Pentylenetetrazol-induced status epilepticus up-regulates the expression of glucose transporter mRNAs but not proteins in the immature rat brain

Effect of valproate on sleep patterns disturbed by epilepsy

Nocturnal epilepsy is a neurological disease that has a significant effect on sleep. Various treatments have been implemented to help mitigate these effects and improve patients' quality of life. The use of experimental animal models for epilepsy has facilitated efficacy assessment and the development of different medications to treat the symptoms of this disease. The objective of this study was to evaluate the effect of valproate on sleep patterns altered by epilepsy. Chronically implanted Wistar rats were used to study sleep patterns over three consecutive days under different experimental conditions. The animals were separated into two groups. The first day was considered the control recording; on the second day, one group received pentylenetetrazol (PTZ) alone, and the other group received valproate prior to induction of convulsive seizures with PTZ administration. The results show that in addition to its antiepileptic effect, valproate has hypnotic properties. It is considered to facilitate the action of GABAergic mechanisms to mitigate the effect of convulsive seizures and increase the occurrence of sleep.

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

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

Role of Modulation of Hippocampal Glucose Following Pilocarpine-Induced Status Epilepticus

Status epilepticus (SE) is defined as continuous and self-sustaining seizures, which trigger hippocampal neurodegeneration, mitochondrial dysfunction, oxidative stress, and energy failure. During SE, the neurons become overexcited, increasing energy consumption. Glucose uptake is increased via the sodium glucose cotransporter 1 (SGLT1) in the hippocampus under epileptic conditions. In addition, modulation of glucose can prevent neuronal damage caused by SE. Here, we evaluated the effect of increased glucose availability in behavior of limbic seizures, memory dysfunction, neurodegeneration process, neuronal activity, and SGLT1 expression. Vehicle (VEH, saline 0.9%, 1 μL) or glucose (GLU; 1, 2 or 3 mM, 1 μL) were administered into hippocampus of male Wistar rats (Rattus norvegicus) before or after pilocarpine to induce SE. Behavioral analysis of seizures was performed for 90 min during SE. The memory and learning processes were analyzed by the inhibitory avoidance test. After 24 h of SE, neurodegeneration process, neuronal activity, and SGLT1 expression were evaluated in hippocampal and extrahippocampal regions. Modulation of hippocampal glucose did not protect memory dysfunction followed by SE. Our results showed that the administration of glucose after pilocarpine reduced the severity of seizures, as well as the number of limbic seizures. Similarly, glucose after SE reduced cell death and neuronal activity in hippocampus, subiculum, thalamus, amygdala, and cortical areas. Finally, glucose infusion elevated the SGLT1 expression in hippocampus. Taken together our data suggest that possibly the administration of intrahippocampal glucose protects brain in the earlier stage of epileptogenic processes via an important support of SGLT1.

The neuropathic phenotype of the K/BxN transgenic mouse with spontaneous arthritis: pain, nerve sprouting and joint remodeling

The adult K/BxN transgenic mouse develops spontaneous autoimmune arthritis with joint remodeling and profound bone loss. We report that both males and females display a severe sustained tactile allodynia which is reduced by gabapentin but not the potent cyclooxygenase inhibitor ketorolac. In dorsal horn, males and females show increased GFAP⁺ astrocytic cells; however, only males demonstrate an increase in Iba1⁺ microglia. In dorsal root ganglia (DRG), there is an increase in CGRP⁺, TH⁺, and Iba1⁺ (macrophage) labeling, but no increase in ATF3⁺ cells. At the ankle there is increased CGRP⁺, TH⁺, and GAP-43⁺ fiber synovial innervation. Thus, based on the changes in dorsal horn, DRG and peripheral innervation, we suggest that the adult K/BxN transgenic arthritic mice display a neuropathic phenotype, an assertion consistent with the analgesic pharmacology seen in this animal. These results indicate the relevance of this model to our understanding of the nociceptive processing which underlies the chronic pain state that evolves secondary to persistent joint inflammation.

