Brain-derived neurotrophic factor immunoreactivity in the limbic system of rats after acute seizures and during spontaneous convulsions: temporal evolution of changes as compared to neuropeptide Y

Excitatory/inhibitory balance in epilepsies and neurodevelopmental disorders: Depolarizing γ-aminobutyric acid as a common mechanism

Epilepsy is one of the most common neurological disorders. Although many factors contribute to epileptogenesis, seizure generation is mostly linked to hyperexcitability due to alterations in excitatory/inhibitory (E/I) balance. The common hypothesis is that reduced inhibition, increased excitation, or both contribute to the etiology of epilepsy. Increasing evidence shows that this view is oversimplistic, and that increased inhibition through depolarizing γ-aminobutyric acid (GABA) similarly contributes to epileptogenisis. In early development, GABA signaling is depolarizing, inducing outward Cl- currents due to high intracellular Cl- concentrations. During maturation, the mechanisms of GABA action shift from depolarizing to hyperpolarizing, a critical event during brain development. Altered timing of this shift is associated with both neurodevelopmental disorders and epilepsy. Here, we consider the different ways that depolarizing GABA contributes to altered E/I balance and epileptogenesis, and discuss that alterations in depolarizing GABA could be a common denominator underlying seizure generation in neurodevelopmental disorders and epilepsies.

Effects of scorpion venom heat-resistant peptide on the hippocampal neurons of kainic acid-induced epileptic rats

Scorpion venom is a Chinese medicine for epilepsy treatment, but the underlying mechanism is not clear. Scorpion venom heat-resistant peptide (SVHRP), a peptide isolated from the venom of Buthus martensii Karsch, has an anti-epileptic effect by reducing seizure behavior according to a modified Racine scale. The present study aimed to investigate the molecular mechanism of SVHRP on temporal lobe epilepsy. The hippocampus and hippocampal neurons from kainic acid-induced epileptic rats were treated with SVHRP at different doses and duration. Quantitative RT-PCR and immunoblotting were used to detect the expression level of brain-derived neurotrophic factor (BDNF), neuropeptide Y (NPY), cAMP-response element binding protein (CREB), stromal interaction molecule (STIM), and calcium release-activated calcium channel protein 1 (ORAI1). In the hippocampal tissues and primary hippocampal neuron cultures, SVHRP treatment resulted in increased mRNA and protein levels of BDNF and NPY under the epileptic condition. The upregulation of BDNF and NPY expression was positively correlated with the dose level and treatment duration of SVHRP in hippocampal tissues from kainic acid-induced epileptic rats. On the other hand, no significant changes in the levels of CREB, STIM, or ORAI1 were observed. SVHRP may exhibit an anti-epileptic effect by upregulating the expression of BDNF and NPY in the epileptic hippocampus.

Genetic and molecular basis of epilepsy-related cognitive dysfunction

Epilepsy is a common neurological disease characterized by recurrent seizures. About 70 million people were affected by epilepsy or epileptic seizures. Epilepsy is a complicated complex or symptomatic syndromes induced by structural, functional, and genetic causes. Meanwhile, several comorbidities are accompanied by epileptic seizures. Cognitive dysfunction is a long-standing complication associated with epileptic seizures, which severely impairs quality of life. Although the definitive pathogenic mechanisms underlying epilepsy-related cognitive dysfunction remain unclear, accumulating evidence indicates that multiple risk factors are probably involved in the development and progression of cognitive dysfunction in patients with epilepsy. These factors include the underlying etiology, recurrent seizures or status epilepticus, structural damage that induced secondary epilepsy, genetic variants, and molecular alterations. In this review, we summarize several theories that may explain the genetic and molecular basis of epilepsy-related cognitive dysfunction.

Activation of BDNF-TrkB signaling pathway-regulated brain inflammation in pentylenetetrazole-induced seizures in zebrafish

Seizures are sustained neuronal hyperexcitability in brain that result in loss of consciousness and injury. Understanding how the brain responds to seizures is critical to help developing new therapeutic strategies for epilepsy, a neurological disorder characterized by recurrent and unprovoked seizures. However, the mechanisms underlying seizure-dependent alterations of biological properties are poorly understood. In this study, we analyzed gene expression profiles of the zebrafish heads that were undergoing seizures and identified 1776 differentially expressed genes. Gene-regulatory network analysis revealed that BDNF-TrkB signaling pathway positively regulated brain inflammation in zebrafish during seizures. Using K252a, a TrkB inhibitor to block BDNF-TrkB signaling pathway, attenuated pentylenetetrazole (PTZ)-induced seizures, which also confirmed BDNF-TrkB mediated inflammatory responses including regulation of il1β and nfκb, and neutrophil and macrophage infiltration of brain. Our results have provided novel insights into seizure-induced brain inflammation in zebrafish and anti-inflammatory related therapy for epilepsy.

Brain-derived neurotrophic factor and epilepsy: a systematic review

Several in vitro, ex vivo and in vivo studies imply brain-derived neurotrophic factor (BDNF) in the pathophysiology of epilepsy. Aim of our work is to report the most important findings regarding BDNF and its potential role in epilepsy. We targeted those publications addressing both in vitro and in vivo evidences of relationship between BDNF and epilepsy. Basic researches, randomized trials, cohort studies, and reviews were contemplated to give a breadth of clinical data. Medline, CENTRAL, and Science Direct were searched till August 2017 using keywords agreed by the authors. Together with a defined role in developmental and mature brain, BDNF has excitatory effects in neuronal cultures and animal brain slices. Furthermore, both BDNF and its conjugated receptor (i.e. Tropomyosin receptor kinase B or TrkB) are increased in animal models and humans with epilepsy, particularly in the temporal and hippocampal areas. Acute injection of BDNF in brain of mice induces seizures, which are almost or totally abolished blocking its transcription and pathway. Chronic infusion of BDNF is conversely associated with a decreased neuronal excitability, probably via several mechanism including an increase in central levels of neuropeptide Y (NPY), altered conductance of chloride, and downregulation of TrkB. While genetic studies are inconclusive, serum BDNF is more frequently higher in patients with epilepsy and appears to be correlated to severity of disease. Current evidences suggest that inhibiting BDNF-TrkB signaling and reinforcing the NPY system could represent a potential therapeutic strategy for epilepsy, especially for temporal lobe epilepsy.

Interactions Between Epilepsy and Plasticity

Undoubtedly, one of the most interesting topics in the field of neuroscience is the ability of the central nervous system to respond to different stimuli (normal or pathological) by modifying its structure and function, either transiently or permanently, by generating neural cells and new connections in a process known as neuroplasticity. According to the large amount of evidence reported in the literature, many stimuli, such as environmental pressures, changes in the internal dynamic steady state of the organism and even injuries or illnesses (e.g., epilepsy) may induce neuroplasticity. Epilepsy and neuroplasticity seem to be closely related, as the two processes could positively affect one another. Thus, in this review, we analysed some neuroplastic changes triggered in the hippocampus in response to seizure-induced neuronal damage and how these changes could lead to the establishment of temporal lobe epilepsy, the most common type of focal human epilepsy.

