Seizures in the Mongolian gerbil are related to a deficiency in cerebral glutamine synthetase

Post-seizure α-tocopherol treatment decreases neuroinflammation and neuronal degeneration induced by status epilepticus in rat hippocampus

Vitamin E (as α-tocopherol, α-T) was shown to have beneficial effects in epilepsy, mainly ascribed to its antioxidant properties. Besides radical-induced neurotoxicity, neuroinflammation is also involved in the pathophysiology of epilepsy, since neuroglial activation and cytokine production exacerbate seizure-induced neurotoxicity and contribute to epileptogenesis. We previously showed that α-T oral supplementation before inducing status epilepticus, markedly reduces astrocytic and microglial activation, neuronal cell death and oxidative stress in the hippocampus, as observed 4 days after seizure. In order to evaluate the possibility that such a neuroprotective and anti-inflammatory effect may also provide a strategy for an acute intervention in epilepsy, in this study, seizures were induced by single intaperitoneal injection of kainic acid and, starting from 3 h after status epilepticus, rats were treated with an intraperitoneal bolus of α-T (250 mg/kg b.w.; once a day) for 4 days, that was the time after which morphological and biochemical analyses were performed on hippocampus. Post-seizure α-T administration significantly reduced astrocytosis and microglia activation, and decreased neuron degeneration and spine loss; these effects were associated with the presence of a lowered lipid peroxidation in hippocampus. These results confirm and further emphasize the anti-inflammatory and neuroprotective role of α-T in kainic acid-induced epilepsy. Moreover, the findings show that post-seizure treatment with α-T provides an effective secondary prevention against post-seizure inflammation-induced brain damages and possibly against their epileptogenic effects.

Glutamine synthetase expression as a valuable marker of epilepsy and longer survival in newly diagnosed glioblastoma multiforme

BACKGROUND

Glutamine synthetase (GS) is an astrocytic enzyme catalyzing the conversion of glutamate and ammonia to glutamine. Its up-regulation has been related to higher tumor proliferation and poor prognosis in extra-cerebral tumors. We have previously reported a GS deficiency in patients with glioblastoma multiforme (GBM) who also developed epilepsy, which is a favorable prognostic factor in glioma. Here, we investigated the prognostic value of GS expression in patients with GBM with or without epilepsy and its correlation with survival.

METHODS

We conducted a clinical and histopathological study on 83 (52 males) consecutive patients with newly diagnosed GBM. Immunohistochemical expression of GS was scored semi-quantitatively on the basis of cell number, staining intensity, and distribution of immunoreactive cells. Several clinical and neuropathological variables were analyzed in relation to survival and GS expression.

RESULTS

Median age at diagnosis was 62 years. At the last evaluation, with a median follow-up of 11.5 months (range, 1.5-58 months), 5 patients (6%) were still alive and 78 (94%) were dead. GS expression patterns in neoplastic cells were inversely correlated to the presence of epilepsy (P < .0001 for intensity and P < .009 for homogeneity of GS distribution, respectively). Univariate analysis showed that RPA score, epilepsy, O6-methylguanine-DNA methyltransferase (MGM)T status, application of Stupp protocol, and GS intensity pattern had a significant impact on survival. Absent/low intensity of GS expression was significantly associated with a longer survival in both uni- (19 vs 8 months; P < .0005) and multivariate (P = .003) analyses.

CONCLUSIONS

Absent/low-intensity GS expression pattern represents a valuable biomarker of both epilepsy and overall survival in GBM.

Characteristics and treatment of seizures in patients with high-grade glioma: a review

High-grade gliomas (HGGs), including anaplastic astrocytoma and glioblastoma multiforme, are the most common primary brain tumors, and are often associated with seizures. Seizure control is a critical but often underappreciated goal in the treatment of patients harboring these malignant lesions. Patients with HGG who also have medically intractable seizures should be considered for a palliative resection guided by electrocorticography and functional mapping. Antiepileptic drugs remain the mainstay of seizure treatment in HGG, and antiepileptic medication should be started after a tumor-related seizure, but should not be used prophylactically in the absence of seizure activity.

