Nerve growth factor accelerates seizure development, enhances mossy fiber sprouting, and attenuates seizure-induced decreases in neuronal density in the kindling model of epilepsy

Novel Alaninamide Derivatives with Drug-like Potential for Development as Antiseizure and Antinociceptive Therapies─In Vitro and In Vivo Characterization

In the present study, a series of original alaninamide derivatives have been designed applying a combinatorial chemistry approach, synthesized, and characterized in the in vivo and in vitro assays. The obtained molecules showed potent and broad-spectrum activity in basic seizure models, namely, the maximal electroshock (MES) test, the 6 Hz (32 mA) seizure model, and notably, the 6 Hz (44 mA) model of pharmacoresistant seizures. Most potent compounds 26 and 28 displayed the following pharmacological values: ED50 = 64.3 mg/kg (MES), ED50 = 15.6 mg/kg (6 Hz, 32 mA), ED50 = 29.9 mg/kg (6 Hz, 44 mA), and ED50 = 34.9 mg/kg (MES), ED50 = 12.1 mg/kg (6 Hz, 32 mA), ED50 = 29.5 mg/kg (6 Hz, 44 mA), respectively. Additionally, 26 and 28 were effective in the ivPTZ seizure threshold test and had no influence on the grip strength. Moreover, lead compound 28 was tested in the PTZ-induced kindling model, and then, its influence on glutamate and GABA levels in the hippocampus and cortex was evaluated by the high-performance liquid chromatography (HPLC) method. In addition, 28 revealed potent efficacy in formalin-induced tonic pain, capsaicin-induced pain, and oxaliplatin- and streptozotocin-induced peripheral neuropathy. Pharmacokinetic studies and in vitro ADME-Tox data proved favorable drug-like properties of 28. The patch-clamp recordings in rat cortical neurons showed that 28 at a concentration of 10 μM significantly inhibited fast sodium currents. Therefore, 28 seems to be an interesting candidate for future preclinical development in epilepsy and pain indications.

Pioglitazone Ameliorates Hippocampal Neurodegeneration, Disturbances in Glucose Metabolism and AKT/mTOR Signaling Pathways in Pentyelenetetrazole-Kindled Mice

Disturbance of glucose metabolism, nerve growth factor (NGF) and m-TOR signaling have been associated with the pathophysiology of epilepsy. Pioglitazone (PGZ) is an anti-diabetic drug that shows a protective effect in neurodegenerative diseases including epilepsy; however, its exact mechanism is not fully elucidated. The present study aimed to investigate the potential neuroprotective effect of PGZ in pentylenetetrazole (PTZ) kindled seizure in mice. Swiss male albino mice were randomly distributed into four groups, each having six mice. Group 1 was considered the control. Epilepsy was induced by PTZ (35 mg/kg i.p.) thrice a week for a total of 15 injections in all other groups. Group 2 was considered the untreated PTZ group while Group 3 and Group 4 were treated by PGZ prior to PTZ injection at two dose levels (5 and 10 mg/kg p.o., respectively). Seizure activity was evaluated after each PTZ injection according to the Fischer and Kittner scoring system. At the end of the experiment, animals were sacrificed under deep anesthesia and the hippocampus was isolated for analysis of glucose transporters by RT-PCR, nerve growth factor (NGF) by ELISA and mTOR by western blotting, in addition to histopathological investigation. The PTZ-treated group showed a significant rise in seizure score, NGF and m-TOR hyperactivation, along with histological abnormalities compared to the control group. Treatment with PGZ demonstrated a significant decrease in NGF, seizure score, m-TOR, GLUT-1 and GLUT-3 in comparison to the PTZ group. In addition, improvement of histological features was observed in both PGZ treated groups. These findings suggest that PGZ provides its neuroprotective effect through modulating m-TOR signaling, glucose metabolism and NGF levels.

Probiotic supplementation alleviates absence seizures and anxiety- and depression-like behavior in WAG/Rij rat by increasing neurotrophic factors and decreasing proinflammatory cytokines

AIM

Epilepsy is one of the most common chronic brain disorders that affect millions of people worldwide. In the present study, we investigated the effects of probiotic supplementation on absence epilepsy and anxiety-and depression-like behavior in WAG/Rij rats.

MATERIAL AND METHOD

Fourteen male WAG/Rij rats (absence-epileptic) and seven male Wistar rats (nonepileptic) were used. The effects of probiotic VSL#3 (12.86 bn living bacteria/kg/day for 30 day/gavage) on absence seizures, and related psychiatric comorbidities were evaluated in WAG/Rij rats. Anxiety-like behavior was evaluated by the open-field test and depression-like behavior by the forced swimming test. In addition, the brain tissues of rats were evaluated histopathologically for nerve growth factor [NGF], brain-derived neurotrophic factor [BDNF], SRY sex-determining region Y-box 2 [SOX2] and biochemically for nitric oxide [NO], tumor necrosis factor-alpha [TNF-α] ,and Interleukin-6 [IL-6].

RESULTS

Compared to Wistar rats, WAG/Rij rats exhibited anxiety- and depression-like behavior, and had lower BDNF, NGF and SOX2 immunoreactivity, and higher TNF-α, IL-6 levels in brain tissue. VSL#3 supplementation reduced the duration and number of spike-wave discharges (SWDs) and exhibited anxiolytic or anti-depressive effect. VSL#3 supplement also increased the NGF immunoreactivity while decreasing IL-6, TNF-α and NO levels in WAG/Rij rat brain.

CONCLUSION

The findings of the present study showed that neurotrophins, SOX2 deficiency, and pro-inflammatory cytokines may play a role in the pathogenesis of absence epilepsy. Our data support the hypothesis that the probiotics have anti-inflammatory effect. The present study is the first to show the positive effects of probiotic bacteria on absence seizures and anxiety- and depression-like behavior.

Therapeutic potential of glial cell line-derived neurotrophic factor and cell reprogramming for hippocampal-related neurological disorders

Hippocampus serves as a pivotal role in cognitive and emotional processes, as well as in the regulation of the hypothalamus-pituitary axis. It is known to undergo mild neurodegenerative changes during normal aging and severe atrophy in Alzheimer’s disease. Furthermore, dysregulation in the hippocampal function leads to epilepsy and mood disorders. In the first section, we summarized the most salient knowledge on the role of glial cell-line-derived neurotrophic factor and its receptors focused on aging, cognition and neurodegenerative and hippocampal-related neurological diseases mentioned above. In the second section, we reviewed the therapeutic approaches, particularly gene therapy, using glial cell-line-derived neurotrophic factor or its gene, as a key molecule in the development of neurological disorders. In the third section, we pointed at the potential of regenerative medicine, as an emerging and less explored strategy for the treatment of hippocampal disorders. We briefly reviewed the use of partial reprogramming to restore brain functions, non-neuronal cell reprogramming to generate neural stem cells, and neural progenitor cells as source-specific neuronal types to be implanted in animal models of specific neurodegenerative disorders.