Seizing Control of KCC2: A New Therapeutic Target for Epilepsy

Deficits in GABAergic inhibition result in the abnormal neuronal activation and synchronization that underlies seizures. However, the molecular mechanisms responsible for transforming a normal brain into an epileptic one remain largely unknown. Hyperpolarizing inhibition mediated by type A GABA (GABAA) receptors is dependent on chloride extrusion by the neuron-specific type 2K+-Cl- cotransporter (KCC2). Loss-of-function mutations in KCC2 are a known cause of infantile epilepsy in humans and KCC2 dysfunction is present in patients with both idiopathic and acquired epilepsy. Here we discuss the growing evidence that KCC2 dysfunction has a central role in the development and severity of the epilepsies.

Increased Expression of Brain-Derived Neurotrophic Factor Transcripts I and VI, cAMP Response Element Binding, and Glucocorticoid Receptor in the Cortex of Patients with Temporal Lobe Epilepsy

A body of evidence supports a relevant role of brain-derived neurotrophic factor (BDNF) in temporal lobe epilepsy (TLE). Magnetic resonance data reveal that the cerebral atrophy extends to regions that are functionally and anatomically connected with the hippocampus, especially the temporal cortex. We previously reported an increased expression of BDNF messenger for the exon VI in the hippocampus of temporal lobe epilepsy patients compared to an autopsy control group. Altered levels of this particular transcript were also associated with pre-surgical use of certain psychotropic. We extended here our analysis of transcripts I, II, IV, and VI to the temporal cortex since this cerebral region holds intrinsic communication with the hippocampus and is structurally affected in patients with TLE. We also assayed the cyclic adenosine monophosphate response element-binding (CREB) and glucocorticoid receptor (GR) genes as there is experimental evidence of changes in their expression associated with BDNF and epilepsy. TLE and pre-surgical pharmacological treatment were considered as the primary clinical independent variables. Transcripts BDNF I and BDNF VI increased in the temporal cortex of patients with pharmacoresistant TLE. The expression of CREB and GR expression follow the same direction. Pre-surgical use of selective serotonin reuptake inhibitors, carbamazepine (CBZ) and valproate (VPA), was associated with the differential expression of specific BDNF transcripts and CREB and GR genes. These changes could have functional implication in the plasticity mechanisms related to temporal lobe epilepsy.

Effects of Electroconvulsive Therapy on Some Inflammatory Factors in Patients With Treatment-Resistant Schizophrenia

OBJECTIVES

Electroconvulsive therapy (ECT) is the most effective option for several psychiatric conditions, including treatment-resistant schizophrenia. However, little is known about the molecular mechanism of action of ECT. The link between inflammatory system and schizophrenia is the focus of recent studies. However, the impact of ECT on inflammatory functioning in this disorder remains elusive. Whether ECT could modulate inflammatory factors in patients with schizophrenia was examined.

METHODS

Plasma levels of interleukin-4 (IL-4), transforming growth factor-β (TGF-β), myeloperoxidase (MPO), and nuclear factor-κB (NF-κB) activation were analyzed in 20 schizophrenic patients, mainly with resistant to antipsychotic medication disorders, and in 20 sex- and age-matched healthy controls. Disease severity was evaluated using the Brief Psychiatric Rating Scale. All patients were followed with measurement of the inflammatory factors before and after ECT treatment and compared with the controls.

RESULTS

Patients with schizophrenia had markedly raised NF-κB and but decreased TGF-β levels compared with healthy controls. On the other hand, no significant differences were found for the levels of IL-4 and MPO levels. The clinical improvement during repeated ECT was accompanied by a gradual and significant increase in IL-4 and TGF-β level, but MPO and NF-κB activation were left unaffected. Increases in TGF-β were negatively correlated with the change in Brief Psychiatric Rating Scale scores after ECT.

CONCLUSIONS

It is shown that ECT, while increasing the anti-inflammatory response such as the levels of IL-4 and TGF-β, it did not affect the levels of MPO and NF-κB activation in this study.

To BDNF or Not to BDNF: That Is the Epileptic Hippocampus

Brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, has drawn much attention as a potential therapeutic target for temporal lobe epilepsy (TLE). TLE seizures are produced by synchronized hyperactivity of neuron populations due to the disruption of a balance between excitatory and inhibitory synaptic transmissions. In epileptogenesis-related brain areas, including the hippocampus, BDNF is up-regulated in the course of the development of epilepsy and induces a collapse of balanced excitation and inhibition, eventually exerting its epileptogenic effects. On the other hand, several reports demonstrate that intrahippocampal infusion of BDNF can attenuate (or retard) the development of epilepsy. This antiepileptogenic effect seems to be mediated mainly by an increase in the expression of neuropeptide Y. These contrasting effects of BDNF have prevented us from concluding whether inhibition or enhancement of BDNF signaling finally achieves the prevention of TLE. To address this question, it is essential to evaluate how BDNF changes its influences depending on conditions, for example, cell specificity, neural networks, and expression timing and loci. In this article, the authors review BDNF-induced acute and long-lasting changes seen in epileptic circuits from the anatomical and functional points of view.

Engineered BDNF producing cells as a potential treatment for neurologic disease

INTRODUCTION

Brain-derived neurotrophic factor (BDNF) has been implicated in wide range of neurological diseases and injury. This neurotrophic factor is vital for neuronal health, survival, and synaptic connectivity. Many therapies focus on the restoration or enhancement of BDNF following injury or disease progression.

AREAS COVERED

The present review will focus on the mechanisms in which BDNF exerts its beneficial functioning, current BDNF therapies, issues and potential solutions for delivery of neurotrophic factors to the central nervous system, and other disease indications that may benefit from overexpression or restoration of BDNF.

EXPERT OPINION

Due to the role of BDNF in neuronal development, maturation, and health, BDNF is implicated in numerous neurological diseases making it a prime therapeutic agent. Numerous studies have shown the therapeutic potential of BDNF in a number of neurodegenerative disease models and in acute CNS injury, however clinical translation has fallen short due to issues in delivering this molecule. The use of MSC as a delivery platform for BDNF holds great promise for clinical advancement of neurotrophic factor restoration. The ease with which MSC can be engineered opens the door to the possibility of using this cell-based delivery system to advance a BDNF therapy to the clinic.