Effect of gabapentin on sleep patterns disturbed by epilepsy

For a long time, numerous sleep alterations induced by nocturnal epilepsy have been described. Such alterations include sleep fragmentation, decrement of sleep efficiency, increment of the wake time after sleep onset (WASO), increment of light sleep, and decrement of sleep depth. On the other hand, gabapentin (GBP), an antiepileptic drug analog of γ-aminobutyric acid (GABA) used as adjunctive and eventually, as a monotherapeutic treatment, induces a significant improvement in patients with both focal and secondarily generalized partial seizures. In experimental epilepsy models, this drug protects against pentylenetetrazol (PTZ)-induced convulsions. In consideration of such GBP properties, the aim of this work was to investigate its efficacy to protect against sleep disturbances provoked by convulsive seizures induced by the administration of PTZ. Nine-hour (9-hour) polygraphic studies were carried out in chronically implanted male adult Wistar rats separated into 4 different groups of 6 individuals. Control recordings in each group were done after saline administration. One group received a SC Subcutaneous (SC) injection of 50 mg/kg of PTZ alone while the other three groups were injected with either 15, 30, or 60 mg/kg IP Intraperitoneal (IP) of GBP 30 min prior to PTZ (50 mg/kg SC) administration. Animals displayed the whole range of electrophysiological and behavioral manifestations of the disease during the epileptic episodes induced by PTZ administration, and the states of vigilance were significantly altered. Insomnia occurred immediately after PTZ injection preceding the appearance of the first epileptic symptoms. Thus, both slow wave sleep (SWS) and rapid eye movement sleep (REM sleep) were completely inhibited during a relatively long period of time. The disturbing effects of epilepsy on sleep decreased when animals were under GBP treatment. Improvement of sleep was dependent on the administered dose of this antiepileptic drug.

SLC2A3 single-nucleotide polymorphism and duplication influence cognitive processing and population-specific risk for attention-deficit/hyperactivity disorder

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is a common, highly heritable neurodevelopmental disorder with profound cognitive, behavioral, and psychosocial impairments with persistence across the life cycle. Our initial genome-wide screening approach for copy number variants (CNVs) in ADHD implicated a duplication of SLC2A3, encoding glucose transporter-3 (GLUT3). GLUT3 plays a critical role in cerebral glucose metabolism, providing energy for the activity of neurons, which, in turn, moderates the excitatory-inhibitory balance impacting both brain development and activity-dependent neural plasticity. We therefore aimed to provide additional genetic and functional evidence for GLUT3 dysfunction in ADHD.

METHODS

Case-control association analyses of SLC2A3 single-nucleotide polymorphisms (SNPs) and CNVs were conducted in several European cohorts of patients with childhood and adult ADHD (SNP, n = 1,886 vs. 1,988; CNV, n = 1,692 vs. 1,721). These studies were complemented by SLC2A3 expression analyses in peripheral cells, functional EEG recordings during neurocognitive tasks, and ratings of food energy content.

RESULTS

Meta-analysis of all cohorts detected an association of SNP rs12842 with ADHD. While CNV analysis detected a population-specific enrichment of SLC2A3 duplications only in German ADHD patients, the CNV + rs12842 haplotype influenced ADHD risk in both the German and Spanish cohorts. Duplication carriers displayed elevated SLC2A3 mRNA expression in peripheral blood cells and altered event-related potentials reflecting deficits in working memory and cognitive response control, both endophenotypic traits of ADHD, and an underestimation of energy units of high-caloric food.

CONCLUSIONS

Taken together, our results indicate that both common and rare SLC2A3 variation impacting regulation of neuronal glucose utilization and energy homeostasis may result in neurocognitive deficits known to contribute to ADHD risk.

Comorbidity and metabolic context are crucial factors determining neurological sequelae of hypoglycaemia

AIM

To determine risk factors for neurological sequelae following hypoglycemia.

METHOD

We analysed the neurological outcome in 164 patients (mean age 10y 10mo, SD 5.9) following hypoglycemia due to three diseases with various metabolic contexts, different ages at onset, and combinations with comorbidity (fever/infection, hypoxia/ischemia): glycogen storage disease type I (GSDI) (21 patients, mean age at first hypoglycemic episode 3.8mo, SD 3.5); fatty acid β-oxidation defects (FAOD) (29 patients, mean age at first hypoglycemic episode 14.8mo, SD 12.6); and hyperinsulinism (HIns) (114 patients, mean age at first hypoglycemic episode 2.3mo, SD 4.7).

RESULTS

Risk factors of poor neurological outcome were aetiology (p<0.006), comorbidity (p<0.001), and prolonged convulsions (p<0.001). Ordinal logistic regression showed that comorbidity (p<0.001) and status epilepticus (p=0.002) were the main determinants of sequelae. Asymptomatic hypoglycemia did not lead to sequelae, whatever the aetiology. Age was not correlated to sequelae, whatever the aetiology. The highest prevalence of hypoglycemic sequelae was found in FAOD and HIns combined with comorbidity, the lowest in GSDI (p<0.001) in which hypoglycemia is often asymptomatic, associated with increased plasma lactate, and rarely combined with comorbidity.