Reactive pericytes in early phase are involved in glial activation and late-onset hypersusceptibility to pilocarpine-induced seizures in traumatic brain injury model mice

In this study, among neurovascular unit (NVU) cells, we focused on pericyte reactivity in mice subjected to controlled cortical impact (CCI) to understand how traumatic brain injury (TBI) causes uncoordinated crosstalk in the NVU and alters neuronal activity. Histological analyses of brain pericytes, microglia and astrocytes were performed for up to 28 days after CCI in the injured ipsilateral hippocampus. To evaluate altered neuronal activity caused by CCI, we measured seizure susceptibility to a sub-threshold dose of pilocarpine on postoperative day 7, 14, 21 and 28. Platelet-derived growth factor receptor (PDGFR) β immunoreactivity in pericytes significantly increased from 1 h to 4 days after CCI. The expression of Iba1 and GFAP, as markers of microglia and astrocytes, respectively, increased from 4 to 28 days after CCI. The severity of seizure induced by pilocarpine gradually increased, becoming significant at 28 days after CCI. Then, we treated CCI mice with an inhibitor of PDGFR signaling, imatinib, during the postoperative day 0-4 period. Imatinib lowered seizure susceptibility to pilocarpine and suppressed microglial activation in the injured hippocampus at postoperative day 28. These findings indicate that brain pericytes with rapidly increased PDGFRβ expression may drive TBI-induced dysregulation of NVU function and brain hyperexcitability.

Identification of epilepsy related pathways using genome-wide DNA methylation measures: A trio-based approach

Genetic generalized epilepsies (GGE) are genetically determined, as their name implies and they are clinically characterized by generalized seizures involving both sides of the brain in the absence of detectable brain lesions or other known causes. GGEs are yet complex and are influenced by many different genetic and environmental factors. Methylation specific epigenetic marks are one of the players of the complex epileptogenesis scenario leading to GGE. In this study, we have set out to perform genome-wide methylation profiling to analyze GGE trios each consisting of an affected parent-offspring couple along with an unaffected parent. We have developed a novel scoring scheme within trios to categorize each locus analyzed as hypo or hypermethylated. This stringent approach classified differentially methylated genes in each trio and helped us to produce trio specific and pooled gene lists with inherited and aberrant methylation levels. In order to analyze the methylation differences from a boarder perspective, we performed enrichment analysis with these lists using the PANOGA software. This collective effort has led us to detect pathways associated with the GGE phenotype, including the neurotrophin signaling pathway. We have demonstrated a trio based approach to genome-wide DNA methylation analysis that identified individual and possibly minor changes in methylation marks that could be involved in epileptogenesis leading to GGE.

CNS Gene Therapy and a Nexus of Complexity: Systems and Biology at a Crossroads

Gene therapy is a potentially promising new treatment for neurodegenerative disorders such as Alzheimer's disease (AD), which has been difficult to treat with conventional therapeutics. Viral vector-mediated somatic gene therapy is a rapidly developing methodology for providing never before achieved capability to deliver specific genes to the CNS in a highly localized and controlled manner. With the advent and refinements of this technology one focus is directed to which genes are the most appropriate to select for specific disease indications. Nerve growth factor (NGF), a potent survival factor for critical cell populations that degenerate in AD, has been chosen already for clinical gene therapy trials in human AD patients. Much knowledge about the pathophysiological underpinnings of AD is still lacking to make clear which patients may benefit from a gene therapy approach. Moreover, a detailed understanding of sustained NGF action in the normal and diseased CNS needs to be resolved before conclusions can be drawn regarding the utility of NGF gene therapy. Systematic efforts to acquire this new knowledge should compel clinically and biologically sophisticated efforts to advance gene therapy for neurodegenerative diseases.

Neurodegeneration and Pathology in Epilepsy: Clinical and Basic Perspectives

Epilepsy is commonly associated with a number of neurodegenerative and pathological alterations in those areas of the brain that are involved in repeated electrographic seizures. These most prominently include neuron loss and an increase in astrocyte number and size but may also include enhanced blood-brain barrier permeability, the formation of new capillaries, axonal sprouting, and central inflammation. In animal models in which seizures are either repeatedly elicited or are self-generated, a similar set of neurodegenerative and pathological alterations in brain anatomy are observed. The primary causal agent responsible for these alterations may be the cascade of events that follow a seizure and lead to an hypoperfusion/hypoxic episode. While epilepsy has long and correctly been considered an electrical disorder, the vascular system likely plays an important causal role in the neurodegeneration and pathology that occur as a consequence of repeated seizures.

Expansion of the dentate mossy fiber-CA3 projection in the brain-derived neurotrophic factor-enriched mouse hippocampus

Structural changes that alter hippocampal functional circuitry are implicated in learning impairments, mood disorders and epilepsy. Reorganization of mossy fiber (MF) axons from dentate granule cells is one such form of plasticity. Increased neurotrophin signaling is proposed to underlie MF plasticity, and there is evidence to support a mechanistic role for brain-derived neurotrophic factor (BDNF) in this process. Transgenic mice overexpressing BDNF in the forebrain under the α-calcium/calmodulin-dependent protein kinase II promoter (TgBDNF mice) exhibit spatial learning deficits at 2-3months of age, followed by the emergence of spontaneous seizures at ∼6months. These behavioral changes suggest that chronic increases in BDNF progressively disrupt hippocampal functional organization. To determine if the dentate MF pathway is structurally altered in this strain, the present study employed Timm staining and design-based stereology to compare MF distribution and projection volumes in transgenic and wild-type mice at 2-3months, and at 6-7months. Mice in the latter age group were assessed for seizure vulnerability with a low dose of pilocarpine given 2h before euthanasia. At 2-3months, TgBDNF mice showed moderate expansion of CA3-projecting MFs (∼20%), with increased volumes measured in the suprapyramidal (SP-MF) and intra/infrapyramidal (IIP-MF) compartments. At 6-7months, a subset of transgenic mice exhibited increased seizure susceptibility, along with an increase in IIP-MF volume (∼30%). No evidence of MF sprouting was seen in the inner molecular layer. Additional stereological analyses demonstrated significant increases in molecular layer (ML) volume in TgBDNF mice at both ages, as well as an increase in granule cell number by 8months of age. Collectively, these results indicate that sustained increases in endogenous BDNF modify dentate structural organization over time, and may thereby contribute to the development of pro-epileptic circuitry.

A Spontaneous Recurrent Seizure Bioassay for Anti-Epileptogenic Molecules

Drug design in epilepsy is now tackling a new target - epileptogenesis. This is the process whereby a normal brain becomes susceptible to recurrent seizures. One of the stumbling blocks in the design and discovery of new chemical entities as antiepileptogenics is the implementation of an appropriate biological model. Current models, such as the maximal electroshock model, are models of seizures, not models of epileptogenesis. To develop such a model, we have extended and modified a chronic pilocarpine spontaneous recurrent seizure (SRS) model for the purposes of developing a bioassay with which to screen new compounds for putative antiepileptogenic bioactivity.