Physical training decreases susceptibility to pilocarpine-induced seizures in the injured rat brain

There is growing evidence that physical activity ameliorates the course of epilepsy in animal models as well as in clinical conditions. Since traumatic brain injury is one of the strongest determinants of epileptogenesis, the present study focuses on the question whether a moderate long-term physical training can decrease susceptibility to seizures evoked following brain damage. Wistar rats received a mechanical brain injury and were subjected to daily running sessions on a treadmill for 21 days. Thereafter, seizures were induced by pilocarpine injections in trained and non-trained, control groups. During the acute period of status epilepticus, the intensity of seizures was assessed within the six-hour observation period. The trained rats showed considerable amelioration of pilocarpine-induced motor symptoms when compared with their non-trained counterparts. Histological investigations of effects of the brain injury and of physical training detected significant quantitative changes in parvalbumin-, calretinin- and NPY-immunopositive neuronal populations. Some of the injury-induced changes, especially those shoved by parvalbumin-immunopositive neurons, were abolished by the subsequent physical training procedure and could, therefore, be considered as neuronal correlates of the observed functional amelioration of the injured brain.

Combined Low-Intensity Exercise and Ascorbic Acid Attenuates Kainic Acid-Induced Seizure and Oxidative Stress in Mice

Physical exercise and vitamins such as ascorbic acid (ASC) have been recognized as an effective strategy in neuroprotection and neurorehabilitatioin. However, there is a need to find an efficient treatment regimen that includes ASC and low-intensity exercise to diminish the risk of overtraining and nutritional treatment by attenuating oxidative stress. In the present study, we investigated the combined effect of low-intensity physical exercise (EX) and ASC on kainic acid (KA)-induced seizure activity and oxidative stress in mice. The mice were randomly assigned into groups as follows: "KA only" (n = 11), "ASC + KA" (n = 11), "Ex + KA" (n = 11), "ASC + Ex + KA" (n = 11). In the present study, low intensity of swimming training period lasted 8 weeks and consisted of 30-min sessions daily (three times per week) without tail weighting. Although no preventive effect of low-intensity exercise or ASC on KA seizure occurrence was evident, there was a decrease of seizure activity, seizure development (latency to first seizures), and mortality in "ASC + Ex + KA" compared to "ASC + KA", "Ex + KA", and "KA only" group. In addition, a preventive synergistic coordination of low-intensity exercise and ASC was evident in glutathione peroxidase and superoxide dismutase activity compared to separate treatment. These results suggest that low-intensity exercise and ASC treatment have preventive effects on seizure activity and development with alternation of oxidative status.

Distinct synaptic and neurochemical changes to the granule cell-CA3 projection in Bassoon mutant mice

Proper synaptic function depends on a finely-tuned balance between events such as protein synthesis and structural organization. In particular, the functional loss of just one synaptic-related protein can have a profound impact on overall neuronal network function. To this end, we used a mutant mouse model harboring a mutated form of the presynaptic scaffolding protein Bassoon (Bsn), which is phenotypically characterized by: (i) spontaneous generalized epileptic seizure activity, representing a chronically-imbalanced neuronal network; and (ii) a dramatic increase in hippocampal brain-derived neurotrophic factor (BDNF) protein concentration, a key player in synaptic plasticity. Detailed morphological and neurochemical analyses revealed that the increased BDNF levels are associated with: (i) modified neuropeptide distribution; (ii) perturbed expression of selected markers of synaptic activation or plasticity; (iii) subtle changes to microglial structure; and (iv) morphological alterations to the mossy fiber (MF) synapse. These findings emphasize the important contribution of Bassoon protein to normal hippocampal function, and further characterize the Bsn-mutant as a useful model for studying the effects of chronic changes to network activity.

Aberrant hippocampal neurogenesis after limbic kindling: Relationship to BDNF and hippocampal-dependent memory

Seizures dramatically increase the number of adult generated neurons in the hippocampus. However, it is not known whether this effect depends on seizures that originate in specific brain regions or whether it is nonspecific to seizure activity regardless of origin. We used kindling of different brain sites to address this question. Rats received 99 kindling stimulations of the basolateral amygdala, dorsal hippocampus, or caudate nucleus over a 6-week period. After kindling, we counted the number of adult generated hippocampal neurons that were birth-dated with the proliferative marker bromodeoxyuridine (BrdU) to evaluate cell proliferation and survival under conditions of repeated seizures. Next, we counted the number of doublecortin immunoreactive (DCX-ir) cells and evaluated their dendritic complexity to determine if limbic and nonlimbic seizures have differential effects on neuronal maturation. We also quantified hippocampal brain-derived neurotrophin factor (BDNF) protein levels using an ELISA kit and assessed memory performance using a hippocampal-dependent fear conditioning paradigm. We found that limbic, but not nonlimbic, seizures dramatically increased hippocampal cell proliferation and the number of hilar-CA3 ectopic granule cells. Further, limbic kindling promoted dendritic outgrowth of DCX-ir cells and the number of DCX-ir cells containing basal dendrites. Limbic kindling also enhanced BDNF protein levels throughout the entire hippocampus and impaired the retrieval of fear memories. Collectively, our results suggest a relationship between limbic seizures, neurogenesis, BDNF protein, and cognition.

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.

Beneficial influence of physical exercise following status epilepticus in the immature brain of rats

Studies in adult animals have demonstrated a beneficial effect of physical exercise on epileptic insults. Although the effects of physical exercise on the mature nervous system are well documented, its influence on the developing nervous system subjected to injuries in childhood has been little explored. The purpose of our study was to investigate whether a physical exercise program applied during brain development could influence the hippocampal plasticity of rats submitted to status epilepticus (SE) induced by pilocarpine model at two different ages of the postnatal period. Male Wistar rats aged 18 (P18) and 28 (P28) days were randomly divided into four groups: Control (CTRL), Exercise (EX), SE (SE) and SE Exercise (SE/EX) (n=17 per group). After the aerobic exercise program, histological and behavioral (water maze) analyses were performed. Our results showed that only animals subjected to pilocarpine-induced SE at P28 presented spontaneous seizures during the observational period. A significant reduction in seizure frequency was observed in the SE/EX group compared to the SE group. In adulthood, animals submitted to early-life SE displayed impairment in long-term memory in the water maze task, while the exercise program reversed this deficit. Reduced mossy fiber sprouting in the dentate gyrus was noted in animals that presented spontaneous seizures (SE/EX vs SE). Exercise increased cell proliferation (Ki-67 staining) and anti-apoptotic response (bcl-2 staining) and reduced pro-apoptotic response (Bax staining) in animals of both ages of SE induction (P18/28). Exercise also modified the brain-derived neurotrophic factor (BDNF) levels in EX and SE/EX animals. Our findings indicate that in animals subjected to SE in the postnatal period a physical exercise program brings about beneficial effects on seizure frequency and hippocampal plasticity in later stages of life.

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.

