Glia and epilepsy: excitability and inflammation

Minocycline inhibits brain inflammation and attenuates spontaneous recurrent seizures following pilocarpine-induced status epilepticus

Mounting evidence suggests that brain inflammation mediated by glial cells may contribute to epileptogenesis. Minocycline is a second-generation tetracycline and has potent antiinflammatory effects independent of its antimicrobial action. The present study aimed to investigate whether minocycline could exert antiepileptogenic effects in a rat lithium-pilocarpine model of temporal lobe epilepsy. The temporal patterns of microglial and astrocytic activation were examined in the hippocampal CA1 and the adjacent cortex following pilocarpine-induced status epilepticus (SE). These findings displayed that SE caused acute and persistent activation of microglia and astrocytes. Based on these findings, Minocycline was administered once daily at 45 mg/kg for 14 days following SE. Six weeks after termination of minocycline treatment, spontaneous recurrent seizures (SRS) were recorded by continuous video monitoring. Minocycline inhibited the SE-induced microglial activation and the increased production of interleukin-1β and tumor necrosis factor-α in the hippocampal CA1 and the adjacent cortex, without affecting astrocytic activation. In addition, Minocycline prevented the SE-induced neuronal loss in the brain regions examined. Moreover, minocycline significantly reduced the frequency, duration, and severity of SRS during the two weeks monitoring period. These results demonstrated that minocycline could mitigate SE-induced brain inflammation and might exert disease-modifying effects in an animal model of temporal lobe epilepsy. These findings offer new insights into deciphering the molecular mechanisms of epileptogenesis and exploring a novel therapeutic strategy for prevention of epilepsy.

In Rasmussen encephalitis, hemichannels associated with microglial activation are linked to cortical pyramidal neuron coupling: a possible mechanism for cellular hyperexcitability

AIMS

Rasmussen encephalitis (RE) is a rare but devastating condition, mainly in children, characterized by sustained brain inflammation, atrophy of one cerebral hemisphere, epilepsy, and progressive cognitive deterioration. The etiology of RE-induced seizures associated with the inflammatory process remains unknown.

METHODS

Cortical tissue samples from children undergoing surgical resections for the treatment of RE (n = 16) and non-RE (n = 12) were compared using electrophysiological, morphological, and immunohistochemical techniques to examine neuronal properties and the relationship with microglial activation using the specific microglia/macrophage calcium-binding protein, IBA1 in conjunction with connexins and pannexin expression.

RESULTS

Compared with non-RE cases, pyramidal neurons from RE cases displayed increased cell capacitance and reduced input resistance. However, neuronal somatic areas were not increased in size. Instead, intracellular injection of biocytin led to increased dye coupling between neurons from RE cases. By Western blot, expression of IBA1 and pannexin was increased while connexin 32 was decreased in RE cases compared with non-RE cases. IBA1 immunostaining overlapped with pannexin and connexin 36 in RE cases.

CONCLUSIONS

In RE, these results support the notion that a possible mechanism for cellular hyperexcitability may be related to increased intercellular coupling from pannexin linked to increased microglial activation. Such findings suggest that a possible antiseizure treatment for RE may involve the use of gap junction blockers.

Using sex differences in the developing brain to identify nodes of influence for seizure susceptibility and epileptogenesis

Sexual differentiation of the developing brain organizes the neural architecture differently between males and females, and the main influence on this process is exposure to gonadal steroids during sensitive periods of prenatal and early postnatal development. Many molecular and cellular processes are influenced by steroid hormones in the developing brain, including gene expression, cell birth and death, neurite outgrowth and synaptogenesis, and synaptic activity. Perturbations in these processes can alter neuronal excitability and circuit activity, leading to increased seizure susceptibility and the promotion of pathological processes that constitute epileptogenesis. In this review, we will provide a general overview of sex differences in the early developing brain that may be relevant for altered seizure susceptibility in early life, focusing on limbic areas of the brain. Sex differences that have the potential to alter the progress of epileptogenesis are evident at molecular and cellular levels in the developing brain, and include differences in neuronal excitability, response to environmental insult, and epigenetic control of gene expression. Knowing how these processes differ between the sexes can help us understand fundamental mechanisms underlying gender differences in seizure susceptibility and epileptogenesis.

Basic mechanisms of epileptogenesis in pediatric cortical dysplasia

Cortical dysplasia (CD) is a neurodevelopmental disorder due to aberrant cell proliferation and differentiation. Advances in neuroimaging have proven effective in early identification of the more severe lesions and timely surgical removal to treat epilepsy. However, the exact mechanisms of epileptogenesis are not well understood. This review examines possible mechanisms based on anatomical and electrophysiological studies. CD can be classified as CD type I consisting of architectural abnormalities, CD type II with the presence of dysmorphic cytomegalic neurons and balloon cells, and CD type III which occurs in association with other pathologies. Use of freshly resected brain tissue has allowed a better understanding of basic mechanisms of epileptogenesis and has delineated the role of abnormal cells and synaptic activity. In CD type II, it was demonstrated that balloon cells do not initiate epileptic activity, whereas dysmorphic cytomegalic and immature neurons play an important role in generation and propagation of epileptic discharges. An unexpected finding in pediatric CD was that GABA synaptic activity is not reduced, and in fact, it may facilitate the occurrence of epileptic activity. This could be because neuronal circuits display morphological and functional signs of dysmaturity. In consequence, drugs that increase GABA function may prove ineffective in pediatric CD. In contrast, drugs that counteract depolarizing actions of GABA or drugs that inhibit the mammalian target of rapamycin (mTOR) pathway could be more effective.

Spinal astrocyte gap junction and glutamate transporter expression contributes to a rat model of bortezomib-induced peripheral neuropathy

There is increasing evidence implicating astrocytes in multiple forms of chronic pain, as well as in the specific context of chemotherapy-induced peripheral neuropathy (CIPN). However, it is still unclear what the exact role of astrocytes may be in the context of CIPN. Findings in oxaliplatin and paclitaxel models have displayed altered expression of astrocytic gap junctions and glutamate transporters as means by which astrocytes may contribute to observed behavioral changes. The current study investigated whether these changes were also generalizable to the bortezomib CIPN. Changes in mechanical sensitivity were verified in bortezomib-treated animals, and these changes were prevented by co-treatment with a glial activation inhibitor (minocycline), a gap junction decoupler (carbenoxolone), and by a glutamate transporter upregulator (ceftriaxone). Immunohistochemistry data at day 30 in bortezomib-treated animals showed increases in expression of glial fibrillary acidic protein (GFAP) and connexin 43 but a decrease in GLAST expression. These changes were prevented by co-treatment with minocycline. Follow-up Western blotting data showed a shift in connexin 43 from a non-phosphorylated state to a phosphorylated state, indicating increased trafficking of expressed connexin 43 to the cell membrane. These data suggest that increases in behavioral sensitivity to cutaneous stimuli may be tied to persistent synaptic glutamate resulting from increased calcium flow between spinal astrocytes.