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.

Neurotrophin receptors expression in mesial temporal lobe epilepsy with and without psychiatric comorbidities and their relation with seizure type and surgical outcome

Epilepsy and psychiatric comorbidities are frequently associated, but their common biological substrate is unknown. We have previously reported altered structural elements and neurotrophins (NTs) expression in mesial temporal lobe epilepsy (MTLE) patients with psychiatric comorbidities. NTs receptors can regulate neurotransmission and promote neuroplasticity, being important candidates in the regulation and manifestation of psychopatological states and seizure-related events. MTLE hippocampi of subjects without psychiatric history, MTLE + major depression, MTLE + interictal psychosis derived from epilepsy surgery, and control necropsies were investigated for p75^NTR, TrkB, TrkA, and TrkC immunohistochemistry. Increased expression of p75^NTR, decreased TrkA, unaltered TrkC, and complex alterations involving TrkB expression were seen in MTLE groups. Increased TrkB expression in patients without complete seizure remission and in those with secondarily generalized seizures was seen. Decreased p75^NTR expression associated with interictal psychosis, and increased TrkB in those with psychosis or major depression was also reported, although their p75^NTR/TrkB ratios were lower than in MTLE without psychiatric comorbidities. Our results provide evidence of alterations in expression of NTs receptors in the epileptogenic hippocampus that are differentially modulated in presence of psychiatric comorbidities. As already explored in animal models, even in chronic human MTLE increased TrkB expression, among other NT receptors alterations, may play a major role in seizure type, frequency and surgery outcome.

Neurotrophins in mesial temporal lobe epilepsy with and without psychiatric comorbidities

Despite the strong association between epilepsy and psychiatric comorbidities, data on clinicopathologic correlations are scant. We previously reported differential mossy fiber sprouting (MFS) in mesial temporal lobe epilepsy (MTLE) patients with psychosis (MTLE + P) and major depression (MTLE + D). Because neurotrophins (NTs) can promote MFS, here, we investigated MFS, neuronal density and immunoreactivity for the NT nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin 3 (NT3) in hippocampi of 14 MTLE patients without a psychiatric history, 13 MTLE + D, 13 MTLE + P, and 10 control necropsies. Mossy fiber sprouting correlated with granular layer NGF immunoreactivity and seizure frequency. Patients with secondarily generalized seizures exhibited less NGF immunoreactivity versus patients with complex partial seizures. There was greater NT immunoreactivity in MTLE versus control groups but lesser NT immunoreactivity in MTLE + P versus MTLE patients; these findings correlated with neuropsychologic scores. Patients with MTLE + D taking fluoxetine showed greater BDNF immunoreactivity than those not taking fluoxetine; MTLE + P patients taking haloperidol had decreased neuronal density and immunoreactivity for NGF and BDNF in specific subfields versus those not taking haloperidol. There were no differences in NT3 immunoreactivity among the groups. These findings support a close association between MFS and NT expression in the hippocampi of MTLE patients and suggest that distinct structural and neurochemical milieu may contribute to the genesis or maintenance of psychiatric comorbidities in MTLE.

Serum brain-derived neurotrophic factor and nerve growth factor concentrations change after alcohol withdrawal: preliminary data of a case-control comparison

BACKGROUND

Brain-derived neurotrophic factor (BDNF) and nerve growth factor (NGF) are involved in neuroadaptation and foster survival of central and peripheral neurons. In this study, we addressed the question whether BDNF and NGF serum concentrations change during subacute alcohol withdrawal in patients with alcohol dependence compared to healthy controls.

METHODS

Fifteen patients (age 48.6 ± 7 years) and 15 healthy age-matched controls (age 48.8 ± 7 years) participated consecutively in a 2-week withdrawal study.

RESULTS

Mean BDNF levels (7.8 ng/ml, IQR = 4.4-10.7 vs. 16.5 ng/ml, IQR = 13.9-25.6; Z = -3.8, p < 0.0001) and NGF levels (5.8 pg/ml, IQR = 3.8-13.0 vs. 18.4 pg/ml, IQR = 10.9-25.1; Z = -2.5, p = 0.012) were significantly decreased in alcohol-dependent subjects when compared to healthy matched controls. NGF concentrations decreased significantly from day 3 to day 14 (Z = -2.36; p = 0.019). Mean BDNF concentrations showed a tendency to increase after withdrawal from day 3 to day 14 (Z = 1.7; p = 0.078).

CONCLUSION

Decreased NGF and BDNF concentrations in patients suffering from alcohol dependence, which stabilize after physical withdrawal, are in line with withdrawal symptoms and neurological risk factors. In turn, increase of BDNF after acute withdrawal might be connected to neurobiological and behavioral stabilization.

Effect of different mild hypoxia manipulations on kainic acid-induced seizures in the hippocampus of rats

The protective effect of the mild hypoxia to the epilepsy has been widely tested. Although it is found that the hypoxia protects the brain by up-regulation of hypoxia-inducible factor-1α, few focused on systematic comparisons between different mild hypoxia manipulations and their effects. The male Sprague-Dawley rats were observed following exposure to hypoxia before and after epilepsy for 3 days with 90 min per day. The effects of different mild hypoxia manipulations on kainic acid-induced epilepsy were compared from the perspective of morphology, molecular biology and behavioral test. Results showed that different mild hypoxia manipulations could inhibit the cell apoptosis of kainic acid-induced rat hippocampus and improve their physiological functions. The effect of preconditioning group was better than that of postconditioning group and that of preconditioning and postconditioning with mild hypoxia group was the best among all the groups. The result showed that the preconditioning and postconditioning of mild hypoxia was recommended pre- and post-epilepsy and exposure to mild hypoxia should be prolonged. These findings might provide new ideas and methods for the clinical treatment of epilepsy.

Increased expression of TRPV1 in the cortex and hippocampus from patients with mesial temporal lobe epilepsy

Transient receptor potential vanilloid type-1 (TRPV1) is a ligand-gated nonselective cation channel that has been well characterized in peripheral pain pathway. Recent evidence from animal models of temporal lobe epilepsy (TLE) has supported the important role of TRPV1 in epileptogenesis. In this study, we investigated the expression and cellular distribution of TRPV1 in the temporal cortex (CTX) and hippocampus (HPC) from 26 patients with mesial TLE (MTLE) compared with 12 histologically normal samples. Reverse transcription-PCR and Western blotting revealed up-regulated mRNA and protein levels of TRPV1 in the MTLE group versus the control group. Immunohistochemistry data demonstrated that TRPV1 was mainly distributed in the cell bodies and dendrites of neurons. Double-labeled immunofluorescence further revealed that TRPV1 was localized on NeuN-positive neurons and GFAP-positive astrocytes, but not on HLA-positive microglia. In addition, its co-localization with glutamate and gamma-aminobutyric acid (GABA) indicated that TRPV1 was distributed on both glutamatergic and GABAergic neurons. Moreover, nerve growth factor, a sensitizing factor for TRPV1, was showed a higher expression pattern in MTLE patients. Taken together, our findings suggest that the overexpression and distribution patterns of TRPV1 might be involved in the pathogenesis and epileptogenesis of human MTLE.