Sequel of spontaneous seizures after kainic acid-induced status epilepticus and associated neuropathological changes in the subiculum and entorhinal cortex

Injection of the seaweed toxin kainic acid (KA) in rats induces a severe status epilepticus initiating complex neuropathological changes in limbic brain areas and subsequently spontaneous recurrent seizures. Although neuropathological changes have been intensively investigated in the hippocampus proper and the dentate gyrus in various seizure models, much less is known about changes in parahippocampal areas. We now established telemetric EEG recordings combined with continuous video monitoring to characterize the development of spontaneous seizures after KA-induced status epilepticus, and investigated associated neurodegenerative changes, astrocyte and microglia proliferation in the subiculum and other parahippocampal brain areas. The onset of spontaneous seizures was heterogeneous, with an average latency of 15 ± 1.4 days (range 3–36 days) to the initial status epilepticus. The frequency of late spontaneous seizures was higher in rats in which the initial status epilepticus was recurrent after its interruption with diazepam compared to rats in which this treatment was more efficient. Seizure-induced neuropathological changes were assessed in the subiculum by losses in NeuN-positive neurons and by Fluoro-Jade C staining of degenerating neurons. Neuronal loss was already prominent 24 h after KA injection and only modestly progressed at the later intervals. It was most severe in the proximal subiculum and in layer III of the medial entorhinal cortex and distinct Fluoro-Jade C labeling was observed there in 75% of rats even after 3 months. Glutamatergic neurons, labeled by in situ hybridization for the vesicular glutamate transporter 1 followed a similar pattern of cell losses, except for the medial entorhinal cortex and the proximal subiculum that appeared more vulnerable. Glutamate decarboxylase65 (GAD65) mRNA expressing neurons were generally less vulnerable than glutamate neurons. Reactive astrocytes and microglia were present after 24 h, however, became prominent only after 8 days and remained high after 30 days. In the proximal subiculum, parasubiculum and entorhinal cortex the number of microglia cells was highest after 30 days. Although numbers of reactive astrocytes and microglia were reduced again after 3 months, they were still present in most rats. The time course of astrocyte and microglia proliferation parallels that of epileptogenesis.

BDNF and its pro-peptide are stored in presynaptic dense core vesicles in brain neurons

Contrasting with the long-established retrograde model for neurotrophin function, specific immunohistochemical localization of brain-derived neurotrophic factor in the central nervous system supports the alternative model of presynaptic localization and anterograde function.

Although brain-derived neurotrophic factor (BDNF) regulates numerous and complex biological processes including memory retention, its extremely low levels in the mature central nervous system have greatly complicated attempts to reliably localize it. Using rigorous specificity controls, we found that antibodies reacting either with BDNF or its pro-peptide both stained large dense core vesicles in excitatory presynaptic terminals of the adult mouse hippocampus. Both moieties were ∼10-fold more abundant than pro-BDNF. The lack of postsynaptic localization was confirmed in Bassoon mutants, a seizure-prone mouse line exhibiting markedly elevated levels of BDNF. These findings challenge previous conclusions based on work with cultured neurons, which suggested activity-dependent dendritic synthesis and release of BDNF. They instead provide an ultrastructural basis for an anterograde mode of action of BDNF, contrasting with the long-established retrograde model derived from experiments with nerve growth factor in the peripheral nervous system.

Minocycline attenuates microglia activation and blocks the long-term epileptogenic effects of early-life seizures

Innate immunity mediated by microglia appears to play a crucial role in initiating and propagating seizure-induced inflammatory responses. To address the role of activated microglia in the pathogenesis of childhood epilepsy, we first examined the time course of microglia activation following kainic acid-induced status epilepticus (KA-SE) in Cx3cr1(GFP/+) transgenic mice whose microglia are fluorescently labeled. We then determined whether this seizure-induced microglia activation primes the central immune response to overreact and to increase the susceptibility to a second seizure later in life. We used an inhibitor of microglia activation, minocycline, to block the seizure-induced inflammation to determine whether innate immunity plays a causal role in mediating the long-term epileptogenic effects of early-life seizure. First status epilepticus was induced at postnatal day (P) 25 and a second status at P39. KA-SE at P25 caused nearly a two-fold increase in microglia activation within 24h. Significant seizure-induced activation persisted for 7 days and returned to baseline by 14 days. P39 animals with prior exposure to KA-SE not only responded with greater microglial activation in response to "second hit" of KA, but shorter latency to express seizures. Inhibition of seizure-induced inflammation by 7 day minocycline post-treatment abrogated both the exaggerated microglia activation and the increased susceptibility to the second seizure later in life. The priming effect of early-life seizures is accompanied by modified and rapidly reactivated microglia. Our results suggest that anti-inflammatory therapy after SE may be useful to block the epileptogenic process and mitigate the long-term damaging effects of early-life seizures.

Epigenetic gene regulation in the adult mammalian brain: multiple roles in memory formation

Brain-derived neurotrophic factor (bdnf) is one of numerous gene products necessary for long-term memory formation and dysregulation of bdnf has been implicated in the pathogenesis of cognitive and mental disorders. Recent work indicates that epigenetic-regulatory mechanisms including the markings of histone proteins and associated DNA remain labile throughout the life-span and represent an attractive molecular process contributing to gene regulation in the brain. In this review, important information will be discussed on epigenetics as a set of newly identified dynamic transcriptional mechanisms serving to regulate gene expression changes in the adult brain with particular emphasis on bdnf transcriptional readout in learning and memory formation. This review will also highlight evidence for the role of epigenetics in aberrant bdnf gene regulation in the pathogenesis of cognitive dysfunction associated with seizure disorders, Rett syndrome, Schizophrenia, and Alzheimer's disease. Such research offers novel concepts for understanding epigenetic transcriptional mechanisms subserving adult cognition and mental health, and furthermore promises novel avenues for therapeutic approach in the clinic.

Brain-derived neurotrophic factor and epilepsy--a missing link?

It has been known for some time that brain-derived neurotrophic factor (BDNF) is critical to normal development of the CNS, and more recently, studies also have documented the ability of BDNF to modify adult CNS structure and function. Therefore, it is no surprise that BDNF has been linked to diseases, such as epilepsy, which may involve abnormal cortical development or altered brain structure and function after maturity. This review evaluates the evidence, particularly from recent studies, that BDNF contributes to the development of temporal lobe epilepsy (TLE).

