Mechanisms of neuronal hyperexcitability caused by partial inhibition of Na+-K+-ATPases in the rat CA1 hippocampal region

Multi-omic Analysis of the Gut Microbiome in Rats with Lithium-Pilocarpine-Induced Temporal Lobe Epilepsy

Evidence supports that the gut microbiota and bacteria-dependent metabolites influence the maintenance of epileptic brain activity. However, the alterations in the gut microbiota between epileptic versus healthy individuals are poorly understood. We used a multi-omic approach to evaluate the changes in the composition of gut metagenome as well in the fecal metabolomic profile in rats before and after being submitted to status epilepticus (SE)-induced temporal lobe epilepsy (TLE). The 16S ribosomal RNA (rRNA) sequencing of fecal samples coupled to bioinformatic analysis revealed taxonomic, compositional, and functional shifts in epileptic rats. The species richness (Chao1 index) was significantly lower in the post-TLE group, and the β-diversity analysis revealed clustering separated from the pre-TLE group. The taxonomic abundance analysis showed a significant increase of phylum Desulfobacterota and a decrease of Patescibacteria in the post-TLE group. The DESEq2 and LEfSe analysis resulted in 18 genera significantly enriched between post-TLE and pre-TLE groups at the genus level. We observed that epileptic rats present a peculiar metabolic phenotype, including a lower concentration of D-glucose and L-lactic acid and a higher concentration of L-glutamic acid and glycine. The microbiota-host metabolic correlation analysis showed that the genera differentially abundant in post-TLE rats are associated with the altered metabolites, especially the proinflammatory Desulfovibrio and Marvinbryantia, which were enriched in epileptic animals and positively correlated with these excitatory neurotransmitters and carbohydrate metabolites. Therefore, our data revealed a correlation between dysbacteriosis in epileptic animals and fecal metabolites that are known to be relevant for maintaining epileptic brain activity by enhancing chronic inflammation, an excitatory-inhibitory imbalance, and/or a metabolic disturbance. These data are promising and suggest that targeting the gut microbiota could provide a novel avenue for preventing and treating acquired epilepsy. However, the causal relationship between these microbial/metabolite components and the SRS occurrence still needs further exploration.

Effects of In Vivo Intracellular ATP Modulation on Neocortical Extracellular Potassium Concentration

Neuronal and glial activity are dependent on the efflux of potassium ions into the extracellular space. Efflux of K is partly energy-dependent as the activity of pumps and channels which are involved in K transportation is ATP-dependent. In this study, we investigated the effect of decreased intracellular ATP concentration ([ATP]i) on the extracellular potassium ion concentration ([K]o). Using in vivo electrophysiological techniques, we measured neocortical [K]o and the local field potential (LFP) while [ATP]i was reduced through various pharmacological interventions. We observed that reducing [ATP]i led to raised [K]o and DC-shifts resembling spreading depolarization-like events. We proposed that most likely, the increased [K]o is mainly due to the impairment of the Na/K ATPase pump and the ATP-sensitive potassium channel in the absence of sufficient ATP, because Na/K ATPase inhibition led to increased [K]o and ATP-sensitive potassium channel impairment resulted in decreased [K]o. Therefore, an important consequence of decreased [ATP]i is an increased [K]o. The results of this study acknowledge one of the mechanisms involved in [K]o dynamics.

Early role for a Na+,K+-ATPase (ATP1A3) in brain development

By evaluating children with a malformed cerebral cortex, we identified an ATPase pump (ATP1A3) with an early role in brain development. The ATP1A3 pump maintains the physiological concentration of sodium and potassium ions in cells, a process critical for osmotic equilibrium and membrane potential across several developing cell populations. We employed single-cell sequencing approaches to identify key enrichments for ATP1A3 expression during human cortex development. Unravelling this early cell-type–specific pathophysiology in the developing brain offers a potential basis for the treatment of ATP1A3-related diseases affecting prenatal and early childhood development.

Osmotic equilibrium and membrane potential in animal cells depend on concentration gradients of sodium (Na⁺) and potassium (K⁺) ions across the plasma membrane, a function catalyzed by the Na⁺,K⁺-ATPase α-subunit. Here, we describe ATP1A3 variants encoding dysfunctional α3-subunits in children affected by polymicrogyria, a developmental malformation of the cerebral cortex characterized by abnormal folding and laminar organization. To gain cell-biological insights into the spatiotemporal dynamics of prenatal ATP1A3 expression, we built an ATP1A3 transcriptional atlas of fetal cortical development using mRNA in situ hybridization and transcriptomic profiling of ∼125,000 individual cells with single-cell RNA sequencing (Drop-seq) from 11 areas of the midgestational human neocortex. We found that fetal expression of ATP1A3 is most abundant to a subset of excitatory neurons carrying transcriptional signatures of the developing subplate, yet also maintains expression in nonneuronal cell populations. Moving forward a year in human development, we profiled ∼52,000 nuclei from four areas of an infant neocortex and show that ATP1A3 expression persists throughout early postnatal development, most predominantly in inhibitory neurons, including parvalbumin interneurons in the frontal cortex. Finally, we discovered the heteromeric Na⁺,K⁺-ATPase pump complex may form nonredundant cell-type–specific α-β isoform combinations, including α3-β1 in excitatory neurons and α3-β2 in inhibitory neurons. Together, the developmental malformation phenotype of affected individuals and single-cell ATP1A3 expression patterns point to a key role for α3 in human cortex development, as well as a cell-type basis for pre- and postnatal ATP1A3-associated diseases.

Melatonin attenuates branch chain fatty acid induced apoptosis mediated neurodegeneration

Valproic acid (VPA)-a short branched chain fatty acid (BCFA), is widely recognized as an anticonvulsant and a mood-stabilizing drug, but various adverse effects of VPA have also been investigated. However, the impact of BCFAs aggregation on brain cells, in the pathogenesis of neurodegeneration remains elusive. The objective of this study is to understand the cellular mechanisms underlying VPA-induced neuronal cell death mediated by oxidative stress, and the neuroprotective role of exogenous melatonin treatment on VPA-induced cell death. Neurotoxicity of VPA and protective role exerted by melatonin were assessed in vitro in SH-SY5Y cells and in vivo in the cerebral cortex and cerebellum regions of Wistar rat brain. The results show that melatonin pre-treatment protects the cells from VPA-induced toxicity by exerting an anti-apoptotic and anti-inflammatory effect by regulating apoptotic proteins and pro-inflammatory cytokines. The findings of the present study emphasize novel insights of melatonin as a supplement for the prevention and treatment of neuronal dysfunction induced by VPA.

Altered hippocampal function and cytokine levels in a rat model of Gulf War illness

AIMS

Gulf War illness (GWI) is a disorder affecting military personnel deployed in the Gulf War (GW) from 1990 to 1991. Here, we will use a rat model of GWI to evaluate hippocampal function and cytokine levels.

MATERIALS AND METHODS

Rats were exposed to diethyltoluamide and permethrin via dermal absorption and pyridostigmine bromide via gavage with or without a 5-min restraint for 28 days. Immediate and delayed effects of GW chemical exposure were evaluated using electrophysiology to quantitate hippocampal function, behavioral tests to assess cognitive effects and biochemical assays to measure neurotransmitter and cytokine levels.

KEY FINDINGS

Behavioral data revealed a statistically significant increase in motor activity at 3 months following completion of exposures, potentially indicating increased excitability, and/or restlessness. Electrophysiology data revealed statistically significant changes in paired pulse facilitation and input-output function of CA1 hippocampal neurons within 24 h and 3 months following completion of exposures. There was also a statistically significant reduction in the frequency of spontaneous firing activity of hippocampal neurons within 24 h following exposures. Naïve hippocampal slices directly incubated in GW chemicals also resulted in similar changes in electrophysiological parameters. Biochemical measurements revealed reduced hippocampal glutamate level at 3 months post-exposure. Furthermore, there was a statistically significant increase in plasma and hippocampal levels of IL-13, as well as decrease in plasma level of IL-1β.