Neuroendocrine alterations in the fragile X mouse

The expression of GABA(A) receptors in the fragile X mouse brain is significantly downregulated. We additionally found that the expression of somatostatin and voltage-sensitive calcium channels (VSCCs) is also reduced. GABA(A) and the VSCCs, through a synergistic interaction, perform a critical role in mediating activity-dependent developmental processes. In the developing brain, GABA is excitatory and its actions are mediated through GABA(A) receptors. Subsequent to GABA-mediated depolarization, the VSCCs are activated and intracellular calcium is increased, which mediates gene transcription and other cellular events. GABAergic excitation mediated through GABA(A) receptors and the subsequent activation of the VSCCs are critically important for the establishment of neuronal connectivity within immature neuronal networks. Data from our laboratories suggest that there is a dysregulation of axonal pathfinding during development in the fragile X mouse brain and that this is likely due to a dysregulation of the synergistic interactions of GABA and VSCC. Thus, we hypothesize that the altered expression of these critical channels in the early stages of brain development leads to altered activity-dependent gene expression that may potentially lead to the developmental delay characteristic of the fragile X syndrome.

Glutamate clearance mechanisms in resected cortical dysplasia

Object

Changes in the expression of glutamate transporters (GLTs) may play a role in the expression of epileptogenicity. Previous studies have shown an increased number of neuronal GLTs in human dysplastic neurons. The expression of glial and neuronal GLTs and glutamine synthetase (GS) in balloon cells (BCs) and BC-containing cortical dysplasia has not been studied.

Methods

The authors analyzed neocortical samples that were resected in 5 patients who had cortical dysplasia–induced medically intractable focal epilepsy and who underwent extraoperative prolonged electrocorticographic (ECoG) recordings. The expressions of glial (GLT1/EAAT2) and neuronal (EAAT3, EAAC1) GLTs and GS proteins were immunohistochemically studied in all 5 resected samples. The authors also assessed in situ colocalization of GLTs and GS with neuronal and glial markers.

Results

Balloon cell–containing cortical dysplasia lesions did not exhibit ictal patterns on prolonged extraoperative ECoG recordings. There was a differential expression of glial and neuronal GLTs in BCs and dysplastic neurons: the majority of BCs highly expressed glial but not neuronal GLTs. Dysplastic neurons showed increased immunohistochemical staining with neuronal EAAT3 but not with EAAT2/GLT1. Moreover, only glial fibrillary acidic protein–positive BCs also expressed GS.

Conclusions

There is a differential GLT expression in dysplastic and balloon cells. The presence of glial GLTs and GS in balloon cell cortical dysplasia suggests a possible antiepileptic role for BCs and is consistent with the reported increased epileptogenicity in GLT1-deficient animals.

Animal models of inherited epilepsy

A significant proportion of the childhood epilepsies have a genetic component. Therefore, animal models that can be bred for seizure expression may provide important information regarding the mechanisms by which molecular defects result in the neuronal hyperexcitability states collectively termed "epilepsy." Because of the rate and ease of breeding, rodent models are the most commonly used. The genetically epilepsy-prone rat has motor seizures in response to auditory stimuli. It is likely that the seizures are generated in the inferior colliculus because of an abnormality in the noradrenergic system. The seizure predisposition is inherited as an autosomal dominant trait. The genetic absence epilepsy rat has age-related spontaneous seizures characterized by motor arrest and head drops that are correlated with generalized spike-wave on the electroencephalogram (EEG). The seizure generating mechanism appears to be located in the lateral thalamic nuclei. The epileptic mongolian gerbil demonstrates behavioral arrest followed by myoclonic, tonic, and tonic-clonic seizures in response to unfamiliar environments. The underlying neuroanatomy involves hippocampal-cortical interactions indicative of a partial epilepsy. The tottering mouse has absence and myoclonic seizures, a 6- to 7-Hz ictal spike-wave EEG, and noradrenergic hyperinnervation that are linked to a mutation on chromosome 8. Hippocampal network hyperexcitability has been found with normal neuronal intrinsic properties. Stargazer is a mouse mutant with almost identical clinical and electrographic features as found in tottering. However, the genetic defect is located on chromosome 15 and no abnormalities of norepinephrine have been discovered. The El mouse demonstrates ictal automatisms in response to vestibular stimulation. Metabolic and structural abnormalities have been found in the hippocampus. Linkage to chromosomes 9 and 2 have been reported recently. The dilute brown agouiti mouse demonstrates motor seizures in response to auditory stimuli. Chromosomes 4 and 17 are linked to seizure expression. Thus, a variety of models exist to study the genetic, biochemical, structural and electrophysiological mechanisms that underlie the predisposition and expression of the inherited epilepsies.