Water maze experience and prenatal choline supplementation differentially promote long-term hippocampal recovery from seizures in adulthood

Status epilepticus (SE) in adulthood dramatically alters the hippocampus and produces spatial learning and memory deficits. Some factors, like environmental enrichment and exercise, may promote functional recovery from SE. Prenatal choline supplementation (SUP) also protects against spatial memory deficits observed shortly after SE in adulthood, and we have previously reported that SUP attenuates the neuropathological response to SE in the adult hippocampus just 16 days after SE. It is unknown whether SUP can ameliorate longer-term cognitive and neuropathological consequences of SE, whether repeatedly engaging the injured hippocampus in a cognitive task might facilitate recovery from SE, and whether our prophylactic prenatal dietary treatment would enable the injured hippocampus to more effectively benefit from cognitive rehabilitation. To address these issues, adult offspring from rat dams that received either a control (CON) or SUP diet on embryonic days 12-17 first received training on a place learning water maze task (WM) and were then administered saline or kainic acid (KA) to induce SE. Rats then either remained in their home cage, or received three additional WM sessions at 3, 6.5, and 10 weeks after SE to test spatial learning and memory retention. Eleven weeks after SE, the brains were analyzed for several hippocampal markers known to be altered by SE. SUP attenuated SE-induced spatial learning deficits and completely rescued spatial memory retention by 10 weeks post-SE. Repeated WM experience prevented SE-induced declines in glutamic acid decarboxylase (GAD) and dentate gyrus neurogenesis, and attenuated increased glial fibrilary acidic protein (GFAP) levels. Remarkably, SUP alone was similarly protective to an even greater extent, and SUP rats that were water maze trained after SE showed reduced hilar migration of newborn neurons. These findings suggest that prophylactic SUP is protective against the long-term cognitive and neuropathological effects of KA-induced SE, and that rehabilitative cognitive enrichment may be partially beneficial.

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.

Neuropeptide Y signalling on hippocampal stem cells in health and disease

Neuropeptides are emerging as key components in the hippocampal neurogenic niche in health and disease, regulating many aspects of neurogenesis and the synaptic integration of newly generated neurons. This review focuses on the role of neuropeptide Y in the control of stem/precursor cells in the postnatal and adult hippocampus. It is likely that neuropeptide Y releasing interneurons are key sensors of neural activity, modulating neurogenesis appropriately. This is likely to be a fruitful area of research for extending our understanding of the control of stem cells in the normal and diseased brain.

Involvement of hippocampal serotonin and neuropeptide Y in depression induced by chronic unpredicted mild stress

Accumulated evidence indicates a role of the hippocampal 5-hydroxy-tryptamine (5-HT) and neuropeptide Y (NPY) in the response to stress and modulation of depression, but it is unclear whether and how the hippocampal 5-HT and NPY systems make contributions to chronic unpredicted mild stress (CUMS)-induced depression. Here we observed that rats receiving a variety of chronic unpredictable mild stressors for 3 weeks showed a variety of depression-like behavioral changes, including a significant reduction in body weight, sucrose preference, and locomotion, rearing and grooming in open field test, and a significant increase in immobility time in forced swimming test. These CUMS-induced behavioral changes were suppressed or blocked by intra-hippocampal injection of 5-HT (31.25 microg/microl) or NPY (10 microg/microl). These data suggest a critical role of reduced hippocampal 5-HT and NPY neurotransmission in CUMS-induced depression.

Nuclear factor-kappa B regulates seizure threshold and gene transcription following convulsant stimulation

We evaluated a role for the nuclear factor-kappa B (NF-kappaB) pathway in the regulation of seizure susceptibility and transcriptional activation during prolonged, continuous seizures (status epilepticus). Using two functionally distinct NF-kappaB inhibitors we observed a decrease in latency to onset of kainate-induced seizures and status epilepticus. To assess NF-kappaB transcriptional activation, we evaluated inhibitor kappa B alpha (IkappaBalpha) and brain-derived neurotrophic factor (bdnf) gene targets. Inhibition of the NF-kappaB signaling pathway significantly attenuated the increases in IkappaBalpha and bdnf mRNA levels that occurred during prolonged seizure activity, suggesting that the NF-kappaB pathway was involved in the up-regulation of these transcripts during status epilepticus. DNA-binding studies and chromatin immunoprecipitation assays using hippocampal extracts from animals with status epilepticus revealed that NF-kappaB subunits were associated with the candidate kappaB-binding elements within promoter 1 of the bdnf gene. The pattern of association was different for the p50 and p65 subunits supporting complex NF-kappaB modifications within promoter 1. In summary, our findings provide additional insights into the role of NF-kappaB transcriptional regulation in hippocampus following status epilepticus and suggest that NF-kappaB pathway activation contributes to seizure susceptibility.

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.

Injury-induced axonal sprouting in the hippocampus is initiated by activation of trkB receptors

Penetrating head injuries are often accompanied by the delayed development of post-traumatic epilepsy. Schaffer collateral transection leads to axonal sprouting and hyperexcitability in area CA3 of hippocampal slice cultures. We used this model to test the hypothesis that the injury-induced axonal sprouting results from increased neurotrophin signaling via trkB receptors near the lesion. Using rats and mice, we established that sprouting CA3 pyramidal cell axons are labeled with an antibody to the growth-associated protein GAP-43. We observed two- to threefold increases in the level of brain-derived neurotrophic factor and trkB protein in area CA3 by 24-48 h after Schaffer collateral transection, preceding the onset of axonal sprouting. Finally, we demonstrated that injury-induced axonal sprouting of GAP-43-immunoreactive axons is impaired in hippocampal slice cultures from mice expressing low levels of trkB receptors. We conclude that injury-induced axonal sprouting is initiated by brain-derived neurotrophic factor-trkB signaling and suggest that this process may be critical for the genesis of post-traumatic epilepsy.

Neuropeptide Y regulates recurrent mossy fiber synaptic transmission less effectively in mice than in rats: Correlation with Y2 receptor plasticity

A unique feature of temporal lobe epilepsy is the formation of recurrent excitatory connections among granule cells of the dentate gyrus as a result of mossy fiber sprouting. This novel circuit contributes to a reduced threshold for granule cell synchronization. In the rat, activity of the recurrent mossy fiber pathway is restrained by the neoexpression and spontaneous release of neuropeptide Y (NPY). NPY inhibits glutamate release tonically through activation of presynaptic Y2 receptors. In the present study, the effects of endogenous and applied NPY were investigated in C57Bl/6 mice that had experienced pilocarpine-induced status epilepticus and subsequently developed a robust recurrent mossy fiber pathway. Whole cell patch clamp recordings made from dentate granule cells in hippocampal slices demonstrated that, as in rats, applied NPY inhibits recurrent mossy fiber synaptic transmission, the Y2 receptor antagonist (S)-N2-[[1-[2-[4-[(R,S)-5,11-dihydro-6(6H)-oxodibenz[b,e]azepin-11-yl]-1-piperazinyl]-2-oxoethyl]cyclopentyl]acetyl]-N-[2-[1,2-dihydro-3,5(4H)-dioxo-1,2-diphenyl-3H-1,2,4-triazol-4-yl]ethyl]-argininamide (BIIE0246) blocks its action and BIIE0246 enhances synaptic transmission when applied by itself. Y5 receptor agonists had no significant effect. Thus spontaneous release of NPY tonically inhibits synaptic transmission in mice and its effects are mediated by Y2 receptor activation. However, both NPY and BIIE0246 were much less effective in mice than in rats, despite apparently equivalent expression of NPY in the recurrent mossy fibers. Immunohistochemistry indicated greater expression of Y2 receptors in the mossy fiber pathway of normal mice than of normal rats. Pilocarpine-induced status epilepticus markedly reduced the immunoreactivity of mouse mossy fibers, but increased the immunoreactivity of rat mossy fibers. Mossy fiber growth into the inner portion of the dentate molecular layer was associated with increased Y2 receptor immunoreactivity in rat, but not in mouse. These contrasting receptor changes can explain the quantitatively different effects of endogenously released and applied NPY on recurrent mossy fiber transmission in mice and rats.