Receptor protein tyrosine phosphatase sigma regulates synapse structure, function and plasticity

The mechanisms that regulate synapse formation and maintenance are incompletely understood. In particular, relatively few inhibitors of synapse formation have been identified. Receptor protein tyrosine phosphatase σ (RPTPσ), a transmembrane tyrosine phosphatase, is widely expressed by neurons in developing and mature mammalian brain, and functions as a receptor for chondroitin sulfate proteoglycans that inhibits axon regeneration following injury. In this study, we address RPTPσ function in the mature brain. We demonstrate increased axon collateral branching in the hippocampus of RPTPσ null mice during normal aging or following chemically induced seizure, indicating that RPTPσ maintains neural circuitry by inhibiting axonal branching. Previous studies demonstrated a role for pre-synaptic RPTPσ promoting synaptic differentiation during development; however, subcellular fractionation revealed enrichment of RPTPσ in post-synaptic densities. We report that neurons lacking RPTPσ have an increased density of pre-synaptic varicosities in vitro and increased dendritic spine density and length in vivo. RPTPσ knockouts exhibit an increased frequency of miniature excitatory post-synaptic currents, and greater paired-pulse facilitation, consistent with increased synapse density but reduced synaptic efficiency. Furthermore, RPTPσ nulls exhibit reduced long-term potentiation and enhanced novel object recognition memory. We conclude that RPTPσ limits synapse number and regulates synapse structure and function in the mature CNS.

Seizure-induced changes in neuropeptide Y-containing cortical neurons: Potential role for seizure threshold and epileptogenesis

Seizure activity induces transient changes in the levels of neuropeptide Y (NPY) and somatostatin (SS) in various brain regions, but it remains unclear whether this effect can persist for long periods and whether it is relevant to epileptogenesis. We report that brief seizures evoked by electroshock produced an increase in the number of NPY neurons in the dentate hilus and retrosplenial cortex, an effect that lasted 10 weeks. The number of hilar SS neurons remained unchanged. However, the pentylenetetrazole seizure threshold was somewhat decreased in electroshock-treated rats. Despite this, no spontaneous seizures were detected in this group. In contrast, status epilepticus (pilocarpine model) produced loss of the hilar NPY and SS cells. Moreover, all rats with status epilepticus showed spontaneous behavioral seizures and their seizure threshold was markedly decreased. These findings support the notion that sustained NPY overexpression induced by brief seizures can be important in preventing epileptogenesis.

Is epilepsy a preventable disorder? New evidence from animal models

Epilepsy accounts for 0.5% of the global burden of disease, and primary prevention of epilepsy represents one of the three 2007 NINDS Epilepsy Research Benchmarks. In the past decade, efforts to understand and intervene in the process of epileptogenesis have yielded fruitful preventative strategies in animal models.This article reviews the current understanding of epileptogenesis, introduces the concept of a "critical period" for epileptogenesis, and examines strategies for epilepsy prevention in animal models of both acquired and genetic epilepsies. We discuss specific animal models, which may yield important insights into epilepsy prevention including kindling, poststatus epilepticus, prolonged febrile seizures, traumatic brain injury, hypoxia, the tuberous sclerosis mouse model, and the WAG/Rij rat model of primary generalized epilepsy. Hopefully, further investigation of antiepileptogenesis in animal models will soon enable human therapeutic trials to be initiated, leading to long-term epilepsy prevention and improved patient quality of life.

Neurotrofinas na epilepsia do lobo temporal

INTRODUÇÃO: A neurotrofinas NGF, BDNF, NT-3 e NT-4 são os principais representantes da família das neurotrofinas no sistema nervoso central de mamíferos. Estão presentes em estágios específicos do crescimento e sobrevivência neuronal como a divisão celular, diferenciação e axogênese e também nos processos naturais de morte celular neuronal. A atividade biológica das neurotrofinas é mediada pelos receptores de tropomiosina quinase Trk. NGF ativa principalmente os receptores TrkA, BDNF e NT-4 interagem com os receptores TrkB e NT-3 com TrkC. Todas as NTs também podem se ligar, com menor afinidade, ao receptor p75NTR. Nesta breve revisão serão levantadas as principais evidências sobre o papel e expressão das principais neurotrofinas no hipocampo, com ênfase nas alterações que ocorrem em modelos animais de epilepsia. RESULTADOS: As neurotrofinas parecem ter um papel chave na plasticidade sináptica relacionada à epilepsia, onde elas poderiam agir tanto como fatores promotores da epileptogênese quanto como substâncias anti-epiléptogênicas endógenas. Além disso a expressão dos genes que codificam os fatores neurotróficos e seus receptores pode ser alterada pela atividade de crises em diversos modelos de epilepsia. CONCLUSÃO: Vários estudos têm demonstrado a relação entre a expressão das neurotrofinas e as alterações na plasticidade dos circuitos neuronais que ocorrem após danos cerebrais, tais como a epilepsia. O conhecimento das alterações na expressão das neurotrofinas na plasticidade neuronal pode nos auxiliar a entender como estas moléculas participam dos mecanismos epileptogênicos e dessa forma, dar início ao estudo de novas terapias e ao desenvolvimento de novas drogas que auxiliem no tratamento da epilepsia.

Neuroprotective effects of IGF-I following kainic acid-induced hippocampal degeneration in the rat

Insulin-like growth factor I (IGF-I) has been shown to act as a neuroprotectant both in in vitro studies and in in vivo animal models of ischemia, hypoxia, trauma in the brain or the spinal cord, multiple and amyotrophic lateral sclerosis, Alzheimer's and Parkinson's disease. In the present study, we investigated the neuroprotective potential of IGF-I in the "kainic acid-induced degeneration of the hippocampus" model of temporal lobe epilepsy. Increased cell death--as detected by FluoroJade B staining--and extensive cell loss--as determined by cresyl violet staining--were observed mainly in the CA3 and CA4 areas of the ipsilateral and contralateral hippocampus, 7 days following intrahippocampal administration of kainic acid. Kainic acid injection also resulted in intense astrogliosis--as assessed by the number of glial fibrillary acidic protein (GFAP) immunopositive cells--in both hemispheres, forming a clear astroglial scar ipsilaterally to the injection site. Heat-shock protein 70 (Hsp70) immunopositive cells were also observed in the ipsilateral dentate gyrus (DG) following kainic acid injection. When IGF-I was administered together with kainic acid, practically no signs of degeneration were detected in the contralateral hemisphere, while in the ipsilateral, there was a smaller degree of cell loss, reduced number of FluoroJade B-stained cells, decreased reactive gliosis and fewer Hsp70-positive cells. Our present results extend further the cases in which IGF-I is shown to exhibit neuroprotective properties in neurodegenerative processes in the CNS.