Neuromodulatory properties of inflammatory cytokines and their impact on neuronal excitability

Increasing evidence underlines that prototypical inflammatory cytokines (IL-1β, TNF-α and IL-6) either synthesized in the central (CNS) or peripheral nervous system (PNS) by resident cells, or imported by immune blood cells, are involved in several pathophysiological functions, including an unexpected impact on synaptic transmission and neuronal excitability. This review describes these unconventional neuromodulatory properties of cytokines, that are distinct from their classical action as effector molecules of the immune system. In addition to the role of cytokines in brain physiology, we report evidence that dysregulation of their biosynthesis and cellular release, or alterations in receptor-mediated intracellular pathways in target cells, leads to neuronal cell dysfunction and modifications in neuronal network excitability. As a consequence, targeting of these cytokines, and related signalling molecules, is considered a novel option for the development of therapies in various CNS or PNS disorders associated with an inflammatory component. This article is part of a Special Issue entitled 'Neuroimmunology and Synaptic Function'.

Early molecular and behavioral response to lipopolysaccharide in the WAG/Rij rat model of absence epilepsy and depressive-like behavior, involves interplay between AMPK, AKT/mTOR pathways and neuroinflammatory cytokine release

The mammalian target of rapamycin (mTOR) pathway has been recently indicated as a suitable drug target for the prevention of epileptogenesis. The mTOR pathway is known for its involvement in the control of the immune system. Since neuroinflammation is recognized as a major contributor to epileptogenesis, we wished to examine whether the neuroprotective effects of mTOR modulation could involve a suppression of the neuroinflammatory process in epileptic brain. We have investigated the early molecular mechanisms involved in the effects of intracerebral administration of the lipopolysaccharide (LPS) in the WAG/Rij rat model of absence epilepsy, in relation to seizure generation and depressive-like behavior; we also tested whether the effects of LPS could be modulated by treatment with rapamycin (RAP), a specific mTOR inhibitor. We determined, in specific rat brain areas, levels of p-mTOR/p-p70S6K and also p-AKT/p-AMPK as downstream or upstream indicators of mTOR activity and tested the effects of LPS and RAP co-administration. Changes in the brain levels of pro-inflammatory cytokines IL-1β and TNF-α and their relative mRNA expression levels were measured, and the involvement of nuclear factor-κB (NF-κB) was also examined in vitro. We confirmed that RAP inhibits the aggravation of absence seizures and depressive-like/sickness behavior induced by LPS in the WAG/Rij rats through the activation of mTOR and show that this effect is correlated with the ability of RAP to dampen and delay LPS increases in neuroinflammatory cytokines IL-1β and TNF-α, most likely through inhibition of the activation of NF-κB. Our results suggest that such a mechanism could contribute to the antiseizure, antiepileptogenic and behavioral effects of RAP and further highlight the potential therapeutic usefulness of mTOR inhibition in the management of human epilepsy and other neurological disorders. Furthermore, we show that LPS-dependent neuroinflammatory effects are also mediated by a complex interplay between AKT, AMPK and mTOR with specificity to selective brain areas. In conclusion, neuroinflammation appears to be a highly coordinated phenomenon, where timing of intervention may be carefully evaluated in order to identify the best suitable target.

Treadmill exercise improves motor coordination through ameliorating Purkinje cell loss in amyloid beta23-35-induced Alzheimer's disease rats

Alzheimer's disease (AD) is a most common age-related neurodegenerative disease. AD is characterized by a progressive loss of neurons causing cognitive dysfunction. The cerebellum is closely associated with integration of movement, including motor coordination, control, and equilibrium. In the present study, we evaluated the effect of tread-mill exercise on the survival of Purkinje neurons in relation with reactive astrocyte in the cerebellum using Aβ25-35-induced AD rats. AD was induced by a bilateral intracerebroventricular (ICV) injection of Aβ25-35. The rats in the exercise groups were forced to run on a motorized treadmill for 30 min once a day for 4 weeks, starting 2 days after Aβ25-35 injection. In the present results, ICV injection of Aβ25-35 deteriorated motor coordination and balance. The number of calbindin-positive cells in the cerebellar vermis was decreased and glial fibrillary acidic protein (GFAP) expression in the cerebellar vermis was increased in the Aβ25-35-induced AD rats. Treadmill exercise improved motor coordination and balance. Treadmill exercise increased the number of Purkinje neurons and suppressed GFAP expression in the cerebellar vermis. The present study demonstrated that treadmill exercises alleviated dysfunction of motor coordination and balance by reduction of Purkinje cell loss through suppressing reactive astrocytes in the cerebellum of AD rats. The present study provides the possibility that treadmill exercise might be an important therapeutic strategy for the symptom improvement of AD patients.

Post-exposure administration of diazepam combined with soluble epoxide hydrolase inhibition stops seizures and modulates neuroinflammation in a murine model of acute TETS intoxication

Tetramethylenedisulfotetramine (TETS) is a potent convulsant poison for which there is currently no approved antidote. The convulsant action of TETS is thought to be mediated by inhibition of type A gamma-aminobutyric acid receptor (GABAAR) function. We, therefore, investigated the effects of post-exposure administration of diazepam, a GABAAR positive allosteric modulator, on seizure activity, death and neuroinflammation in adult male Swiss mice injected with a lethal dose of TETS (0.15mg/kg, ip). Administration of a high dose of diazepam (5mg/kg, ip) immediately following the second clonic seizure (approximately 20min post-TETS injection) effectively prevented progression to tonic seizures and death. However, this treatment did not prevent persistent reactive astrogliosis and microglial activation, as determined by GFAP and Iba-1 immunoreactivity and microglial cell morphology. Inhibition of soluble epoxide hydrolase (sEH) has been shown to exert potent anti-inflammatory effects and to increase survival in mice intoxicated with other GABAAR antagonists. The sEH inhibitor TUPS (1mg/kg, ip) administered immediately after the second clonic seizure did not protect TETS-intoxicated animals from tonic seizures or death. Combined administration of diazepam (5mg/kg, ip) and TUPS (1mg/kg, ip, starting 1h after diazepam and repeated every 24h) prevented TETS-induced lethality and influenced signs of neuroinflammation in some brain regions. Significantly decreased microglial activation and enhanced reactive astrogliosis were observed in the hippocampus, with no changes in the cortex. Combining an agent that targets specific anti-inflammatory mechanisms with a traditional antiseizure drug may enhance treatment outcome in TETS intoxication.

p75NTR, but not proNGF, is upregulated following status epilepticus in mice

ProNGF and p75(NTR) are upregulated and induce cell death following status epilepticus (SE) in rats. However, less is known about the proneurotrophin response to SE in mice, a more genetically tractable species where mechanisms can be more readily dissected. We evaluated the temporal- and cell-specific induction of the proneurotrophins and their receptors, including p75(NTR), sortilin, and sorCS2, following mild SE induced with kainic acid (KA) or severe SE induced by pilocarpine. We found that mature NGF, p75(NTR), and proBDNF were upregulated following SE, while proNGF was not altered, indicating potential mechanistic differences between rats and mice. ProBDNF was localized to mossy fibers and microglia following SE. p75(NTR) was transiently induced primarily in axons and axon terminals following SE, as well as in neuron and astrocyte cell bodies. ProBDNF and p75(NTR) increased independently of cell death and their localization was different depending on the severity of SE. We also examined the expression of proneurotrophin co-receptors, sortilin and sorCS2. Following severe SE, sorCS2, but not sortilin, was elevated in neurons and astrocytes. These data indicate that important differences exist between rat and mouse in the proneurotrophin response following SE. Moreover, the proBDNF and p75(NTR) increase after seizures in the absence of significant cell death suggests that proneurotrophin signaling may play other roles following SE.

