K+ channel openers prevent global ischemia-induced expression of c-fos, c-jun, heat shock protein, and amyloid beta-protein precursor genes and neuronal death in rat hippocampus

Nicorandil Exerts Anticonvulsant Effects in Pentylenetetrazol-Induced Seizures and Maximal-Electroshock-Induced Seizures by Downregulating Excitability in Hippocampal Pyramidal Neurons

N-(2-hydroxyethyl) nicotinamide nitrate (nicorandil), a nitrate that activates adenosine triphosphate (ATP)-sensitive potassium (K_ATP) channels, is generally used in the treatment of angina and offers long-term cardioprotective effects. It has been reported that several K_ATP channel openers can effectively alleviate the symptoms of seizure. The purpose of this study was to investigate the improvement in seizures induced by nicorandil. In this study, seizure tests were used to evaluate the effect of different doses of nicorandil by analysing seizure incidence, including minimal clonic seizure and generalised tonic-clonic seizure. We used a maximal electroshock seizure (MES) model, a metrazol maximal seizure (MMS) model and a chronic pentylenetetrazol (PTZ)-induced seizure model to evaluate the effect of nicorandil in improving seizures. Each mouse in the MES model was given an electric shock, while those in the nicorandil group received 0.5, 1, 2, 3 and 6 mg/kg of nicorandil by intraperitoneal injection, respectively. In the MMS model, the mice in the PTZ group and the nicorandil group were injected subcutaneously with PTZ (90 mg/kg), and the mice in the nicorandil group were injected intraperitoneally with 1, 3 and 5 mg/kg nicorandil, respectively. In the chronic PTZ-induced seizure model, the mice in the PTZ group and the nicorandil group were injected intraperitoneally with PTZ (40 mg/kg), and the mice in the nicorandil group were each given 1 and 3 mg/kg of PTZ at a volume of 200 nL. Brain slices containing the hippocampus were prepared, and cell-attached recording was used to record the spontaneous firing of pyramidal neurons in the hippocampal CA1 region. Nicorandil (i.p.) significantly increased both the maximum electroconvulsive protection rate in the MES model and the seizure latency in the MMS model. Nicorandil infused directly onto the hippocampal CA1 region via an implanted cannula relieved symptoms in chronic PTZ-induced seizures. The excitability of pyramidal neurons in the hippocampal CA1 region of the mice was significantly increased after both the acute and chronic administration of PTZ. To a certain extent, nicorandil reversed the increase in both firing frequency and proportion of burst spikes caused by PTZ (P < 0.05). Our results suggest that nicorandil functions by downregulating the excitability of pyramidal neurons in the hippocampal CA1 region of mice and is a potential candidate for the treatment of seizures.

Selective block of adenosine A2A receptors prevents ischaemic-like effects induced by oxygen and glucose deprivation in rat medium spiny neurons

BACKGROUND AND PURPOSE

Ischaemia is known to cause massive neuronal depolarization, termed anoxic depolarization (AD), due to energy failure and loss of membrane ion gradients. The neuromodulator adenosine accumulates extracellularly during ischaemia and activates four metabotropic receptors: A1 , A2A , A2B and A3 . Striatal medium spiny neurons (MSNs) express high levels of A2A receptors and are particularly vulnerable to ischaemic insults. A2A Receptor blockade reduces acute striatal post-ischaemic damage but the cellular mechanisms involved are still unknown.

EXPERIMENTAL APPROACH

We performed patch-clamp recordings of MSNs in rat striatal slices subjected to oxygen and glucose deprivation (OGD) to investigate the effects of A2A receptor ligands or ion channel blockers on AD and OGD-induced ionic imbalance, measured as a positive shift in Erev of ramp currents.