SIGNIFICANCE

Our data support an effect on glutamate signaling within the hippocampus as indicated by changes in PPF and hippocampal level of glutamate, with some activation of T helper type 2 immune response.

The Janus face of ouabain in Na+ /K+ -ATPase and calcium signalling in neurons

Na⁺ /K⁺ -ATPase, a transmembrane protein essential for maintaining the electrochemical gradient across the plasma membrane, acts as a receptor for cardiotonic steroids such as ouabain. Cardiotonic steroids binding to Na⁺ /K⁺ -ATPase triggers signalling pathways or inhibits Na⁺ /K⁺ -ATPas activity in a concentration-dependent manner, resulting in a modulation of Ca²⁺ levels, which are essential for homeostasis in neurons. However, most of the pharmacological strategies for avoiding neuronal death do not target Na⁺ /K⁺ -ATPase activity due to its complexity and the poor understanding of the mechanisms involved in Na⁺ /K⁺ -ATPase modulation. The present review aims to discuss two points regarding the interplay between Na⁺ /K⁺ -ATPase and Ca²⁺ signalling in the brain. One, Na⁺ /K⁺ -ATPase impairment causing illness and neuronal death due to Ca²⁺ signalling and two, benefits to the brain by modulating Na⁺ /K⁺ -ATPase activity. These interactions play an essential role in neuronal cell fate determination and are relevant to find new targets for the treatment of neurodegenerative diseases.

Metabolic Control of Epilepsy: A Promising Therapeutic Target for Epilepsy

Epilepsy is a common neurological disease that is not always controlled, and the ketogenic diet shows good antiepileptic effects drug-resistant epilepsy or seizures caused by specific metabolic defects via regulating the metabolism. The brain is a vital organ with high metabolic demands, and epileptic foci tend to exhibit high metabolic characteristics. Accordingly, there has been growing interest in the relationship between brain metabolism and epilepsy in recent years. To date, several new antiepileptic therapies targeting metabolic pathways have been proposed (i.e., inhibiting glycolysis, targeting lactate dehydrogenase, and dietary therapy). Promising strategies to treat epilepsy via modulating the brain's metabolism could be expected, while a lack of thorough understanding of the role of brain metabolism in the control of epilepsy remains. Herein, this review aims to provide insight into the state of the art concerning the brain's metabolic patterns and their association with epilepsy. Regulation of neuronal excitation via metabolic pathways and antiepileptic therapies targeting metabolic pathways are emphasized, which could provide a better understanding of the role of metabolism in epilepsy and could reveal potential therapeutic targets.

Astrocytes as Guardians of Neuronal Excitability: Mechanisms Underlying Epileptogenesis

Astrocytes are key homeostatic regulators in the central nervous system and play important roles in physiology. After brain damage caused by e.g., status epilepticus, traumatic brain injury, or stroke, astrocytes may adopt a reactive phenotype. This process of reactive astrogliosis is important to restore brain homeostasis. However, persistent reactive astrogliosis can be detrimental for the brain and contributes to the development of epilepsy. In this review, we will focus on physiological functions of astrocytes in the normal brain as well as pathophysiological functions in the epileptogenic brain, with a focus on acquired epilepsy. We will discuss the role of astrocyte-related processes in epileptogenesis, including reactive astrogliosis, disturbances in energy supply and metabolism, gliotransmission, and extracellular ion concentrations, as well as blood-brain barrier dysfunction and dysregulation of blood flow. Since dysfunction of astrocytes can contribute to epilepsy, we will also discuss their role as potential targets for new therapeutic strategies.

Na+-K+-ATPase functions in the developing hippocampus: regional differences in CA1 and CA3 neuronal excitability and role in epileptiform network bursting

The Na⁺-K⁺-ATPase (Na⁺-K⁺ pump) is essential for setting resting membrane potential and restoring transmembrane Na⁺ and K⁺ gradients after neuronal firing, yet its roles in developing neurons are not well understood. This study examined the contribution of the Na⁺-K⁺ pump to resting membrane potential and membrane excitability of developing CA1 and CA3 neurons and its role in maintaining synchronous network bursting. Experiments were conducted in postnatal day (P)9 to P13 rat hippocampal slices using whole cell patch-clamp and extracellular field-potential recordings. Blockade of the Na⁺-K⁺ pump with strophanthidin caused marked depolarization (23.1 mV) in CA3 neurons but only a modest depolarization (3.3 mV) in CA1 neurons. Regarding other membrane properties, strophanthidin differentially altered the voltage-current responses, input resistance, action-potential threshold and amplitude, rheobase, and input-output relationship in CA3 vs. CA1 neurons. At the network level, strophanthidin stopped synchronous epileptiform bursting in CA3 induced by 0 Mg²⁺ and 4-aminopyridine. Furthermore, dual whole cell recordings revealed that strophanthidin disrupted the synchrony of CA3 neuronal firing. Finally, strophanthidin reduced spontaneous excitatory postsynaptic current (sEPSC) bursts (i.e., synchronous transmitter release) and transformed them into individual sEPSC events (i.e., nonsynchronous transmitter release). These data suggest that the Na⁺-K⁺ pump plays a more profound role in membrane excitability in developing CA3 neurons than in CA1 neurons and that the pump is essential for the maintenance of synchronous network bursting in CA3. Compromised Na⁺-K⁺ pump function leads to cessation of ongoing synchronous network activity, by desynchronizing neuronal firing and neurotransmitter release in the CA3 synaptic network. These findings have implications for the regulation of network excitability and seizure generation in the developing brain.NEW & NOTEWORTHY Despite the extensive literature showing the importance of the Na⁺-K⁺ pump in various neuronal functions, its roles in the developing brain are not well understood. This study reveals that the Na⁺-K⁺ pump differentially regulates the excitability of CA3 and CA1 neurons in the developing hippocampus, and the pump activity is crucial for maintaining network activity. Compromised Na⁺-K⁺ pump activity desynchronizes neuronal firing and transmitter release, leading to cessation of ongoing epileptiform network bursting.

Effect of acute mitochondrial dysfunction on hyperexcitable network activity in rat hippocampus in vitro

Metabolic stress imposed by epileptic seizures can result in mitochondrial dysfunction, believed to act as positive feedback on epileptogenesis and seizure susceptibility. As the mechanism behind this positive feedback is unclear, the aim of the present study was to investigate the causal link between acute mitochondrial dysfunction and increased seizure susceptibility in hyperexcitable hippocampal networks. Following the induction of spontaneous interictal-like discharges, acute selective pharmacological blockade of either of the mitochondrial respiratory complexes (MRC) I-IV induced seizure-like events (SLE) in 78-100% of experiments. A similar result was obtained by uncoupling the oxidative phosphorylation (OXPHOS) but not by selective blockade of MRCV (ATP synthase) which did not induce SLE. The reactive oxygen species (ROS) scavenger 4-hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (tempol, 2 mM) significantly reduced the proconvulsant effect of blocking MRCI but did not reduce the proconvulsant effect of OXPHOS uncoupling. These findings indicate that acute mitochondrial dysfunction can lead to a convulsive state within a short timeframe, and that increased ROS production makes substantial contribution to such induction in addition to other mitochondrial related factors, which appears to be independent of changes in ROS and ATP production.