Sustained down-regulation of β-dystroglycan and associated dysfunctions of astrocytic endfeet in epileptic cerebral cortex

Epilepsy is characterized by the abnormal activation of neurons in the cerebral cortex, but the molecular and cellular mechanisms contributing to the development of recurrent seizures are largely unknown. Recently, the critical involvement of astrocytes in the pathophysiology of epilepsy has been proposed. However, the nature of plastic modulations of astrocytic proteins in the epileptic cortex remains poorly understood. In this study, we utilized the zero magnesium in vitro model of epilepsy and examined the potential molecular changes of cortical astrocytes, focusing specifically on endfeet, where specialized biochemical compartments exist. We find that the continuous epileptic activation of neurons for 1 h decreases the expression level of β-dystroglycan (βDG) in acute cortical brain slices prepared from mice. This change is completely abolished by the pharmacological blockade of NMDA-type glutamate receptors as well as by matrix metalloproteinase inhibitors. Consistent with the highly specialized localization of βDG at astrocytic endfeet, where it plays a pivotal role in anchoring endfeet-enriched proteins in astrocytes, the down-regulation of βDG is accompanied by a decrease in the expression of AQP4 but not laminin. Importantly, this down-regulation of βDG persists for at least 1 h, even after the apparent recovery of neuronal activation. Finally, we show that the down-regulation of βDG is associated with the dysfunction of the endfeet at the blood-brain interface as a diffusion barrier. These results suggest that the sustained down-regulation of βDG leads to dysfunctions of astrocytic endfeet in the epileptic cerebral cortex and may contribute to the pathogenesis of epilepsy.

Expression of astrocyte-related receptors in cortical dysplasia with intractable epilepsy

Epilepsy is one of the major neurologic diseases, and astrocytes play important roles in epileptogenesis. To investigate possible roles of astrocyte-related receptors in patients with intractable epilepsy associated with focal cortical dysplasia (FCD) and other conditions, we examined resected epileptic foci from 31 patients, including 23 with FCD type I, IIa, or IIb, 5 with tuberous sclerosis complex, and 3 with low-grade astrocytoma. Control samples were from 21 autopsied brains of patients without epilepsy or neurologic deficits and 5 patients with pathologic gliosis without epilepsy. Immunohistochemical and immunoblot analyses with antibodies against purinergic receptor subtypes P2RY1, P2RY2, P2RY4, potassium channels Kv4.2 and Kir4.1, and metabotropic receptor subtypes mGluR1 and mGluR5 were performed. Anti-glial fibrillary acidic protein, anti-NeuN, and anti-CD68 immunostaining was used to identify astrocytes, neurons, and microglia, respectively. Most glial fibrillary acidic protein-immunopositive astrocyte cells in the brain samples from patients with epilepsy were P2RY1-, P2RY2-, P2RY4-, Kv4.2-, Kir4.1-, mGluR1-, and mGluR5-positive, whereas samples from controls and pathologic gliosis showed lower expression levels of these astrocyte-related receptors. Our findings suggest that, although these receptors are necessary for astrocyte transmission, formation of the neuron-glia network, and other physiologic functions, overexpression in the brains of patients with intractable epilepsy may be associated with activation of intracellular and glio-neuronal signaling pathways that contribute to epileptogenesis.

Experimental studies in epilepsy: immunologic and inflammatory mechanisms

In this article, we review the literature based on experimental studies lending credence to a relationship between epilepsy and immune-mediated mechanisms linked to central nervous system innate immunity. The brain innate immunity responses to neuronal injury or excessive neuronal activity are mediated by resident microglia and astroglia, but also neurons play an immunomodulatory role. Antigens or antibodies applied to the brain trigger an epileptogenic and inflammatory response. Furthermore, seizure activity and status epilepticus elicit the production and release of proinflammatory cytokines and chemokines. The immune pathogenesis of epilepsy involves complex cell-to-cell interactions including a cross talk between astrocytes and neurons, between astrocytes and brain microvascular endothelial cells, as well as reciprocal leukocyte-endothelial interactions in the context of disruption of the blood-brain barrier. There is a large body of literature from experimental studies showing that seizures can initiate a cascade of innate and adaptive immune responses from various cellular sources and perpetuate neuroinflammation through mechanisms involving transcription of inflammatory genes or posttranslational changes in cytokine release machinery. These inflammatory processes could also possibly contribute to the pathogenesis of comorbidities often associated with epilepsy. This opens exciting possibilities for the development of disease-modifying drugs aimed at mitigating neuroinflammation as a means of ameliorating epileptogenesis and lessening or preventing postictal brain injury.

Focal epilepsies: immunologic and inflammatory mechanisms

There is increasing evidence documenting activation of inflammatory processes in focal epilepsies. This review article summarizes current data regarding immune mediated inflammatory processes in patients with symptomatic partial epilepsies such as mesial temporal sclerosis, focal cortical dysplasia, and Rasmussen's encephalitis. We have also reviewed several neuronal surface antibody-associated syndromes, which have been recently described with focal seizures as an important part of clinical presentation, such as antibody-associated limbic encephalitis and N-methyl-D-aspartic acid receptor antibody syndrome. An autoimmune mechanism may be one pathogenic factor in some symptomatic epilepsies acting as a triggering event in the process leading to the development of epilepsy.