INTERPRETATION

Hypoglycemia is severely deleterious for the brain in the context of fever/infection and/or hypoxia/ischemia, and status epilepticus. The metabolic context providing alternative fuels may improve neurological outcome.

From omics to drug metabolism and high content screen of natural product in zebrafish: a new model for discovery of neuroactive compound

The zebrafish (Danio rerio) has recently become a common model in the fields of genetics, environmental science, toxicology, and especially drug screening. Zebrafish has emerged as a biomedically relevant model for in vivo high content drug screening and the simultaneous determination of multiple efficacy parameters, including behaviour, selectivity, and toxicity in the content of the whole organism. A zebrafish behavioural assay has been demonstrated as a novel, rapid, and high-throughput approach to the discovery of neuroactive, psychoactive, and memory-modulating compounds. Recent studies found a functional similarity of drug metabolism systems in zebrafish and mammals, providing a clue with why some compounds are active in zebrafish in vivo but not in vitro, as well as providing grounds for the rationales supporting the use of a zebrafish screen to identify prodrugs. Here, we discuss the advantages of the zebrafish model for evaluating drug metabolism and the mode of pharmacological action with the emerging omics approaches. Why this model is suitable for identifying lead compounds from natural products for therapy of disorders with multifactorial etiopathogenesis and imbalance of angiogenesis, such as Parkinson's disease, epilepsy, cardiotoxicity, cerebral hemorrhage, dyslipidemia, and hyperlipidemia, is addressed.

Fueling and imaging brain activation

Metabolic signals are used for imaging and spectroscopic studies of brain function and disease and to elucidate the cellular basis of neuroenergetics. The major fuel for activated neurons and the models for neuron–astrocyte interactions have been controversial because discordant results are obtained in different experimental systems, some of which do not correspond to adult brain. In rats, the infrastructure to support the high energetic demands of adult brain is acquired during postnatal development and matures after weaning. The brain's capacity to supply and metabolize glucose and oxygen exceeds demand over a wide range of rates, and the hyperaemic response to functional activation is rapid. Oxidative metabolism provides most ATP, but glycolysis is frequently preferentially up-regulated during activation. Underestimation of glucose utilization rates with labelled glucose arises from increased lactate production, lactate diffusion via transporters and astrocytic gap junctions, and lactate release to blood and perivascular drainage. Increased pentose shunt pathway flux also causes label loss from C1 of glucose. Glucose analogues are used to assay cellular activities, but interpretation of results is uncertain due to insufficient characterization of transport and phosphorylation kinetics. Brain activation in subjects with low blood-lactate levels causes a brain-to-blood lactate gradient, with rapid lactate release. In contrast, lactate flooding of brain during physical activity or infusion provides an opportunistic, supplemental fuel. Available evidence indicates that lactate shuttling coupled to its local oxidation during activation is a small fraction of glucose oxidation. Developmental, experimental, and physiological context is critical for interpretation of metabolic studies in terms of theoretical models.

New insight on the mechanisms of epileptogenesis in the developing brain

The incidence of epilepsy is at its highest in childhood and seizures can persist for a lifetime. As brain tissue from pediatric patients with epilepsy is rarely available, the analysis of molecular and cellular changes during epileptogenesis, which could serve as targets for treatment approaches, has to rely largely on the analysis of tissue from animal models. However, these data have to be analyzed in the context of the developmental stage when the insult occurs. Here we review the current status of the available animal models, the molecular analysis done in these models, as well as treatment attempts to prevent epileptogenesis in the immature brain. Considering that epilepsy is one of the major childhood neurological diseases, it is remarkable how little is known on epileptogenesis in the immature brain at a molecular level. It is a true challenge for the future to expand the armamentarium of clinically relevant animal models, and systematic analysis of molecular and cellular data to enhance the probability of developing syndrome specific antiepileptogenic treatments and biomarkers for acquired pediatric epileptogenesis.

Temporal changes in mRNA expression of the brain nutrient transporters in the lithium-pilocarpine model of epilepsy in the immature and adult rat