TRPV1: a potential target for antiepileptogenesis

Epilepsy is one of the most common diseases in neurology department. It is caused by many different kinds of perturbances of normal balance of excitation and inhibition within the central nervous system. Current clinical antiepileptic drugs (AEDs) targets include ion channels, neurotransmitter transporters and neurotransmitter metabolic enzymes. They could control about 70-80% of the patients' symptoms; 20-30% patients develop to be intractable epilepsy sufferers. Moreover, antiepileptic drugs could not prevent formation of foci and disease process, but only alleviate symptoms of seizures at risk of different adverse effects as the consequences of large doses. Recently, impressive data on the actions of transient receptor potential vanilloid receptor 1 (TRPV1) prove it to be an inspiring antiepileptogenic target. TRPV1 activation modulates activity-dependent synaptic efficacy: (i) facilitating long-term potentiation (LTP) and suppressing long-term depression (LTD) of hippocampal neurons (ii) selectively inhibiting excitatory synapses onto hippocampal interneurons, which is expected to increase the excitability of innervated pyramidal cells. Nerve growth factor (NGF) can acutely and chronically upregulates TRPV1 expression, suggesting that TRPV1 channels would play an important role in the course of NGF regulated epileptogenesis. Endocannabinoid anandamide (AEA) is one of the TRPV1 endogenous agonists. It has been proved that, in the course of epilepsy, AEA levels increases due to enhanced formation and both exogenously administered and endogenously produced AEA display proconvulsant activity. Moreover, TRPV1 activation triggers apoptotic neuronal death of rat cortical cultures, which may be responsible, at least in part, for the volume loss of neocortex in chronic epilepsy. Our hypothesis may broaden the drug screening and designing for clinical strategies for epilepsy treatment.

Separating kindling and LTP: lessons from studies of PKM zeta in developing and adult rats

The kindling model of temporal lobe epilepsy (TLE) and the memory model of long-term potentiation (LTP) may have common underlying mechanisms. This is evident by the demonstration that certain signaling molecules play a key role in both. Recently, a brain specific isoform of protein kinase C (PKMzeta) has been shown to play a significant role in both maintaining LTP and memory storage. We were interested in determining if this kinase had a crossover role in kindling-induced epileptogenesis. Using developing and adult rats we examined the role of PKMzeta in kindling. In developing (P15) rats we determined the effect of PKMzeta on retention of amygdala kindling and kindling rate by intra-amygdala administration of a selective PKMzeta antagonist, ZIP (10 nmol). In adult rats we examined the effect of PKMzeta inhibition, ZIP (10 nmol), on after discharge (AD) thresholds and kindling retention using rapid hippocampal kindling. Inhibition of PKMzeta by the antagonist ZIP did not affect kindling rate or retention in developing rats. In addition there was also no observed effect on AD thresholds and kindling retention in adult rats. Our results show that, despite the similarities between kindling and LTP in their induction, there is dissociation in the role that PKMzeta plays within the two in maintenance. This may be of importance in establishing a separation between the pathophysiological processes involved in sustaining kindling and the physiological mechanisms involved in maintaining LTP and memory storage.

Progress in neuroprotective strategies for preventing epilepsy

Neuroprotection is increasingly considered as a promising therapy for preventing and treating temporal lobe epilepsy (TLE). The development of chronic TLE, also termed as epileptogenesis, is a dynamic process. An initial precipitating injury (IPI) such as the status epilepticus (SE) leads to neurodegeneration, abnormal reorganization of the brain circuitry and a significant loss of functional inhibition. All of these changes likely contribute to the development of chronic epilepsy, characterized by spontaneous recurrent motor seizures (SRMS) and learning and memory deficits. The purpose of this review is to discuss the current state of knowledge pertaining to neuroprotection in epileptic conditions, and to highlight the efficacy of distinct neuroprotective strategies for preventing or treating chronic TLE. Although the administration of certain conventional and new generation anti-epileptic drugs is effective for primary neuroprotection such as reduced neurodegeneration after acute seizures or the SE, their competence for preventing the development of chronic epilepsy after an IPI is either unknown or not promising. On the other hand, alternative strategies such as the ketogenic diet therapy, administration of distinct neurotrophic factors, hormones or antioxidants seem useful for preventing and treating chronic TLE. However, long-term studies on the efficacy of these approaches introduced at different time-points after the SE or an IPI are lacking. Additionally, grafting of fetal hippocampal cells at early time-points after an IPI holds considerable promise for preventing TLE, though issues regarding availability of donor cells, ethical concerns, timing of grafting after SE, and durability of graft-mediated seizure suppression need to be resolved for further advances with this approach. Overall, from the studies performed so far, there is consensus that neuroprotective strategies need to be employed as quickly as possible after the onset of the SE or an IPI for considerable beneficial effects. Nevertheless, ideal strategies that are capable of facilitating repair and functional recovery of the brain after an IPI and preventing the evolution of IPI into chronic epilepsy are still hard to pin down.

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.

Hippocampal mossy fiber sprouting and elevated trkB receptor expression following systemic administration of low dose domoic acid during neonatal development

We have previously reported that serial systemic injections of low-dose (subconvulsive) domoic acid (DOM) during early postnatal development produces changes in both behavior and hippocampal cytoarchitecture in aged rats (17 months) that are similar to those seen in existing animal models of temporal lobe epilepsy. Herein we report further hippocampal changes, consisting of mossy fiber sprouting and associated changes in the trkB receptor population in young adult (3 months) rats, and further, report that these changes show regional variation throughout the septo-temporal axis of the hippocampus. Groups of Sprague Dawley rat pups were injected daily from postnatal day 8-14 with either saline (n = 23) or 20 microg/kg DOM (n = 25), tested for key indicators of neonatal neurobehavioral development, and then left undisturbed until approximately 90 days of age, at which time brain tissue was removed, hippocampi were dissected, fixed and processed using either Timm's stain to visualize hippocampal mossy fiber sprouting (MFS) or trkB immunohistochemistry to visualize full length trkB receptors. Multiple sections from dorsal, mid, and ventral hippocampus were analyzed separately and all measures were conducted using image analysis software. The results indicate significant increases in MFS in the inner molecular layer in treated animals with corresponding changes in trkB receptor density. Further we identified significant increases in trkB receptor density in the hilus of the dentate gyrus and area CA3 and report increased mossy fiber terminal density in the stratum lucidum in treated rats. The magnitude of these changes differed between sections from dorsal, mid, and ventral hippocampus. We conclude that low dose neonatal DOM produces cytoarchitectural changes indicative of abnormal development and/or synaptic plasticity that are progressive with age and show regional variation within the hippocampal formation.