KEY RESULTS

Our data indicate that the A2A receptor antagonist SCH58261 (10 μM) significantly attenuated ionic imbalance and AD appearance in MSNs exposed to OGD. The K+ channel blocker Ba2+ (2 mM) or the Na+ channel blocker tetrodotoxin (1 μM) exacerbated and attenuated, respectively, OGD-induced changes. Spontaneous excitatory post-synaptic current (sEPSC) analysis in MSNs revealed that the A2A receptor agonist CGS21680 (1 μM) prevented OGD-induced decrease of sEPSCs within the first 5 min of the insult, an effect shared by the K+ channel blocker Ba2+ , indicating facilitated glutamate release.

CONCLUSION AND IMPLICATIONS

Adenosine, released during striatal OGD, activates A2A receptors that may exacerbate OGD-induced damage through K+ channel inhibition. Our results could help to develop A2A receptor-selective therapeutic tools for the treatment of brain ischaemia.

Effect of nicorandil on the spatial arrangement of primary motor cortical neurons in the sub-acute phase of stroke in a rat model

INTRODUCTION

Ischemic stroke remains a major cause of disability and death worldwide. The density and the spatial distribution of the primary motor (M1) cortical neurons are important in signal transmission and control the movement-related functions. Recently, the neuroprotective effect of nicorandil in cerebral ischemia was described through its anti-apoptosis, antioxidant and anti-inflammatory properties. This study aimed to determine the effects of nicorandil on the neurobehavioral outcome, infarct size, and density, and spatial distribution of M1 cortical neurons after cerebral ischemia.

METHODS

Thirty Sprague-Dawley rats were randomly divided into three groups. Sham underwent surgery without middle cerebral artery occlusion (MCAO) and drug. The MCAO and treatment groups after MCAO received saline or nicorandil 2, 24, 48, and 72 h after the induction of brain ischemia. Neurobehavioral tests were performed, brains removed, sectioned, and stained by 2,3,5-triphenyltetrazolium chloride (TTC) to estimate the size of the infarction and Nissl staining to evaluate the numerical density, mean area, and the distribution pattern of M1 cortical neurons, using Voronoi spatial tessellation.

RESULTS

Although nicorandil treatment significantly decreased the neurological deficits and density of neuronal neighbors, it could not preserve the normal regular spatial distributions of M1 cortical neurons after MCAO. It also could not significantly improve motor function or reduce ischemic lesion size.

CONCLUSIONS

Treatment using the present dose of nicorandil during sub-acute ischemic stroke could not increase neuronal density or preserve the normal regular spatial distributions after MCAO. However, it had beneficial effects on neurobehavioral and motor function and somewhat reduced ischemic lesion size.

Inhibition of eIF5A hypusination pathway as a new pharmacological target for stroke therapy

In eukaryotes, the polyamine pathway generates spermidine that activates the hypusination of the translation factor eukaryotic initiation factor 5A (eIF5A). Hypusinated-eIF5A modulates translation, elongation, termination and mitochondrial function. Evidence in model organisms like drosophila suggests that targeting polyamines synthesis might be of interest against ischemia. However, the potential of targeting eIF5A hypusination in stroke, the major therapeutic challenge specific to ischemia, is currently unknown. Using in vitro models of ischemic-related stress, we documented that GC7, a specific inhibitor of a key enzyme in the eIF5A activation pathway, affords neuronal protection. We identified the preservation of mitochondrial function and thereby the prevention of toxic ROS generation as major processes of GC7 protection. To represent a thoughtful opportunity of clinical translation, we explored whether GC7 administration reduces the infarct volume and functional deficits in an in vivo transient focal cerebral ischemia (tFCI) model in mice. A single GC7 pre- or post-treatment significantly reduces the infarct volume post-stroke. Moreover, GC7-post-treatment significantly improves mouse performance in the rotarod and Morris water-maze, highlighting beneficial effects on motor and cognitive post-stroke deficits. Our results identify the targeting of the polyamine-eIF5A-hypusine axis as a new therapeutic opportunity and new paradigm of research in stroke and ischemic diseases.