Neuronal modeling of alternating hemiplegia of childhood reveals transcriptional compensation and replicates a trigger-induced phenotype

Alternating hemiplegia of childhood (AHC) is a rare neurodevelopmental disease caused by heterozygous de novo missense mutations in the ATP1A3 gene that encodes the neuronal specific α3 subunit of the Na,K-ATPase (NKA) pump. Mechanisms underlying patient episodes including environmental triggers remain poorly understood, and there are no empirically proven treatments for AHC. In this study, we generated patient-specific induced pluripotent stem cells (iPSCs) and isogenic controls for the E815K ATP1A3 mutation that causes the most phenotypically severe form of AHC. Using an in vitro iPSC-derived cortical neuron disease model, we found elevated levels of ATP1A3 mRNA in AHC lines compared to controls, without significant perturbations in protein expression. Microelectrode array analyses demonstrated that in cortical neuronal cultures, ATP1A3^+/E815K iPSC-derived neurons displayed less overall activity than neurons differentiated from isogenic mutation-corrected and unrelated control cell lines. However, induction of cellular stress by elevated temperature revealed a hyperactivity phenotype following heat stress in ATP1A3^+/E815K neurons compared to control lines. Treatment with flunarizine, a drug commonly used to prevent AHC episodes, did not impact this stress-triggered phenotype. These findings support the use of iPSC-derived neuronal cultures for studying complex neurodevelopmental conditions such as AHC and provide a platform for mechanistic discovery in a human disease model.

Molecular mechanisms of K+ clearance and extracellular space shrinkage-Glia cells as the stars

Neuronal signaling in the central nervous system (CNS) associates with release of K⁺ into the extracellular space resulting in transient increases in [K⁺ ]_o . This elevated K⁺ is swiftly removed, in part, via uptake by neighboring glia cells. This process occurs in parallel to the [K⁺ ]_o elevation and glia cells thus act as K⁺ sinks during the neuronal activity, while releasing it at the termination of the pulse. The molecular transport mechanisms governing this glial K⁺ absorption remain a point of debate. Passive distribution of K⁺ via Kir4.1-mediated spatial buffering of K⁺ has become a favorite within the glial field, although evidence for a quantitatively significant contribution from this ion channel to K⁺ clearance from the extracellular space is sparse. The Na⁺ /K⁺ -ATPase, but not the Na⁺ /K⁺ /Cl^- cotransporter, NKCC1, shapes the activity-evoked K⁺ transient. The different isoform combinations of the Na⁺ /K⁺ -ATPase expressed in glia cells and neurons display different kinetic characteristics and are thereby distinctly geared toward their temporal and quantitative contribution to K⁺ clearance. The glia cell swelling occurring with the K⁺ transient was long assumed to be directly associated with K⁺ uptake and/or AQP4, although accumulating evidence suggests that they are not. Rather, activation of bicarbonate- and lactate transporters appear to lead to glial cell swelling via the activity-evoked alkaline transient, K⁺ -mediated glial depolarization, and metabolic demand. This review covers evidence, or lack thereof, accumulated over the last half century on the molecular mechanisms supporting activity-evoked K⁺ and extracellular space dynamics.

Targeting Purinergic Signaling and Cell Therapy in Cardiovascular and Neurodegenerative Diseases

Extracellular purines exert several functions in physiological and pathophysiological mechanisms. ATP acts through P2 receptors as a neurotransmitter and neuromodulator and modulates heart contractility, while adenosine participates in neurotransmission, blood pressure, and many other mechanisms. Because of their capability to differentiate into mature cell types, they provide a unique therapeutic strategy for regenerating damaged tissue, such as in cardiovascular and neurodegenerative diseases. Purinergic signaling is pivotal for controlling stem cell differentiation and phenotype determination. Proliferation, differentiation, and apoptosis of stem cells of various origins are regulated by purinergic receptors. In this chapter, we selected neurodegenerative and cardiovascular diseases with clinical trials using cell therapy and purinergic receptor targeting. We discuss these approaches as therapeutic alternatives to neurodegenerative and cardiovascular diseases. For instance, promising results were demonstrated in the utilization of mesenchymal stem cells and bone marrow mononuclear cells in vascular regeneration. Regarding neurodegenerative diseases, in general, P2X7 and A_2A receptors mostly worsen the degenerative state. Stem cell-based therapy, mainly through mesenchymal and hematopoietic stem cells, showed promising results in improving symptoms caused by neurodegeneration. We propose that purinergic receptor activity regulation combined with stem cells could enhance proliferative and differentiation rates as well as cell engraftment.

Role of NKCC1 and KCC2 in Epilepsy: From Expression to Function

As a main inhibitory neurotransmitter in the central nervous system, γ-aminobutyric acid (GABA) activates chloride-permeable GABAa receptors (GABAa Rs) and induces chloride ion (Cl⁻) flow, which relies on the intracellular chloride concentration ([Cl⁻]_i) of the postsynaptic neuron. The Na-K-2Cl cotransporter isoform 1 (NKCC1) and the K-Cl cotransporter isoform 2 (KCC2) are two main cation-chloride cotransporters (CCCs) that have been implicated in human epilepsy. NKCC1 and KCC2 reset [Cl⁻]_i by accumulating and extruding Cl⁻, respectively. Previous studies have shown that the profile of NKCC1 and KCC2 in neonatal neurons may reappear in mature neurons under some pathophysiological conditions, such as epilepsy. Although increasing studies focusing on the expression of NKCC1 and KCC2 have suggested that impaired chloride plasticity may be closely related to epilepsy, additional neuroelectrophysiological research aimed at studying the functions of NKCC1 and KCC2 are needed to understand the exact mechanism by which they induce epileptogenesis. In this review, we aim to briefly summarize the current researches surrounding the expression and function of NKCC1 and KCC2 in epileptogenesis and its implications on the treatment of epilepsy. We will also explore the potential for NKCC1 and KCC2 to be therapeutic targets for the development of novel antiepileptic drugs.

Exposure to 1-bromopropane vapors during pregnancy enhances the development of hippocampal neuronal excitability in rat pups during lactation

OBJECTIVES

Although 1-Bromopropane (1-BP) exposure has been reported to cause neurotoxicity in adult humans and animals, its effects on the development of the central nervous system remain unclear. Recently, we reported delayed developmental neurotoxicity (DNT) upon 1-BP exposure in rats. Here we aimed to study the effect of prenatal 1-BP exposure on the hippocampal excitability in the juvenile offspring.

METHODS

Pregnant Wistar rats were exposed to vaporized 1-BP for 20 days (6 h/d) with concentrations of 0 (control), 400, or 700 ppm. Hippocampal slices were prepared from male offspring during postnatal days (PNDs) 13, 14, and 15. Field excitatory postsynaptic potential (fEPSP) and population spike (PS) were recorded simultaneously from the CA1 region.

RESULTS

In the exposed groups, the stimulation/response relationships of fEPSP slope and PS amplitude were enhanced more than in the control group at PND 14. Analysis of fEPSP-spike coupling demonstrated increased values of Top and Eslope50 in the exposed groups. Real-time PCR analysis showed a significant increase in the mRNA levels of the adult type Nav 1.1 Na+ channel subunit and the GluR1 glutamate receptor subunit in the hippocampus of the 700 ppm group at PND 14.

CONCLUSIONS

Our results provide evidence that prenatal exposure to 1-BP accelerates developmental enhancement of hippocampal excitability in the pups before eye-opening. The current study suggests that our evaluation method of DNT is applicable to the industrial chemical 1-BP.

Recessive Inheritance of Congenital Hydrocephalus With Other Structural Brain Abnormalities Caused by Compound Heterozygous Mutations in ATP1A3

Background

ATP1A3 encodes the α3 subunit of the Na⁺/K⁺ ATPase, a fundamental ion-transporting enzyme. Primarily expressed in neurons, ATP1A3 is mutated in several autosomal dominant neurological diseases. To our knowledge, damaging recessive genotypes in ATP1A3 have never been associated with any human disease. Atp1a3 deficiency in zebrafish results in hydrocephalus; however, no known association exists between ATP1A3 and human congenital hydrocephalus (CH).

Methods

We utilized whole-exome sequencing (WES), bioinformatics, and computational modeling to identify and characterize novel ATP1A3 mutations in a patient with CH. We performed immunohistochemical studies using mouse embryonic brain tissues to characterize Atp1a3 expression during brain development.

