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At least 415 records · Page 23Linked to original sources
PubMed2000

Increased synchrony with increase of a low-threshold calcium conductance in a model thalamic network: a phase-shift mechanism.

A computer model of a thalamic network was used in order to examine the effects of an isolated augmentation in a low-threshold calcium current. Such an isolated augmentation has been observed in the reticular thalamic (RE) nucleus of the genetic absence epilepsy rat from the Strasbourg (GAERS) model of absence epilepsy. An augmentation of the low-threshold calcium conductance in the RE neurons (gTs) of the model thalamic network was found to lead to an increase in the synchronized firing of the network. This supports the hypothesis that the isolated increase in gTs may be responsible for epileptic activity in the GAERS rat. The increase of gTs in the RE neurons led to a slight increase in the period of the isolated RE neuron firing. In contrast, the low-threshold spike of the RE neuron remained relatively unchanged by the increase of gTs. This suggests that the enhanced synchrony in the network was primarily due to a phase shift in the firing of the RE neurons with respect to the thalamocortical neurons. The ability of this phase-shift mechanism to lead to changes in synchrony was further examined using the model thalamic network. A similar increase in the period of RE neuron oscillations was obtained through an increase in the conductance of the calcium-mediated potassium channel. This change was once again found to increase synchronous firing in the network.

Action Potentials↗
PubMed2004

Lovastatin exacerbates atypical absence seizures with only minimal effects on brain sterols.

AY-9944 (AY) exacerbates chronic recurrent seizures in rats that are analogous to atypical absence epilepsy in humans. The mechanism by which AY affects the slow spike-and-wave discharges associated with these seizures is not known, but is thought to involve inhibition of cholesterol synthesis. We tested the hypothesis that seizures seen with AY are due to significant reduction in brain cholesterol and/or elevated brain 7-dehydrocholesterol by assessing whether three other cholesterol synthesis inhibitors mimic AY seizures in rats. Effects of AY on brain sterols and spike-and-wave discharge duration were compared with those of two other late-stage cholesterol inhibitors [BM 15.766 (BM) and U18666A (UA)] and to an HMG-CoA reductase (early-stage cholesterol) inhibitor, lovastatin. With BM or UA, prolongation of seizure duration and brain sterol changes was similar to that caused by AY. AY effects on both brain sterols and seizure duration were dose-related. Lovastatin, with or without concurrent AY, mimicked AY seizures but reduced brain cholesterol by <10% and did not significantly change brain 7-dehydrocholesterol. Either lovastatin has a different mechanism of action than these late-stage cholesterol inhibitors or the brain sterol changes are not directly responsible for seizures in this model.

Animals↗
PubMed1998

[Pharmacology of the GABA receptor functions in the central nervous systems].

gamma-Aminobutyric acid (GABA) is a major inhibitory neurotransmitter in the central nervous system. GABA receptors have been classified into at least two categories, GABA(A) receptors, which are heterogeneous multimeric ligand-gated Cl channels, and GABA(B) receptors, which are coupled to G-proteins. GABA(B) receptors have not only a physiological role in synaptic transmission, but also are important in pathological conditions associated with absence epilepsy, cognitive disorders and nociception. This review describes our current knowledge of the neuropharmacology and neurochemistry of GABA(B) receptors, including their heterogeneity as well as the therapeutic potential of the drugs which interact with these sites.

Animals↗
PubMed2006

Aberrant GABA(A) receptor expression in the dentate gyrus of the epileptic mutant mouse stargazer.

