Changes in intracellular chloride after oxygen-glucose deprivation of the adult hippocampal slice: effect of diazepam

Oxytocin Exhibits Neuroprotective Effects on Hippocampal Cultures under Severe Oxygen-Glucose Deprivation Conditions

Perinatal asphyxia (PA) and hypoxic-ischemic encephalopathy can result in severe, long-lasting neurological deficits. In vitro models, such as oxygen-glucose deprivation (OGD), are used experimentally to investigate neuronal response to metabolic stress. However, multiple variables can affect the severity level of OGD/PA and may confound any measured treatment effect. Oxytocin (OXT) has emerged as a potential neuroprotective agent against the deleterious effects of PA. Previous studies have demonstrated OXT's potential to enhance neuronal survival in immature hippocampal cultures exposed to OGD, possibly by modulating gamma-aminobutyric acid-A receptor activity. Moreover, OXT's precise impact on developing hippocampal neurons under different severities of OGD/PA remains uncertain. In this study, we investigated the effects of OXT (0.1 µM and 1 µM) on 7-day-old primary rat hippocampal cultures subjected to 2 h OGD/sham normoxic conditions. Cell culture viability was determined using the resazurin assay. Our results indicate that the efficacy of 1 µM OXT treatment varied according to the severity of the OGD-induced lesion, exhibiting a protective effect (p = 0.022) only when cellular viability dropped below 49.41% in non-treated OGD cultures compared to normoxic ones. Furthermore, administration of 0.1 µM OXT did not yield significant effects, irrespective of lesion severity (p > 0.05). These findings suggest that 1 µM OXT treatment during OGD confers neuroprotection exclusively in severe lesions in hippocampal neurons after 7 days in vitro. Further research is warranted to elucidate the mechanisms involved in OXT-mediated neuroprotection.

The role of SLC12A family of cation-chloride cotransporters and drug discovery methodologies

The solute carrier family 12 (SLC12) of cation-chloride cotransporters (CCCs) comprises potassium chloride cotransporters (KCCs, e.g. KCC1, KCC2, KCC3, and KCC4)-mediated Cl- extrusion, and sodium potassium chloride cotransporters (N[K]CCs, NKCC1, NKCC2, and NCC)-mediated Cl- loading. The CCCs play vital roles in cell volume regulation and ion homeostasis. Gain-of-function or loss-of-function of these ion transporters can cause diseases in many tissues. In recent years, there have been considerable advances in our understanding of CCCs' control mechanisms in cell volume regulations, with many techniques developed in studying the functions and activities of CCCs. Classic approaches to directly measure CCC activity involve assays that measure the transport of potassium substitutes through the CCCs. These techniques include the ammonium pulse technique, radioactive or nonradioactive rubidium ion uptake-assay, and thallium ion-uptake assay. CCCs' activity can also be indirectly observed by measuring γ-aminobutyric acid (GABA) activity with patch-clamp electrophysiology and intracellular chloride concentration with sensitive microelectrodes, radiotracer 36Cl-, and fluorescent dyes. Other techniques include directly looking at kinase regulatory sites phosphorylation, flame photometry, 22Na+ uptake assay, structural biology, molecular modeling, and high-throughput drug screening. This review summarizes the role of CCCs in genetic disorders and cell volume regulation, current methods applied in studying CCCs biology, and compounds developed that directly or indirectly target the CCCs for disease treatments.

Bumetanide Attenuates Cognitive Deficits and Brain Damage in Rats Subjected to Hypoxia-Ischemia at Two Time Points of the Early Postnatal Period

Neonatal hypoxia-ischemia (HI) is one of the main causes of tissue damage, cell death, and imbalance between neuronal excitation and inhibition and synaptic loss in newborns. GABA, the major inhibitory neurotransmitter of the central nervous system (CNS) in adults, is excitatory at the onset of neurodevelopment and its action depends on the chloride (Cl-) cotransporters NKCC1 (imports Cl-) and KCC2 (exports Cl-) expression. Under basal conditions, the NKCC1/KCC2 ratio decreases over neurodevelopment. Thus, changes in this ratio caused by HI may be related to neurological disorders. The present study evaluated the effects of bumetanide (NKCC cotransporters inhibitor) on HI impairments in two neurodevelopmental periods. Male Wistar rat pups, 3 (PND3) and 11 (PND11) days old, were submitted to the Rice-Vannucci model. Animals were divided into 3 groups: SHAM, HI-SAL, and HI-BUM, considering each age. Bumetanide was administered intraperitoneally at 1, 24, 48, and 72 h after HI. NKCC1, KCC2, PSD-95, and synaptophysin proteins were analyzed after the last injection by western blot. Negative geotaxis, righting reflex, open field, object recognition test, and Morris water maze task were performed to assess neurological reflexes, locomotion, and memory function. Tissue atrophy and cell death were evaluated by histology. Bumetanide prevented neurodevelopmental delay, hyperactivity, and declarative and spatial memory deficits. Furthermore, bumetanide reversed HI-induced brain tissue damage, reduced neuronal death and controlled GABAergic tone, maintained the NKCC1/KCC2 ratio, and synaptogenesis close to normality. Thereby, bumetanide appears to play an important therapeutic role in the CNS, protecting the animals against HI damage and improving functional performance.

Cerebrospinal Fluid Chloride Is Associated with Disease Activity of Relapsing-Remitting Multiple Sclerosis: A Retrospective Cohort Study

BACKGROUND

Blood-brain barrier dysfunction in active multiple sclerosis (MS) lesions leads to pathological changes in the cerebrospinal fluid (CSF). This study aimed to investigate the possible association between routine CSF findings, especially CSF chloride, at the time of the first lumbar puncture and the relapse risk and disability progression of relapsing-remitting MS (RRMS).

METHODS

This retrospective study included 77 patients with RRMS at the MS Center of our institution from January 2012 to December 2020. The Anderson and Gill (AG) model and Spearman correlation analysis were used to explore predictors of relapse and disability during follow-up.

RESULTS

In the multivariate AG model, patients with elevated CSF chloride level (hazard ratio [HR], 1.1; 95% confidence interval [CI]: 1.06-1.22; p = 0.001) had a high risk of MS relapse. Using median values of CSF chloride (123.2 mmol/L) as a cut-off, patients with CSF chloride level ≥ 123.2 mmol/L had a 120% increased relapse risk compared with those with CSF chloride level < 123.2 mmol/L (HR = 2.20; 95% CI: 1.19-4.05; p = 0.012).

CONCLUSIONS

Elevated CSF chloride levels might be a biologically unfavorable predictive factor for disease relapse in RRMS.

Role of NKCC1 and KCC2 during hypoxia-induced neuronal swelling in the neonatal neocortex

Neonatal hypoxia causes cytotoxic neuronal swelling by the entry of ions and water. Multiple water pathways have been implicated in neurons because these cells lack water channels, and their membrane has a low water permeability. NKCC1 and KCC2 are cation-chloride cotransporters (CCCs) involved in water movement in various cell types. However, the role of CCCs in water movement in neonatal neurons during hypoxia is unknown. We studied the effects of modulating CCCs pharmacologically on neuronal swelling in the neocortex (layer IV/V) of neonatal mice (post-natal day 8-13) during prolonged and brief hypoxia. We used acute brain slices from Clomeleon mice which express a ratiometric fluorophore sensitive to Cl^- and exposed them to oxygen-glucose deprivation (OGD) while imaging neuronal size and [Cl^-]_i by multiphoton microscopy. Neurons were identified using a convolutional neural network algorithm, and changes in the somatic area and [Cl^-]_i were evaluated using a linear mixed model for repeated measures. We found that (1) neuronal swelling and Cl^- accumulation began after OGD, worsened during 20 min of OGD, or returned to baseline during reoxygenation if the exposure to OGD was brief (10 min). (2) Neuronal swelling did not occur when the extracellular Cl^- concentration was low. (3) Enhancing KCC2 activity did not alter OGD-induced neuronal swelling but prevented Cl^- accumulation; (4) blocking KCC2 led to an increase in Cl^- accumulation during prolonged OGD and aggravated neuronal swelling during reoxygenation; (5) blocking NKCC1 reduced neuronal swelling during early but not prolonged OGD and aggravated Cl^- accumulation during prolonged OGD; and (6) treatment with the "broad" CCC blocker furosemide reduced both swelling and Cl^- accumulation during prolonged and brief OGD, whereas simultaneous NKCC1 and KCC2 inhibition using specific pharmacological blockers aggravated neuronal swelling during prolonged OGD. We conclude that CCCs, and other non-CCCs, contribute to water movement in neocortical neurons during OGD in the neonatal period.