Results

We identified two germline mutations in ATP1A3 (p. Arg19Cys and p.Arg463Cys), each of which was inherited from one of the patient’s unaffected parents, in a single patient with severe obstructive CH due to aqueductal stenosis, along with open schizencephaly, type 1 Chiari malformation, and dysgenesis of the corpus callosum. Both mutations are predicted to be highly deleterious and impair protein stability. Immunohistochemical studies demonstrate robust Atp1a3 expression in neural stem cells (NSCs), differentiated neurons, and choroid plexus of the mouse embryonic brain.

Conclusion

These data provide the first evidence of a recessive human phenotype associated with mutations in ATP1A3, and implicate impaired Na⁺/K⁺ ATPase function in the pathogenesis of CH.

Mitochondrial dysfunction and role in spreading depolarization and seizure

The effect of pathological phenomena such as epileptic seizures and spreading depolarization (SD) on mitochondria and the potential feedback of mitochondrial dysfunction into the dynamics of those phenomena are complex and difficult to study experimentally due to the simultaneous changes in many variables governing neuronal behavior. By combining a model that accounts for a wide range of neuronal behaviors including seizures, normoxic SD, and hypoxic SD (HSD), together with a detailed model of mitochondrial function and intracellular Ca²⁺ dynamics, we investigate mitochondrial dysfunction and its potential role in recovery of the neuron from seizures, HSD, and SD. Our results demonstrate that HSD leads to the collapse of mitochondrial membrane potential and cellular ATP levels that recover only when normal oxygen supply is restored. Mitochondrial organic phosphate and pH gradients determine the strength of the depolarization block during HSD and SD, how quickly the cell enters the depolarization block when the oxygen supply is disrupted or potassium in the bath solution is raised beyond the physiological value, and how fast the cell recovers from SD and HSD when normal potassium concentration and oxygen supply are restored. Although not as dramatic as phosphate and pH gradients, mitochondrial Ca²⁺ uptake has a similar effect on neuronal behavior during these conditions.

Factors in the disease severity of ATP1A3 mutations: Impairment, misfolding, and allele competition

Dominant mutations of ATP1A3, a neuronal Na,K-ATPase α subunit isoform, cause neurological disorders with an exceptionally wide range of severity. Several new mutations and their phenotypes are reported here (p.Asp366His, p.Asp742Tyr, p.Asp743His, p.Leu924Pro, and a VUS, p.Arg463Cys). Mutations associated with mild or severe phenotypes [rapid-onset dystonia-parkinsonism (RDP), alternating hemiplegia of childhood (AHC), or early infantile epileptic encephalopathy (EIEE)] were expressed in HEK-293 cells. Paradoxically, the severity of human symptoms did not correlate with whether there was enough residual activity to support cell survival. We hypothesized that distinct cellular consequences may result not only from pump inactivation but also from protein misfolding. Biosynthesis was investigated in four tetracycline-inducible isogenic cell lines representing different human phenotypes. Two cell biological complications were found. First, there was impaired trafficking of αβ complex to Golgi apparatus and plasma membrane, as well as changes in cell morphology, for two mutations that produced microcephaly or regions of brain atrophy in patients. Second, there was competition between exogenous mutant ATP1A3 (α3) and endogenous ATP1A1 (α1) so that their sum was constant. This predicts that in patients, the ratio of normal to mutant ATP1A3 proteins will vary when misfolding occurs. At the two extremes, the results suggest that a heterozygous mutation that only impairs Na,K-ATPase activity will produce relatively mild disease, while one that activates the unfolded protein response could produce severe disease and may result in death of neurons independently of ion pump inactivation.

Regulation of Neuronal Na+/K+-ATPase by Specific Protein Kinases and Protein Phosphatases

The Na⁺/K⁺-ATPase (NKA) is a ubiquitous membrane-bound enzyme responsible for generating and maintaining the Na⁺ and K⁺ electrochemical gradients across the plasmalemma of living cells. Numerous studies in non-neuronal tissues have shown that this transport mechanism is reversibly regulated by phosphorylation/dephosphorylation of the catalytic α subunit and/or associated proteins. In neurons, Na⁺/K⁺ transport by NKA is essential for almost all neuronal operations, consuming up to two-thirds of the neuron's energy expenditure. However, little is known about its cellular regulatory mechanisms. Here we have used an electrophysiological approach to monitor NKA transport activity in male rat hippocampal neurons in situ We report that this activity is regulated by a balance between serine/threonine phosphorylation and dephosphorylation. Phosphorylation by the protein kinases PKG and PKC inhibits NKA activity, whereas dephosphorylation by the protein phosphatases PP-1 and PP-2B (calcineurin) reverses this effect. Given that these kinases and phosphatases serve as downstream effectors in key neuronal signaling pathways, they may mediate the coupling of primary messengers, such as neurotransmitters, hormones, and growth factors, to the NKAs, through which multiple brain functions can be regulated or dysregulated.SIGNIFICANCE STATEMENT The Na⁺/K⁺-ATPase (NKA), known as the "Na⁺ pump," is a ubiquitous membrane-bound enzyme responsible for generating and maintaining the Na⁺ and K⁺ electrochemical gradients across the plasma membrane of living cells. In neurons, as in most types of cells, the NKA generates the negative resting membrane potential, which is the basis for almost all aspects of cellular function. Here we used an electrophysiological approach to monitor physiological NKA transport activity in single hippocampal pyramidal cells in situ We have found that neuronal NKA activity is oppositely regulated by phosphorylation and dephosphorylation, and we have identified the main protein kinases and phosphatases mediating this regulation. This fundamental form of NKA regulation likely plays a role in multiple brain functions.

Circadian Disruptions in the Myshkin Mouse Model of Mania Are Independent of Deficits in Suprachiasmatic Molecular Clock Function

BACKGROUND

Alterations in environmental light and intrinsic circadian function have strong associations with mood disorders. The neural origins underpinning these changes remain unclear, although genetic deficits in the molecular clock regularly render mice with altered mood-associated phenotypes.

METHODS

A detailed circadian and light-associated behavioral characterization of the Na+/K+-ATPase α3 Myshkin (Myk/+) mouse model of mania was performed. Na+/K+-ATPase α3 does not reside within the core circadian molecular clockwork, but Myk/+ mice exhibit concomitant disruption in circadian rhythms and mood. The neural basis of this phenotype was investigated through molecular and electrophysiological dissection of the master circadian pacemaker, the suprachiasmatic nuclei (SCN). Light input and glutamatergic signaling to the SCN were concomitantly assessed through behavioral assays and calcium imaging.

RESULTS

In vivo assays revealed several circadian abnormalities including lengthened period and instability of behavioral rhythms, and elevated metabolic rate. Grossly aberrant responses to light included accentuated resetting, accelerated re-entrainment, and an absence of locomotor suppression. Bioluminescent recording of circadian clock protein (PERIOD2) output from ex vivo SCN revealed no deficits in Myk/+ molecular clock function. Optic nerve crush rescued the circadian period of Myk/+ behavior, highlighting that afferent inputs are critical upstream mediators. Electrophysiological and calcium imaging SCN recordings demonstrated changes in the response to glutamatergic stimulation as well as the electrical output indicative of altered retinal input processing.

CONCLUSIONS

The Myshkin model demonstrates profound circadian and light-responsive behavioral alterations independent of molecular clock disruption. Afferent light signaling drives behavioral changes and raises new mechanistic implications for circadian disruption in affective disorders.

Germline De Novo Mutations in ATP1A1 Cause Renal Hypomagnesemia, Refractory Seizures, and Intellectual Disability

Over the last decades, a growing spectrum of monogenic disorders of human magnesium homeostasis has been clinically characterized, and genetic studies in affected individuals have identified important molecular components of cellular and epithelial magnesium transport. Here, we describe three infants who are from non-consanguineous families and who presented with a disease phenotype consisting of generalized seizures in infancy, severe hypomagnesemia, and renal magnesium wasting. Seizures persisted despite magnesium supplementation and were associated with significant intellectual disability. Whole-exome sequencing and conventional Sanger sequencing identified heterozygous de novo mutations in the catalytic Na⁺, K⁺-ATPase α1 subunit (ATP1A1). Functional characterization of mutant Na⁺, K⁺-ATPase α1 subunits in heterologous expression systems revealed not only a loss of Na⁺, K⁺-ATPase function but also abnormal cation permeabilities, which led to membrane depolarization and possibly aggravated the effect of the loss of physiological pump activity. These findings underline the indispensable role of the α1 isoform of the Na⁺, K⁺-ATPase for renal-tubular magnesium handling and cellular ion homeostasis, as well as maintenance of physiologic neuronal activity.