Mitochondria, oxidative stress, and temporal lobe epilepsy

Mitochondrial oxidative stress and dysfunction are contributing factors to various neurological disorders. Recently, there has been increasing evidence supporting the association between mitochondrial oxidative stress and epilepsy. Although certain inherited epilepsies are associated with mitochondrial dysfunction, little is known about its role in acquired epilepsies such as temporal lobe epilepsy (TLE). Mitochondrial oxidative stress and dysfunction are emerging as key factors that not only result from seizures, but may also contribute to epileptogenesis. The occurrence of epilepsy increases with age, and mitochondrial oxidative stress is a leading mechanism of aging and age-related degenerative disease, suggesting a further involvement of mitochondrial dysfunction in seizure generation. Mitochondria have critical cellular functions that influence neuronal excitability including production of adenosine triphosphate (ATP), fatty acid oxidation, control of apoptosis and necrosis, regulation of amino acid cycling, neurotransmitter biosynthesis, and regulation of cytosolic Ca(2+) homeostasis. Mitochondria are the primary site of reactive oxygen species (ROS) production making them uniquely vulnerable to oxidative stress and damage which can further affect cellular macromolecule function, the ability of the electron transport chain to produce ATP, antioxidant defenses, mitochondrial DNA stability, and synaptic glutamate homeostasis. Oxidative damage to one or more of these cellular targets may affect neuronal excitability and increase seizure susceptibility. The specific targeting of mitochondrial oxidative stress, dysfunction, and bioenergetics with pharmacological and non-pharmacological treatments may be a novel avenue for attenuating epileptogenesis.

Emergency and critical care of rodents

Rodents may be presented on an emergency basis with various conditions causing debilitation and disease. Common causes of emergent presentations include trauma, respiratory disease, dental disease, gastrointestinal disease, reproductive disorders, and urinary tract obstruction. Emergency treatment should always include immediate stabilization of the patient until the patient is able to tolerate diagnostic testing and additional therapeutics. Rodent patients benefit from supportive care, including thermal, fluid, and nutritional support. Administration of cardiopulmonary resuscitation, antibiotics, and analgesics through various routes is also appropriate. This article presents an overview of emergency medicine in rodents, including emergency procedures, handling and restraint, triage and patient assessment, sample collection, and supportive care procedures. The most common emergency presentations for rodents are also discussed.

Haploinsufficiency of glutamine synthetase increases susceptibility to experimental febrile seizures

Glutamine synthetase (GS) is a pivotal glial enzyme in the glutamate-glutamine cycle. GS is important in maintaining low extracellular glutamate concentrations and is downregulated in the hippocampus of temporal lobe epilepsy patients with mesial-temporal sclerosis, an epilepsy syndrome that is frequently associated with early life febrile seizures (FS). Human congenital loss of GS activity has been shown to result in brain malformations, seizures and death within days after birth. Recently, we showed that GS knockout mice die during embryonic development and that haploinsufficient GS mice have no obvious abnormalities or behavioral seizures. In the present study, we investigated whether reduced expression/activity of GS in haploinsufficient GS mice increased the susceptibility to experimentally induced FS. FS were elicited by warm-air-induced hyperthermia in 14-day-old mice and resulted in seizures in most animals. FS susceptibility was measured as latencies to four behavioral FS characteristics. Our phenotypic data show that haploinsufficient mice are more susceptible to experimentally induced FS (P < 0.005) than littermate controls. Haploinsufficient animals did not differ from controls in hippocampal amino acid content, structure (Nissl and calbindin), glial properties (glial fibrillary acidic protein and vimentin) or expression of other components of the glutamate-glutamine cycle (excitatory amino acid transporter-2 and vesicular glutamate transporter-1). Thus, we identified GS as a FS susceptibility gene. GS activity-disrupting mutations have been described in the human population, but heterozygote mutations were not clearly associated with seizures or epilepsy. Our results indicate that individuals with reduced GS activity may have reduced FS seizure thresholds. Genetic association studies will be required to test this hypothesis.