Chloride ion dysregulation in epileptogenic neuronal networks

GABA is the major inhibitory neurotransmitter in the mature CNS. When GABA_A receptors are activated the membrane potential is driven towards hyperpolarization due to chloride entry into the neuron. However, chloride ion dysregulation that alters the ionic gradient can result in depolarizing GABAergic post-synaptic potentials instead. In this review, we highlight that GABAergic inhibition prevents and restrains focal seizures but then reexamine this notion in the context of evidence that a static and/or a dynamic chloride ion dysregulation, that increases intracellular chloride ion concentrations, promotes epileptiform activity and seizures. To reconcile these findings, we hypothesize that epileptogenic pathologically interconnected neuron (PIN) microcircuits, representing a small minority of neurons, exhibit static chloride dysregulation and should exhibit depolarizing inhibitory post-synaptic potentials (IPSPs). We speculate that chloride ion dysregulation and PIN cluster activation may generate fast ripples and epileptiform spikes as well as initiate the hypersynchronous seizure onset pattern and microseizures. Also, we discuss the genetic, molecular, and cellular players important in chloride dysregulation which regulate epileptogenesis and initiate the low-voltage fast seizure onset pattern. We conclude that chloride dysregulation in neuronal networks appears to be critical for epileptogenesis and seizure genesis, but feed-back and feed-forward inhibitory GABAergic neurotransmission plays an important role in preventing and restraining seizures as well.

Multi-target action of β-alanine protects cerebellar tissue from ischemic damage

Brain ischemic stroke is among the leading causes of death and long-term disability. New treatments that alleviate brain cell damage until blood supply is restored are urgently required. The emerging focus of anti-stroke strategies has been on blood-brain-barrier permeable drugs that exhibit multiple sites of action. Here, we combine single-cell electrophysiology with live-cell imaging to find that β-Alanine (β-Ala) protects key physiological functions of brain cells that are exposed to acute stroke-mimicking conditions in ex vivo brain preparations. β-Ala exerts its neuroprotective action through several distinct pharmacological mechanisms, none of which alone could reproduce the neuroprotective effect. Since β-Ala crosses the blood-brain barrier and is part of a normal human diet, we suggest that it has a strong potential for acute stroke treatment and facilitation of recovery.

Dual functional luminescent nanoprobes for monitoring oxygen and chloride concentration changes in cells

A dual functional nanoprobe Pd-Q+@PDMS was proposed to simultaneously monitor Cl- and O2, leading to the determination of an average Cl- concentration of 85.7 ± 5.5 mM in lysosomes of HeLa cells. Mimicking ischemic conditions, the cells exhibited a luminescence change corresponding to a decreasing subcellular Cl- concentration.

Drug development in targeting ion channels for brain edema

Cerebral edema is a pathological hallmark of various central nervous system (CNS) insults, including traumatic brain injury (TBI) and excitotoxic injury such as stroke. Due to the rigidity of the skull, edema-induced increase of intracranial fluid significantly complicates severe CNS injuries by raising intracranial pressure and compromising perfusion. Mortality due to cerebral edema is high. With mortality rates up to 80% in severe cases of stroke, it is the leading cause of death within the first week. Similarly, cerebral edema is devastating for patients of TBI, accounting for up to 50% mortality. Currently, the available treatments for cerebral edema include hypothermia, osmotherapy, and surgery. However, these treatments only address the symptoms and often elicit adverse side effects, potentially in part due to non-specificity. There is an urgent need to identify effective pharmacological treatments for cerebral edema. Currently, ion channels represent the third-largest target class for drug development, but their roles in cerebral edema remain ill-defined. The present review aims to provide an overview of the proposed roles of ion channels and transporters (including aquaporins, SUR1-TRPM4, chloride channels, glucose transporters, and proton-sensitive channels) in mediating cerebral edema in acute ischemic stroke and TBI. We also focus on the pharmacological inhibitors for each target and potential therapeutic strategies that may be further pursued for the treatment of cerebral edema.

Sex-specific alterations in GABA receptor-mediated responses in laterodorsal tegmentum are associated with prenatal exposure to nicotine

Smoking during pregnancy is associated with deleterious physiological and cognitive effects on the offspring, which are likely due to nicotine-induced alteration in the development of neurotransmitter systems. Prenatal nicotine exposure (PNE) in rodents is associated with changes in behaviors controlled in part by the pontine laterodorsal tegmentum (LDT), and LDT excitatory signaling is altered in a sex and age-dependent manner by PNE. As effects on GABAergic LDT signaling are unknown, we used calcium imaging to evaluate GABA_A receptor- (GABA_A R as well as GABA_A -_ρ R) and GABA_B receptor (GABA_B R)-mediated calcium responses in LDT brain slices from female and male PNE mice in two different age groups. Overall, in older PNE females, changes in calcium induced by stimulation of GABA_A R and GABA_B R, including GABA_A -_ρ R were shifted toward calcium rises. In both young and old males, PNE was associated with alterations in calcium mediated by all three receptors; however, the GABA_A R was the most affected. These results show for the first time that PNE is associated with alterations in GABAergic transmission in the LDT in a sex- and age-dependent manner, and these data are the first to show PNE-associated alterations in functionality of GABA receptors in any nucleus. PNE-associated alterations in LDT GABAergic transmission within the LDT would be expected to alter output to target regions and could play a role in LDT-implicated, negative behavioral outcomes following gestational exposure to smoking. Accordingly, our data provide further supportive evidence of the importance of eliminating the consumption of nicotine during pregnancy.

Sodium/calcium exchanger as main effector of endogenous neuroprotection elicited by ischemic tolerance

The ischemic tolerance (IT) paradigm represents a fundamental cell response to certain types or injury able to render an organ more "tolerant" to a subsequent, stronger, insult. During the 16th century, the toxicologist Paracelsus described for the first time the possibility that a noxious event might determine a state of tolerance. This finding was summarized in one of his most important mentions: "The dose makes the poison". In more recent years, ischemic tolerance in the brain was first described in 1991, when it was demonstrated by Kirino and collaborators that two minutes of subthreshold brain ischemia in gerbils produced tolerance against global brain ischemia. Based on the time in which the conditioning stimulus is applied, it is possible to define preconditioning, perconditioning and postconditioning, when the subthreshold insult is applied before, during or after the ischemic event, respectively. Furthermore, depending on the temporal delay from the ischemic event, two different modalities are distinguished: rapid or delayed preconditioning and postconditioning. Finally, the circumstance in which the conditioning stimulus is applied on an organ distant from the brain is referred as remote conditioning. Over the years the "conditioning" paradigm has been applied to several brain disorders and a number of molecular mechanisms taking part to these protective processes have been described. The mechanisms are usually classified in three distinct categories identified as triggers, mediators and effectors. As concerns the putative effectors, it has been hypothesized that brain cells appear to have the ability to adapt to hypoxia by reducing their energy demand through modulation of ion channels and transporters, which delays anoxic depolarization. The purpose of the present review is to summarize the role played by plasmamembrane proteins able to control ionic homeostasis in mediating protection elicited by brain conditioning, particular attention will be deserved to the role played by Na⁺/Ca²⁺ exchanger.

Neuronal Transmembrane Chloride Transport Has a Time-Dependent Influence on Survival of Hippocampal Cultures to Oxygen-Glucose Deprivation

Neuronal ischemia results in chloride gradient alterations which impact the excitatory–inhibitory balance, volume regulation, and neuronal survival. Thus, the Na⁺/K⁺/Cl⁻ co-transporter (NKCC1), the K⁺/ Cl⁻ co-transporter (KCC2), and the gamma-aminobutyric acid A (GABA_A) receptor may represent therapeutic targets in stroke, but a time-dependent effect on neuronal viability could influence the outcome. We, therefore, successively blocked NKCC1, KCC2, and GABA_A (with bumetanide, DIOA, and gabazine, respectively) or activated GABA_A (with isoguvacine) either during or after oxygen-glucose deprivation (OGD). Primary hippocampal cultures were exposed to a 2-h OGD or sham normoxia treatment, and viability was determined using the resazurin assay. Neuronal viability was significantly reduced after OGD, and was further decreased by DIOA treatment applied during OGD (p < 0.01) and by gabazine applied after OGD (p < 0.05). Bumetanide treatment during OGD increased viability (p < 0.05), while isoguvacine applied either during or after OGD did not influence viability. Our data suggests that NKCC1 and KCC2 function has an important impact on neuronal viability during the acute ischemic episode, while the GABA_A receptor plays a role during the subsequent recovery period. These findings suggest that pharmacological modulation of transmembrane chloride transport could be a promising approach during stroke and highlight the importance of the timing of treatment application in relation to ischemia-reoxygenation.