Physical training decreases susceptibility to subsequent pilocarpine-induced seizures in the rat

Regular motor activity has many benefits for mental and physical condition but its implications for epilepsy are still controversial. In order to elucidate this problem, we have studied the effect of long-term physical activity on susceptibility to subsequent seizures. Male Wistar rats were subjected to repeated training sessions in a treadmill and swimming pool. Thereafter, seizures were induced by pilocarpine injections in trained and non-trained control groups. During the acute period of status epilepticus, we measured: (1) the latency of the first motor sign, (2) the intensity of seizures, (3) the time when it occurred within the 6-h observation period, and (4) the time when the acute period ended. All these behavioral parameters showed statistically significant changes suggesting that regular physical exercises decrease susceptibility to subsequently induced seizures and ameliorate the course of experimentally induced status epilepticus.

The influence of gonadal hormones on neuronal excitability, seizures, and epilepsy in the female

It is clear from both clinical observations of women, and research in laboratory animals, that gonadal hormones exert a profound influence on neuronal excitability, seizures, and epilepsy. These studies have led to a focus on two of the primary ovarian steroid hormones, estrogen and progesterone, to clarify how gonadal hormones influence seizures in women with epilepsy. The prevailing view is that estrogen is proconvulsant, whereas progesterone is anticonvulsant. However, estrogen and progesterone may not be the only reproductive hormones to consider in evaluating excitability, seizures, or epilepsy in the female. It seems unlikely that estrogen and progesterone would exert single, uniform actions given our current understanding of their complex pharmacological and physiological relationships. Their modulatory effects are likely to depend on endocrine state, relative concentration, metabolism, and many other factors. Despite the challenges these issues raise to future research, some recent advances have helped clarify past confusion in the literature. In addition, testable hypotheses have developed for complex clinical problems such as "catamenial epilepsy." Clinical and animal research, designed with the relevant endocrinological and neurobiological issues in mind, will help advance this field in the future.

What is the biological significance of BDNF mRNA targeting in the dendrites? Clues from epilepsy and cortical development

The neurotrophin brain-derived neurotrophic factor (BDNF) is a regulatory factor of several, partially contrasting, aspects of the biology of neural cells, including survival, growth, differentiation, and cell death. Regulation of the local availability of BDNF at distinct subcellular domains such as the cell soma, dendrites, axons, and spines appears to be the key to conferring spatial and temporal specificity of the different effects elicited by this neurotrophin. This article reviews recent findings in the context of epileptogenesis and visual cortex maturation that showed that different BDNF messenger RNA (mRNA) transcripts are localized at different subcellular locations in hippocampal and cortical neurons. It also reviews findings demonstrating that strong depolarizing stimuli, both in vitro and in vivo, elicit accumulation of BDNF mRNA and protein in the distal dendrites through a signaling pathway involving the activation of the N-methyl-D-aspartate and tyrosine kinase B receptors and an intracellular increase in Ca2+ concentration. Finally, this article proposes that the regulation of the delivery of BDNF mRNA and protein to the different subcellular domains--particularly the dendritic compartment--may represent a fundamental aspect of the processes of cellular and synaptic morphological rearrangements underlying epileptogenesis and postnatal development of the visual cortex.

Status epilepticus: pathophysiology and management in adults

As in Clark and Prout's classic work, we identify three phases of generalised convulsive status epilepticus, which we call impending, established, and subtle. We review physiological and subcellular changes that might play a part in the transition from single seizures to status epilepticus and in the development of time-dependent pharmacoresistance. We review the principles underlying the treatment of status epilepticus and suggest that prehospital treatment is beneficial, that therapeutic drugs should be used in rapid sequence according to a defined protocol, and that refractory status epilepticus should be treated with general anaesthesia. We comment on our preference for drugs with a short elimination half-life and discuss some therapeutic choices.

Plasticity of neuropeptide Y in the dentate gyrus after seizures, and its relevance to seizure-induced neurogenesis

In summary, NPY is clearly an important peptide in the adult rat dentate gyrus because it has the potential to influence synaptic transmission and neurogenesis. It may even have other functions, as yet undiscovered, mediated by glia or vasculature. The remarkable plasticity of NPY puts it in a position to allow dentate gyrus function to be modified in a changing environment. The importance of this plasticity in the context of epilepsy cannot be emphasized enough. It could help explain a range of observations about epilepsy that currently is poorly understood. For example, rapid increases in NPY could mediate postictal depression, the period of depression that can last for several hours after generalized seizures. It may mediate the "priming effect," which is a reduction in seizure threshold following an initial period of seizures. Finally, it could contribute to the resistance of dentate granule cells to degeneration after seizures. However, despite the focus in this review on seizure-induced changes, the changes described here also appear to occur after other types of manipulations, which considerably broadens the scope of NPY's role in the brain.

Brain-derived neurotrophic factor, phosphorylated cyclic AMP response element binding protein and neuropeptide Y decline as early as middle age in the dentate gyrus and CA1 and CA3 subfields of the hippocampus

The hippocampus is very susceptible to aging. Severely diminished dentate neurogenesis at middle age is one of the most conspicuous early changes in the aging hippocampus, which is likely linked to an early decline in the concentration of neurotrophic factors and signaling proteins that influence neurogenesis. We analyzed three proteins that are well-known to promote dentate neurogenesis and learning and memory function in the dentate gyrus and the hippocampal CA1 and CA3 subfields of young, middle-aged and aged F344 rats. These include the brain-derived neurotrophic factor (BDNF), the transcription factor phosphorylated cyclic AMP response element binding protein (p-CREB) and the neuropeptide neuropeptide Y (NPY). The BDNF was analyzed via ELISA and BDNF immunohistochemistry, the p-CREB through densitometric analysis of p-CREB immunopositive cells, and the NPY via stereological counting of NPY-immunopositive interneurons. We provide new evidence that the BDNF concentration, the p-CREB immunoreactivity and the number of NPY immunopositive interneurons decline considerably by middle age in both dentate gyrus and CA1 and CA3 subfields of the hippocampus. However, both BDNF concentration and NPY immunopositive interneuron numbers exhibit no significant decrease between middle age and old age. In contrast, the p-CREB immunoreactivity diminishes further during this period, which is also associated with reduced BDNF immunoreaction within the soma of dentate granule cells and hippocampal pyramidal neurons. Collectively, these results suggest that severely dampened dentate neurogenesis observed at middle age is linked at least partially to reduced concentrations of BDNF, p-CREB and NPY, as each of these proteins is a positive regulator of dentate neurogenesis. Dramatically diminished CREB phosphorylation (and persistently reduced levels of BDNF and NPY) at old age may underlie the learning and memory impairments observed during senescence.