The lithium-pilocarpine model mimics most features of human temporal lobe epilepsy. Following our prior studies of cerebral metabolic changes, here we explored the expression of transporters for glucose (GLUT1 and GLUT3) and monocarboxylates (MCT1 and MCT2) during and after status epilepticus (SE) induced by lithium-pilocarpine in PN10, PN21, and adult rats. In situ hybridization was used to study the expression of transporter mRNAs during the acute phase (1, 4, 12 and 24h of SE), the latent phase, and the early and late chronic phases. During SE, GLUT1 expression was increased throughout the brain between 1 and 12h of SE, more strongly in adult rats; GLUT3 increased only transiently, at 1 and 4h of SE and mainly in PN10 rats; MCT1 was increased at all ages but 5-10-fold more in adult than in immature rats; MCT2 expression increased mainly in adult rats. At all ages, MCT1 and MCT2 up-regulation was limited to the circuit of seizures while GLUT1 and GLUT3 changes were more widespread. During the latent and chronic phases, the expression of nutrient transporters was normal in PN10 rats. In PN21 rats, GLUT1 was up-regulated in all brain regions. In contrast, in adult rats GLUT1 expression was down-regulated in the piriform cortex, hilus and CA1 as a result of extensive neuronal death. The changes in nutrient transporter expression reported here further support previous findings in other experimental models demonstrating rapid transcriptional responses to marked changes in cerebral energetic/glucose demand.

The ketogenic diet has no effect on the expression of spike-and-wave discharges and nutrient transporters in genetic absence epilepsy rats from Strasbourg

The genetic absence epilepsy rat from Strasbourg is considered an isomorphic, predictive, and homologous model of typical childhood absence epilepsy. It is characterized by the expression of spike-and-wave discharges (SWDs) in the thalamus and cortex. The ketogenic diet (KD) is successfully used in humans and animals with various types of seizures, but was not effective in children with intractable atypical absence epilepsy. Here, we studied its potential impact on the occurrence of SWDs in genetic absence epilepsy rat from Strasbourg. Rats were fed the KD for 3 weeks during which they were regularly subjected to the electroencephalographic recording of SWDs. The KD did not influence the number and duration of SWDs despite a 15-22% decrease in plasma glucose levels and a large increase in beta-hydroxybutyrate levels. Likewise, the KD did not affect the level of expression of the blood-brain barrier glucose transporter GLUT1 or of the monocarboxylate transporters, MCT1 and MCT2. This report extends the observation in humans that the KD does not appear to show effectiveness in intractable atypical absence epilepsy to this model of typical childhood absence epilepsy which responds to specific antiepileptic drugs.

The facilitative glucose transporter GLUT3: 20 years of distinction

Glucose metabolism is vital to most mammalian cells, and the passage of glucose across cell membranes is facilitated by a family of integral membrane transporter proteins, the GLUTs. There are currently 14 members of the SLC2 family of GLUTs, several of which have been the focus of this series of reviews. The subject of the present review is GLUT3, which, as implied by its name, was the third glucose transporter to be cloned (Kayano T, Fukumoto H, Eddy RL, Fan YS, Byers MG, Shows TB, Bell GI. J Biol Chem 263: 15245-15248, 1988) and was originally designated as the neuronal GLUT. The overriding question that drove the early work on GLUT3 was why would neurons need a separate glucose transporter isoform? What is it about GLUT3 that specifically suits the needs of the highly metabolic and oxidative neuron with its high glucose demand? More recently, GLUT3 has been studied in other cell types with quite specific requirements for glucose, including sperm, preimplantation embryos, circulating white blood cells, and an array of carcinoma cell lines. The last are sufficiently varied and numerous to warrant a review of their own and will not be discussed here. However, for each of these cases, the same questions apply. Thus, the objective of this review is to discuss the properties and tissue and cellular localization of GLUT3 as well as the features of expression, function, and regulation that distinguish it from the rest of its family and make it uniquely suited as the mediator of glucose delivery to these specific cells.

Alterations of NR2B and PSD-95 expression after early-life epileptiform discharges in developing neurons

As an extreme form of abnormally synchronized activity, epilepsy may modify patterns of organization in the nervous system. It is clear that enhanced glutamatergic excitatory synaptic transmission with alterations in the expression of ionotropic glutamate receptors is a mechanism critical for seizure susceptibility and excitotoxicity. However, the exact quomodo and the roles of regulated N-methyl-D-aspartate receptor (NMDAR) composition and expression of a major postsynaptic density (PSD) scaffolding molecule, PSD-95, are as yet unclear. To study protein expression changes after epileptiform discharges in cultured immature rat cortical neurons, we divided cells into three groups which were transiently exposed to regular Neurobasal/B27 (control group), physiological solution (PS group) and magnesium-free physiological solution (MGF group) at cultured day 6. Neurons at three different culture ages (DIV7, DIV12 and DIV17) were collected for immunoblotting analysis. We found a decrease in expression of NR2B NMDAR subunit and PSD-95 (P<0.05) shortly after insult (within 24 h), which may show that brief magnesium-free media treatment of primary cultured rat cortical neurons, an in vitro model of seizure brain injury, has a major influence on the expression of NR2B subunit and PSD-95.