The KATP channel opener, nicorandil, ameliorates brain damage by modulating synaptogenesis after ischemic stroke

With population growth and aging, more and more patients with cerebral infarction have varying degrees of disability. ATP-sensitive potassium (KATP) channels regulate many cellular functions by coupling metabolic status with cell membrane electrical activity. Nicorandil (N-(2-hydroxyethyl)-nicotinamide nitrate) is the first KATP channel opener approved for clinical use. It has been reported that it might exert protective effects on the cerebral infarction by increasing cerebral blood flow and reducing inflammation. However, only a few studies explored its role in synaptogenesis. We made the rat model of middle cerebral artery occlusion (MCAO). Nicorandil was administered to rats via oral administration immediately after the surgery at a dose of 7.5 mg/kg and then daily for the next days. Infarct volume, cerebral edema, neurological deficits, cognitive impairment, and the level of Synaptophysin (SYP)、Growth associated protein-43 (GAP43) and neuronal nuclear antigen (NeuN) levels were measured to evaluate the effect of nicorandil. Our data showed that nicorandil treatment could decrease brain damage, improve learning and memory, and increase SYP、GAP43 and NeuN level. Taken together, we propose that nicorandil, as an opener of the KATP channel, provides a neuroprotective role in MCAO by promoting synaptic connections.

The dorsal and the ventral side of hypoglossal motor nucleus showed different response to chronic intermittent hypoxia in rats

PURPOSE

To study neurochemical reactions to chronic intermittent hypoxia (CIH) in the hypoglossal nucleus (HN) of rats.

METHODS

Adult male Sprague-Dawley rats (n = 12) were randomly divided into two groups (the CIH and the control group). The CIH rats were housed in a hypoxic chamber with the fraction of oxygen volume alternating between 21% and 5% by providing air for 60 s and then providing nitrogen for 60 s from 8:30 am to 16:30 pm each day for 35 days. The control group was housed in a cabin with normal oxygen levels. We studied the expression of c-fos protein, 5-hydroxytryptamine (5-HT) positive terminals, and its 2A receptors in hypoglossal nuclei by immunohistochemistry.

RESULTS

The expression of c-fos, 5-HT positive terminals, and accordingly 5-HT 2A receptors in the CIH group were significantly higher than that in the controls (p < 0.05). The ventral side of the HN showed a clearly higher expression of 5-HT and its 2A receptors than the dorsal side (p < 0.05).

CONCLUSION

There were 2 responses of the HN to CIH. First, CIH induced a higher expression of 5-HT positive terminals and its 2A receptors, and second, this reaction was much more evident in ventral side than in the dorsal side. We postulate that these responses may serve to be a protective and compensatory mechanism for CIH.

Mechanisms Underlying Neuroprotection by the NSAID Mefenamic Acid in an Experimental Model of Stroke

Stroke is a devastating neurological event with limited treatment opportunities. Recent advances in understanding the underlying pathogenesis of cerebral ischemia support the involvement of multiple biochemical pathways in the development of the ischemic damage. Fenamates are classical non-steroidal anti-inflammatory drugs but they are also highly subunit-selective modulators of GABA_A receptors, activators of I_KS potassium channels and antagonists of non-selective cation channels and the NLRP3 inflammosome. In the present study we investigated the effect of mefenamic acid (MFA) in a rodent model of ischemic stroke and then addressed the underlying pharmacological mechanisms in vitro for its actions in vivo. The efficacy of MFA in reducing ischemic damage was evaluated in adult male Wistar rats subjected to a 2-h middle cerebral artery occlusion. Intracerebroventricular (ICV) infusion of MFA (0.5 or 1 mg/kg) for 24 h, significantly reduced the infarct volume and the total ischemic brain damage. In vitro, the fenamates, MFA, meclofenamic acid, niflumic acid, and flufenamic acid each reduced glutamate-evoked excitotoxicity in cultured embryonic rat hippocampal neurons supporting the idea that this is a drug class action. In contrast the non-fenamate NSAIDs, ibuprofen and indomethacin did not reduce excitotoxicity in vitro indicating that neuroprotection by MFA was not dependent upon anti-inflammatory actions. Co-application of MFA (100 μM) with either of the GABA_A antagonists picrotoxin (100 μM) or bicuculline (10 μM) or the potassium channel blocker tetraethylammonium (30 mM) did not prevent neuroprotection with MFA, suggesting that the actions of MFA also do not depend on GABA_A receptor modulation or potassium channel activation. These new findings indicate that fenamates may be valuable in the adjunctive treatment of ischemic stroke.

