Using a new brain-derived neurotrophic factor (BDNF) specific enzyme-immunoassay, we determined the basal cellular content of BDNF protein in neonatal rat astrocytes in primary culture, thus confirming the ability of astrocytes to synthesize BDNF in addition to nerve growth factor (NGF). We subsequently monitored the influence of different pharmacological agents: neurotransmitter receptor agonists, cytokines, and second messenger up-regulators, on the synthesis of BDNF and NGF. Marked differences in the regulation of their synthesis by the above pharmacological agents were observed in our study. The basal cellular levels of BDNF protein in cultured neonatal rat cortical and cerebellar astrocytes were 15.9 +/- 0.3 and 18.7 +/- 0.4 pg BDNF/mg cell protein, respectively, and differ significantly between astrocytes from different brain regions, whereas NGF levels were the same (16.1 +/- 0.3 and 16.2 +/- 0.7 pg NGF/mg cell protein, respectively). Screening different neurotransmitter systems for their influence on BDNF and NGF synthesis in cortical astrocytes revealed that dopamine (0.15 mM) is a potent up-regulator of BDNF protein synthesis in astrocytes, while kainic acid (50 microM) and histamine (1 microM) did not raise the cellular level of BDNF protein. Dopamine had no influence on NGF synthesis, while kainic acid caused minor, and histamine marked, elevation of NGF cellular content. Tumor necrosis factor-alpha (30 ng/ml) and interleukin-1beta (10 U/ml) treatments did not influence BDNF synthesis, whereas they markedly increased NGF protein cellular level. We also confirmed (using forskolin (20 microM) and phorbol 12-myristate 13-acetate (TPA) (100 nM)) that adenylate cyclase and protein kinase C participate in the downstream signaling responsible for the stimulation of BDNF synthesis, whereas in the regulation of NGF synthesis only the participation of protein kinase C was confirmed. Our results indicate that astrocyte-derived neurotrophins could play a role in distinct brain functions under physiological conditions and in the pathogenesis as well as possible treatment of different neurodegenerative disorders.

Intranasal administration of human IL-6 increases the severity of chemically induced seizures in rats

Here we study the role of a pleiotropic pro-inflammatory cytokine, interleukin-6 (IL-6), in epilepsy. To examine this problem, we used human recombinant IL-6 applied intranasally (400 ng/40 microl) to rats 1h before seizures induced by systemic injection of pentylenenetrazole (PTZ, 75 mg/kg). Overall, compared to the saline-treated control animals (n = 11 in each group), IL-6-treated rats demonstrated elevated levels of IL-6 in the frontal lobe (measured by ELISA) and increased severity of PTZ-induced seizures (shorter latency, longer duration and higher mortality). Our findings show that IL-6 plays a pro-convulsant role in the brain and suggest that the IL-6 system may be a novel target for the development of anticonvulsant drugs.