Opposing effects of 2-deoxy-d-glucose on interictal- and ictal-like activity when K+ currents and GABAA receptors are blocked in rat hippocampus in vitro

The ketogenic diet (KD), a high-fat, carbohydrate-restricted diet, is used as an alternative treatment for drug-resistant epileptic patients. Evidence suggests that compromised glucose metabolism has a significant role in the anticonvulsant action of the KD; however, it is unclear what part of the glucose metabolism that is important. The present study investigates how selective alterations in glycolysis and oxidative phosphorylation influence epileptiform activity induced by blocking K+ currents and GABAA and NMDA receptors in the hippocampal slice preparation. Blocking glycolysis with the glucose derivative 2-deoxy-d-glucose (2-DG; 10 mM) gave a fast reduction of the frequency of interictal discharge (IED) consistent with findings in other in vitro models. However, this was followed by the induction of seizure-like discharges in area CA1 and CA3. Substituting glucose with sucrose (glucopenia) had effects similar to those of 2-DG, whereas substitution with l-lactate or pyruvate reduced the IED but had a less proconvulsant effect. Blockade of ATP-sensitive K+ channels, glycine or adenosine 1 receptors, or depletion of the endogenous anticonvulsant compound glutathione did not prevent the actions of 2-DG. Baclofen (2 μM) reproduced the effect of 2-DG on IED activity. The proconvulsant effect of 2-DG could be reproduced by blocking the oxidative phosphorylation with the complex I toxin rotenone (4 μM). The data suggest that inhibition of IED, induced by 2-DG and glucopenia, is a direct consequence of impairment of glycolysis, likely exerted via a decreased recurrent excitatory synaptic transmission in area CA3. The accompanying proconvulsant effect is caused by an excitatory mechanism, depending on impairment of oxidative phosphorylation.

NEW & NOTEWORTHY This study reveals two opposing effects of 2-deoxy-d-glucose (2-DG) and glucopenia on in vitro epileptiform discharge observed during combined blockade of K+ currents and GABAA receptors. Interictal-like activity is inhibited by a mechanism that selectively depends on impairment of glycolysis and that results from a decrease in the strength of excitatory recurrent synaptic transmission in area CA3. In contrast, 2-DG and glucopenia facilitate ictal-like activity by an excitatory mechanism, depending on impairment of mitochondrial oxidative phosphorylation.

Epilepsy-associated alterations in hippocampal excitability

The hippocampus exhibits a wide range of epilepsy-related abnormalities and is situated in the mesial temporal lobe, where limbic seizures begin. These abnormalities could affect membrane excitability and lead to overstimulation of neurons. Multiple overlapping processes refer to neural homeostatic responses develop in neurons that work together to restore neuronal firing rates to control levels. Nevertheless, homeostatic mechanisms are unable to restore normal neuronal excitability, and the epileptic hippocampus becomes hyperexcitable or hypoexcitable. Studies show that there is hyperexcitability even before starting recurrent spontaneous seizures, suggesting although hippocampal hyperexcitability may contribute to epileptogenesis, it alone is insufficient to produce epileptic seizures. This supports the concept that the hippocampus is not the only substrate for limbic seizure onset, and a broader hyperexcitable limbic structure may contribute to temporal lobe epilepsy (TLE) seizures. Nevertheless, seizures also occur in conditions where the hippocampus shows a hypoexcitable phenotype. Since TLE seizures most often originate in the hippocampus, it could therefore be assumed that both hippocampal hypoexcitability and hyperexcitability are undesirable states that make the epileptic hippocampal network less stable and may, under certain conditions, trigger seizures.

Brain sodium MRI in human epilepsy: Disturbances of ionic homeostasis reflect the organization of pathological regions

In light of technical advancements supporting exploration of MR signals other than ¹H, sodium (²³Na) has received attention as a marker of ionic homeostasis and cell viability. Here, we evaluate for the first time the possibility that ²³Na-MRI is sensitive to pathological processes occurring in human epilepsy. A normative sample of 27 controls was used to normalize regions of interest (ROIs) from 1424 unique brain locales on quantitative ²³Na-MRI and high-resolution ¹H-MPRAGE images. ROIs were based on intracerebral electrodes in ten patients undergoing epileptic network mapping. The stereo-EEG gold standard was used to define regions as belonging to primarily epileptogenic, secondarily irritative and to non-involved regions. Estimates of total sodium concentration (TSC) on ²³Na-MRI and cerebrospinal fluid (CSF) on ¹H imaging were extracted for each patient ROI, and normalized against the same region in controls. ROIs with disproportionate CSF contributions (Z_CSF≥1.96) were excluded. TSC levels were found to be elevated in patients relative to controls except in one patient, who suffered non-convulsive seizures during the scan, in whom we found reduced TSC levels. In the remaining patients, an ANOVA (F₁₁₀₀= 12.37, p<0.0001) revealed a highly significant effect of clinically-defined zones (F₁₁₀₀= 11.13, p<0.0001), with higher normalized TSC in the epileptogenic zone relative to both secondarily irritative (F₁₁₀₀= 11, p=0.0009) and non-involved regions (F₁₁₀₀= 17.8, p<0.0001). We provide the first non-invasive, in vivo evidence of a chronic TSC elevation alongside Z_CSF levels within the normative range, associated with the epileptogenic region even during the interictal period in human epilepsy, and the possibility of reduced TSC levels due to seizure. In line with modified homeostatic mechanisms in epilepsy - including altered mechanisms underlying ionic gating, clearance and exchange - we provide the first indication of ²³Na-MRI as an assay of altered sodium concentrations occurring in epilepsy associated with the organization of clinically relevant divisions of pathological cortex.

Noradrenergic β-Adrenoceptor-Mediated Intracellular Molecular Mechanism of Na-K ATPase Subunit Expression in C6 Cells

Rapid eye movement sleep deprivation-associated elevated noradrenaline increases and decreases neuronal and glial Na-K ATPase activity, respectively. In this study, using C6 cell-line as a model, we investigated the possible intracellular molecular mechanism of noradrenaline-induced decreased glial Na-K ATPase activity. The cells were treated with noradrenaline in the presence or absence of adrenoceptor antagonists, modulators of extra- and intracellular Ca⁺⁺ and modulators of intracellular signalling pathways. We observed that noradrenaline acting on β-adrenoceptor decreased Na-K ATPase activity and mRNA expression of the catalytic α2-Na-K ATPase subunit in the C6 cells. Further, cAMP and protein kinase-A mediated release of intracellular Ca⁺⁺ played a critical role in such decreased α2-Na-K ATPase expression. In contrast, noradrenaline acting on β-adrenoceptor up-regulated the expression of regulatory β2-Na-K ATPase subunit, which although was cAMP and Ca⁺⁺ dependent, was independent of protein kinase-A and protein kinase-C. Combining these with previous findings (including ours) we have proposed a working model for noradrenaline-induced suppression of glial Na-K ATPase activity and alteration in its subunit expression. The findings help understanding noradrenaline-associated maintenance of brain excitability during health and altered states, particularly in relation to rapid eye movement sleep and its deprivation when the noradrenaline level is naturally altered.