Tandem pore TWIK-related potassium channels and neuroprotection

TWIK-related potassium channels (TREK) belong to a subfamily of the two-pore domain potassium channels family with three members, TREK1, TREK2 and TWIK-related arachidonic acid-activated potassium channels. The two-pore domain potassium channels is the last big family of channels being discovered, therefore it is not surprising that most of the information we know about TREK channels predominantly comes from the study of heterologously expressed channels. Notwithstanding, in this review we pay special attention to the limited amount of information available on native TREK-like channels and real neurons in relation to neuroprotection. Mainly we focus on the role of free fatty acids, lysophospholipids and other neuroprotective agents like riluzole in the modulation of TREK channels, emphasizing on how important this modulation may be for the development of new therapies against neuropathic pain, depression, schizophrenia, epilepsy, ischemia and cardiac complications.

The Traditional Chinese Medicine MLC901 inhibits inflammation processes after focal cerebral ischemia

Inflammation is considered as a major contributor to brain injury following cerebral ischemia. The therapeutic potential of both MLC601/MLC901, which are herbal extract preparations derived from Chinese Medicine, has been reported both in advanced stroke clinical trials and also in animal and cellular models. The aim of this study was to investigate the effects of MLC901 on the different steps of post-ischemic inflammation in focal ischemia in mice. In vivo injury was induced by 60 minutes of middle cerebral artery occlusion (MCAO) followed by reperfusion. MLC901 was administered in post-treatment 90 min after the onset of ischemia and once a day during reperfusion. MLC901 treatment resulted in a reduction in infarct volume, a decrease of Blood Brain Barrier leakage and brain swelling, an improvement in neurological scores and a reduction of mortality rate at 24 hours after MCAO. These beneficial effects of MLC901 were accompanied by an inhibition of astrocytes and microglia/macrophage activation, a drastically decreased neutrophil invasion into the ischemic brain as well as by a negative regulation of pro-inflammatory mediator expression (cytokines, chemokines, matrix metalloproteinases). MLC901 significantly inhibited the expression of Prx6 as well as the transcriptional activity of NFκB and the activation of Toll-like receptor 4 (TLR4) signaling, an important pathway in the immune response in the ischemic brain. MLC901 effects on the neuroinflammation cascade induced by cerebral ischemia probably contribute, in a very significant way, in its potential therapeutic value.

The role of KATP channels in cerebral ischemic stroke and diabetes

ATP-sensitive potassium (KATP) channels are ubiquitously expressed on the plasma membrane of cells in multiple organs, including the heart, pancreas and brain. KATP channels play important roles in controlling and regulating cellular functions in response to metabolic state, which are inhibited by ATP and activated by Mg-ADP, allowing the cell to couple cellular metabolic state (ATP/ADP ratio) to electrical activity of the cell membrane. KATP channels mediate insulin secretion in pancreatic islet beta cells, and controlling vascular tone. Under pathophysiological conditions, KATP channels play cytoprotective role in cardiac myocytes and neurons during ischemia and/or hypoxia. KATP channel is a hetero-octameric complex, consisting of four pore-forming Kir6.x and four regulatory sulfonylurea receptor SURx subunits. These subunits are differentially expressed in various cell types, thus determining the sensitivity of the cells to specific channel modifiers. Sulfonylurea class of antidiabetic drugs blocks KATP channels, which are neuroprotective in stroke, can be one of the high stoke risk factors for diabetic patients. In this review, we discussed the potential effects of KATP channel blockers when used under pathological conditions related to diabetics and cerebral ischemic stroke.