Angels and demons: neurotrophic factors and epilepsy

Several lines of evidence indicate that neurotrophic factors (NTFs) could be key causal mediators in the development of acquired epileptic syndromes. Yet the trophic properties of NTFs indicate that they might be used to treat epilepsy-associated damage. Accordingly, different NTFs, or even the same NTF, could produce functionally contrasting effects in the context of epilepsy. Recent experimental evidence begins to shed light on the mechanisms underlying these contrasting effects. Understanding these mechanisms will be instrumental for the development of effective therapies, which must be based on a careful consideration of the biological properties of NTFs. Here, we critically evaluate new information emerging in this area and discuss its implications for clinical treatment.

The Progression of Epilepsy

Prognosis for seizure control and cognitive development varies considerably among syndromes. Several factors may interact to influence outcome of an epilepsy including a causative etiology, ictal and interictal discharges, seizure-related trauma or systemic perturbations, and antiepileptic drug (AED) effects. Clinical evidence convincingly supporting Gowers' hypothesis that seizures beget seizures is lacking. Short-term seizure suppression by early treatment does not appear to influence long-term prognosis. Malignant epilepsy syndromes usually begin in infancy or childhood, have a high seizure frequency, resist the initial AED, and are often associated with progressive cognitive dysfunction. Prompt management of some severe epilepsy syndromes may lessen cognitive decline. However, aggressive AEDs therapy must be balanced against the potential for cognitive side effects, particularly if multiple AEDs are used. Several experimental paradigms closely parallel human TLE as both have an initial precipitating injury (IPI), a latent period, then recurrent spontaneous seizures. In humans, an IPI is any medical event with neurological implications. Although transition from a latent period to a seizure disorder certainly constitutes "progression" of the disorder, convincing clinical evidence of subsequent worsening has not emerged. Substantial clinical and experimental evidence indicates some cognitive regression and focal atrophy with time for TLE and other intractable syndromes. However, seizure frequency and severity, established early in the disorder, appear stable in most patients, and even regress in benign syndromes. Factors mitigating or extinguishing epilepsies need to be further sought.

Differential regulation of c-Fos and FosB in the rat brain after amygdala kindling

Members of the inducible transcription factor Fos family, that are part of the AP-1 complex that binds to the corresponding promoter site, are implicated in the regulation of gene transcription after acute and chronic seizures. However, little is known about the temporal expression of the AP-1 transcription factors and if individual proteins composing this complex have distinct roles in development and maintenance of permanent epilepsy. In this study, the AP-1 binding capacity, its content of different Fos proteins, and the anatomical specificity, were analyzed 2 or 18 h after achieving full kindling in rats. The same analysis was performed in fully kindled animal receiving a new stimulus after a 3-week pause to determine the extent of stability of the AP-1 transcription factors. While both c-Fos and FosB were induced in all cortical areas after a single stimulus, only FosB-immunoreactivity remained after 18 h. A single stimulation to kindled animals left undisturbed for 3 weeks induced a long-lasting upregulation of AP-1 binding in the frontal cortex, but not in the hippocampus suggesting a permanent exposure of AP-1 heterocomplexes in the frontal cortex. Supershift assays showed that FosB is the dominant component of the long-term AP-1 complex. It is concluded that the AP-1 binding complex in fully kindled rats is composed of different proteins, and that FosB-containing AP-1 complexes mediate long-term effects in the frontal cortex.

Influence of ionizing radiation on the course of kindled epileptogenesis

Several clinical and experimental reports suggest that low-dose irradiation of an established epileptic focus can reduce the occurrence of spontaneous seizures. Conversely, some recent reports suggest that under some conditions low-dose irradiation may have disinhibitory effects on seizure expression. Here, we have investigated mechanistic aspects of this phenomenon in the kindling model of epilepsy by applying focal irradiation at various points during kindling development. Rats were kindled to stage 5 by afterdischarge-threshold electrostimulation of the left amygdala. Treatment groups were irradiated using a collimated X-ray beam (18 MV) either prior to kindling, at kindling stage 3, or at kindling stage 5, by exposure of the left amygdala to a single-fraction central-axis dose of 25 Gy. Generalized seizure thresholds (GSTs) were subsequently assayed at weekly intervals for 10 weeks and at monthly intervals for an additional 3 months, along with the severity of the evoked seizures. Irradiation produced no significant effects on seizure threshold, but did produce persistent changes in seizure severity which varied as a function of the timing of irradiation. Relative to sham irradiated controls, the occurrence of stage 6 seizures was significantly increased by irradiation prior to kindling, but was unaffected by irradiation at kindling stage 3, and significantly reduced by irradiation at kindling stage 5. Quantitative immunohistochemical assays for neuron and astrocyte densities within the amygdala and hippocampus revealed only subtle changes in neuronal density within the dentate granule cell layer. These results are discussed in relation to mechanisms of seizure- and radiation-induced plasticity.

Collateral Sprouting as a Target for Improved Function after Spinal Cord Injury

Functional recovery after spinal cord injury might be improved by enhancing the extent of innervation through stimulation of collateral sprouting, which is the growth of a new axon along the shaft of a non-injured axon. This review discusses (1) the spontaneous collateral sprouting of uninjured motor and sensory systems that has been shown after spinal cord injury in animal models, (2) experimental treatment strategies that are being developed to enhance collateral sprouting in motor systems and to reduce sensory sprouting which is associated with autonomic dysreflexia and pain, and (3) cell-surface and intracellular signaling mechanisms that are known to regulate axonal branching. The conclusion is that relatively little is known about collateral sprouting in adult mammals after spinal cord injury but that it may contribute to spontaneous functional motor recovery and causes sensory dysfunction. There is some promising data in rodents that collateral sprouting can be modulated for improved function, but the applicability to primates and relevance to human spinal cord injury remains to be determined.

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.