Loss of glutamine synthetase in the human epileptogenic hippocampus: possible mechanism for raised extracellular glutamate in mesial temporal lobe epilepsy

BACKGROUND

High extracellular glutamate concentrations have been identified as a likely trigger of epileptic seizures in mesial temporal lobe epilepsy (MTLE), but the underlying mechanism remains unclear. We investigated whether a deficiency in glutamine synthetase, a key enzyme in catabolism of extracellular glutamate in the brain, could explain the perturbed glutamate homoeostasis in MTLE.

METHODS

The anteromedial temporal lobe is the focus of the seizures in MTLE, and surgical resection of this structure, including the hippocampus, leads to resolution of seizures in many cases. By means of immunohistochemistry, western blotting, and functional enzyme assays, we assessed the distribution, quantity, and activity of glutamine synthetase in the MTLE hippocampus.

FINDINGS

In western blots, the expression of glutamine synthetase in the hippocampus was 40% lower in MTLE than in non-MTLE samples (median 44 [IQR 30-58] vs 69 [56-87]% of maximum concentration in standard curve; p=0.043; n=8 and n=6, respectively). The enzyme activity was lower by 38% in MTLE vs non-MTLE (mean 0.0060 [SD 0.0031] vs 0.0097 [0.0042] U/mg protein; p=0.045; n=6 and n=9, respectively). Loss of glutamine synthetase was particularly pronounced in areas of the MTLE hippocampus with astroglial proliferation, even though astrocytes normally have high content of the enzyme. Quantitative immunoblotting showed no significant change in the amount of EAAT2, the predominant glial glutamate transporter in the hippocampus.

INTERPRETATION

A deficiency in glutamine synthetase in astrocytes is a possible molecular basis for extracellular glutamate accumulation and seizure generation in MTLE. Further studies are needed to define the cause, but the loss of glutamine synthetase may provide a new focus for therapeutic interventions in MTLE.

The enhanced expression of c-Jun immunoreactivity in the adrenalectomized gerbil hippocampus

Recent in vitro and in vivo studies have shown that glucocorticoids have a profound influence on the survival of hippocampal neurones, and that the depletion of glucocorticoids as a result of adrenalectomy (ADX) reduces nerve growth factor levels in the hippocampus. It is also believed that ADX is associated with the seizure susceptibility of the Mongolian gerbil. In the present study, the choronological changes of c-jun immunoreactivity were investigated after ADX in the hippocampal formations in the seizure-prone gerbil model. In the sham hippocampus, c-jun immunoreactivity was not observed in the neurones of the hippocampus proper and dentate gyrus. C-jun immunoreactive neurones appeared 3 h after ADX in the neurones of the CA1 area and dentate gyrus, and these immunoreactivities peaked 24 h after ADX and then gradually decreased. These results suggest that, in the adrenalectomized gerbil, c-jun may be expressed in the neurones of the hippocampus in compensation for glucocorticoid deficit. The result of enhanced c-jun expression of the hippocampal formation provides anatomical support for the hypothesis that c-jun may play a role in the reduction of seizure activity.

Effects of anti-epileptic drugs on glutamine synthetase activity in mouse brain

1. Glutamine synthetase (GS) is a key enzyme in the regulation of glutamate neurotransmission in the central nervous system. It is responsible for the conversion of glutamate to glutamine, and for the detoxification of ammonia. 2. We have investigated the effects of single and repeated intraperitoneal administration of a range of established and new anti-epileptic drugs on GS activity in mouse brain. 3. Four hours after the final dose, animals were sacrificed and the brains removed for analysis of GS activity. 4. Both single and repeated doses of phenytoin and carbamazepine were found to reduce enzyme activity (P<0.05). 5. Single doses of phenobarbitone, felbamate and topiramate were without effect, however repeated administration of these drugs dose-dependently reduced GS activity (P<0.05). 6. Single and repeated doses of sodium valproate, vigabatrin, lamotrigine, gabapentin, tiagabine, levetiracetam and desglycinyl-remacemide were found to have no effect on GS activity. 7. The reduction in enzyme activity demonstrated is unlikely to be related to the anti-epileptic actions of these drugs, but may contribute to their toxicity.