Alterations in GABAA-Receptor Trafficking and Synaptic Dysfunction in Brain Disorders

GABA_A receptors (GABA_AR) are the major players in fast inhibitory neurotransmission in the central nervous system (CNS). Regulation of GABA_AR trafficking and the control of their surface expression play important roles in the modulation of the strength of synaptic inhibition. Different pieces of evidence show that alterations in the surface distribution of GABA_AR and dysregulation of their turnover impair the activity of inhibitory synapses. A diminished efficacy of inhibitory neurotransmission affects the excitatory/inhibitory balance and is a common feature of various disorders of the CNS characterized by an increased excitability of neuronal networks. The synaptic pool of GABA_AR is mainly controlled through regulation of internalization, recycling and lateral diffusion of the receptors. Under physiological condition these mechanisms are finely coordinated to define the strength of GABAergic synapses. In this review article, we focus on the alteration in GABA_AR trafficking with an impact on the function of inhibitory synapses in various disorders of the CNS. In particular we discuss how similar molecular mechanisms affecting the synaptic distribution of GABA_AR and consequently the excitatory/inhibitory balance may be associated with a wide diversity of pathologies of the CNS, from psychiatric disorders to acute alterations leading to neuronal death. A better understanding of the cellular and molecular mechanisms that contribute to the impairment of GABAergic neurotransmission in these disorders, in particular the alterations in GABA_AR trafficking and surface distribution, may lead to the identification of new pharmacological targets and to the development of novel therapeutic strategies.

Effect of Co-administration of Bumetanide and Phenobarbital on Seizure Attacks in Temporal Lobe Epilepsy

Introduction:

The resistance of temporal lobe epilepsy to classic drugs is thought to be due to disruption in the excitation/inhibition of this pathway. Two chloride transporters, NKCC1 and KCC2, are expressed differently for the excitatory state of Gamma-Amino Butyric Acid (GABA). The present study explored the effect of bumetanide as a selective NKCC1 inhibitor either alone or in combination with the phenobarbital in the pilocarpine model of epilepsy.

Methods:

An animal model of Status Epilepticus (SE) was induced with pilocarpine in Wistar male rats followed by phenobarbital and or bumetanide or saline administration for 45 days after the induction of SE by Intraperitoneal (IP) injection. The rats were monitored, their behavior was recorded, and after 24 hours they were sacrificed to study the expression of NKCC1 and KCC2 using real time PCR.

Results:

The data showed that the effects of a combination of bumetanide with phenobarbital on frequency rate and duration of seizure attack were more than those of the phenobarbital alone. In addition, in the bumetanide and combined treatment groups, NKCC1 expression decreased significantly, compared with untreated epileptic animals. A delayed decrement in NKCC1/KCC2 expression ratio after bumetanide application was also observed.

Conclusion:

The combination of bumetanide with phenobarbital increases the inhibition of SE and maximizes the potential of GABA signaling pathway, and can be considered as an effective therapeutic strategy in patients with epilepsy.

Chloride Homeostasis in Neurons With Special Emphasis on the Olivocerebellar System: Differential Roles for Transporters and Channels

The intraneuronal ionic composition is an important determinant of brain functioning. There is growing evidence that aberrant homeostasis of the intracellular concentration of Cl- ([Cl-]i) evokes, in addition to that of Na+ and Ca2+, robust impairments of neuronal excitability and neurotransmission and thereby neurological conditions. More specifically, understanding the mechanisms underlying regulation of [Cl-]i is crucial for deciphering the variability in GABAergic and glycinergic signaling of neurons, in both health and disease. The homeostatic level of [Cl-]i is determined by various regulatory mechanisms, including those mediated by plasma membrane Cl- channels and transporters. This review focuses on the latest advances in identification, regulation and characterization of Cl- channels and transporters that modulate neuronal excitability and cell volume. By putting special emphasis on neurons of the olivocerebellar system, we establish that Cl- channels and transporters play an indispensable role in determining their [Cl-]i and thereby their function in sensorimotor coordination.

NKCC1 Chloride Importer Antagonists Attenuate Many Neurological and Psychiatric Disorders

In physiological conditions, adult neurons have low intracellular Cl^- [(Cl^-)_I] levels underlying the γ-aminobutyric acid (GABA)ergic inhibitory drive. In contrast, neurons have high (Cl^-)_I levels and excitatory GABA actions in a wide range of pathological conditions including spinal cord lesions, chronic pain, brain trauma, cerebrovascular infarcts, autism, Rett and Down syndrome, various types of epilepsies, and other genetic or environmental insults. The diuretic highly specific NKCC1 chloride importer antagonist bumetanide (PubChem CID: 2461) efficiently restores low (Cl^-)_I levels and attenuates many disorders in experimental conditions and in some clinical trials. Here, I review the mechanisms of action, therapeutic effects, promises, and pitfalls of bumetanide.

Chloride Dysregulation, Seizures, and Cerebral Edema: A Relationship with Therapeutic Potential

Pharmacoresistant seizures and cytotoxic cerebral edema are serious complications of ischemic and traumatic brain injury. Intraneuronal Cl^- concentration ([Cl^-]_i) regulation impacts on both cell volume homeostasis and Cl^--permeable GABA_A receptor-dependent membrane excitability. Understanding the pleiotropic molecular determinants of neuronal [Cl^-]_i - cytoplasmic impermeant anions, polyanionic extracellular matrix (ECM) glycoproteins, and plasmalemmal Cl^- transporters - could help the identification of novel anticonvulsive and neuroprotective targets. The cation/Cl^- cotransporters and ECM metalloproteinases may be particularly druggable targets for intervention. We establish here a paradigm that accounts for recent data regarding the complex regulatory mechanisms of neuronal [Cl^-]_i and how these mechanisms impact on neuronal volume and excitability. We propose approaches to modulate [Cl^-]_i that are relevant for two common clinical sequela of brain injury: edema and seizures.

Functional promoter polymorphisms direct the expression of cystathionine gamma-lyase gene in mouse models of essential hypertension

Despite the well-known role of cystathionine γ-lyase (Cth) in cardiovascular pathophysiology, transcriptional regulation of Cth remains incompletely understood. Sequencing of the Cth promoter region in mouse models of genetic/essential hypertension (viz. Blood Pressure High [BPH], Blood Pressure Low [BPL] and Blood Pressure Normal [BPN] mice) identified several genetic variations. Transient transfections of BPH/BPL-Cth promoter-reporter plasmids into various cell types revealed higher promoter activity of BPL-Cth than that of BPH-Cth. Corroboratively, endogenous Cth mRNA levels in kidney and liver tissues were also elevated in BPL mice. Computational analysis of the polymorphic Cth promoter region predicted differential binding affinity of c-Rel, HOXA3 and IRF1 with BPL/BPH-Cth promoter domains. Over-expression of c-Rel/HOXA3/IRF1 modulated BPL/BPH-Cth promoter activities in a consistent manner. Gel shift assays using BPH/BPL-Cth-promoter oligonucleotides with/without binding sites for c-Rel/HOXA3/IRF1 displayed formation of specific complexes with c-Rel/HOXA3/IRF1; addition of antibodies to reaction mixtures resulted in supershifts/inhibition of Cth promoter-transcription factor complexes. Furthermore, chromatin immunoprecipitation (ChIP) assays proved differential binding of c-Rel, HOXA3 and IRF1 with the polymorphic promoter region of BPL/BPH-Cth. Tumor necrosis factor-α (TNF-α) reduced the activities of BPL/BPH-Cth promoters to different extents that were further declined by ectopic expression of IRF1; on the other hand, siRNA-mediated down-regulation of IRF1 rescued the TNF-α-mediated suppression of the BPL/BPH-Cth promoter activities. In corroboration, ChIP analysis revealed enhanced binding of IRF1 with BPH/BPL-Cth promoter following TNF-α treatment. BPL/BPH-Cth promoter activity was diminished upon exposure of hepatocytes and cardiomyoblasts to ischemia-like pathological condition due to reduced binding of c-Rel with BPL/BPH-Cth-promoter. Taken together, this study reveals the molecular basis for the differential expression of Cth in mouse models of essential hypertension under basal and pathophysiological conditions.

Expanding Spectrum of Sodium Potassium Chloride Co-transporters in the Pathophysiology of Diseases

Sodium potassium chloride co-transporter (NKCC) belongs to cation-dependent chloride co-transporter family, whose activation allows the entry of Na(+), K(+) and 2Cl(-) inside the cell. It acts in concert with K(+) Cl(-) co-transporter (KCC), which extrudes K(+) and Cl(-) ions from cell. NKCC1 is widely distributed throughout the body, while NKCC2 is exclusively present in kidney. Protein kinase A, protein kinase C, Ste20-related proline-alanine-rich kinase, oxidative stress responsive kinases, With No K=lysine kinase and protein phosphatase type 1 control the phosphorylation/dephosphorylation of key threonine residues of in regulatory domain of NKCC1. The selective inhibitors of NKCC1 including bumetanide and furosemide are conventionally employed as diuretics. However, recent studies have indicated that NKCC1 may be involved in the pathophysiology of anxiety, cerebral ischemia, epilepsy, neuropathic pain, fragile X syndrome, autism and schizophrenia. The inhibitors of NKCC1 are shown to produce anxiolytic effects; attenuate cerebral ischemia-induced neuronal injury; produce antiepileptic effects and attenuate neuropathic pain. In the early developing brain, GABAA activation primarily produces excitatory actions due to high NKCC1/KCC2 ratio. However, as the development progresses, the ratio of NKCC1/KCC2 ratio reverses and there is switch in the polarity of GABAA actions and latter acquires the inhibitory actions. The recapitulation of developmental-like state during pathological state may be associated with increase in the expression and functioning of NKCC1, which decreases the strength of inhibitory GABAergic neurotransmission. The present review describes the expanding role and mechanism of NKCC1 in the pathophysiology of different diseases.