Stargazer (stg) mutant mice fail to express stargazin [transmembrane AMPA receptor regulatory protein gamma2 (TARPgamma2)] and consequently experience absence seizure-like thalamocortical spike-wave discharges that pervade the hippocampal formation via the dentate gyrus (DG). As in other seizure models, the dentate granule cells of stg develop elaborate reentrant axon collaterals and transiently overexpress brain-derived neurotrophic factor. We investigated whether GABAergic parameters were affected by the stg mutation in this brain region. GABA(A) receptor (GABAR) alpha4 and beta3 subunits were consistently upregulated, GABAR delta expression appeared to be variably reduced, whereas GABAR alpha1, beta2, and gamma2 subunits and the GABAR synaptic anchoring protein gephyrin were essentially unaffected. We established that the alpha4 betagamma2 subunit-containing, flunitrazepam-insensitive subtype of GABARs, not normally a significant GABAR in DG neurons, was strongly upregulated in stg DG, apparently arising at the expense of extrasynaptic alpha4 betadelta-containing receptors. This change was associated with a reduction in neurosteroid-sensitive GABAR-mediated tonic current. This switch in GABAR subtypes was not reciprocated in the tottering mouse model of absence epilepsy implicating a unique, intrinsic adaptation of GABAergic networks in stg. Contrary to previous reports that suggested that TARPgamma2 is expressed in the dentate, we find that TARPgamma2 was neither detected in stg nor control DG. We report that TARPgamma8 is the principal TARP isoform found in the DG and that its expression is compromised by the stargazer mutation. These effects on GABAergic parameters and TARPgamma8 expression are likely to arise as a consequence of failed expression of TARPgamma2 elsewhere in the brain, resulting in hyperexcitable inputs to the dentate.

Animals↗
PubMedDate not supplied

[Anxiety and behavior in WAG/Rij strain rats with genetically induced absence attacks].

Behavior of nonlinear rats and animals from Wistar and WAG/Rij (with inborn generalized absence epilepsy) strains was examined in the elevated plus-maze and the hole board. WAG/Rij rats demonstrated low exploratory behavior in both tests. In the elevated plus-maze, WAG/Rij rats were more balanced and more anxious than Wistar and nonlinear rats. Administration of ethosuximide completely eliminated spike-wave discharges but did not change behavioral interstrain differences. Since the spike-wave patterns develop in WAG/Rij at the age of 3 months, the behavior of young (2-moth-old) pups from different strains was compared and significant differences were revealed. Correlation between the genetically defined features (spike-wave discharges) and behavioral peculiarities in WAG/Rij rats is supposed.

Aging↗
PubMed2000

Modulation of absence seizures by the GABA(A) receptor: a critical rolefor metabotropic glutamate receptor 4 (mGluR4).

Experimental absence seizures are associated with perturbations in the presynaptic release of GABA and glutamate within thalamocortical circuitry. The release of both glutamate and GABA is regulated by group III metabotropic glutamate receptors (mGluRs). Therefore, we examined the susceptibility of mice lacking the mGluR4 subtype of mGluR (mGluR4(-/-)) versus their wild-type controls (mGluR4(+/+)) to absence seizures induced either by gamma-hydroxybutyrate (GHB) or the GABA(B) agonist (-) baclofen or by low doses of the GABA(A) receptor (GABA(A)R) antagonists pentylenetetrazole, bicuculline, or picrotoxin. There was no difference between mGluR4(-/-) and mGluR4(+/+) mice in threshold to absence seizures induced by either GHB or (-) baclofen. In contrast, the mGluR4(-/-) mice were markedly resistant to absence seizures induced by low doses of GABA(A)R antagonists. No differences were observed between mGluR4(-/-) and mGluR4(+/+) mice in threshold to clonic or tonic seizures induced by higher doses of GABA(A)R antagonists, strychnine, or electroshock, indicating that seizure resistance in the mGluR4(-/-) mice was restricted solely to absence seizures. The resistance of mGluR4(-/-) mice to absence seizures induced by GABA(A)R antagonists was mimicked by bilateral administration of a mGluR4 antagonist into the nucleus reticularis thalami (nRT) of mGluR4(+/+) mice. Conversely, intra-nRT administration of a mGluR4 agonist in mGluR4(+/+) mice exacerbated GABA(A)R-induced absence seizures. These data indicate that the presence of mGluR4 within nRT is critical to GABAergic modulation of thalamocortical synchronization in normal and pathological states, such as generalized absence epilepsy.