Targeting of microglial KCa3.1 channels by TRAM-34 exacerbates hippocampal neurodegeneration and does not affect ictogenesis and epileptogenesis in chronic temporal lobe epilepsy models

Blockade of KCa3.1 channels has been suggested as a novel strategy to reduce microglia activation. The concept has been confirmed by neuroprotective effects in a rat brain ischemia-reperfusion model and reduced microglia activation surrounding glioblastomas. Cumulating evidence exists that microglia activation significantly contributes to epileptogenesis as well as intrinsic severity in the chronic epileptic brain. Taken together these data raised the question whether the KCa3.1 channel blocker triarylmethane-34 (TRAM-34) might also exert beneficial effects in chronic epilepsy models. In a rat post-status epilepticus model TRAM-34 treatment following the insult did not result in neuroprotective effects. Whereas status epilepticus-associated neurodegeneration remained unaffected in the piriform cortex, loss of pyramidal cells in the hippocampal CA1 and CA3a region and of neuropeptide Y-positive interneurons in the hilus proved to be exacerbated by pharmacological KCa3.1 blockade. The development of spontaneous seizures and of behavioral and cognitive alterations was comparable in animals receiving TRAM-34 treatment or the respective vehicle. The kindling model of temporal lobe epilepsy with a massive stimulation paradigm with frequent seizure elicitation in fully kindled rats was used to assess a putative disease-modifying effect. However, sub-chronic TRAM-34 treatment failed to exert relevant effects on seizure generation and thresholds. In conclusion, the data obtained in two different chronic epilepsy models argue against using KCa3.1 blockers as disease-modifying or antiepileptogenic agents. Exacerbation of neuronal cell loss in TRAM-34 pre-treated epileptic animals rather indicates that translational development of the compound needs to carefully consider the pathophysiological mechanisms associated with different brain insults.

Spreading depression requires microglia and is decreased by their M2a polarization from environmental enrichment

Microglia play an important role in fine-tuning neuronal activity. In part, this involves their production of tumor necrosis factor-alpha (TNFα), which increases neuronal excitability. Excessive synaptic activity is necessary to initiate spreading depression (SD). Increased microglial production of proinflammatory cytokines promotes initiation of SD, which, when recurrent, may play a role in conversion of episodic to high frequency and chronic migraine. Previous work shows that this potentiation of SD occurs through increased microglial production of TNFα and reactive oxygen species, both of which are associated with an M1-skewed microglial population. Hence, we explored the role of microglia and their M1 polarization in SD initiation. Selective ablation of microglia from rat hippocampal slice cultures confirmed that microglia are essential for initiation of SD. Application of minocycline to dampen M1 signaling led to increased SD threshold. In addition, we found that SD threshold was increased in rats exposed to environmental enrichment. These rats had increased neocortical levels of interleukin-11 (IL-11), which decreases TNFα signaling and polarized microglia to an M2a-dominant phenotype. M2a microglia reduce proinflammatory signaling and increase production of anti-inflammatory cytokines, and therefore may protect against SD. Nasal administration of IL-11 to mimic effects of environmental enrichment likewise increased M2a polarization and increased SD threshold, an effect also seen in vitro. Similarly, application of conditioned medium from M2a polarized primary microglia to slice cultures also increased SD threshold. Thus, microglia and their polarization state play an essential role in SD initiation, and perhaps by extension migraine with aura and migraine.

Neuronal networks and energy bursts in epilepsy

Epilepsy can be defined as the abnormal activities of neurons. The occurrence, propagation and termination of epileptic seizures rely on the networks of neuronal cells that are connected through both synaptic- and non-synaptic interactions. These complicated interactions contain the modified functions of normal neurons and glias as well as the mediation of excitatory and inhibitory mechanisms with feedback homeostasis. Numerous spread patterns are detected in disparate networks of ictal activities. The cortical-thalamic-cortical loop is present during a general spike wave seizure. The thalamic reticular nucleus (nRT) is the major inhibitory input traversing the region, and the dentate gyrus (DG) controls CA3 excitability. The imbalance between γ-aminobutyric acid (GABA)-ergic inhibition and glutamatergic excitation is the main disorder in epilepsy. Adjustable negative feedback that mediates both inhibitory and excitatory components affects neuronal networks through neurotransmission fluctuation, receptor and transmitter signaling, and through concomitant influences on ion concentrations and field effects. Within a limited dynamic range, neurons slowly adapt to input levels and have a high sensitivity to synaptic changes. The stability of the adapting network depends on the ratio of the adaptation rates of both the excitatory and inhibitory populations. Thus, therapeutic strategies with multiple effects on seizures are required for the treatment of epilepsy, and the therapeutic functions on networks are reviewed here. Based on the high-energy burst theory of epileptic activity, we propose a potential antiepileptic therapeutic strategy to transfer the high energy and extra electricity out of the foci.

Modeling glial contributions to seizures and epileptogenesis: cation-chloride cotransporters in Drosophila melanogaster

Flies carrying a kcc loss-of-function mutation are more seizure-susceptible than wild-type flies. The kcc gene is the highly conserved Drosophila melanogaster ortholog of K+/Cl- cotransporter genes thought to be expressed in all animal cell types. Here, we examined the spatial and temporal requirements for kcc loss-of-function to modify seizure-susceptibility in flies. Targeted RNA interference (RNAi) of kcc in various sets of neurons was sufficient to induce severe seizure-sensitivity. Interestingly, kcc RNAi in glia was particularly effective in causing seizure-sensitivity. Knockdown of kcc in glia or neurons during development caused a reduction in seizure induction threshold, cell swelling, and brain volume increase in 24-48 hour old adult flies. Third instar larval peripheral nerves were enlarged when kcc RNAi was expressed in neurons or glia. Results suggest that a threshold of K+/Cl- cotransport dysfunction in the nervous system during development is an important determinant of seizure-susceptibility in Drosophila. The findings presented are the first attributing a causative role for glial cation-chloride cotransporters in seizures and epileptogenesis. The importance of elucidating glial cell contributions to seizure disorders and the utility of Drosophila models is discussed.

The inflammatory molecules IL-1β and HMGB1 can rapidly enhance focal seizure generation in a brain slice model of temporal lobe epilepsy

Epilepsy is a neurological disorder characterized by a hyperexcitable brain tissue and unpredictable seizures, i.e., aberrant firing discharges in large neuronal populations. It is well established that proinflammatory cytokines, in addition to their canonical involvement in the immune response, have a crucial role in the mechanism of seizure generation. The purpose of the present study was to investigate the role of interleukin-1β (IL-1β) and high mobility group B1 (HMGB1) in the generation of seizure-like discharges using two models of focal epilepsy in a rat entorhinal cortex slice preparation. Seizure like-discharges were evoked by either slice perfusion with low Mg²⁺ and picrotoxin or with a double NMDA local stimulation in the presence of the proconvulsant 4-amino-pyridine. The effects of IL-1β or HMGB1 were evaluated by monitoring seizure discharge generation through laser scanning microscope imaging of Ca²⁺ signals from neurons and astrocytes. In the picrotoxin model, we revealed that both cytokines increased the mean frequency of spontaneous ictal-like discharges, whereas only IL-1β reduced the latency and prolonged the duration of the first ictal-like event. In the second model, a single NMDA pulse, per se ineffective, became successful when it was performed after IL-β or HMGB1 local applications. These findings demonstrate that both IL-1β and HMGB1 can rapidly lower focal ictal event threshold and strengthen the possibility that targeting these inflammatory pathways may represent an effective therapeutic strategy to prevent seizures.