Spontaneous release of neuropeptide Y tonically inhibits recurrent mossy fiber synaptic transmission in epileptic brain

In the pilocarpine model of temporal lobe epilepsy, mossy fibers coexpress the inhibitory transmitter neuropeptide Y (NPY) with glutamate. The effects of endogenous and applied NPY on recurrent mossy fiber synaptic transmission were investigated with the use of whole-cell voltage-clamp and field recordings in rat hippocampal slices. Applied NPY reversibly inhibited synaptic transmission at recurrent mossy fiber synapses on dentate granule cells but not at perforant path or associational-commissural synapses. It also reduced the frequency of miniature EPSCs (mEPSCs) in granule cells from epileptic, but not control, rats and depressed granule cell epileptiform activity dependent on the recurrent mossy fiber pathway. These actions of NPY were mediated by activation of presynaptic Y2 receptors. The Y2 receptor antagonist (S)-N2-[[1-[2-[4-[(R,S)-5,11-dihydro-6(6H)-oxodibenz[b,e]azepin-11-yl]-1-piperazinyl]-2-oxoethyl]cyclopentyl]acetyl]-N-[2-[1,2-dihydro-3,5(4H)-dioxo-1,2-diphenyl-3H-1,2,4-triazol-4-yl]ethyl]argininamide (BIIE0246) not only blocked the effects of NPY but also enhanced recurrent mossy fiber synaptic transmission, the frequency of mEPSCs, and the magnitude of mossy fiber-evoked granule cell epileptiform activity when applied by itself. Several observations supported the selectivity of BIIE0246. These results suggest that even the spontaneous release of NPY (or an active metabolite) from recurrent mossy fibers is sufficient to depress glutamate release from this pathway. Tonic release of NPY accounts at least partially for the low probability of glutamate release from recurrent mossy fiber terminals, impedes the ability of these fibers to synchronize granule cell discharge, and may protect the hippocampus from seizures that involve the entorhinal cortex. This pathway may synchronize granule cell discharge more effectively in human brain than in rat because of its lower expression of NPY.

The seizure-related phenotype of brain-derived neurotrophic factor knockdown mice

The present investigation focused on the seizure-related phenotype of mice lacking one allele of brain-derived neurotrophic factor. Thresholds for producing seizures in brain-derived neurotrophic factor wild-type and brain-derived neurotrophic factor heterozygous mice were compared in several seizure models, including thresholds for electrically-induced clonic, tonic-clonic and 6 Hz limbic seizures, as well as seizures induced chemically by kainate, pilocarpine and pentylenetetrazol. In addition, the rate of amygdala kindling, as well as pre- and post-kindling seizure thresholds was determined. Seizure thresholds for clonic and tonic-clonic electrically induced seizures did not differ between brain-derived neurotrophic factor wild-type and heterozygous mice. However, heterozygous mice had higher thresholds for 6 Hz limbic seizures compared with wild-type mice. Heterozygous mice also required larger doses of kainate to produce limbic seizures. Somewhat surprisingly, heterozygous mice required significantly lower doses of pilocarpine to produce limbic seizures. However, heterozygous mice required a higher dose of pentylenetetrazol to induce twitches, but not clonic seizures, compared with wild-type mice. In addition, heterozygous mice required more current to elicit focal afterdischarges in the amygdala both pre- and post-kindling than did wild-type mice, and, heterozygous mice kindled more slowly than wild-type mice. The present findings provide additional support for the hypothesis that brain-derived neurotrophic factor is involved not only in normal excitability, but may also be involved in abnormal excitability such as occurs in seizure disorders and epileptogenesis.

Growth-associated Protein 43 Expression in Hippocampal Molecular Layer of Chronic Epileptic Rats Treated with Cycloheximide

PURPOSE

GAP43 has been thought to be linked with mossy fiber sprouting (MFS) in various experimental models of epilepsy. To investigate how GAP43 expression (GAP43-ir) correlates with MFS, we assessed the intensity (densitometry) and extension (width) of GAP43-ir in the inner molecular layer of the dentate gyrus (IML) of rats subject to status epilepticus induced by pilocarpine (Pilo), previously injected or not with cycloheximide (CHX), which has been shown to inhibit MFS.

METHODS

CHX was injected before the Pilo injection in adult Wistar rats. The Pilo group was injected with the same drugs, except for CHX. Animals were killed between 30 and 60 days later, and brain sections were processed for GAP43 immunohistochemistry.

RESULTS

Densitometry showed no significant difference regarding GAP43-ir in the IML between Pilo, CHX+Pilo, and control groups. However, the results of the width of the GAP43-ir band in the IML showed that CHX+Pilo and control animals had a significantly larger band (p = 0.03) as compared with that in the Pilo group.

CONCLUSIONS

Our current finding that animals in the CHX+Pilo group have a GAP43-ir band in the IML, similar to that of controls, reinforces prior data on the blockade of MFS in these animals. The change in GAP43-ir present in Pilo-treated animals was a thinning of the band to a very narrow layer just above the granule cell layer that is likely to be associated with the loss of hilar cell projections that express GAP-43.