Increased neurogenesis and the ectopic granule cells after intrahippocampal BDNF infusion in adult rats

There is evidence that BDNF influences the birth of granule cells in the dentate gyrus, which is one of the few areas of the brain that demonstrates neurogenesis throughout life. However, studies to date have not examined this issue directly. To do so, we compared the effects of BDNF, phosphate-buffered saline (PBS), or bovine serum albumin (BSA) on neurogenesis after infusion into the hippocampus of the normal adult rat, using osmotic pumps that were implanted unilaterally in the dorsal hilus. BDNF, PBS, and BSA were infused for 2 weeks. The mitotic marker bromodeoxyuridine (BrdU) was administered twice daily during the 2-week infusion period. At least 1 month after infusion ended, brains were processed immunocytochemically using antibodies to BrdU, a neuronal nuclear protein (NeuN), or calbindin D28K (CaBP), which labels mature granule cells. Stereology was used to quantify BrdU-labeled cells in the dorsal hippocampus that were double-labeled with NeuN or CaBP. There was a statistically significant increase in BrdU(+)/NeuN(+) double-labeled cells in the granule cell layer after BDNF infusion relative to controls. The values for BrdU(+)/NeuN(+) cells were similar to BrdU(+)/CaBP(+) cells, indicating that most new neurons were likely to be granule cells. In addition, BrdU(+)/NeuN(+)-labeled cells developed in the hilar region after BDNF infusion, which have previously only been identified after severe continuous seizures (status epilepticus) and associated pathological changes. Remarkably, neurogenesis was also increased contralaterally, but BDNF did not appear to spread to the opposite hemisphere. Thus, infusion of BDNF to a local area can have widespread effects on hippocampal neurogenesis. The results demonstrate that BDNF administration to the dentate gyrus leads to increased neurogenesis of granule cells. They also show that ectopic granule cells develop after BDNF infusion, which suggests that ectopic migration is not necessarily confined to pathological conditions. These results are discussed in light of the evidence that BDNF increases neuronal activity in hippocampus. Thus, the mechanisms underlying neurogenesis following BDNF infusion could be due to altered activity as well as direct effects of BDNF itself, and this is relevant to studies of other growth factors because many of them have effects on neuronal excitability that are often not considered.

In vitro1H NMR spectroscopy shows an increase in N-acetylaspartylglutamate and glutamine content in the hippocampus of amygdaloid-kindled rats

We examined energy metabolism and amino acid content in the hippocampus of amygdaloid-kindled rats using (1)H NMR spectroscopy. Three weeks after the last stage 5 seizure, kindled rats were killed by microwave irradiation. The hippocampus was dissected out and subjected to MeOH/CHCl(3) extraction. All (1)H spectra were analyzed to quantify absolute concentrations using a non-linear least squares method, combined with a prior knowledge of chemical shifts. Saturation effects were compensated for by the T1 measurement of each component. Levels of energy metabolism-related compounds, phosphocreatine, creatine, glucose and succinate were the same in both kindled rats and sham controls. Lactate concentration had a tendency to increase, although this was not statistically significant. When compared with sham controls, levels of aspartate, glutamate, glycine and glutamine, as well as GABA and inositol, were increased in the ipsilateral but not the contralateral hippocampus. In contrast, levels of taurine, alanine and threonine were unchanged. Finally, N-acetylaspartylglutamate content was elevated, whereas N-acetyl-l-aspartate content was unaltered in the ipsilateral hippocampus of kindled animals. Our results suggest that amygdala kindling may affects amino acid metabolism, but not energy metabolism.

Genetic background regulates semaphorin gene expression and epileptogenesis in mouse brain after kainic acid status epilepticus

The host response to neural injury, which can include axonal sprouting and synaptic reorganization is likely to be under tight genetic regulatory control at the level of the genome and may be implicated in epileptogenesis. Despite its importance, however, the molecular basis of synaptic reorganization is unclear. We have studied the development of synaptic reorganization, semaphorin gene expression, and epileptogenesis in hippocampus of epileptogenic sensitive (FVB/NJ) and epileptogenic resistant (C57BL/6J) mice (i.e. distinct genetic backgrounds) after kainic acid-induced status epilepticus. Our results support the hypothesis that disruption of transcriptional regulation of axon guidance genes leads to a differential loss of tonic neuropilin-2 dependent activation of semaphorin 3F receptors on hippocampal neurons on distinct genetic backgrounds. This results in rearranged synaptic circuitry and thus promotes epileptogenesis. These findings may define biologic principles underlying the role of semaphorin signaling which may broadly apply to other systems undergoing neural regeneration.

Chronic temporal lobe epilepsy: spatial extent and degree of metabolic dysfunction studied with magnetic resonance spectroscopy (MRS)

INTRODUCTION

Proton magnetic resonance spectroscopy ((1)H MRS) has been proposed as a lateralizing method for the presurgical evaluation of patients with medically intractable temporal lobe epilepsy (TLE). Studies have shown correlations between temporal lobe (TL) NAA and seizure frequency, and TL NAA/Cr and the duration of epilepsy in patients with TLE. This latter finding may suggest that progressive neuronal dysfunction may occur in both temporal lobes in patients with TLE, even when the seizures originate in only one temporal lobe. We analyzed our data in an attempt to find a possible correlation between extension of neuronal dysfunction based on NAA measures and duration of epilepsy.

METHODS

We studied 45 consecutive patients with the diagnosis of TLE, who were referred for presurgical evaluation. Duration of epilepsy was defined as the interval between the age of seizure onset and the time of the MRS examination. All studies were performed in the inter-ictal state, prior to intracranial monitoring or resection. We performed two-tailed Pearson correlation analysis between ipsilateral NAA/Cr and extension of the abnormality (voxels involved) and the duration of the seizure disorder in years.

RESULTS

The average duration of epilepsy in this group was 20 years. No significant correlation was found between duration of epilepsy and mean hippocampal NAA/Cr (r=-.131, p=.390); nor was a correlation found between duration of epilepsy in years or the extent of metabolic lesion (voxels involved) (r=-.264, p=.079).

CONCLUSIONS

Hippocampal NAA/Cr does not correlate with duration of epilepsy in TLE. Our findings suggest that cross-sectional group measures of hippocampal neuronal function do not suggest damage progression.

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

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

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.

Differential Effects of Aging and Insulin-like Growth Factor-1 on Synapses in CA1 of Rat Hippocampus

Aging-related impairments of learning and memory can be ameliorated by 28 days of intracerebroventricular (icv) infusion of insulin-like growth factor-1 (IGF-1) in old rats. The present study investigated whether there is an aging-related synaptic decline in the stratum radiatum of hippocampal CA1 and whether IGF-1 can ameliorate that decline. Five young (4 months), five middle-aged (18 months) and five old (29 months) Fischer 344xBrown Norway rats received saline infusion; five old (29 months) rats received IGF-1 infusion for 28 days preceding sacrifice. Pyramidal neurons, total synaptic profiles as well as synaptic profiles in multiple spine bouton (MSB) complexes in CA1 were quantified stereologically with the physical disector technique and the postsynaptic density (PSD) length was determined as well. The results indicated a decrease of total synapses between middle and old age but a maintenance of PSD length and MSB synapses throughout life. IGF-1 infusion in old rats did not reverse the aging-related decline in total synapses but did increase PSD length and the number of MSB synapses. These changes in synaptic configurations are morphological correlates of enhanced synaptic efficacy. Thus, aging and IGF-1 affect different, but complementary, aspects of synapses in hippocampal CA1.

