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Query: UMLS:C0036572 (seizures)
 80,221 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
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PMID:Kindling and status epilepticus models of epilepsy: rewiring the brain. 1519 78

Epileptogenesis is the process whereby a normal brain becomes epileptic. We hypothesized that the neurotrophin brain-derived neurotrophic factor (BDNF) activates its receptor, TrkB, in the hippocampus during epileptogenesis and that BDNF-mediated activation of TrkB is required for epileptogenesis. We tested these hypotheses in Synapsin-Cre conditional BDNF(-/-) and TrkB(-/-) mice using the kindling model. Despite marked reductions of BDNF expression, only a modest impairment of epileptogenesis and increased hippocampal TrkB activation were detected in BDNF(-/-) mice. In contrast, reductions of electrophysiological measures and no behavioral evidence of epileptogenesis were detected in TrkB(-/-) mice. Importantly, TrkB(-/-) mice exhibited behavioral endpoints of epileptogenesis, tonic-clonic seizures. Whereas TrkB can be activated, and epileptogenesis develops in BDNF(-/-) mice, the plasticity of epileptogenesis is eliminated in TrkB(-/-) mice. Its requirement for epileptogenesis in kindling implicates TrkB and downstream signaling pathways as attractive molecular targets for drugs for preventing epilepsy.
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PMID:Conditional deletion of TrkB but not BDNF prevents epileptogenesis in the kindling model. 1523 15

Aberrant sprouting and synaptic reorganization of the mossy fiber (MF) axons are commonly found in the hippocampus of temporal lobe epilepsy patients and result in the formation of excitatory feedback loops in the dentate gyrus, a putative cellular basis for recurrent epileptic seizures. Using ex vivo hippocampal cultures, we show that prolonged hyperactivity induces MF sprouting and the resultant network reorganizations and that brain-derived neurotrophic factor (BDNF) is necessary and sufficient to evoke these pathogenic plasticities. Hyperexcitation induced an upregulation of BDNF protein expression in the MF pathway, an effect mediated by L-type Ca2+ channels. The neurotrophin receptor tyrosine kinase (Trk)B inhibitor K252a or function-blocking anti-BDNF antibody prevented hyperactivity-induced MF sprouting. Even under blockade of neural activity, local application of BDNF to the hilus, but not other subregions, was capable of initiating MF axonal remodeling, eventually leading to dentate hyperexcitability. Transfecting granule cells with dominant-negative TrkB prevented axonal branching. Thus, excessive activation of L-type Ca2+ channels causes granule cells to express BDNF, and extracellularly released BDNF stimulates TrkB receptors present on the hilar segment of the MFs to induce axonal branching, which may establish hyperexcitable dentate circuits.
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PMID:Brain-derived neurotrophic factor induces hyperexcitable reentrant circuits in the dentate gyrus. 1531 47

Environmental restriction or deprivation early in development can induce social, cognitive, affective, and motor abnormalities similar to those associated with autism. Conversely, rearing animals in larger, more complex environments results in enhanced brain structure and function, including increased brain weight, dendritic branching, neurogenesis, gene expression, and improved learning and memory. Moreover, in animal models of CNS insult (e.g., gene deletion), a more complex environment has attenuated or prevented the sequelae of the insult. Of relevance is the prevention of seizures and attenuation of their neuropathological sequelae as a consequence of exposure to a more complex environment. Relatively little attention, however, has been given to the issue of sensitive periods associated with such effects, the relative importance of social versus inanimate stimulation, or the unique contribution of exercise. Our studies have examined the effects of environmental complexity on the development of the restricted, repetitive behavior commonly observed in individuals with autism. In this model, a more complex environment substantially attenuates the development of the spontaneous and persistent stereotypies observed in deer mice reared in standard laboratory cages. Our findings support a sensitive period for such effects and suggest that early enrichment may have persistent neuroprotective effects after the animal is returned to a standard cage environment. Attenuation or prevention of repetitive behavior by environmental complexity was associated with increased neuronal metabolic activity, increased dendritic spine density, and elevated neurotrophin (BDNF) levels in brain regions that are part of cortical-basal ganglia circuitry. These effects were not observed in limbic areas such as the hippocampus.
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PMID:Environmental complexity and central nervous system development and function. 1536 62

Brain-derived neurotrophic factor (BDNF) belongs to the neurotrophin family which interacts with high-affinity protein kinase receptors (Trk) and the unselective p75(NGFR) receptor. The BDNF gene has a complex structure with multiple regulatory elements and four promoters that are differentially expressed in central or peripheral tissue. BDNF expression is regulated by neuronal activity or peripheral hormones. Neurotrophins regulate the survival and differentiation of neurons during development but growing evidence indicates that they are also involved in several functions in adulthood, including plasticity processes. BDNF expression in the central nervous system (CNS) is modified by various kinds of brain insult (stress, ischemia, seizure activity, hypoglycemia, etc.) and alterations in its expression may contribute to some pathologies such as depression, epilepsy, Alzheimer's, and Parkinson's disease. Apart from very traumatic situations, the brain functioning is resilient to stress and capable of adaptive plasticity. Neurotrophins might act as plasticity mediators enhancing this trait which seems to be crucial in adaptive processes. In addition to documenting all of the topics mentioned above in the CNS, we review the state of the art concerning neurotrophins and their receptors, including our personal contribution which is essentially focused on the stress response.
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PMID:Physiology of BDNF: focus on hypothalamic function. 1557 56