Immunohistochemical Localization of Translationally Controlled Tumor Protein in Axon Terminals of Mouse Hippocampal Neurons

Translationally controlled tumor protein (TCTP) is a cytosolic protein with microtubule stabilization and calcium-binding activities. TCTP is expressed in most organs including the nervous system. However, detailed distribution and functional significance of TCTP in the brain remain unexplored. In this study, we investigated the global and subcellular distributions of TCTP in the mouse brain. Immunohistochemical analyses with anti-TCTP revealed that TCTP was widely distributed in almost all regions of the brain including the cerebral cortex, thalamus, hypothalamus, hippocampus, and amygdala, wherein it was localized in axon tracts and axon terminals. In the hippocampus, TCTP was prominently localized to axon terminals of the perforant path in the dentate gyrus, the mossy fibers in the cornu ammonis (CA)3 region, and the Schaffer collaterals in the CA1 field, but not in cell bodies of granule cells and pyramidal neurons, and in their dendritic processes. Widespread distribution of TCTP in axon tracts and axon terminals throughout the brain suggests that TCTP is likely involved in neurotransmitter release and/or maintaining synaptic structures in the brain, and that it might have a role in maintaining synaptic functions and synaptic configurations important for normal cognitive, stress and emotional functions.

Correlative study of peripheral ATP1A1 gene expression level to anxiety severity score on major depressive disorder patients

BACKGROUND

Major depressive disorder (MDD) frequently co-occurs with other psychiatric problems. Our previous study showed that ATP1A1 gene expression level was significantly decreased in MDD patients. This research explores the potential correlations between the ATP1A1 expression level reduction and MDD patients' clinical manifestation.

METHODS

All participant patients were diagnosed by Diagnostic and Statistical Manual of Mental Disorders - 4th edition (DSM-IV). Hamilton rating scale for depression (HAM-D) and anxiety (HAM-A) were applied to group patients into different categories. ATP1A1 expression level was measured by reverse transcript real-time polymerase chain reaction.

RESULTS

ATP1A1 expression levels of all MDD subgroups showed significant reduction compared to the control group (p<0.01). Further, the trend of ATP1A1 expression level reduction is significantly related to MDD patients' HAM-A scores (p<0.01). However, there was no significance between ATP1A1 level and HAM-D scores (p>0.05).

CONCLUSIONS

ATP1A1 expression level reduction is related to MDD anxiety score, which may be an explanation for the clinical manifestations and the underlining physiological mechanisms.

The effect of subchronic supplementation with folic acid and l-arginine on homocysteine-induced seizures

The aim of the present study was to examine the effect of subchronic co-administration of folic acid (F) and l-arginine (A) on behavioural and electroencephalographic (EEG) characteristics of dl homocysteine thiolactone (H) induced seizures in adult rats. The activity of membrane ATPases in different brain regions were also investigated. Rats were treated with F, A, or vehicle for 15 days (regimen: F 5 mg/kg + A 500 mg/kg (F5A500); F 10 mg/kg + A 300 mg/kg (F10A300)). Seizures were elicited by convulsive dose of H (H, F5A500H, F10A300H) Subchronic supplementation with F and A did not affect seizure incidence, number of seizure episodes, and severity in F5A500H and F10A300H groups vs. H group. However, a tendency to increase latency and decrease the number of seizure episodes was noticed in the F10A300H group. EEG mean spectral power densities during ictal periods were significantly lower in F10A300H vs. H group. The activity of Na+/K+-ATPase and Mg2+-ATPase was significantly increased in almost all examined structures in rats treated with F and A. We can conclude that subchronic supplementation with folic acid and l-arginine has an antiepileptic effect in dl homocysteine thiolactone induced epilepsy.

Insights into the Pathology of the α3 Na(+)/K(+)-ATPase Ion Pump in Neurological Disorders; Lessons from Animal Models

The transmembrane Na(+)-/K(+) ATPase is located at the plasma membrane of all mammalian cells. The Na(+)-/K(+) ATPase utilizes energy from ATP hydrolysis to extrude three Na(+) cations and import two K(+) cations into the cell. The minimum constellation for an active Na(+)-/K(+) ATPase is one alpha (α) and one beta (β) subunit. Mammals express four α isoforms (α1-4), encoded by the ATP1A1-4 genes, respectively. The α1 isoform is ubiquitously expressed in the adult central nervous system (CNS) whereas α2 primarily is expressed in astrocytes and α3 in neurons. Na(+) and K(+) are the principal ions involved in action potential propagation during neuronal depolarization. The α1 and α3 Na(+)-/K(+) ATPases are therefore prime candidates for restoring neuronal membrane potential after depolarization and for maintaining neuronal excitability. The α3 isoform has approximately four-fold lower Na(+) affinity compared to α1 and is specifically required for rapid restoration of large transient increases in [Na(+)]i. Conditions associated with α3 deficiency are therefore likely aggravated by suprathreshold neuronal activity. The α3 isoform been suggested to support re-uptake of neurotransmitters. These processes are required for normal brain activity, and in fact autosomal dominant de novo mutations in ATP1A3 encoding the α3 isoform has been found to cause the three neurological diseases Rapid Onset Dystonia Parkinsonism (RDP), Alternating Hemiplegia of Childhood (AHC), and Cerebellar ataxia, areflexia, pes cavus, optic atrophy, and sensorineural hearing loss (CAPOS). All three diseases cause acute onset of neurological symptoms, but the predominant neurological manifestations differ with particularly early onset of hemiplegic/dystonic episodes and mental decline in AHC, ataxic encephalopathy and impairment of vision and hearing in CAPOS syndrome and late onset of dystonia/parkinsonism in RDP. Several mouse models have been generated to study the in vivo consequences of Atp1a3 modulation. The different mice show varying degrees of hyperactivity, gait problems, and learning disability as well as stress-induced seizures. With the advent of several Atp1a3-gene or chemically modified animal models that closely phenocopy many aspects of the human disorders, we will be able to reach a much better understanding of the etiology of RDP, AHC, and CAPOS syndrome.

The role of TRPC6 in seizure susceptibility and seizure-related neuronal damage in the rat dentate gyrus

Transient receptor potential canonical channel-6 (TRPC6) forms Ca(2+)-permeable non-selective cation channels in neurons. Although TRPC6 plays an important role in neurite outgrowth and neuronal survival during development, TRPC6 expression profiles available to identify distinctive hippocampal neuronal damage and hippocampal excitability in epilepsy are less defined. As compared to normal animals, TRPC6 expression was down-regulated in chronic epileptic rats showing spontaneous recurrent seizures. TRPC6 knockdown increased seizure susceptibility, excitability ratio and paired-pulse inhibition in the dentate gyrus (DG) of normal animals. Furthermore, TRPC6 knockdown promoted programmed neuronal necrosis in dentate granule cells, but prevented it in CA1 and CA3 neurons following status epilepticus. The present data suggest for the first time that TRPC6 may inhibit seizure susceptibility and neuronal vulnerability in the rat DG.

Increased expression of GAP43 in interneurons in a rat model of experimental polymicrogyria

To investigate seizure susceptibility in polymicrogyria, the seizure threshold and growth-associated protein GAP43 expression were analyzed in a rat experimental model of polymicrogyria induced by intracerebral injection of ibotenate. A total of 72 neonates from 9 pregnant rats were used. Intraperitoneal pentylenetetrazole injection did not induce any seizure activity in the control rats, although it elicited seizures of variable severity in the polymicrogyria rats. Fluoro-Jade B-positive degenerating interneurons were found in the polymicrogyria brains; however, no such neurons were detected in the control brains. In the polymicrogyria rats, the GAP43 expression was significantly and widely distributed in the brain, and the percentage of parvalbumin-positive interneurons in the GAP43-positive cells was significantly higher than that observed in the nonphosphorylated neurofilament-positive pyramidal cells. We conclude that the relatively selective vulnerability of inhibitory interneurons constitutes the basis for the decreased seizure threshold observed in this model of polymicrogyria.