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

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

EphA/ephrin-A interactions regulate epileptogenesis and activity-dependent axonal sprouting in adult rats

The Eph family of tyrosine kinase receptors and their ligands, ephrins, are distributed in gradients and serve as molecular guidance cues for axonal patterning during neuronal development. Most of these molecules are also expressed in mature brain. Thus, we examine here the potential roles of such molecules in plasticity and activity-dependent mossy fiber sprouting of adult CNS. We show that the ligand ephrin-A3 and the receptor EphA5 are expressed in complementary gradients in the adult rat mossy fiber system. Using the kindling model, we demonstrate that exogenous immunoadhesins that affect the interaction of endogenous EphA receptors and ephrin-A ligands modulate the development of kindling, one type of long-term plasticity, in mature rat brain. These immunoadhesins, combined with epileptogenic stimulations, alter both the extent and the pattern of collateral axonal sprouting in the mossy fiber pathway. Our results suggest that EphA receptors and ephrin-A ligands modify neuronal plasticity and may serve as spatial cues that modulate the development and pattern of activation-dependent axonal growth in adult CNS.

Truncation of the Shaker-like voltage-gated potassium channel, Kv1.1, causes megencephaly

The megencephaly mouse, mceph/mceph, displays dramatically increased brain volume and hypertrophic brain cells. Despite overall enlargement, the mceph/mceph brain appears structurally normal, without oedema, hydrocephaly or leukodystrophy, and with only minor astrocytosis. Furthermore, it presents striking disturbances in expression of trophic and neuromodulating factors within the hippocampus and cortex. Using a positional cloning approach we have identified the mceph mutation. We show that mceph/mceph mice carry an 11-base-pair deletion in the gene encoding the Shaker-like voltage-gated potassium channel subtype 1, Kcna1. The mutation leads to a frame shift and the predicted MCEPH protein is truncated at amino acid 230 (out of 495), terminating with six aberrant amino acids. The expression of Kcna1 mRNA is increased in the mceph/mceph brain. However, the C-terminal domains of the corresponding Kv1.1 protein are absent. The putative MCEPH protein retains only the N-terminal domains for channel assembly and may congregate nonfunctional complexes of multiple Shaker-like subunits. Indeed, whereas Kcna2 and Kcna3 mRNA expression is normal, the mceph/mceph hippocampus displays decreased amounts of Kv1.2 and Kv1.3 proteins, suggesting interactions at the protein level. We show that mceph/mceph mice have disturbed brain electrophysiology and experience recurrent behavioural seizures, in agreement with the abnormal electrical brain activity found in Shaker mutants. However, in contrast to the commonly demonstrated epilepsy-induced neurodegeneration, we find that the mceph mutation leads to seizures with a concomitant increase in brain size, without overt neural atrophy.

Hippocampal neurotrophin levels in a kainate model of temporal lobe epilepsy: a lack of correlation between brain-derived neurotrophic factor content and progression of aberrant dentate mossy fiber sprouting

A significant upregulation of neurotrophins particularly brain-derived neurotrophic factor (BDNF) is believed to be involved in the initiation of epileptogenic changes such as the aberrant axonal sprouting and synaptic reorganization in the injured hippocampus. However, it is unknown which of the neurotrophins are upregulated during the peak period of aberrant mossy fiber sprouting in the chronically injured hippocampus. We measured chronic changes in the levels of BDNF, nerve growth factor (NGF) and neurotrophin-3 (NT-3) in the adult hippocampus using enzyme-linked immunosorbent assay (ELISA) after a unilateral intracerebroventricular administration of kainic acid (KA), a model of temporal lobe epilepsy. For comparison, neurotrophins were also measured from the control intact hippocampus. Further, to see the association between changes in neurotrophin levels and the progression of mossy fiber sprouting, chronic changes in the mossy fiber distribution within the dentate supragranular layer (DSGL) were quantified. In the KA-lesioned hippocampus, the neurotrophins BDNF and NGF were upregulated at 4 days post-lesion, in comparison to their levels in the intact hippocampus. However, the concentration of BDNF reached the baseline level at 45 days post-lesion and dramatically diminished at 120 days post-lesion. In contrast, the upregulation of NGF observed at 4 days post-lesion was sustained at both 45 days and 120 days post-lesion. The concentration of NT-3 was upregulated at 45 days post-lesion but remained comparable to baseline levels at 4 days and 120 days post-lesion. Interestingly, analysis of mossy fiber sprouting revealed that most of the aberrant sprouting in the lesioned hippocampus occurs between 45 days and 120 days post-lesion. Taken together, these results suggest that the period of robust mossy fiber sprouting does not correlate with the phase of post-lesion BDNF upregulation. Rather, it shows a relationship with the time of upregulation of neurotrophins NGF and NT-3.

A ligand of the p65/p95 receptor suppresses perforant path kindling, kindling-induced mossy fiber sprouting, and hilar area changes in adult rats

Kindling, an animal model of epilepsy, results in an increased volume of the hilus of the dentate gyrus and sprouting of the mossy fiber pathway in the hippocampus. Our previous studies have revealed that chronic infusion of neurotrophins can regulate not only seizure development, but also these kindling-induced structural changes. Kindling, in turn, can alter the expression of neurotrophins and their receptors. We previously showed that intraventricular administration of a synthetic peptide that interferes with nerve growth factor stability and thus its binding to TrkA and p75(NTR) receptors suppressed kindling and sprouting. However, the precise involvement of TrkA, p75(NTR), and downstream signaling effectors of neurotrophins on kindling, sprouting and hilar changes are unknown. One of these downstream effectors is Ras. In the present study, we find that intraventricular infusion of the synthetic peptide Reo3Y, which binds to p65/p95 receptors and causes a rapid inactivation of Ras protein, impairs development of perforant path kindling, reduces the growth in afterdischarge duration, blocks kindling-induced mossy fiber sprouting in area CA3 of hippocampus and in inner molecular layer of the dentate gyrus, and prevents kindling-induced increases in hilar area. These results are consistent with a mediation of neurotrophin effects on kindling, hilar area, and axonal sprouting via Trk receptors, and suggest important roles for Ras in kindling and in kindling-induced structural changes.

Neurotrophins

Nerve growth factor was the first identified protein with anti-apoptotic activity on neurons. This prototypic neurotrophic factor, together with the three structurally and functionally related growth factors brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT3) and neurotrophin-4/5 (NT4/5), forms the neurotrophin protein family. Target T cells for neurotrophins include many neurons affected by neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis and peripheral polyneuropathies. In addition, the neurotrophins act on neurons affected by other neurological and psychiatric pathologies including ischemia, epilepsy, depression and eating disorders. Work with cell cultures and animal models provided solid support for the hypothesis that neurotrophins prevent neuronal death. While no evidence exists that a lack of neurotrophins underlies the etiology of any neurodegenerative disease, these studies have spurred on hopes that neurotrophins might be useful symptomatic-therapeutic agents. However first clinical trials led to variable results and severe side effects were observed. For future therapeutic use of the neurotrophins it is therefore crucial to expand our knowledge about their physiological functions as well as their pharmacokinetic properties. A major challenge is to develop methods for their application in effective doses and in a precisely timed and localized fashion.