Calpains and neuronal damage in the ischemic brain: The swiss knife in synaptic injury

The excessive extracellular accumulation of glutamate in the ischemic brain leads to an overactivation of glutamate receptors with consequent excitotoxic neuronal death. Neuronal demise is largely due to a sustained activation of NMDA receptors for glutamate, with a consequent increase in the intracellular Ca(2+) concentration and activation of calcium- dependent mechanisms. Calpains are a group of Ca(2+)-dependent proteases that truncate specific proteins, and some of the cleavage products remain in the cell, although with a distinct function. Numerous studies have shown pre- and post-synaptic effects of calpains on glutamatergic and GABAergic synapses, targeting membrane- associated proteins as well as intracellular proteins. The resulting changes in the presynaptic proteome alter neurotransmitter release, while the cleavage of postsynaptic proteins affects directly or indirectly the activity of neurotransmitter receptors and downstream mechanisms. These alterations also disturb the balance between excitatory and inhibitory neurotransmission in the brain, with an impact in neuronal demise. In this review we discuss the evidence pointing to a role for calpains in the dysregulation of excitatory and inhibitory synapses in brain ischemia, at the pre- and post-synaptic levels, as well as the functional consequences. Although targeting calpain-dependent mechanisms may constitute a good therapeutic approach for stroke, specific strategies should be developed to avoid non-specific effects given the important regulatory role played by these proteases under normal physiological conditions.

The K(+)-Cl(-) Cotransporter KCC2 and Chloride Homeostasis: Potential Therapeutic Target in Acute Central Nervous System Injury

The K(+)-Cl(-) cotransporter-2 (KCC2) is a well-known member of the electroneutral cation-chloride cotransporters with a restricted expression pattern to neurons. This transmembrane protein mediates the efflux of Cl(-) out of neurons and exerts a critical role in inhibitory γ-aminobutyric acidergic (GABAergic) and glycinergic neurotransmission. Moreover, KCC2 participates in the regulation of various physiological processes of neurons, including cell migration, dendritic outgrowth, spine morphology, and dendritic synaptogenesis. It is important to note that down-regulation of KCC2 is associated with the pathogenesis of multiple neurological diseases, which is of particular relevance to acute central nervous system (CNS) injury. In this review, we aim to survey the pathogenic significance of KCC2 down-regulation under the condition of acute CNS injuries. We propose that further elucidation of the molecular mechanisms regarding KCC2 down-regulation after acute CNS injuries is necessary because of potential promising avenues for prevention and treatment of acute CNS injury.

Prenatal Hypoxia-Ischemia Induces Abnormalities in CA3 Microstructure, Potassium Chloride Co-Transporter 2 Expression and Inhibitory Tone

Infants who suffer perinatal brain injury, including those with encephalopathy of prematurity, are prone to chronic neurological deficits, including epilepsy, cognitive impairment, and behavioral problems, such as anxiety, inattention, and poor social interaction. These deficits, especially in combination, pose the greatest hindrance to these children becoming independent adults. Cerebral function depends on adequate development of essential inhibitory neural circuits and the appropriate amount of excitation and inhibition at specific stages of maturation. Early neuronal synaptic responses to γ-amino butyric acid (GABA) are initially excitatory. During the early postnatal period, GABA_AR responses switch to inhibitory with the upregulation of potassium-chloride co-transporter KCC2. With extrusion of chloride by KCC2, the Cl⁻ reversal potential shifts and GABA and glycine responses become inhibitory. We hypothesized that prenatal hypoxic–ischemic brain injury chronically impairs the developmental upregulation of KCC2 that is essential for cerebral circuit formation. Following late gestation hypoxia–ischemia (HI), diffusion tensor imaging in juvenile rats shows poor microstructural integrity in the hippocampal CA3 subfield, with reduced fractional anisotropy and elevated radial diffusivity. The loss of microstructure correlates with early reduced KCC2 expression on NeuN-positive pyramidal neurons, and decreased monomeric and oligomeric KCC2 protein expression in the CA3 subfield. Together with decreased inhibitory post-synaptic currents during a critical window of development, we document for the first time that prenatal transient systemic HI in rats impairs hippocampal CA3 inhibitory tone. Failure of timely development of inhibitory tone likely contributes to a lower seizure threshold and impaired cognitive function in children who suffer perinatal brain injury.

Molecular mechanism of monoamine oxidase A gene regulation under inflammation and ischemia-like conditions: key roles of the transcription factors GATA2, Sp1 and TBP

Monoamine oxidase A (MAOA) plays important roles in the pathogenesis of several neurological and cardiovascular disorders. The mechanism of transcriptional regulation of MAOA under basal and pathological conditions, however, remains incompletely understood. Here, we report systematic identification and characterization of cis elements and transcription factors that govern the expression of MAOA gene. Extensive computational analysis of MAOA promoter, followed by 5'-promoter deletion/reporter assays, revealed that the -71/-40 bp domain was sufficient for its basal transcription. Gel-shift and chromatin immunoprecipitation assays provided evidence of interactions of the transcription factors GATA-binding protein 2 (GATA2), Sp1 and TATA-binding protein (TBP) with this proximal promoter region. Consistently, over-expression of GATA2, Sp1 and TBP augmented MAOA promoter activity in a coordinated manner. In corroboration, siRNA-mediated down-regulation of GATA2/Sp1/TBP repressed the endogenous MAOA expression as well as transfected MAOA promoter activity. Tumor necrosis factor-α and forskolin activated MAOA transcription that was reversed by Sp1 siRNA; in support, tumor necrosis factor-α- and forskolin-induced activities were enhanced by ectopic over-expression of Sp1. On the other hand, MAOA transcription was diminished upon exposure of neuroblasts or cardiac myoblasts to ischemia-like conditions because of reduced binding of GATA2/Sp1/TBP with MAOA promoter. In conclusion, this study revealed previously unknown roles of GATA2, Sp1 and TBP in modulating MAOA expression under basal as well as pathophysiological conditions such as inflammation and ischemia, thus providing new insights into the molecular basis of aberrant MAOA expression in neuronal/cardiovascular disease states. Dysregulation of monoamine oxidase A (MAOA) have been implicated in several behavioral and neuronal disease states. Here, we identified three crucial transcription factors (GATA2, Sp1 and TBP) that regulate MAOA gene expression in a coordinated manner. Aberrant MAOA expression under pathophysiological conditions including inflammation and ischemia is mediated by altered binding of GATA2/Sp1/TBP with MAOA proximal promoter. Thus, these findings provide new insights into pathogenesis of several common diseases. GATA2, GATA-binding protein 2; Sp1, specificity protein 1; TBP, TATA-binding protein.

Characterization of inhibitory GABA-A receptor activation during spreading depolarization in brain slice

Spreading depolarization (SD) is a slowly propagating wave of near complete depolarizations of neurons and glia. Previous studies have reported large GABA releases during SD, but there is limited understanding of how GABA release and receptor activation are regulated and influence the propagating SD wavefront, as well as an excitatory phase immediately following the passage of SD. The present study characterized GABA-A type receptor (GABA_AR) currents during SD generated by KCl microinjection in acute hippocampal slices from adult mice. Spontaneous GABA_AR-mediated currents (sIPSCs) were initially enhanced, and were followed by a large outward current at the wavefront. sIPSC were then transiently supressed during the late SD phase, resulting in a significant reduction of the sIPSC/sEPSC ratio. The large outward current generated during SD was eliminated by the GABA_AR antagonist gabazine, but the channel potentiator/agonist propofol failed to potentiate the current, likely because of a ceiling effect. Extracellular Cl⁻ decreases recorded during SD were reduced by the antagonist but were not increased by the potentiator. Together with effects of GABA_AR modulators on SD propagation rate, these results demonstrate a significant inhibitory role of the initial GABA_AR activation and suggest that intracellular Cl⁻ loading is insufficient to generate excitatory GABA_AR responses during SD propagation. These results provide a mechanistic explanation for facilitating effects of GABA_AR antagonists, and the lack of inhibitory effect of GABA_AR potentiators on SD propagation. In addition, selective suppression of GABA transmission in the late SD period and the lack of effect of GABA_A modulators on the duration of SD suggests that GABA modulation may not be effective approach to protect neurons during the vulnerable phase of SD.