Molecular mechanisms of epilepsy

Decades of experimental work have established an imbalance of excitation and inhibition as the leading mechanism of the transition from normal brain function to seizure. In epilepsy, these transitions are rare and abrupt. Transition processes incorporating positive feedback, such as activity-dependent disinhibition, could provide these uncommon timing features. A rapidly expanding array of genetic etiologies will help delineate the molecular mechanism(s). This delineation will entail quite a bit of cell biology. The genes discovered so far are more remarkable for their diversity than their similarities.

Sodium butyrate and mood stabilizers block ouabain-induced hyperlocomotion and increase BDNF, NGF and GDNF levels in brain of Wistar rats

Bipolar Disorder (BD) is one of the most severe psychiatric disorders. Despite adequate treatment, patients continue to have recurrent mood episodes, residual symptoms, and functional impairment. Some preclinical studies have shown that histone deacetylase inhibitors may act on manic-like behaviors. Neurotrophins have been considered important mediators in the pathophysiology of BD. The present study aims to investigate the effects of lithium (Li), valproate (VPA), and sodium butyrate (SB), an HDAC inhibitor, on BDNF, NGF and GDNF in the brain of rats subjected to an animal model of mania induced by ouabain. Wistar rats received a single ICV injection of ouabain or artificial cerebrospinal fluid. From the day following ICV injection, the rats were treated for 6 days with intraperitoneal injections of saline, Li, VPA or SB twice a day. In the 7th day after ouabain injection, locomotor activity was measured using the open-field test. The BDNF, NGF and GDNF levels were measured in the hippocampus and frontal cortex by sandwich-ELISA. Li, VPA or SB treatments reversed ouabain-related manic-like behavior. Ouabain decreased BDNF, NGF and GDNF levels in hippocampus and frontal cortex of rats. The treatment with Li, VPA or SB reversed these impairment induced by ouabain. In addition, Li, VPA and SB per se increased NGF and GDNF levels in hippocampus of rats. Our data support the notion that neurotrophic factors play a role in BD and in the mechanisms of the action of Li, VPA and SB.

Electrogenic properties of the Na⁺/K⁺ ATPase control transitions between normal and pathological brain states

Ionic concentrations fluctuate significantly during epileptic seizures. In this study, using a combination of in vitro electrophysiology, computer modeling, and dynamical systems analysis, we demonstrate that changes in the potassium and sodium intra- and extracellular ion concentrations ([K(+)] and [Na(+)], respectively) during seizure affect the neuron dynamics by modulating the outward Na(+)/K(+) pump current. First, we show that an increase of the outward Na(+)/K(+) pump current mediates termination of seizures when there is a progressive increase in the intracellular [Na(+)]. Second, we show that the Na(+)/K(+) pump current is crucial in maintaining the stability of the physiological network state; a reduction of this current leads to the onset of seizures via a positive-feedback loop. We then present a novel dynamical mechanism for bursting in neurons with a reduced Na(+)/K(+) pump. Overall, our study demonstrates the profound role of the current mediated by Na(+)/K(+) ATPase on the stability of neuronal dynamics that was previously unknown.

Long-term decrease in Na+,K+-ATPase activity after pilocarpine-induced status epilepticus is associated with nitration of its alpha subunit

Temporal lobe epilepsy (TLE) is the most common type of epilepsy with about one third of TLE patients being refractory to antiepileptic drugs. Knowledge about the mechanisms underlying seizure activity is fundamental to the discovery of new drug targets. Brain Na(+),K(+)-ATPase activity contributes to the maintenance of the electrochemical gradients underlying neuronal resting and action potentials as well as the uptake and release of neurotransmitters. In the present study we tested the hypothesis that decreased Na(+),K(+)-ATPase activity is associated with changes in the alpha subunit phosphorylation and/or redox state. Activity of Na(+),K(+)-ATPase decreased in the hippocampus of C57BL/6 mice 60 days after pilocarpine-induced status epilepticus (SE). In addition, the Michaelis-Menten constant for ATP of α2/3 isoforms increased at the same time point. Nitration of the α subunit may underlie decreased Na(+),K(+)-ATPase activity, however no changes in expression or phosphorylation state at Ser(943) were found. Further studies are necessary define the potential of nitrated Na(+),K(+)-ATPase as a new therapeutic target for seizure disorders.

Epilepsy, energy deficiency and new therapeutic approaches including diet

Metabolic dysfunction leading to epilepsy is well recognised. Dietary therapy, in particular the ketogenic diet, is now considered an effective option. Recent genetic studies have highlighted the central role that metabolism can play in setting seizure susceptibility. Here we discuss various metabolic disorders implicated in epilepsy focusing on energy deficiency due to genetic and environmental causes. We argue that low, uncompensated brain glucose levels can precipitate seizures. We will also explore mechanisms of disease and therapy in an attempt to identify common metabolic pathways involved in modulating seizure susceptibility. Finally, newer therapeutic approaches based on diet manipulation in the context of energy deficiency are discussed.

Distinct neurological disorders with ATP1A3 mutations

Genetic research has shown that mutations that modify the protein-coding sequence of ATP1A3, the gene encoding the α3 subunit of Na(+)/K(+)-ATPase, cause both rapid-onset dystonia parkinsonism and alternating hemiplegia of childhood. These discoveries link two clinically distinct neurological diseases to the same gene, however, ATP1A3 mutations are, with one exception, disease-specific. Although the exact mechanism of how these mutations lead to disease is still unknown, much knowledge has been gained about functional consequences of ATP1A3 mutations using a range of in-vitro and animal model systems, and the role of Na(+)/K(+)-ATPases in the brain. Researchers and clinicians are attempting to further characterise neurological manifestations associated with mutations in ATP1A3, and to build on the existing molecular knowledge to understand how specific mutations can lead to different diseases.

Development of an animal model for gestational hypermethioninemia in rat and its effect on brain Na⁺,K⁺-ATPase/Mg²⁺-ATPase activity and oxidative status of the offspring

In the present study we developed a chemically induced experimental model for gestational hypermethioninemia in rats and evaluated in the offspring the activities of Na(+),K(+)-ATPase and Mg(2+)-ATPase, as well as oxidative stress parameters, namely sulfhydryl content, thiobarbituric acid-reactive substances and the antioxidant enzymes superoxide dismutase and catalase in encephalon. Serum and encephalon levels of methionine and total homocysteine were also evaluated in mother rats and in the offspring. Pregnant Wistar rats received two daily subcutaneous injections of methionine throughout the gestational period (21 days). During the treatment, a group of pregnant rats received dose 1 (1.34 μmol methionine/g body weight) and the other one received dose 2 (2.68 μmol methionine/g body weight). Control group received saline. After the rats give birth, a first group of pups was killed at the 7th day of life and the second group at the 21th day of life for removal of serum and encephalon. Mother rats were killed at the 21th day postpartum for removal of serum and encephalon. Both doses 1 and 2 increased methionine levels in encephalon of the mother rats and dose 2 increased methionine levels in encephalon of the offspring. Maternal hypermethioninemia also decreased the activities of Na(+),K(+)-ATPase, Mg(2+)-ATPase and catalase, as well as reduced total sulfhydryl content in the encephalon of the pups. This chemical model seems to be appropriate for studies aiming to investigate the effect of maternal hypermethioninemia on the developing brain during gestation in order to clarify possible neurochemical changes in the offspring.