Widespread activation of microglial cells in the hippocampus of chronic epileptic rats correlates only partially with neurodegeneration

Activation of microglial cells (brain macrophages) soon after status epilepticus has been suggested to be critical for the pathogenesis of mesial temporal lobe epilepsy (MTLE). However, microglial activation in the chronic phase of experimental MTLE has been scarcely addressed. In this study, we questioned whether microglial activation persists in the hippocampus of pilocarpine-treated, epileptic Wistar rats and to which extent it is associated with segmental neurodegeneration. Microglial cells were immunostained for the universal microglial marker, ionized calcium-binding adapter molecule-1 and the activation marker, CD11b (also known as OX42, Mac-1). Using quantitative morphology, i.e., stereology and Neurolucida-based reconstructions, we investigated morphological correlates of microglial activation such as cell number, ramification, somatic size and shape. We find that microglial cells in epileptic rats feature widespread, activation-related morphological changes such as increase in cell number density, massive up-regulation of CD11b and de-ramification. The parameters show heterogeneity in different hippocampal subregions. For instance, de-ramification is most prominent in the outer molecular layer of the dentate gyrus, whereas CD11b expression dominates in hilus. Interestingly, microglial activation only partially correlates with segmental neurodegeneration. Major neuronal death in the hilus, CA3 and CA1 coincides with strong up-regulation of CD11b. However, microglial activation is also observed in subregions that do not feature neurodegeneration, such as the molecular and granular layer of the dentate gyrus. This in vivo study provides solid experimental evidence that microglial cells feature widespread heterogeneous activation that only partially correlates with hippocampal segmental neuronal loss in experimental MTLE.

Modeling the functional network of primary intercellular Ca2+ wave propagation in astrocytes and its application to study drug effects

We introduce a simple procedure of multivariate signal analysis to uncover the functional connectivity among cells composing a living tissue and describe how to apply it for extracting insight on the effect of drugs in the tissue. The procedure is based on the covariance matrix of time resolved activity signals. By determining the time-lag that maximizes covariance, one derives the weight of the corresponding connection between cells. Introducing simple constraints, it is possible to conclude whether pairs of cells are functionally connected and in which direction. After testing the method against synthetic data we apply it to study intercellular propagation of Ca(2+) waves in astrocytes following an external stimulus, with the aim of uncovering the functional cellular connectivity network. Our method proves to be particularly suited for this type of networking signal propagation where signals are pulse-like and have short time-delays, and is shown to be superior to standard methods, namely a multivariate Granger algorithm. Finally, based on the statistical analysis of the connection weight distribution, we propose simple measures for assessing the impact of drugs on the functional connectivity between cells.

Physiological bases of the K+ and the glutamate/GABA hypotheses of epilepsy

Epilepsy is a heterogeneous family of neurological disorders that manifest as seizures, i.e. the hypersynchronous activity of large population of neurons. About 30% of epileptic patients do not respond to currently available antiepileptic drugs. Decades of intense research have elucidated the involvement of a number of possible signaling pathways, however, at present we do not have a fundamental understanding of epileptogenesis. In this paper, we review the literature on epilepsy under a wide-angle perspective, a mandatory choice that responds to the recurrent and unanswered question about what is epiphenomenal and what is causal to the disease. While focusing on the involvement of K+ and glutamate/GABA in determining neuronal hyperexcitability, emphasis is given to astrocytic contribution to epileptogenesis, and especially to loss-of-function of astrocytic glutamine synthetase following reactive astrogliosis, a hallmark of epileptic syndromes. We finally introduce the potential involvement of abnormal glycogen synthesis induced by excess glutamate in increasing susceptibility to seizures.

The potential of antiseizure drugs and agents that act on novel molecular targets as antiepileptogenic treatments

A major goal of contemporary epilepsy research is the identification of therapies to prevent the development of recurrent seizures in individuals at risk, including those with brain injuries, infections, or neoplasms; status epilepticus; cortical dysplasias; or genetic epilepsy susceptibility. In this review we consider the evidence largely from preclinical models for the antiepileptogenic activity of a diverse range of potential therapies, including some marketed antiseizure drugs, as well as agents that act by immune and inflammatory mechanisms; reduction of oxidative stress; activation of the mammalian target of rapamycin or peroxisome proliferator-activated receptors γ pathways; effects on factors related to thrombolysis, hematopoesis, and angiogenesis; inhibition of 3-hydroxy-3-methylglutaryl-coenzyme A reducatase; brain-derived neurotrophic factor signaling; and blockade of α2 adrenergic and cannabinoid receptors. Antiepileptogenesis refers to a therapy of which the beneficial action is to reduce seizure frequency or severity outlasting the treatment period. To date, clinical trials have failed to demonstrate that antiseizure drugs have such disease-modifying activity. However, studies in animal models with levetiracetam and ethosuximide are encouraging, and clinical trials with these agents are warranted. Other promising strategies are inhibition of interleukin 1β signaling by drugs such as VX-765; modulation of sphingosine 1-phosphate signaling by drugs such as fingolimod; activation of the mammalian target of rapamycin by drugs such as rapamycin; the hormone erythropoietin; and, paradoxically, drugs such as the α2 adrenergic receptor antagonist atipamezole and the CB1 cannabinoid antagonist SR141716A (rimonabant) with proexcitatory activity. These approaches could lead to a new paradigm in epilepsy drug therapy where treatment for a limited period prevents the occurrence of spontaneous seizures, thus avoiding lifelong commitment to symptomatic treatment.

Rationale for using intermittent calorie restriction as a dietary treatment for drug resistant epilepsy

There has been resurgence in the use of dietary treatment, principally the classical ketogenic diet and its variants, for people with epilepsy. These diets generally require significant medical and dietician support. An effective but less restrictive dietary regimen is likely to be more acceptable and more widely used. Calorie-restricted diets appear to produce a range of biochemical and metabolic changes including reduced glucose levels, reduced inflammatory markers, increased sirtuins, increased AMPK signaling, inhibition of mTOR signaling, and increase in autophagy. There are studies in animal seizure models that suggest that these biochemical and metabolic changes may decrease ictogenesis and epileptogenesis. A calorie-restricted diet might be effective in reducing seizures in people with epilepsy. Hence, there is a sufficient rationale to undertake clinical trials to assess the efficacy and safety of calorie-restricted diets in people with epilepsy.

Ndae1 expression and regulation in Drosophila embryos

The construction and prediction of cell fate maps at the whole embryo level require the establishment of an accurate atlas of gene expression patterns throughout development and the identification of the corresponding cis-regulatory sequences. However, while the expression and regulation of genes encoding upstream developmental regulators such as transcription factors or signaling pathway components have been analyzed in detail, up to date the number of cis-regulatory sequences identified for downstream effector genes, like ion channels, pumps and exchangers, is very low. The control and regulation of ion homeostasis in each cell, including at blastoderm stages, are essential for normal embryonic development. In this study, we analyzed in detail the embryonic expression pattern and cis-regulatory modules of the Drosophila Na+-driven anion exchanger 1 (Ndae1) gene, involved in the regulation of pH homeostasis. We show that Ndae1 is expressed in a tight and complex spatial-temporal pattern. In particular, we report that this downstream effector gene is under the control of the canonical dorsal-ventral patterning cascade through dorsal, Toll, twist and snail at early embryogenesis. Moreover, we identify several cis-regulatory modules, some of which control discrete and non-overlapping aspects of endogenous gene expression throughout development.