Condition-specific transcriptional regulation of neuronal ion channel genes in brain ischemia

In the context of seeking novel therapeutic targets for treating ischemic stroke, the preconditioning ischemia-induced brain ischemic tolerance has been used as a model of endogenously operative, broad-based neuroprotective mechanisms. Targeting such mechanisms is considered potentially less prone to adverse side effects, as those seen in many failed clinical trials that focus on single targets using exogenous compounds. Results from previous studies have revealed an overall decrease in potassium channel activity in tolerance development. The objective of this study is to identify ion channel genes that are differentially regulated under different brain ischemic conditions, as a mean to identify those ion channels that are associated with ischemic brain injury and ischemic tolerance. In mice in vivo, transient focal cerebral ischemia was induced by middle cerebral artery occlusion. In cultured neuronal cells in vitro, simulated ischemia was modeled by oxygen-glucose deprivation. For both in vivo and in vitro studies, three principal ischemic conditions were included: ischemic-preconditioned, injured and tolerant, respectively, plus appropriate controls. In these model systems, transcript levels of a panel of 84 neuronal ion channels genes were analyzed with a quantitative real-time PCR mini-array. The results showed that, both in vivo and in vitro, there was a predominant down regulation in neuronal ion channel genes under ischemic-tolerant conditions, and an up regulation in ischemic injury. Similar changes were observed among potassium, sodium and calcium channel genes. A number of regulated genes exhibited opposing changes under ischemic-injured and ischemic-tolerant conditions. This subset of ion channel genes exemplifies potentially novel leads for developing multi-factorial therapeutic targets for treating ischemic stroke.

CoQ10 Augments Rosuvastatin Neuroprotective Effect in a Model of Global Ischemia via Inhibition of NF-κB/JNK3/Bax and Activation of Akt/FOXO3A/Bim Cues

Statins were reported to lower the Coenzyme Q10 (CoQ10) content upon their inhibition of HMG-CoA reductase enzyme and both are known to possess neuroprotective potentials; therefore, the aim is to assess the possible use of CoQ10 as an adds-on therapy to rosuvastatin to improve its effect using global I/R model. Rats were allocated into sham, I/R, rosuvastatin (10 mg/kg), CoQ10 (10 mg/kg) and their combination. Drugs were administered orally for 7 days before I/R. Pretreatment with rosuvastatin and/or CoQ10 inhibited the hippocampal content of malondialdehyde, nitric oxide, and boosted glutathione and superoxide dismutase. They also opposed the upregulation of gp91^phox, and p47^phox subunits of NADPH oxidase. Meanwhile, both agents reduced content/expression of TNF-α, iNOS, NF-κBp65, ICAM-1, and MPO. Besides, all regimens abated cytochrome c, caspase-3 and Bax, but increased Bcl-2 in favor of cell survival. On the molecular level, they increased p-Akt and its downstream target p-FOXO3A, with the inhibition of the nuclear content of FOXO3A to downregulate the expression of Bim, a pro-apoptotic gene. Additionally, both treatments downregulate the JNK3/c-Jun signaling pathway. The effect of the combination regimen overrides that of either treatment alone. These effects were reflected on the alleviation of the hippocampal damage in CA1 region inflicted by I/R. Together, these findings accentuate the neuroprotective potentials of both treatments against global I/R by virtue of their rigorous multi-pronged actions, including suppression of hippocampal oxidative stress, inflammation, and apoptosis with the involvement of the Akt/FOXO3A/Bim and JNK3/c-Jun/Bax signaling pathways. The study also nominates CoQ10 as an adds-on therapy with statins.

Integrity of Cerebellar Fastigial Nucleus Intrinsic Neurons Is Critical for the Global Ischemic Preconditioning