Contributions of the Na⁺/K⁺-ATPase, NKCC1, and Kir4.1 to hippocampal K⁺ clearance and volume responses

Network activity in the brain is associated with a transient increase in extracellular K(+) concentration. The excess K(+) is removed from the extracellular space by mechanisms proposed to involve Kir4.1-mediated spatial buffering, the Na(+)/K(+)/2Cl(-) cotransporter 1 (NKCC1), and/or Na(+)/K(+)-ATPase activity. Their individual contribution to [K(+)]o management has been of extended controversy. This study aimed, by several complementary approaches, to delineate the transport characteristics of Kir4.1, NKCC1, and Na(+)/K(+)-ATPase and to resolve their involvement in clearance of extracellular K(+) transients. Primary cultures of rat astrocytes displayed robust NKCC1 activity with [K(+)]o increases above basal levels. Increased [K(+)]o produced NKCC1-mediated swelling of cultured astrocytes and NKCC1 could thereby potentially act as a mechanism of K(+) clearance while concomitantly mediate the associated shrinkage of the extracellular space. In rat hippocampal slices, inhibition of NKCC1 failed to affect the rate of K(+) removal from the extracellular space while Kir4.1 enacted its spatial buffering only during a local [K(+)]o increase. In contrast, inhibition of the different isoforms of Na(+)/K(+)-ATPase reduced post-stimulus clearance of K(+) transients. The astrocyte-characteristic α2β2 subunit composition of Na(+)/K(+)-ATPase, when expressed in Xenopus oocytes, displayed a K(+) affinity and voltage-sensitivity that would render this subunit composition specifically geared for controlling [K(+)]o during neuronal activity. In rat hippocampal slices, simultaneous measurements of the extracellular space volume revealed that neither Kir4.1, NKCC1, nor Na(+)/K(+)-ATPase accounted for the stimulus-induced shrinkage of the extracellular space. Thus, NKCC1 plays no role in activity-induced extracellular K(+) recovery in native hippocampal tissue while Kir4.1 and Na(+)/K(+)-ATPase serve temporally distinct roles.

A sodium-pump-mediated afterhyperpolarization in pyramidal neurons

The sodium-potassium ATPase (i.e., the "sodium pump") plays a central role in maintaining ionic homeostasis in all cells. Although the sodium pump is intrinsically electrogenic and responsive to dynamic changes in intracellular sodium concentration, its role in regulating neuronal excitability remains unclear. Here we describe a physiological role for the sodium pump in regulating the excitability of mouse neocortical layer 5 and hippocampal CA1 pyramidal neurons. Trains of action potentials produced long-lasting (∼20 s) afterhyperpolarizations (AHPs) that were insensitive to blockade of voltage-gated calcium channels or chelation of intracellular calcium, but were blocked by tetrodotoxin, ouabain, or the removal of extracellular potassium. Correspondingly, the AHP time course was similar to the decay of activity-induced increases in intracellular sodium, whereas intracellular calcium decayed at much faster rates. To determine whether physiological patterns of activity engage the sodium pump, we replayed in vitro a place-specific burst of 15 action potentials recorded originally in vivo in a CA1 "place cell" as the animal traversed the associated place field. In both layer 5 and CA1 pyramidal neurons, this "place cell train" generated small, long-lasting AHPs capable of reducing neuronal excitability for many seconds. Place-cell-train-induced AHPs were blocked by ouabain or removal of extracellular potassium, but not by intracellular calcium chelation. Finally, we found calcium contributions to the AHP to be temperature dependent: prominent at room temperature, but largely absent at 35°C. Our results demonstrate a previously unappreciated role for the sodium-potassium ATPase in regulating the excitability of neocortical and hippocampal pyramidal neurons.

Decreased Na+/K+ ATPase α1 (ATP1A1) gene expression in major depression patients’ peripheral blood

Major depression affects the central nervous system and thereafter the autonomic nervous system, immune system, and endocrine system. Na+/K+ ATPase, as a major mediator of cellular transmembrane ionic gradients, plays an important role in nervous signal transduction. Three types of Na+/K+ ATPase α subunit isoforms (ATP1A1, ATP1A2, and ATP1A3) are found in brain but vary in the type of cell and level of expression. It has been confirmed that reduced expression of ATP1A2 and ATP1A3 are related to depressive disorder. However, there is no reported correlation between ATP1A1 and major depression. This study investigated the potential correlation between ATP1A1 gene expression level and major depression. The expression levels of ATP1A1 gene in the peripheral circulation of both depressive patients and healthy human controls were quantified by using reverse transcripted quantitative polymerase chain reaction. Statistical analysis showed a significant decrease of ATP1A1 expression level in major depression patients when compared to that of healthy controls (P<0.01). The differences of gene nucleotide sequences and protein structures among ATP1A1, ATP1A2, and ATP1A3 were also illustrated. This study demonstrates, for the first time, that ATP1A1 gene expression level is significantly associated with major depression and suggests that ATP1A1 could be a significant molecular marker for diagnosis.

Nanomolar ouabain augments Ca2+ signalling in rat hippocampal neurones and glia

Linkage of certain neurological diseases to Na(+) pump mutations and some mood disorders to altered Na(+) pump function has renewed interest in brain Na(+) pumps. We tested nanomolar ouabain on Ca(2+) signalling (fura-2) in rat hippocampal neurone-astrocyte co-cultures. The neurones and astrocytes express Na(+) pumps with a high-ouabain-affinity catalytic subunit (α3 and α2, respectively); both also express pumps with a ouabain-resistant α1 subunit. Neurones and astrocytes were identified by immunocytochemistry and by stimulation; 3-4 μM L-glutamate (Glu) and 3 μM carbachol (CCh) evoked rapid Ca(2+) transients only in neurones, and small, delayed transients in some astrocytes, whereas 0.5-1 μM ATP evoked Ca(2+) transients only in astrocytes. Both cell types responded to 5-10 μM Glu or ATP. The signals evoked by 3-4 μM Glu in neurones were markedly inhibited by 3-10 μm MPEP (blocks metabotropic glutamate receptor mGluR5) and 10 μm LY341495 (non-selective mGluR blocker), but not by 80 μm AP5 (NMDA receptor blocker) or by selective block of mGluR1 or mGluR2. Pre-incubation (0.5-10 min) with 1-10 nm ouabain (EC50 < 1 nm) augmented Glu- and CCh-evoked signals in neurones. This augmentation was abolished by a blocker of the Na(+)-Ca(2+) exchanger, SEA0400 (300 nm). Ouabain (3 nm) pre-incubation also augmented 10 μM cyclopiazonic acid plus 10 mm caffeine-evoked release of Ca(2+) from the neuronal endoplasmic reticulum (ER). The implication is that nanomolar ouabain inhibits α3 Na(+) pumps, increases (local) intracellular Na(+), and promotes Na(+)-Ca(2+) exchanger-mediated Ca(2+) gain and increased storage in the adjacent ER. Ouabain (3 nm) also increased ER Ca(2+) release and enhanced 0.5 μM ATP-evoked transients in astrocytes; these effects were mediated by α2 Na(+) pumps. Thus, nanomolar ouabain may strongly influence synaptic transmission in the brain as a result of its actions on the high-ouabain-affinity Na(+) pumps in both neurones and astrocytes. The significance of these effects is heightened by the evidence that ouabain is endogenous in mammals.

Na⁺-K⁺-ATPase, a potent neuroprotective modulator against Alzheimer disease

Alzheimer disease (AD) is a neurodegenerative disorder clinically characterized by progressive cognitive and memory dysfunction, which is the most common form of dementia. Although the pathogenesis of neuronal injury in AD is not clear, recent evidences suggest that Na⁺-K⁺-ATPase plays an important role in AD, and may be a potent neuroprotective modulator against AD. This review aims to provide readers with an in-depth understanding of Na⁺-K⁺-ATPase in AD through these modulations of some factors that are as follows, which leads to the change of learning and memory in the process of AD. 1. The deficiency in Na⁺, K⁺-ATPase α1, α2 and α3 isoform genes induced learning and memory deficits, and α isoform was evidently changed in AD, revealing that Na⁺, K⁺-ATPase α isoform genes may play an important role in AD. 2. Some factors, such as β-amyloid, cholinergic and oxidative stress, can modulate learning and memory in AD through the mondulation of Na⁺-K⁺-ATPase activity. 3. Some substances, such as Zn, s-Ethyl cysteine, s-propyl cysteine, citicoline, rivastigmine, Vit E, memantine, tea polyphenol, curcumin, caffeine, Alpinia galanga (L.) fractions, and Bacopa monnieri could play a role in improving memory performance and exert protective effects against AD by increasing expression or activity of Na⁺, K⁺-ATPase.