Chemokine CXCL8 promotes HIV-1 replication in human monocyte-derived macrophages and primary microglia via nuclear factor-κB pathway

BACKGROUND

Chemokine CXCL8 is an important neutrophil chemoattractant implicated in various neurodegenerative disorders. Cytokine/chemokine imbalance, with an increase in proinflammatory cytokines like interleukin-1β and tumor necrosis factor-α within the central nervous system, is a hallmark of human immunodeficiency virus (HIV)-1 infection. We previously reported that HIV-1 infection is linked to upregulation of CXCL8 in brain tissues and human astrocytes. Chemokines play crucial roles in trafficking of leukocytes and trafficking of HIV-1-infected across the blood-brain barrier play an important role in HIV-1 central nervous system disease. In the post-antiretroviral therapy era, low level of productive replication of HIV-1 in brain is a critical component of neuropathogenesis regulation. The present study investigated the effect of CXCL8 on productive infection of HIV-1 in human monocytes-derived macrophages (MDM) and primary human microglia.

RESULTS

Human MDM and microglia were infected with the blood or brain derived HIV-1 isolates, HIV-1ADA or HIV-1JRFL. Treatment with CXCL8 significantly upregulated HIV-1p24 levels in supernatants of both HIV-1-infected MDM as well as microglia. In addition, the formation of 2-long terminal repeat (LTR) circles, a measure of viral genome integration, was significantly higher in CXCL8-treated, HIV-1-infected MDM and microglia. Transient transfection of U937 cells with HIV-1 LTR luciferase reporter construct resulted in increased promoter activity when treated with CXCL8. Moreover, increased nuclear translocation of nuclear factor-κB was seen in HIV-1-infected MDM following CXCL8 treatment. Blocking CXCL8 receptors CXCR1 and CXCR2 abrogated the CXCL8-mediated enhanced HIV-1 replication.

CONCLUSION

Our results show that CXCL8 mediates productive infection of HIV-1 in MDM and microglia via receptors CXCR1 and CXCR2. These results demonstrate that CXCL8 exerts its downstream effects by increasing translocation of nuclear factor-κB into the nucleus, thereby promoting HIV-1 LTR activity.

Reactive gliosis and the multicellular response to CNS damage and disease

The CNS is prone to heterogeneous insults of diverse etiologies that elicit multifaceted responses. Acute and focal injuries trigger wound repair with tissue replacement. Diffuse and chronic diseases provoke gradually escalating tissue changes. The responses to CNS insults involve complex interactions among cells of numerous lineages and functions, including CNS intrinsic neural cells, CNS intrinsic nonneural cells, and CNS extrinsic cells that enter from the circulation. The contributions of diverse nonneuronal cell types to outcome after acute injury, or to the progression of chronic disease, are of increasing interest as the push toward understanding and ameliorating CNS afflictions accelerates. In some cases, considerable information is available, in others, comparatively little, as examined and reviewed here.

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.

Diversity of astroglial functions alludes to subcellular specialisation

Rapid signal exchange between astroglia and neurons has emerged as an essential element of neural circuits of the brain. However, the increasing variety of mechanisms contributing to this signalling appears to be facing a conceptual stalemate. The communication medium of astroglia involves intracellular [Ca(2+)] waves, which until recently have been associated with slow, global [Ca(2+)] rises. How such a uniform trigger could handle fast and diverse molecular messages remains unexplained. Recent studies have, however, revealed a variety of apparently independent Ca(2+) activities within individual astrocytic compartments, also indicating the prevalence of subcellular segregation for some signalling mechanisms. These signs of intracellular compartmentalisation might provide the key to the multitude of adaptive roles played by astroglia.

Gene expression alterations in the cerebellum and granule neurons of Cstb(-/-) mouse are associated with early synaptic changes and inflammation

Progressive myoclonus epilepsy of Unverricht-Lundborg type (EPM1) is an autosomal recessively inherited neurodegenerative disease, manifesting with myoclonus, seizures and ataxia, caused by mutations in the cystatin B (CSTB) gene. With the aim of understanding the molecular basis of pathogenetic events in EPM1 we characterized gene expression changes in the cerebella of pre-symptomatic postnatal day 7 (P7) and symptomatic P30 cystatin B -deficient (Cstb(-/-) ) mice, a model for the disease, and in cultured Cstb(-/-) cerebellar granule cells using a pathway-based approach. Differentially expressed genes in P7 cerebella were connected to synaptic function and plasticity, and in cultured cerebellar granule cells, to cell cycle, cytoskeleton, and intracellular transport. In particular, the gene expression data pinpointed alterations in GABAergic pathway. Electrophysiological recordings from Cstb(-/-) cerebellar Purkinje cells revealed a shift of the balance towards decreased inhibition, yet the amount of inhibitory interneurons was not declined in young animals. Instead, we found diminished number of GABAergic terminals and reduced ligand binding to GABAA receptors in Cstb(-/-) cerebellum. These results suggest that alterations in GABAergic signaling could result in reduced inhibition in Cstb(-/-) cerebellum leading to the hyperexcitable phenotype of Cstb(-/-) mice. At P30, the microarray data revealed a marked upregulation of immune and defense response genes, compatible with the previously reported early glial activation that precedes neuronal degeneration. This further implies the role of early-onset neuroinflammation in the pathogenesis of EPM1.

Kynurenines in CNS disease: regulation by inflammatory cytokines

The kynurenine pathway (KP) metabolizes the essential amino acid tryptophan and generates a number of neuroactive metabolites collectively called the kynurenines. Segregated into at least two distinct branches, often termed the “neurotoxic” and “neuroprotective” arms of the KP, they are regulated by the two enzymes kynurenine 3-monooxygenase and kynurenine aminotransferase, respectively. Interestingly, several enzymes in the pathway are under tight control of inflammatory mediators. Recent years have seen a tremendous increase in our understanding of neuroinflammation in CNS disease. This review will focus on the regulation of the KP by inflammatory mediators as it pertains to neurodegenerative and psychiatric disorders.

Difference in anxiety symptoms between children and their parents facing a first seizure or epilepsy

Many studies have shown that anxiety disorders are common in children with epilepsy. We explored symptoms of anxiety simultaneously in children and their parents. We conducted a cross-sectional study using the Revised Children's Manifest Anxiety Scale in children and the State-Trait Anxiety Inventory for Adult in parents. We included 118 parents and 67 children, who were divided into three groups: (1) first seizure, (2) epilepsy, and (3) nonepileptic paroxysmal event. We found that the level of anxiety in parents and children differed. We observed a significant increase in the anxiety level of parents whose children have had a first seizure, while we found a significant increase in the anxiety level of children and adolescents followed for epilepsy. These findings suggest that there is no direct relationship in the anxiety of the parents and their child. Further studies are needed to understand this variation over time.