3-Nitropropionic acid-induced ischemia tolerance in the rat brain is mediated by reduced metabolic activity and cerebral blood flow

Tissue tolerance to ischemia can be achieved by noxious stimuli that are below a threshold to cause irreversible damage ('preconditioning'). Understanding the mechanisms underlying preconditioning may lead to the identification of novel therapeutic targets for diseases such as stroke. We here used the oxidative chain inhibitor 3-nitropropionic acid (NPA) to induce ischemia tolerance in a rat middle cerebral artery occlusion (MCAO) stroke model. Cerebral blood flow (CBF) and structural integrity were characterized by longitudinal magnetic resonance imaging (MRI) in combination with behavioral, histologic, and biochemical assessment of NPA-preconditioned animals and controls. Using this approach we show that the ischemia-tolerant state is characterized by a lower energy charge potential and lower CBF, indicating a reduced baseline metabolic demand, and therefore a cellular mechanism of neural protection. Blood vessel density and structural integrity were not altered by NPA treatment. When subjected to MCAO, preconditioned animals had a characteristic MRI signature consisting of enhanced CBF maintenance within the ischemic territory and intraischemic reversal of the initial cytotoxic edema, resulting in reduced infarct volumes. Thus, our data show that tissue protection through preconditioning occurs early during ischemia and indicate that a reduced cellular metabolism is associated with tissue tolerance to ischemia.

KCC2 expression changes in Diazepam-treated neonatal rats with hypoxia-ischaemia brain damage

Hypoxia-ischaemia brain damage (HIBD) is a major type of perinatal brain injury in newborns. In this study, we investigate the short- and long-term neuroprotective effects of Diazepam on neonatal rats with HIBD and the potential mechanisms underlying its protective effects. Seven-day-old Sprague-Dawley rats were subjected to left carotid artery ligation followed by a 2-h exposure to 8% oxygen and 92% nitrogen. Diazepam was administered immediately via intraperitoneal (i.p.) injection after inducing HIBD at a dose of 10 mg kg(-1)8h(-1) for three consecutive days. Three days after HIBD, rats were decapitated, and the extent of brain injury was evaluated using 2,3,5-triphenyltetrazolium chloride (TTC) staining. Additionally, the expression of Potassium-chloride cotransporter-2 (KCC2) was analysed using real-time PCR, Western blot analysis and immunohistochemistry. Three weeks after HIBD, rats were subjected to the Morris water maze (MWM) test and the locomotor activity test to determine the long-term therapeutic effects of Diazepam. We observed that the volume of infarction in the Diazepam group was significantly less (P<0.01) compared with the HIBD group. We also observed that the learning and memory abilities of the Diazepam rats improved significantly compared with the untreated rats (P<0.05) and that the decrease in KCC2 expression was prevented (P<0.01). Early treatment with Diazepam appears to attenuate HIBD and can efficiently improve the long-term learning and memory capabilities of the animal. A potential mechanism underlying these effects may involve preventing the decrease in KCC2 expression.

Controversies and evolving new mechanisms in subarachnoid hemorrhage

Despite decades of study, subarachnoid hemorrhage (SAH) continues to be a serious and significant health problem in the United States and worldwide. The mechanisms contributing to brain injury after SAH remain unclear. Traditionally, most in vivo research has heavily emphasized the basic mechanisms of SAH over the pathophysiological or morphological changes of delayed cerebral vasospasm after SAH. Unfortunately, the results of clinical trials based on this premise have mostly been disappointing, implicating some other pathophysiological factors, independent of vasospasm, as contributors to poor clinical outcomes. Delayed cerebral vasospasm is no longer the only culprit. In this review, we summarize recent data from both experimental and clinical studies of SAH and discuss the vast array of physiological dysfunctions following SAH that ultimately lead to cell death. Based on the progress in neurobiological understanding of SAH, the terms "early brain injury" and "delayed brain injury" are used according to the temporal progression of SAH-induced brain injury. Additionally, a new concept of the vasculo-neuronal-glia triad model for SAH study is highlighted and presents the challenges and opportunities of this model for future SAH applications.

Bumetanide protects focal cerebral ischemia-reperfusion injury in rat

OBJECTIVE

Bumetanide has been reported to attenuate ischemia-evoked cerebral edema. However, whether bumetanide can protect cerebral ischemia-reperfusion injury (IRI) in vivo is unclear. In the present study, we aim to determine whether intravenously injection bumetanide can attenuate cerebral IRI and if its protection effect might be related to the modification of cerebral NKCC1 and KCC2 protein expression.

METHODS

Focal cerebral ischemia was induced by occluding the right middle cerebral artery (MCAO) for 2-h, followed by 3-h, 24-h or 48-h of reperfusion respectively. Brain edema, neurological deficits, and infarction volume were determined by (wet weights-dry weights)/dry weights×100, 5-point neurological function score evaluation system, and TTC staining, respectively. The expression levels of NKCC1 and KCC2 were determined by immunohistochemical staining.

RESULTS

Reperfusion increased brain edema, neurological deficits, and infarction volume. Bumetanide decreased brain edema, attenuated the neurological defects and reduced post-ischemic cerebral infarction. Cerebral ischemia-reperfusion injury increased NKCC1 expression level and decreased KCC2 expression level. Interestingly, bumetanide down-regulated the NKCC1 protein expression level without changing the KCC2 protein expression level in rat brain cortex.

CONCLUSION

These results suggest that bumetanide protects focal cerebral ischemia-reperfusion injury in rat, which might through the inhibition of NKCC1.

Current view on the functional regulation of the neuronal K(+)-Cl(-) cotransporter KCC2

In the mammalian central nervous system (CNS), the inhibitory strength of chloride (Cl(-))-permeable GABAA and glycine receptors (GABAAR and GlyR) depends on the intracellular Cl(-) concentration ([Cl(-)]i). Lowering [Cl(-)]i enhances inhibition, whereas raising [Cl(-)]i facilitates neuronal activity. A neuron's basal level of [Cl(-)]i, as well as its Cl(-) extrusion capacity, is critically dependent on the activity of the electroneutral K(+)-Cl(-) cotransporter KCC2, a member of the SLC12 cation-Cl(-) cotransporter (CCC) family. KCC2 deficiency compromises neuronal migration, formation and the maturation of GABAergic and glutamatergic synaptic connections, and results in network hyperexcitability and seizure activity. Several neurological disorders including multiple epilepsy subtypes, neuropathic pain, and schizophrenia, as well as various insults such as trauma and ischemia, are associated with significant decreases in the Cl(-) extrusion capacity of KCC2 that result in increases of [Cl(-)]i and the subsequent hyperexcitability of neuronal networks. Accordingly, identifying the key upstream molecular mediators governing the functional regulation of KCC2, and modifying these signaling pathways with small molecules, might constitute a novel neurotherapeutic strategy for multiple diseases. Here, we discuss recent advances in the understanding of the mechanisms regulating KCC2 activity, and of the role these mechanisms play in neuronal Cl(-) homeostasis and GABAergic neurotransmission. As KCC2 mediates electroneutral transport, the experimental recording of its activity constitutes an important research challenge; we therefore also, provide an overview of the different methodological approaches utilized to monitor function of KCC2 in both physiological and pathological conditions.

Does epilepsy cause a reversion to immature function?

Seizures have variable effects on brain. Numerous studies have examined the consequences of seizures, in light of the way that these may alter the susceptibility of the brain to seizures, promote epileptogenesis, or functionally alter brain leading to seizure-related comorbidities. In many -but not all- situations, seizures shift brain function towards a more immature state, promoting the birth of newborn neurons, altering the dendritic structure and neuronal connectivity, or changing neurotransmitter signaling towards more immature patterns. These effects depend upon many factors, including the seizure type, age of seizure occurrence, sex, and brain region studied. Here we discuss some of these findings proposing that these seizure-induced immature features do not simply represent rejuvenation of the brain but rather a de-synchronization of the homeostatic mechanisms that were in place to maintain normal physiology, which may contribute to epileptogenesis or the cognitive comorbidities.

Effects of essential amino acid deficiency: down-regulation of KCC2 and the GABAA receptor; disinhibition in the anterior piriform cortex

The anterior piriform cortex (APC) is activated by, and is the brain area most sensitive to, essential (indispensable) amino acid (IAA) deficiency. The APC is required for the rapid (20 min) behavioral rejection of IAA deficient diets and increased foraging, both crucial adaptive functions supporting IAA homeostasis in omnivores. The biochemical mechanisms signaling IAA deficiency in the APC block initiation of translation in protein synthesis via uncharged tRNA and the general amino acid control kinase, general control nonderepressing kinase 2. Yet, how inhibition of protein synthesis activates the APC is unknown. The neuronal K(+) Cl(-) cotransporter, neural potassium chloride co-transporter (KCC2), and GABAA receptors are essential inhibitory elements in the APC with short plasmalemmal half-lives that maintain control in this highly excitable circuitry. After a single IAA deficient meal both proteins were reduced (vs. basal diet controls) in western blots of APC (but not neocortex or cerebellum) and in immunohistochemistry of APC. Furthermore, electrophysiological analyses support loss of inhibitory elements such as the GABAA receptor in this model. As the crucial inhibitory function of the GABAA receptor depends on KCC2 and the Cl(-) transmembrane gradient it establishes, these results suggest that loss of such inhibitory elements contributes to disinhibition of the APC in IAA deficiency. The circuitry of the anterior piriform cortex (APC) is finely balanced between excitatory (glutamate, +) and inhibitory (GABA, -) transmission. GABAA receptors use Cl(-), requiring the neural potassium chloride co-transporter (KCC2). Both are rapidly turning-over proteins, dependent on protein synthesis for repletion. In IAA (indispensable amino acid) deficiency, within 20 min, blockade of protein synthesis prevents restoration of these inhibitors; they are diminished; disinhibition ensues. GCN2 = general control non-derepressing kinase 2, eIF2α = α-subunit of the eukaryotic initiation factor 2.