Animals↗
PubMedDate not supplied

[Effect of dopamine enriched ganglion xenografts from the immature CNS of Helix aspersa L. snail on the learning time during acquisition of an operant food-procuring reflex in WAG/RIJ rats].

Xenografts from the ganglia of a newborn terrestrial snail Helix aspersa L. were implanted into the right parietal area of the brain cortex of WAG/Rij rats with absence epilepsy. Rats with implanted xenografts were trained for reaching a food ball from a tube (reaching test). It was shown that the mean duration of each leaning stage and total time necessary for acquisition of the instrumental conditioning (till the learning criterion) were shorter in animals with xenografts than in control groups of animals.

Adaptation, Physiological↗
PubMed2003

Inhibitory interconnections control burst pattern and emergent network synchrony in reticular thalamus.

Inhibitory connections between neurons of the thalamic reticular (RE) nucleus are thought to help prevent spike-wave discharge (SWD), characteristic of generalized absence epilepsy, in thalamic and thalamocortical circuits. Indeed, oscillations in thalamic slices resemble SWD when intra-RE inhibition is blocked and are suppressed when intra-RE inhibition is enhanced. To elucidate the cellular mechanisms underlying these network changes, we recorded from RE cells during oscillations in thalamic slices and either blocked intra-RE inhibition with picrotoxin or enhanced it with clonazepam. We found that intra-RE inhibition limits the number and synchrony, but not the duration, of RE cell bursts. We then performed simulations that demonstrate how inhibition can shift network activity into a desynchronized mode simply by vetoing occasional RE cell bursts. In contrast, when intra-RE inhibition is blocked, RE cells burst synchronously, enabling even short RE cell bursts to promote epileptogenesis in two ways: first, by activating GABA(B) receptors, and second, through the GABA(B) receptor-independent emergence of network synchrony.

Action Potentials↗
PubMed2005

[Characteristics of small neurons in the reticular thalamic nucleus of WAG/Rij rat].

The aim of this investigation was to study the ultrastructure of small neurons in the reticular thalamic nucleus (RTN) in rats of the WAG/Rij strain, which is a recognized model for human absence epilepsy. 24 rats were used in these studies. The paraffin sections of the brain taken from 10 rats were stained with Nissl's cresyl violet and were used for the study of neuronal cytoarchitecture and cytological characteristics. For electron microscopic study, RTN was dissected under microscopic control and fixed in cooled 2.5% glutaraldehyde solution in 0.1 M sodium phosphate buffer (pH 7.4). Small neurons were found to constitute 5-8% of the total number of RTN neurons. They had ovoid cell body, scanty pale-staining cytoplasm, often were seen in pairs. The ultrastructure of these neurons was characterized by poor development of membranes, axonal branching close to the cell body, multiple contacts of axon with cell body and dendrites. It is suggested that the neurons described are short-axonal.

Animals↗
PubMed2005

[Ion channels and neurological disorders].

Ion channels are a family of protein molecules that mediate the electrical activities, including synaptic transmission, of the nervous system. Recent studies revealed that genetic mutations are associated with various neurological disorders. Although identification of the genetic defects is certainly a big step towards elucidation of pathophysiology and development of therapeutic strategies, it is not always easy to correlate the genetic abnormalities with the neurological symptoms. Recently, we have analyzed the pathophysiological mechanism of cerebellar ataxia and absence epilepsy in calcium channel mutant mice. The results demonstrate diversity of the cellular and network changes caused by the genetic defects. Understanding the underlying mechanism of the diverse changes would contribute to better understanding of human neurological diseases.

Animals↗
PubMed2005

Typical childhood absence seizures are associated with thalamic activation.