[How do antiepileptic drugs work?]

BACKGROUND

There are currently around 25 antiepileptic drugs in use in Norway, of which 15 have entered the market in the last 20 years. All have somewhat different effect- and adverse effect profiles and mechanisms of action. Here we present a brief overview of current knowledge regarding the basic mechanisms of action of these drugs.

METHOD

The review is based on a discretionary selection of relevant articles found through a literature search in PubMed and our own clinical and research experience.

RESULTS

There are, roughly speaking, four main mechanisms; 1) modulation of ion channels (sodium and calcium channel blockers, potassium channel openers), 2) potentiation of GABAergic inhibition, 3) reduction of glutamatergic excitation and 4) modulation of presynaptic neurotransmitter release. Some of the drugs have several mechanisms of action, and for some of them it is unclear which mechanism is clinically most important. To some extent, the drugs' mechanisms of action predict their effect against different types of epilepsy and seizures. For instance, sodium channel blockers work best against focal seizures, while calcium channel blockers work best against absences, a type of generalised seizure.

INTERPRETATION

Optimal treatment of patients with epilepsy requires not only thorough knowledge of seizure- and epilepsy classification, but also insight into the mechanisms of action of antiepileptic drugs.

Novel frontiers in epilepsy treatments: preventing epileptogenesis by targeting inflammation

Currently available epilepsy drugs only affect the symptoms (seizures), and there is a need for innovative treatments that target the underlying disease. Increasing evidence points to inflammation as a potentially important mechanism in epileptogenesis. In the last decade, a new generation of etiologically realistic syndrome-specific experimental models have been developed, which are expected to capture the epileptogenic mechanisms operating in corresponding patient populations, and to exhibit similar treatment responsiveness. Recently, an intervention known to have broad-ranging anti-inflammatory effects (selective brain cooling) has been found to prevent the development of spontaneously occurring seizures in an etiologically realistic rat model of post-traumatic epilepsy. Several drugs used clinically for other indications also have the potential for inhibiting inflammation, and should be investigated for antiepileptogenic activity in these models. If results of such studies are positive, these compounds could rapidly enter Phase III trials in patients at high risk of developing epilepsy.

Astrocyte-neuron interactions: from experimental research-based models to translational medicine

In this chapter, we review the principal astrocyte functions and the interactions between neurons and astrocytes. We then address how the experimentally observed functions have been verified in computational models and review recent experimental literature on astrocyte-neuron interactions. Benefits of computational neuroscience work are highlighted through selected studies with neurons and astrocytes by analyzing the existing models qualitatively and assessing the relevance of these models to experimental data. Common strategies to mathematical modeling and computer simulation in neuroscience are summarized for the nontechnical reader. The astrocyte-neuron interactions are then further illustrated by examples of some neurological and neurodegenerative diseases, where the miscommunication between glia and neurons is found to be increasingly important.

Brain protein expression changes in WAG/Rij rats, a genetic rat model of absence epilepsy after peripheral lipopolysaccharide treatment

Peripheral injection of bacterial lipopolysaccharide (LPS) facilitates 8-10Hz spike-wave discharges (SWD) characterizing absence epilepsy in WAG/Rij rats. It is unknown however, whether peripherally administered LPS is able to alter the generator areas of epileptic activity at the molecular level. We injected 1mg/kg dose of LPS intraperitoneally into WAG/Rij rats, recorded the body temperature and EEG, and examined the protein expression changes of the proteome 12h after injection in the fronto-parietal cortex and thalamus. We used fluorescent two-dimensional differential gel electrophoresis to investigate the expression profile. We found 16 differentially expressed proteins in the fronto-parietal cortex and 35 proteins in the thalamus. It is known that SWD genesis correlates with the transitional state of sleep-wake cycle thus we performed meta-analysis of the altered proteins in relation to inflammation, epilepsy as well as sleep. The analysis revealed that all categories are highly represented by the altered proteins and these protein-sets have considerable overlap. Protein network modeling suggested that the alterations in the proteome were largely induced by the immune response, which invokes the NFkB signaling pathway. The proteomics and computational analysis verified the known functional interplay between inflammation, epilepsy and sleep and highlighted proteins that are involved in their common synaptic mechanisms. Our physiological findings support the phenomenon that high dose of peripheral LPS injection increases SWD-number, modifies its duration as well as the sleep-wake stages and decreases body temperature.

Does brain inflammation mediate pathological outcomes in epilepsy?

Inflammation in the central nervous system (CNS) is associated with epilepsy and is characterized by the increased levels of a complex set of soluble molecules and their receptors in epileptogenic foci with profound neuromodulatory effects. These molecules activate receptor-mediated pathways in glia and neurons that contribute to hyperexcitability in neural networks that underlie seizure generation. As a consequence, exciting new opportunities now exist for novel therapies targeting the various components of the immune system and the associated inflammatory mediators, especially the IL-1β system. This review summarizes recent findings that increased our understanding of the role of inflammation in reducing seizure threshold, contributing to seizure generation, and participating in epileptogenesis. We will discuss preclinical studies supporting the hypothesis that pharmacological inhibition of specific proinflammatory signalings may be useful to treat drug-resistant seizures in human epilepsy, and possibly delay or arrest epileptogenesis.

Upregulation of adenosine kinase in Rasmussen encephalitis

Rasmussen encephalitis (RE) is a rare neurologic disorder of childhood characterized by unihemispheric inflammation, progressive neurologic deficits, and intractable focal epilepsy. The pathogenesis of RE is still enigmatic. Adenosine is a key endogenous signaling molecule with anticonvulsive and anti-inflammatory effects, and our previous work demonstrated that dysfunction of the adenosine kinase (ADK)–adenosine system and astrogliosis are the hallmarks of epilepsy. We hypothesized that the epileptogenic mechanisms underlying RE are related to changes in ADK expression and that those changes might be associated with the development of epilepsy in RE patients. Immunohistochemistry was used to examine the expression of ADK and glial fibrillary acidic protein in surgically resected human epileptic cortical specimens from RE patients (n = 12) and compared with control cortical tissues (n = 6). Adenosine kinase expression using Western blot and enzymatic activity for ADK were assessed in RE versus control samples. Focal astrogliosis and marked expression of ADK were observed in the lesions of RE. Significantly greater ADK expression in RE versus controls was demonstrated by Western blot, and greater enzymatic activity for ADK was demonstrated using an enzyme-coupled bioluminescent assay. These results suggest that upregulation of ADK is a common pathologic hallmark of RE and that ADK might be a target in the treatment of epilepsy associated with RE.