STE20/SPS1-related proline/alanine-rich kinase is involved in plasticity of GABA signaling function in a mouse model of acquired epilepsy

The intracellular concentration of chloride ([Cl^-]_i) determines the strength and polarity of GABA neurotransmission. STE20/SPS1-related proline/alanine-rich kinase (SPAK) is known as an indirect regulator of [Cl^-]_i for its activation of Na-K-2 Cl^-co-transporters (NKCC) and inhibition of K-Cl^-co-transporters (KCC) in many organs. NKCC1 or KCC2 expression changes have been demonstrated previously in the hippocampal neurons of mice with pilocarpine-induced status epilepticus (PISE). However, it remains unclear whether SPAK modulates [Cl^-]_i via NKCC1 or KCC2 in the brain. Also, there are no data clearly characterizing SPAK expression in cortical or hippocampal neurons or confirming an association between SPAK and epilepsy. In the present study, we examined SPAK expression and co-expression with NKCC1 and KCC2 in the hippocampal neurons of mice with PISE, and we investigated alterations in SPAK expression in the hippocampus of such mice. Significant increases in SPAK mRNA and protein levels were detected during various stages of PISE in the PISE mice in comparison to levels in age-matched sham (control) and blank treatment (control) mice. SPAK and NKCC1 expression increased in vitro, while KCC2 was down-regulated in hippocampal neurons following hypoxic conditioning. However, SPAK overexpression did not influence the expression levels of NKCC1 or KCC2. Using co-immunoprecipitation, we determined that the intensity of interaction between SPAK and NKCC1 and between SPAK and KCC2 increased markedly after oxygen-deprivation, whereas SPAK overexpression strengthened the relationships. The [Cl^-]_i of hippocampal neurons changed in a corresponding manner under the different conditions. Our data suggests that SPAK is involved in the plasticity of GABA signaling function in acquired epilepsy via adjustment of [Cl^-]_i in hippocampal neurons.

GABA(A) receptor chloride channels are involved in the neuroprotective role of GABA following oxygen and glucose deprivation in the rat cerebral cortex but not in the hippocampus

Assays on "ex vivo" sections of rat hippocampus and rat cerebral cortex, subjected to oxygen and glucose deprivation (OGD) and a three-hour reperfusion-like (RL) recovery, were performed in the presence of either GABA or the GABA(A) receptor binding site antagonist, bicuculline. Lactate dehydrogenase (LDH) and propidium iodide were used to quantify cell mortality. We also measured, using real-time quantitative polymerase chain reaction (qPCR), the early transcriptional response of a number of genes of the glutamatergic and GABAergic systems. Specifically, glial pre- and post-synaptic glutamatergic transporters (namely GLAST1a, EAAC-1, GLT-1 and VGLUT1), three GABAA receptor subunits (α1, β2 and γ2), and the GABAergic presynaptic marker, glutamic acid decarboxylase (GAD65), were studied. Mortality assays revealed that GABAA receptor chloride channels play an important role in the neuroprotective effect of GABA in the cerebral cortex, but have a much smaller effect in the hippocampus. We also found that GABA reverses the OGD-dependent decrease in GABA(A) receptor transcript levels, as well as mRNA levels of the membrane and vesicular glutamate transporter genes. Based on the markers used, we conclude that OGD results in differential responses in the GABAergic presynaptic and postsynaptic systems.

Disrupted Cl(-) homeostasis contributes to reductions in the inhibitory efficacy of diazepam during hyperexcited states

The K(+) -Cl(-) cotransporter type 2 is the major Cl(-) extrusion mechanism in most adult neurons. This process in turn leads to Cl(-) influx upon activation of γ-aminobutyric acid type A (GABAA ) receptors and the canonical hyperpolarising inhibitory postsynaptic potential. Several neurological disorders are treated with drugs that target and enhance GABAA receptor signaling, including the commonly used benzodiazepine diazepam and the anesthetic propofol. Some of these disorders are also associated with deficits in GABAA signaling and become less sensitive to therapeutic drugs that target GABAA receptors. To date, it is unknown if alterations in the neuronal Cl(-) gradient affect the efficacies of diazepam and propofol. We therefore used the in vitro model of glutamate-induced hyperexcitability to test if alterations in the Cl(-) gradient affect the efficacy of GABAA modulators. We exclusively utilised the gramicidin perforated-patch-clamp configuration to preserve the endogenous Cl(-) gradient in rat neurons. Brief exposure to glutamate reduced the inhibitory efficacy of diazepam within 5 min, which was caused by the collapse of the Cl(-) gradient, and not due to reductions in GABAA receptor number. Unlike diazepam, propofol retained its efficacy by shunting the membrane conductance despite the glutamate-induced appearance of depolarising GABAA -mediated currents. Similarly, pharmacological inhibition of K(+) -Cl(-) cotransporter type 2 by furosemide disrupted Cl(-) homeostasis and reduced the efficacy of diazepam but not propofol. Collectively our results suggest that pathological hyperexcitable conditions could cause the rapid accumulation of intracellular Cl(-) and the appearance of depolarising GABAA -mediated currents that would decrease the efficacy of diazepam.

Activations of GABAergic signaling, HSP70 and MAPK cascades are involved in baicalin's neuroprotection against gerbil global ischemia/reperfusion injury

Baicalin, a flavonoid compound isolated from the plant Scutellaria baicalensis Georgi, is known as a protective agent against delayed neuronal cell death after ischemia/reperfusion. To investigate the neuroprotective mechanism of baicalin, the present study was conducted to explore whether the alterations of GABAergic signaling, heat shock protein 70 (HSP70) and mitogen-activated protein kinases (MAPKs) were involved in its neuroprotection on gerbils global ischemia. The bilateral carotid arteries were occluded by 5 min and baicalin at the dose of 200 mg/kg was intraperitoneally injected into the gerbils immediately after cerebral ischemia. Seven days after reperfusion, neurological deficit was scored and changes in hippocampal neuronal cell death were assessed by Nissl staining as well as NeuN immunohistochemistry. The mRNA and protein expressions of GABAergic signal molecules (GABA(A)R α1, GABA(A)R γ2, KCC2 and NKCC1) were determined in ischemic hippocampus by real-time RT-PCR and Western blot, respectively. In addition, HSP70 and MAPKs cascades (ERK, JNK and p38) were also detected using western blot assay. Our results illustrated that baicalin treatment significantly facilitated neurological function, suppressed the ischemia-induced neuronal damage. Besides, administration of baicalin also caused a striking increase of GABA(A)R α1, GABA(A)R γ2 and KCC2 together with the decrease of NKCC1 at mRNA and protein levels in gerbils hippocampus following an ischemic insult. Furthermore, the protein expressions of HSP70 and phosphorylated ERK (p-ERK) were evidently augmented while the phosphorylated JNK (p-JNK) and phosphorylated p38 (p-p38) were strikingly diminished in ischemic gerbils with baicalin treatment. These findings suggest that baicalin activates GABAergic signaling, HSP70 and MAPKs cascades in global ischemia, which may be a mechanism underlying the baicalin's neuroprotection.

Electro interstitial scan system: assessment of 10 years of research and development

BACKGROUND

Ten years of research and development have allowed an understanding of how the electro interstitial scan (EIS) works and what its clinical applications may be.

MATERIALS AND METHODS

The EIS is a galvanic skin response device. The measurements are performed by electrical stimulation of the post sympathetic cholinergic fiber with weak DC current and voltage 1.28V applied during 2 minutes and in bipolar mode. CURRENT SCIENTIFIC KNOWLEDGE: EIS ELECTRICAL MEASUREMENTS ARE RELATED TO: (1) the concentration of free chloride ions in the interstitial fluid, which affects the transfer of electrical current and the ratio intensity/voltage; (2) the morphology of the interstitial fluid, which is related to the electrical dispersion calculated from the Cole equation (α parameter); (3) electrical stimulation, which causes a change in sweat rate at the passive electrodes - post sympathetic cholinergic fiber electrical stimulation appears to be responsible for activating M2 receptors, which regulate nitric oxide (NO) production in the endothelial cell and cause vasodilation and a released sweat response; and (4) the electrochemical redox reactions (electrolysis) of the released sweat on electrodes, which are different on the bulk of the metal electrodes (O2 + [4H(+)] + [4e(-)]) and on the Ag/AgCl disposable electrodes (AgCl precipitation).