Functional MRI with simultaneously acquired EEG (fMRI/EEG) can identify areas of signal change associated with interictal discharges. We report the fMRI/EEG study of a child with newly-diagnosed IGE, performed prior to the start of antiepileptic medication. The 7-years-old girl had very frequent absences, associated with eyelid myoclonia. Her EEG showed frequent, typical 3/sec discharges. Functional MRI was performed with a 3T scanner using whole brain gradient echo-planar imaging, and the EEG was recorded with 18, non-metallic, scalp electrodes. Ten bursts of generalized discharges were captured during 30 minutes fMRI/EEG acquisition. The bursts lasted 3.4 (SD +/- 0.6) seconds. Event-related analysis was performed with SPM2 and iBrain software. Functional MRI showed prominent, bilateral thalamic activation, and less pronounced areas of cortical activation and deactivation. This study demonstrates thalamic activation in typical, untreated childhood absence epilepsy. The cortical signal change may be related to a thalamo-cortical circuit.

Brain Mapping↗
PubMed1987

[Fatal hepatic failure in a normally developed 5-year-old boy caused by VPA monotherapy].

A five-year-old, normally developed boy who had been healthy except for an absence epilepsy prior to valproate (VPA) treatment died 16 weeks after the introduction of VPA-monotherapy due to liver failure and intractable bleeding disorder. This case emphasizes that the restriction of VPA-therapy to children of more than two years of age, on monotherapy, and without evidence of other diseases or retardation does not exclude fatal complications. Until today world-wide about 100 patients have died during VPA-treatment.

Chemical and Drug Induced Liver Injury↗
PubMedDate not supplied

[Clinical electroencephalographic diagnosis of myoclonus in various types of epilepsy].

Twenty-six epileptics, 16 males and 10 females, with various types of myoclonia were studied. In all patients routine EEG, 24-hour EEG and/or Video-EEG, also with EMG recording were done. Combined detailed clinical-electrophysiological analysis was possible owing to the modern methods of diagnostic examinations and it enabled five epileptic syndromes to be isolated in this group, that is: childhood epilepsy with absence attacks (CAE), juvenile absence epilepsy (JAE), juvenile myoclonic epilepsy (JME), progressive myoclonic epilepsy (PME) and photogenic epilepsy. Clinical features of four types of myoclonia occurring in these cases are described in detail since they make possible differential diagnosis of epilepsy syndromes. This is important since the diagnostic and therapeutic methods differ in these cases, and similarly the prognosis varies in these epilepsy types. Stress is laid on juvenile myoclonic epilepsy which is as yet too rarely or erroneously diagnosed.

Adolescent↗
PubMed1994

[Polygraphical sleep study on typical absence: relationship between the effect of sodium valproate and nigrostriatal function].

In order to clarify the mechanism of the effect of sodium valproate (VPA) on absence seizures, we performed sleep polygraph recordings in 10 patients with typical absence. VPA was effective in six cases (group A), partially effective in two (group B), and ineffective in two (group C). In 5 of 9 cases, the tonic sleep components were abnormal. In 4 cases, the percentage of slow wave sleep increased before administration of VPA, and did not change remarkably by its administration. In group A and B, twitch movements (TM), one of the phasic sleep components detected in the mentalis muscle on surface EMG, decreased or were unchanged after administration of VPA, especially during the REM period. In contrast, TM increased in group C. We speculate that the changes of TM (especially in the REM periods) after administration of VPA are well related to its effectiveness. Since TMs are thought to be controlled by the nigrostriatal dopaminergic pathway, the different response of basal ganglia to VPA among cases with absence epilepsy would have some relation to the different effectiveness of VPA in controlling seizures.

Child↗
PubMed1996

Modern management of epilepsy: Adolescents.