Neurovascular unit dysfunction with blood-brain barrier hyperpermeability contributes to major depressive disorder: a review of clinical and experimental evidence

About one-third of people with major depressive disorder (MDD) fail at least two antidepressant drug trials at 1 year. Together with clinical and experimental evidence indicating that the pathophysiology of MDD is multifactorial, this observation underscores the importance of elucidating mechanisms beyond monoaminergic dysregulation that can contribute to the genesis and persistence of MDD. Oxidative stress and neuroinflammation are mechanistically linked to the presence of neurovascular dysfunction with blood-brain barrier (BBB) hyperpermeability in selected neurological disorders, such as stroke, epilepsy, multiple sclerosis, traumatic brain injury, and Alzheimer’s disease. In contrast to other major psychiatric disorders, MDD is frequently comorbid with such neurological disorders and constitutes an independent risk factor for morbidity and mortality in disorders characterized by vascular endothelial dysfunction (cardiovascular disease and diabetes mellitus). Oxidative stress and neuroinflammation are implicated in the neurobiology of MDD. More recent evidence links neurovascular dysfunction with BBB hyperpermeability to MDD without neurological comorbidity. We review this emerging literature and present a theoretical integration between these abnormalities to those involving oxidative stress and neuroinflammation in MDD. We discuss our hypothesis that alterations in endothelial nitric oxide levels and endothelial nitric oxide synthase uncoupling are central mechanistic links in this regard. Understanding the contribution of neurovascular dysfunction with BBB hyperpermeability to the pathophysiology of MDD may help to identify novel therapeutic and preventative approaches.

Astrocytes: the missing link in neurologic disease?

The central nervous system is comprised of numerous cell types that work in concert to facilitate proper function and homeostasis. Disruption of these carefully orchestrated networks results in neuronal dysfunction, manifesting itself in a variety of neurologic disorders. Although neuronal dysregulation is causative of symptoms that manifest in the clinic, the etiology of these disorders is often more complex than simply a loss of neurons or intrinsic dysregulation of their function. In the adult brain, astrocytes comprise the most abundant cell type and play key roles in central nervous system physiology; therefore, it stands to reason that dysregulation of normal astrocyte function contributes to the etiology and progression of varied neurologic disorders. We review here some neurologic disorders associated with an astrocyte factor and discuss how the related astrocyte dysfunction contributes to the etiology or progression of these disorders or both.

Neurogenic neuroinflammation: inflammatory CNS reactions in response to neuronal activity

The CNS is endowed with an elaborated response repertoire termed 'neuroinflammation', which enables it to cope with pathogens, toxins, traumata and degeneration. On the basis of recent publications, we deduce that orchestrated actions of immune cells, vascular cells and neurons that constitute neuroinflammation are not only provoked by pathological conditions but can also be induced by increased neuronal activity. We suggest that the technical term 'neurogenic neuroinflammation' should be used for inflammatory reactions in the CNS in response to neuronal activity. We believe that neurogenic neuro-inflammation maintains homeostasis to enable the CNS to cope with enhanced metabolic demands and increases the computational power and plasticity of CNS neuronal networks. However, neurogenic neuroinflammation may also become maladaptive and aggravate the outcomes of pain, stress and epilepsy.

P2X receptors as targets for the treatment of status epilepticus

Prolonged seizures are amongst the most common neurological emergencies. Status epilepticus is a state of continuous seizures that is life-threatening and prompt termination of status epilepticus is critical to protect the brain from permanent damage. Frontline treatment comprises parenteral administration of anticonvulsants such as lorazepam that facilitate γ-amino butyric acid (GABA) transmission. Because status epilepticus can become refractory to anticonvulsants in a significant proportion of patients, drugs which act on different neurotransmitter systems may represent potential adjunctive treatments. P2X receptors are a class of ligand-gated ion channel activated by ATP that contributes to neuro- and glio-transmission. P2X receptors are expressed by both neurons and glia in various brain regions, including the hippocampus. Electrophysiology, pharmacology and genetic studies suggest certain P2X receptors are activated during pathologic brain activity. Expression of several members of the family including P2X₂, P2X₄, and P2X₇ receptors has been reported to be altered in the hippocampus following status epilepticus. Recent studies have shown that ligands of the P2X₇ receptor can have potent effects on seizure severity during status epilepticus and mice lacking this receptor display altered seizures in response to chemoconvulsants. Antagonists of the P2X₇ receptor also modulate neuronal death, microglial responses and neuroinflammatory signaling. Recent work also found altered neuronal injury and inflammation after status epilepticus in mice lacking the P2X₄ receptor. In summary, members of the P2X receptor family may serve important roles in the pathophysiology of status epilepticus and represent novel targets for seizure control and neuroprotection.

Role of astrocytes in major neurological disorders: the evidence and implications

Given the huge amount and great complexity of astrocyte functions in the maintenance of brain homeostasis, it is easily understood how alterations in their physiology may be involved in the pathogenesis of many, if not all, neurological disorders. This assumption is strongly supported by accumulated evidence produced in humans and in experimental models of pathology. Based on these considerations, it is reasonable to encourage studies aimed at improving the knowledge about the implicated mechanisms, and astroglial cells can be considered as the innovative target for new, and possibly more effective, drug therapies.

Homeostatic control of brain function - new approaches to understand epileptogenesis

Neuronal excitability of the brain and ongoing homeostasis depend not only on intrinsic neuronal properties, but also on external environmental factors; together these determine the functionality of neuronal networks. Homeostatic factors become critically important during epileptogenesis, a process that involves complex disruption of self-regulatory mechanisms. Here we focus on the bioenergetic homeostatic network regulator adenosine, a purine nucleoside whose availability is largely regulated by astrocytes. Endogenous adenosine modulates complex network function through multiple mechanisms including adenosine receptor-mediated pathways, mitochondrial bioenergetics, and adenosine receptor-independent changes to the epigenome. Accumulating evidence from our laboratories shows that disruption of adenosine homeostasis plays a major role in epileptogenesis. Conversely, we have found that reconstruction of adenosine's homeostatic functions provides new hope for the prevention of epileptogenesis. We will discuss how adenosine-based therapeutic approaches may interfere with epileptogenesis on an epigenetic level, and how dietary interventions can be used to restore network homeostasis in the brain. We conclude that reconstruction of homeostatic functions in the brain offers a new conceptual advance for the treatment of neurological conditions which goes far beyond current target-centric treatment approaches.

PET imaging of inflammation biomarkers

Inflammation plays a significant role in many disease processes. Development in molecular imaging in recent years provides new insight into the diagnosis and treatment evaluation of various inflammatory diseases and diseases involving inflammatory process. Positron emission tomography using (18)F-FDG has been successfully applied in clinical oncology and neurology and in the inflammation realm. In addition to glucose metabolism, a variety of targets for inflammation imaging are being discovered and utilized, some of which are considered superior to FDG for imaging inflammation. This review summarizes the potential inflammation imaging targets and corresponding PET tracers, and the applications of PET in major inflammatory diseases and tumor associated inflammation. Also, the current attempt in differentiating inflammation from tumor using PET is also discussed.