RESULTS

FOR EACH OF THE EIS CLINICAL RESULTS, VARIOUS EXPLANATIONS WERE POSITED, SUCH AS: (1) electrical stimulation of the postsympathetic cholinergic fiber-activating NO production in the endothelial cell, which causes vasodilation and a released sweat response (diabetes detection); (2) estimation of interstitial fluid's acid-base balance, which is reflected in an electrochemical reaction on the bulk of the electrodes through the released sweat (prostate cancer detection); (3) estimation of cerebral interstitial fluid chloride ions (detection of ADHD in children); and (4) estimation of the morphology of the interstitial fluid (selective serotonin reuptake inhibitor treatment response).

CONCLUSION

After 10 years of development, the analysis of current scientific knowledge and results of clinical investigations have allowed a better understanding of EIS electrical measurements.

Traumatic alterations in GABA signaling disrupt hippocampal network activity in the developing brain

Severe head trauma causes widespread neuronal shear injuries and acute seizures. Shearing of neural processes might contribute to seizures by disrupting the transmembrane ion gradients that subserve normal synaptic signaling. To test this possibility, we investigated changes in intracellular chloride concentration ([Cl(-)](i)) associated with the widespread neural shear injury induced during preparation of acute brain slices. In hippocampal slices and intact hippocampal preparations from immature CLM-1 mice, increases in [Cl(-)](i) correlated with disruption of neural processes and biomarkers of cell injury. Traumatized neurons with higher [Cl(-)](i) demonstrated excitatory GABA signaling, remained synaptically active, and facilitated network activity as assayed by the frequency of extracellular action potentials and spontaneous network-driven oscillations. These data support a more inhibitory role for GABA in the unperturbed immature brain, demonstrate the utility of the acute brain slice preparation for the study of the consequences of trauma, and provide potential mechanisms for both GABA-mediated excitatory network events in the slice preparation and early post-traumatic seizures.

Upregulation of KCC2 activity by zinc-mediated neurotransmission via the mZnR/GPR39 receptor

Vesicular Zn(2+) regulates postsynaptic neuronal excitability upon its corelease with glutamate. We previously demonstrated that synaptic Zn(2+) acts via a distinct metabotropic zinc-sensing receptor (mZnR) in neurons to trigger Ca(2+) responses in the hippocampus. Here, we show that physiological activation of mZnR signaling induces enhanced K(+)/Cl(-) cotransporter 2 (KCC2) activity and surface expression. As KCC2 is the major Cl(-) outward transporter in neurons, Zn(2+) also triggers a pronounced hyperpolarizing shift in the GABA(A) reversal potential. Mossy fiber stimulation-dependent upregulation of KCC2 activity is eliminated in slices from Zn(2+) transporter 3-deficient animals, which lack synaptic Zn(2+). Importantly, activity-dependent ZnR signaling and subsequent enhancement of KCC2 activity are also absent in slices from mice lacking the G-protein-coupled receptor GPR39, identifying this protein as the functional neuronal mZnR. Our work elucidates a fundamentally important role for synaptically released Zn(2+) acting as a neurotransmitter signal via activation of a mZnR to increase Cl(-) transport, thereby enhancing inhibitory tone in postsynaptic cells.

Chloride cotransporters, chloride homeostasis, and synaptic inhibition in the developing auditory system

The role of glycine and GABA as inhibitory neurotransmitters in the adult vertebrate nervous system has been well characterized in a variety of model systems, including the auditory, which is particularly well suited for analyzing inhibitory neurotransmission. However, a full understanding of glycinergic and GABAergic transmission requires profound knowledge of how the precise organization of such synapses emerges. Likewise, the role of glycinergic and GABAergic signaling during development, including the dynamic changes in regulation of cytosolic chloride via chloride cotransporters, needs to be thoroughly understood. Recent literature has elucidated the developmental expression of many of the molecular components that comprise the inhibitory synaptic phenotype. An equally important focus of research has revealed the critical role of glycinergic and GABAergic signaling in sculpting different developmental aspects in the auditory system. This review examines the current literature detailing the expression patterns and function (chapter 1), as well as the regulation and pharmacology of chloride cotransporters (chapter 2). Of particular importance is the ontogeny of glycinergic and GABAergic transmission (chapter 3). The review also surveys the recent work on the signaling role of these two major inhibitory neurotransmitters in the developing auditory system (chapter 4) and concludes with an overview of areas for further research (chapter 5).

Taurine-like GABA aminotransferase inhibitors prevent rabbit brain slices against oxygen-glucose deprivation-induced damage

The activation of the GABAergic system has been shown to protect brain tissues against the damage that occurs after cerebral ischaemia. On the other hand, the taurine analogues (±)Piperidine-3-sulphonic- (PSA), 2-aminoethane phosphonic- (AEP), 2-(N-acetylamino) cyclohexane sulfonic-acids (ATAHS) and 2-aminobenzene sulfonate-acids (ANSA) have been reported to block GABA metabolism by inhibiting rabbit brain GABA aminotransferase and to increase GABA content in rabbit brain slices. The present investigation explored the neuroprotection provided by GABA, Vigabatrin (VIGA) and taurine analogues in the course of oxygen-glucose deprivation and reperfusion induced damage of rabbit brain slices. Tissue damage was assessed by measuring the release of glutamate and lactate dehydrogenase (LDH) during reperfusion and by determining final tissue water gain, measured as the index of cell swelling. GABA (30-300 μM) and VIGA (30-300 μM) significantly antagonised LDH and glutamate release, as well as tissue water gain caused by oxygen-glucose deprivation and reperfusion. Lower (1-10 μM) or higher concentrations (up to 3,000 μM) were ineffective. ANSA, PSA and ATAHS significantly reduced glutamate and LDH release and tissue water gain in a range of concentrations between 30 and 300 μM. Lower (0-10 μM) or higher (up to 3,000 μM) concentrations were ineffective. Both mechanisms suggest hormetic ("U-shaped") effects. These results indicate that the GABAergic system activation performed directly by GABA or indirectly through GABA aminotransferase inhibition is a promising approach for protecting the brain against ischemia and reperfusion-induced damage.

NMDA receptor activity downregulates KCC2 resulting in depolarizing GABAA receptor-mediated currents

KCC2 is a neuron-specific K(+)-Cl(-) co-transporter that maintains a low intracellular Cl(-) concentration that is essential for hyperpolarizing inhibition mediated by GABA(A) receptors. Deficits in KCC2 activity occur in disease states associated with pathophysiological glutamate release. However, the mechanisms by which elevated glutamate alters KCC2 function are unknown. The phosphorylation of KCC2 residue Ser940 is known to regulate its surface activity. We found that NMDA receptor activity and Ca(2+) influx caused the dephosphorylation of Ser940 in dissociated rat neurons, leading to a loss of KCC2 function that lasted longer than 20 min. Protein phosphatase 1 mediated the dephosphorylation events of Ser940 that coincided with a deficit in hyperpolarizing GABAergic inhibition resulting from the loss of KCC2 activity. Blocking dephosphorylation of Ser940 reduced the glutamate-induced downregulation of KCC2 and substantially improved the maintenance of hyperpolarizing GABAergic inhibition. Reducing the downregulation of KCC2 therefore has therapeutic potential in the treatment of neurological disorders.

Age-Induced Alterations in Hippocampal Function and Metabolism

As the nervous system ages, a variety of changes occur in metabolism supporting glial and neuronal function, resulting in greater susceptibility to disease conditions. Changes with aging in the metabolic unit (i.e., neurons, glial cells and blood vessels) have been reported to include alterations of vascular reactivity, impaired transport of critical substrates underlying metabolism, enhanced reactive oxygen species production and alterations in calcium signaling. Some diseases are focused on the elderly, particularly cerebral ischemia, cognitive limitations, iatrogenic hypoglycemia, malignant brain tumors (i.e., glioblastoma), and Alzheimer's disease, partly due to metabolic alterations with aging. These metabolic changes with aging are discussed in light of primary theories of aging of the brain, which include mitochondrial, calcium dysfunction and enhanced oxidative damage. Here we focus on metabolic changes with aging which can influence the susceptibility of the brain to ischemia and cognitive function. Lastly, we describe treatment possibilities for these abnormal responses to aging, particularly the topic of caloric/dietary restriction, and possible mechanisms underlying this treatment direction.

Developmental regulation of gene expression and astrocytic processes may explain selective hippocampal vulnerability

The hippocampus plays a central role in the brain network that is essential for memory function. Paradoxically, the hippocampus is also the brain structure that is most sensitive to hypoxic-ischemic episodes. Here, we show that the expression of genes associated with glycolysis and glutamate metabolism in astrocytes and the coverage of excitatory synapses by astrocytic processes undergo significant decreases in the CA1 field of the monkey hippocampus during postnatal development. Given the established role of astrocytes in the regulation of glutamate concentration in the synaptic cleft, our findings suggest that a developmental decrease in astrocytic processes could underlie the selective vulnerability of CA1 during hypoxic-ischemic episodes in adulthood, its decreased susceptibility to febrile seizures with age, as well as contribute to the emergence of selective, adultlike memory function.