Epilepsy most commonly starts in the first two decades of life. Adolescence is a time of great change both in the epilepsy itself and in a number of other areas. Growth into adulthood, issues of preparation for university or employment, driving, drinking, preparation for marriage/conception and a general increase of responsibility add to the complexity of this time of life. Epilepsy affects all these areas to a significant degree. The incidence of several epilepsy syndromes peaks in adolescence. These include juvenile myoclonic epilepsy, juvenile absence epilepsy, epilepsy with grand mal on awakening, benign partial seizures of adolescence and reading epilepsy. Photosensitivity also appears to peak around puberty and needs to be managed well to avoid both unreasonable risks and unnecessary restrictions. Early diagnosis and correct management of the epilepsy and the specific epilepsy syndrome are the main factors in minimizing the difficulties. Epilepsy may change in the early adolescent years, with seizures starting and stopping or altering in form, all of which add to the uncertainty. Denial of the epilepsy may lead to risk-taking which may include be provided on the high risk of the unsupervised bath, the effect of irregular sleep, alcohol, driving, sport, employment, genetic implications, advantages/adverse effects of specific antiepileptic drugs and the role of surgery. The doctor should listen, counsel and inform. Adolescents generally do not appreciate being given advice. They should be empowered by the doctor to make informed decisions and encouraged to take control in a situation which they may view as implying devastating loss of control, unless it is managed wisely.

Adolescent↗
PubMedDate not supplied

[Epilepsy with myoclonic absences].

Within generalized epilepsy, the syndrome of epilepsy with myoclonic absences is considered as intermediate between idiopathic and symptomatic forms. This syndrome is characterized by developing in childhood with a male predominance. Critical EEG shows paroxysms of PO at 3 Hz, and in the polygraphic recording rhythmic 3 Hz myoclonus is observed with a strict correspondence between EEG spike and myoclonus. The response to therapy is generally poor, and 18% develop generalized symptomatic epilepsy. We report 3 patients with epilepsy with myoclonic absences and good outcome, to emphasize the importance of a precise diagnosis by means of the polygraphic recording of the attack, the fact the association of sodium valproate and ethosuximide is the most useful therapy and, finally, the possibility that some patients with epilepsy with myoclonic absence may develop Janz's juvenile myoclonic epilepsy.

Adult↗
PubMed2005

Behavioral characteristics of WAG/Rij rats susceptible and non-susceptible to audiogenic seizures.

Some rats of the WAG/Rij (Wistar Albino Glaxo from Rijswijk) and Wistar strain are susceptible for audiogenic (convulsive) seizures. In the present study, behavior of susceptible and non-susceptible rats from the WAG/Rij strain, genetically predisposed to absence epilepsy, and outbred Wistar strain, genetically not predisposed to absence epilepsy, was compared to assess the level of anxiety (in the open field, light-dark choice and elevated plus-maze tests) and the level of depression (in the sucrose consumption and forced swimming tests). Increased level of anxiety was found only in audiogenic susceptible rats both from WAG/Rij and Wistar strain, but increased level of depression was found only in WAG/Rij rats independently of their susceptibility to audiogenic seizures. The results suggest that enhanced level of depression in WAG/Rij strain rats is associated with absence epilepsy but enhanced level of anxiety with susceptibility to audiogenic seizures.

Analysis of Variance↗
PubMed1996

Epilepsy in children.

Childhood epilepsies comprise a broad range of disorders which vary from benign to progressive and disabling. Accurate diagnosis of epilepsy type and determination of aetiology, when possible, are essential for appropriate treatment. The most common seizure type encountered in children is febrile seizures. These represent a benign condition which is not, in fact, epilepsy and usually does not require antiepileptic medication. When partial seizures occur in childhood, benign syndromes with spontaneous remission, such as rolandic epilepsy, must be distinguished from symptomatic epilepsies which may be refractory to medical management. Complex partial seizures in young children may appear different than in adults. The adverse effect profiles and dosing regimens of antiepileptic drugs in children are also different than in adults, and influence the choice of treatment. Epilepsy surgery should be considered for some children with intractible partial seizures. Generalized epilepsies also have a broader spectrum in children. The idiopathic generalized absence epilepsies are usually easy to control with medication. They range from childhood absence epilepsy which tends to remit in adolescence to juvenile myoclonic epilepsy which is a lifelong condition. In contrast, the seizures of West syndrome and Lennox-Gastaut syndrome are difficult to control, and treatment involves therapeutic modalities rarely used in adults such as ACTH and the ketogenic diet. Many childhood epilepsy syndromes have a familial predisposition, and the genetic bases for several disorders have been described.

Anticonvulsants↗