Area-specific effects of brain-derived neurotrophic factor (BDNF) genetic ablation on various neuronal subtypes of the mouse brain

The effects of brain-derived neurotrophic factor (BDNF) on the development of presynaptic terminals and of neuronal subtypes in various brain areas were studied in BDNF-knockout (BDNF-/-) mice at postnatal days 15-17. Western analysis revealed no changes in the overall amount of a variety of synaptic proteins in BDNF-/- mice as compared to wild type mice. In addition, the complex between the vesicular proteins, synaptophysin and synaptobrevin, as well as their respective homodimers were unaltered. Moreover, no changes in the density of neurons were found in, e.g., the CA3 region of the hippocampus and the nucleus nervi facialis of BDNF-/- mice. However, cholinergic cells were reduced by 20% in the medial septum of BDNF-/- mice associated with a decrease in the activity of choline acetyltransferase and protein levels of nerve growth factor in the hippocampus by 16% and 44%, respectively. In the striatum, however, the total number of cholinergic cells were comparable in both groups, although the activity of choline acetyltransferase was decreased by 46%. In GABAergic interneurons, the expression of neuropeptides in various brain areas was differentially affected by BDNF deletion as revealed by immunohistochemistry. In the hippocampus and cortex of BDNF-/- mice, the density of neuropeptide Y-, somatostatin-, and parvalbumin-immunoreactive cells was drastically reduced, whereas the density of calretinin-positive cells was increased. The extent of these changes in neuropeptide-containing cells varied among hippocampal subregions. In the striatum, only the density of parvalbumin-immunoreactive cells was decreased by approximately 45%. In conclusion, BDNF deficiency is accompanied by a differential dysregulation in the expression of neuropeptides and calcium-binding proteins in otherwise intact GABAergic and glutamatergic neurons in a region-specific manner.

N-methyl-D-aspartic acid-induced and Ca-dependent neuronal swelling and its retardation by brain-derived neurotrophic factor in the epileptic hippocampus

Dentate granule cell (DGC) swelling was studied by imaging changes in light transmittance from hippocampal slices in the rat pilocarpine model of epilepsy and human epileptic specimens. Brief bath-application of N-methyl-D-aspartic acid (NMDA) induced swelling in the control rat DGC (physiological swelling). Physiological swelling was short-lasting, and rapidly recovered upon removal of NMDA. In contrast, the swelling induced in the pilocarpine-treated rat hippocampus and human epileptic hippocampus (epileptic swelling) was long-lasting, and often recovered slowly over an hour. Both types of swelling were blocked by the NMDA receptor (NMDAR) antagonist, D-APV, suggesting that they shared the same induction mechanism. However, the swellings differed in their sensitivity to a calcium chelator, 1.2-bis(2-aminophenoxy)ethane-N,N,N,N-tetra-acetate (BAPTA), and an endoplasmic reticulum (ER) Ca2+-ATPase inhibitor, thapsigargin (TG). BAPTA and TG affected only epileptic swelling, and physiological swelling was spared. This suggested that the NMDAR-induced epileptic swelling might involve an additional mechanism for its maintenance, likely recruiting ER Ca2+ stores. Brain-derived neurotrophic factor (BDNF) slightly attenuated physiological swelling, and blocked epileptic swelling. The present study suggests a functional link between the activation of NMDAR and a release of Ca2+ from internal stores during the induction of epileptic swelling, and a neuroprotective role of BDNF on the NMDAR-induced swelling in the epileptic hippocampus.

Neuropeptide Y suppresses absence seizures in a genetic rat model

Evidence from studies in rodents and humans support an anti-seizure action of neuropeptide Y (NPY) in focal, acquired epilepsy. However, the effects of NPY in generalized genetic epilepsy remain unexplored. In this study, adult male Genetic Absence Epilepsy Rats of Strasbourg (GAERS) were implanted with extradural electrodes and an intracerebroventricular (icv) cannula. Six and 12 nmol NPY or vehicle was administered icv in a random order (n=6), and the effect of NPY on seizure activity quantitated from a 90-min EEG recording. A rapid onset and sustained seizure suppression was observed following NPY treatment compared to vehicle, with both 6 and 12 nmol NPY having a significantly decreased mean percentage time in seizure (5.7 +/- 1.4% and 5.0 +/- 1.7% vs. 15.8 +/- 3.4%) and mean number of seizures per minute (0.5 +/- 0.1 and 0.4 +/- 0.1 vs. 1.1 +/- 0.1). There was no significant difference between the degree of seizure suppression after 6 and 12 nmol NPY. The results of this study demonstrate that NPY suppresses absence seizures in GAERS. This suggests that NPY modulates pathological oscillatory thalamocortical activity and may represent a new therapeutic approach for the treatment of generalized epilepsies.

Changes in phosphorylation of the NMDA receptor in the rat hippocampus induced by status epilepticus

Systemic administration of pilocarpine preceded by lithium induces status epilepticus (SE) that results in neurodegeneration and may lead to the development of spontaneous recurrent seizures. We investigated the effect of Li/pilocarpine-induced SE on phosphorylation of the NMDA receptor in rat hippocampus. Phosphorylation of NR1 by PKC on Ser890 was decreased to 45% of control values immediately following 1 h of SE. During the first 3 h following the termination of SE, phosphorylation of Ser890 increased 4-fold before declining to control values by 24 h. Phosphorylation of NR1 by PKA was also depressed relative to controls immediately following SE and transiently increased above control values upon the termination of SE. SE was accompanied by a general increase in tyrosine phosphorylation of hippocampal proteins that lasted for several hours following the termination of seizures. Tyrosine phosphorylation of the NR2A and NR2B subunits of the NMDAR increased 3-4-fold over control values during SE, continued to increase during the first hour following SE and then declined to control levels by 24 h. SE resulted in the activation of Src and Pyk2 associated with the postsynaptic apparatus, suggesting a role for these enzymes in the SE-induced increase in tyrosine phosphorylation. Changes in phosphorylation of the NMDA receptor may play a role in the pathophysiological consequences of SE.

Hippocampal neurotrophin levels after injury: Relationship to the age of the hippocampus at the time of injury

Aging impairs the competence of the hippocampus for synaptic reorganization after injury. This potentially is due to the inability of the aging hippocampus to up-regulate the critical neurotrophic factors for prolonged periods after injury to levels at which they can stimulate neurite outgrowth and facilitate synaptic reorganization. We hypothesize that the concentrations of neurotrophins in the hippocampus after injury depend on the age at the time of injury. We quantified the concentrations of brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF), and neurotrophin-3 (NT-3) in the hippocampus of young, middle-aged, and aged Fischer 344 rats at 4 days after kainic acid (KA)-induced injury. In comparison with the age-matched intact hippocampus, the KA-lesioned hippocampus exhibited increased levels of BDNF and NGF in all three age groups. In contrast, the NT-3 concentration was unaltered after KA lesion. Notwithstanding similar percentage increases in BDNF after injury, the lesioned middle-aged and aged hippocampus contained 45-52% less BDNF than the lesioned young hippocampus. NGF and NT-3 levels after injury were comparable across the three age groups, however. Furthermore, lower BDNF concentration in the injured aging hippocampus was associated with normal astrocytic response but significantly diminished microglial reaction. Thus, in comparison with the injured young hippocampus, the injured aging hippocampus contains considerably less BDNF but similar levels of NGF and NT-3. Lower BDNF levels in the injured aging hippocampus might underlie the diminished spontaneous healing response observed in the aging hippocampus after injury, particularly in terms of synaptic reorganization and dentate neurogenesis.