Adult rat hippocampal slices as in vitro models for neurodegeneration: Studies on cell viability and apoptotic processes

Adult hippocampal slice cultures were used in the modeling of apoptotic aspects of neurodegeneration. Slice viability was determined by the use of trypan blue (TB) staining, and apoptosis was assessed by caspase-3 immunohistochemistry. A large number of pyramidal cells showed signs of degeneration 30 min after sectioning (58.4% of the total number of pyramidal cells), as they exhibited TB uptake, and about 71.6% of these neurons became stained by the third day in culture, when patches in the stratum oriens also demonstrated distinct TB staining. By the sixth day of culturing, almost all cells in the pyramidal cell layer became TB positive (88.4%). The caspase-3 immunoreactivity displayed a different pattern, as the most intense immunoreactivity, detected mainly in the pyramidal cells, peaked 6 h after culturing, and then decreased steadily. The present data show that in adult hippocampal slices a large number of pyramidal cells initiate apoptotic processes as a result of irreparable damage sustained during slice preparation and culture maintenance, and support the notion that apoptosis is an integral part of the neurodegenerative processes not only in vivo but also in vitro. Elucidation of mechanisms for the apoptotic processes in adult hippocampal slice cultures could lead to the development of new therapeutic strategies; moreover, the utilization of adult hippocampal slice cultures could be a viable alternative technique to in vivo experiments in studying the mechanisms responsible for neurodegeneration.

Possible involvement of DNA methylation in NKCC1 gene expression during postnatal development and in response to ischemia

In CNS, GABA(A) receptor-mediated responses switch from depolarization to hyperpolarization during postnatal development. This switch is mediated by developmental down-regulation of inwardly directed Na(+)-K(+)-2Cl(-) co-transporter type 1 (NKCC1) and up-regulation of outwardly directed K(+)-Cl(-) co-transporter type 2. While several factors have been shown to regulate K(+)-Cl(-) co-transporter type 2 expression, little is known about the mechanisms by which the expression of NKCC1 is regulated during postnatal development. Here, we report a novel epigenetic mechanism underlying the developmental regulation of NKCC1 gene expression in the rat cerebral cortex. In vitro DNA methylation of the NKCC1 promoter region, which contains a high density of cytosine-phosphodiester-guanine islands, significantly decreased the expression of NKCC1 mRNA, and the degree of methylation of the NKCC1 promoter region significantly increased during postnatal development. In addition, treatment with 5-aza-2'-deoxycytidine, a specific DNA methyltransferase inhibitor, elicited an increase in the expression of NKCC1 mRNA and protein in cortical slice cultures. Focal ischemic injury induced by the occlusion of the middle cerebral artery led to the re-expression of NKCC1 mRNA and protein even in the mature rat cortex. The re-expression of NKCC1 mRNA and protein in the injured cerebral cortex was related to a decrease in the methylation status of the NKCC1 promoter region. Our results indicate that epigenetic mechanisms, such as DNA methylation, might be involved in the regulation of NKCC1 gene expression during postnatal development as well as under pathological conditions.

GABAergic synaptic transmission regulates calcium influx during spike-timing dependent plasticity

Coincident pre- and postsynaptic activity of hippocampal neurons alters the strength of gamma-aminobutyric acid (GABA(A))-mediated inhibition through a Ca(2+)-dependent regulation of cation-chloride cotransporters. This long-term synaptic modulation is termed GABAergic spike-timing dependent plasticity (STDP). In the present study, we examined whether the properties of the GABAergic synapses themselves modulate the required postsynaptic Ca(2+) influx during GABAergic STDP induction. To do this we first identified GABAergic synapses between cultured hippocampal neurons based on their relatively long decay time constants and their reversal potentials which lay close to the resting membrane potential. GABAergic STDP was then induced by coincidentally (±1 ms) firing the pre- and postsynaptic neurons at 5 Hz for 30 s, while postsynaptic Ca(2+) was imaged with the Ca(2+)-sensitive fluorescent dye Fluo4-AM. In all cases, the induction of GABAergic STDP increased postsynaptic Ca(2+) above resting levels. We further found that the magnitude of this increase correlated with the amplitude and polarity of the GABAergic postsynaptic current (GPSC); hyperpolarizing GPSCs reduced the Ca(2+) influx in comparison to both depolarizing GPSCs, and postsynaptic neurons spiked alone. This relationship was influenced by both the driving force for Cl(-) and GABA(A) conductance (which had positive correlations with the Ca(2+) influx). The spike-timing order during STDP induction did not influence the correlation between GPSC amplitude and Ca(2+) influx, which is likely accounted for by the symmetrical GABAergic STDP window.

Brain slices as models for neurodegenerative disease and screening platforms to identify novel therapeutics

Recent improvements in brain slice technology have made this biological preparation increasingly useful for examining pathophysiology of brain diseases in a tissue context. Brain slices maintain many aspects of in vivo biology, including functional local synaptic circuitry with preserved brain architecture, while allowing good experimental access and precise control of the extracellular environment, making them ideal platforms for dissection of molecular pathways underlying neuronal dysfunction. Importantly, these ex vivo systems permit direct treatment with pharmacological agents modulating these responses and thus provide surrogate therapeutic screening systems without recourse to whole animal studies. Virus or particle mediated transgenic expression can also be accomplished relatively easily to study the function of novel genes in a normal or injured brain tissue context.In this review we will discuss acute brain injury models in organotypic hippocampal and co-culture systems and the effects of pharmacological modulation on neurodegeneration. The review will also cover the evidence of developmental plasticity in these ex vivo models, demonstrating emergence of injury-stimulated neuronal progenitor cells, and neurite sprouting and axonal regeneration following pathway lesioning. Neuro-and axo-genesis are emerging as significant factors contributing to brain repair following many acute and chronic neurodegenerative disorders. Therefore brain slice models may provide a critical contextual experimental system to explore regenerative mechanisms in vitro.

A mutant thyroid hormone receptor alpha1 alters hippocampal circuitry and reduces seizure susceptibility in mice

Thyroid hormone deficiency during early developmental stages causes a multitude of functional and morphological deficits in the brain. In the present study we investigate the effects of a mutated thyroid hormone receptor TR alpha 1 and the resulting receptor-mediated hypothyroidism on the development of GABAergic neurotransmission and seizure susceptibility of neuronal networks. We show that mutant mice have a strong resistance to seizures induced by antagonizing the GABA(A) receptor complex. Likewise the hippocampal network of mutant mice shows a decreased likelihood to transform physiological into pathological rhythmic network activity such as seizure-like interictal waves. As we demonstrate the cellular basis for this behavior is formed by the excitatory nature of GABAergic neurotransmission in the mutant mice, possibly caused by altered Cl(-) homeostasis, and/or the altered patterning of calretinin-positive cells in the hippocampal hilus. This study is, to our knowledge, the first to show an effect of maternal and early postnatal hypothyroidism via TR alpha 1 on the development of GABAergic neurotransmission and susceptibility to epileptic seizures.

Vesicular GABA release delays the onset of the Purkinje cell terminal depolarization without affecting tissue swelling in cerebellar slices during simulated ischemia

Neurosteroids that can enhance GABA(A) receptor sensitivity protect cerebellar Purkinje cells against transient episodes of global brain ischemia, but little is known about how ischemia affects GABAergic transmission onto Purkinje cells. Here we use patch-clamp recording from Purkinje cells in acutely prepared slices of rat cerebellum to determine how ischemia affects GABAergic signaling to Purkinje cells. In voltage-clamped Purkinje cells, exposing slices to solutions designed to simulate brain ischemia caused an early, partial suppression of the frequency of spontaneous inhibitory post synaptic currents (sIPSCs), but after 5-8 min GABA accumulated in the extracellular space around Purkinje cells, generating a large (approximately 17 nS), sustained GABA(A) receptor-mediated conductance. The sustained GABA(A) conductance occurred in parallel with an even larger (approximately 117 nS) glutamate receptor-mediated conductance, but blocking GABA(A) receptors did not affect the timing or magnitude of the glutamate conductance, and blocking glutamate receptors did not affect the timing or magnitude of the GABA(A) conductance. Despite the lack of interaction between GABA and glutamate, blocking GABA(A) receptors significantly accelerated the onset of the Purkinje cell "ischemic" depolarization (ID), as assessed with current-clamp recordings from Purkinje cells or field potential recordings in the dendritic field of the Purkinje cells. The Purkinje cell ID occurred approximately 2 min prior to the sustained glutamate release under control conditions and a further 1-2 min earlier when GABA(A) receptors were blocked. Tissue swelling, as assessed by monitoring light transmittance through the slice, peaked just after the ID, prior to the sustained glutamate release, but was not affected by blocking GABA(A) receptors. These data indicate that ischemia induces the Purkinje cell ID and tissue swelling prior to the sustained glutamate release, and that blocking GABA(A) receptors accelerates the onset of the ID without affecting tissue swelling. Taken together these data may explain why Purkinje cells are one of the most ischemia sensitive neurons in the brain despite lacking NMDA receptors, and why neurosteroids that enhance GABA(A) receptor function protect Purkinje cells against transient episodes of global brain ischemia.