Apart from the essential role of 1alpha,25-dihydroxyvitamin D3 in calcium and phosphorus metabolism, this compound and its analogs are involved in regulating the functions of the central nervous and immune systems. Active forms of vitamin D3 have been reported to stimulate neurotrophin gene expression and to prevent neuronal damage against a variety of insults. In the present study, we evaluated the effects of PRI-2191-a low-calcemic analog of 1alpha,25-dihydroxyvitamin D3 (50 ng/kg i.p., once daily for 8 days) on seizure-related neuronal degeneration, changes in some brain gene expression and immune system activity. Seizures were induced by pilocarpine (400 mg/kg; i.p.) administration. An in situ hybridization study showed that the pilocarpine-induced seizures led to time-dependent changes in the brain-derived neurotrophic factor (BDNF), heat shock protein 70 (HSP-70) and prepro-thyreoliberin (prepro-TRH) gene expression in several cortical and hippocampal regions. The maximal induction of gene expression was 3 h for BDNF and 24 h for HSP-70 and prepro-TRH; however, only in the case of prepro-TRH that effect was long-lasting. PRI-2191 alone had no effect on gene expression, but it enhanced the seizure-evoked expression of HSP-70, had an opposite effect on BDNF mRNA level and did not affect prepro-TRH mRNA level. Moreover, PRI-2191 had a moderate inhibitory effect on the seizure-related hippocampal damage in the CA1 field only. An immunological study revealed that PRI-2191 reversed the seizure-induced decrease in the proliferative activity of splenocytes and their ability to produce interferon-gamma. Summing up, the present study demonstrated that subchronic administration of PRI-2191 significantly modulated the seizure-related changes in both the brain and the peripheral immune system of rats.
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PMID:Effects of PRI-2191--a low-calcemic analog of 1,25-dihydroxyvitamin D3 on the seizure-induced changes in brain gene expression and immune system activity in the rat. 1578 Oct 40

To study the role of neurotrophin-responsive neurons in brain growth and developmental resistance to seizure-induced injury, we infused saporin-conjugated 192-IgG (192 IgG-saporin), a monoclonal antibody directed at the P75 neurotrophin receptors (p75(NTR)), into the ventricles of postnatal day 8 (P8) rat pups. 7-10 days after immunotoxin treatment, loss of p75(NTR) immunoreactivity was associated with depletion of basal forebrain cholinergic projection to the neocortex and hippocampus. Kainic acid (KA)-induced seizures on P15 resulted in hippocampal neuronal injury in the majority of toxin-treated animals (13/16), but only rarely in saline-injected controls (2/25) (P < 0.001). In addition, widespread cerebral atrophy and a significant decrease in brain weight with preserved body weight were observed. Volumetric analysis of the hippocampal hilar region revealed a 2-fold reduction in perikaryal size and a 1.7-fold increase in cell packing density after 192 IgG-saporin injection. These observations indicate that neurotrophin-responsive neurons including basal forebrain magnocellular cholinergic neurons may be critical for normal brain growth and play a protective role in preventing excitotoxic neuronal injury during development.
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PMID:Susceptibility to seizure-induced injury and acquired microencephaly following intraventricular injection of saporin-conjugated 192 IgG in developing rat brain. 1602 71

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.
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PMID:To BDNF or not to BDNF: that is the epileptic hippocampus. 1606 15

Recent advances in our understanding of the actions of sex steroids on the brain and the pathophysiology of depression have provided a hypothetical framework that may functionally connect epilepsy, ovarian hormone levels, and depression. The hippocampus plays a critical role in both seizure activity and mood disorders, which suggests that pathology in this area of the brain might provide a link between epilepsy and depression. Recent findings support the view that neurogenesis is not the only factor that contributes to the pathomechanism of depression and antidepressant responses, which may involve other hippocampal cellular or molecular changes, or both. Specifically, remodeling of the hippocampal spine synapses may play a significant role in the neurobiology of depression and the effects of antidepressant therapy. Because the effects of estrogens on hippocampal synaptogenesis parallel those of antidepressants, loss of estrogen appears to be a critical contributor to the etiology of depressive disorders. The increased incidence of depression observed in women with epilepsy might therefore reflect a hormonal deficiency state because epilepsy is frequently associated with defects in reproductive function. In women with catamenial epilepsy, changes in gonadal steroid production are seen to link seizure frequency with reproductive state, emphasizing the importance of gonadal steroid levels not only in depression but also in seizure activity. Paradoxical features of epilepsy, i.e., seizure-induced increases in hippocampal neurotrophin expression and neurogenesis, suggest that the most important factor in the neurobiology of depression might be the extent to which the hippocampus can adapt appropriately to changes in the environment through alterations in hippocampal synaptic connectivity.
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PMID:Neurologic links between epilepsy and depression in women: is hippocampal neuroplasticity the key? 1656 37

In this report, we provide direct demonstration that the neurotrophin nerve growth factor (NGF) is released in the extracellular space in an activity-dependent manner in its precursor form (proNGF) and that it is in this compartment that its maturation and degradation takes place because of the coordinated release and the action of proenzymes and enzyme regulators. This converting protease cascade and its endogenous regulators (including tissue plasminogen activator, plasminogen, neuroserpin, precursor matrix metalloproteinase 9, and tissue inhibitor metalloproteinase 1) are colocalized in neurons of the cerebral cortex and released upon neuronal stimulation. We also provide evidence that this mechanism operates in in vivo conditions, as the CNS application of inhibitors of converting and degrading enzymes lead to dramatic alterations in the tissue levels of either precursor NGF or mature NGF. Pathological alterations of this cascade in the CNS might cause or contribute to a lack of proper neuronal trophic support in conditions such as cerebral ischemia, seizure and Alzheimer's disease or, conversely, to excessive local production of neurotrophins as reported in inflammatory arthritis pain.
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PMID:Activity-dependent release of precursor nerve growth factor, conversion to mature nerve growth factor, and its degradation by a protease cascade. 1661 25


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