Excitation of intrinsic neurons of cerebellar fastigial nucleus (FN) renders brain tolerant to local and global ischemia. This effect reaches a maximum 72 h after the stimulation and lasts over 10 days. Comparable neuroprotection is observed following sublethal global brain ischemia, a phenomenon known as preconditioning. We hypothesized that FN may participate in the mechanisms of ischemic preconditioning as a part of the intrinsic neuroprotective mechanism. To explore potential significance of FN neurons in brain ischemic tolerance we lesioned intrinsic FN neurons with excitotoxin ibotenic acid five days before exposure to 20 min four-vessel occlusion (4-VO) global ischemia while analyzing neuronal damage in Cornu Ammoni area 1 (CA1) hippocampal area one week later. In FN-lesioned animals, loss of CA1 cells was higher by 22% compared to control (phosphate buffered saline (PBS)-injected) animals. Moreover, lesion of FN neurons increased morbidity following global ischemia by 50%. Ablation of FN neurons also reversed salvaging effects of five-minute ischemic preconditioning on CA1 neurons and morbidity, while ablation of cerebellar dentate nucleus neurons did not change effect of ischemic preconditioning. We conclude that FN is an important part of intrinsic neuroprotective system, which participates in ischemic preconditioning and may participate in naturally occurring neuroprotection, such as "diving response".

Alleviation by GABAB Receptors of Neurotoxicity Mediated by Mitochondrial Permeability Transition Pore in Cultured Murine Cortical Neurons Exposed to N-Methyl-D-aspartate

Mitochondrial permeability transition pore (PTP) is supposed to at least in part participate in molecular mechanisms underlying the neurotoxicity seen after overactivation of N-methyl-D-aspartate (NMDA) receptor (NMDAR) in neurons. In this study, we have evaluated whether activation of GABA_B receptor (GABA_BR), which is linked to membrane G protein-coupled inwardly-rectifying K⁺ ion channels (GIRKs), leads to protection of the NMDA-induced neurotoxicity in a manner relevant to mitochondrial membrane depolarization in cultured embryonic mouse cortical neurons. The cationic fluorescent dye 3,3'-dipropylthiacarbocyanine was used for determination of mitochondrial membrane potential. The PTP opener salicylic acid induced a fluorescence increase with a vitality decrease in a manner sensitive to the PTP inhibitor ciclosporin, while ciclosporin alone was effective in significantly preventing both fluorescence increase and viability decrease by NMDA as seen with an NMDAR antagonist. The NMDA-induced fluorescence increase and viability decrease were similarly prevented by pretreatment with the GABA_BR agonist baclofen, but not by the GABA_AR agonist muscimol, in a fashion sensitive to a GABA_BR antagonist. Moreover, the GIRK inhibitor tertiapin canceled the inhibition by baclofen of the NMDA-induced fluorescence increase. These results suggest that GABA_BR rather than GABA_AR is protective against the NMDA-induced neurotoxicity mediated by mitochondrial PTP through a mechanism relevant to opening of membrane GIRKs in neurons.

"New Old Pathologies": AD, PART, and Cerebral Age-Related TDP-43 With Sclerosis (CARTS)

The pathology-based classification of Alzheimer's disease (AD) and other neurodegenerative diseases is a work in progress that is important for both clinicians and basic scientists. Analyses of large autopsy series, biomarker studies, and genomics analyses have provided important insights about AD and shed light on previously unrecognized conditions, enabling a deeper understanding of neurodegenerative diseases in general. After demonstrating the importance of correct disease classification for AD and primary age-related tauopathy, we emphasize the public health impact of an underappreciated AD "mimic," which has been termed "hippocampal sclerosis of aging" or "hippocampal sclerosis dementia." This pathology affects >20% of individuals older than 85 years and is strongly associated with cognitive impairment. In this review, we provide an overview of current hypotheses about how genetic risk factors (GRN, TMEM106B, ABCC9, and KCNMB2), and other pathogenetic influences contribute to TDP-43 pathology and hippocampal sclerosis. Because hippocampal sclerosis of aging affects the "oldest-old" with arteriolosclerosis and TDP-43 pathologies that extend well beyond the hippocampus, more appropriate terminology for this disease is required. We recommend "cerebral age-related TDP-43 and sclerosis" (CARTS). A detailed case report is presented, which includes neuroimaging and longitudinal neurocognitive data. Finally, we suggest a neuropathology-based diagnostic rubric for CARTS.

l-Lactate mediates neuroprotection against ischaemia by increasing TREK1 channel expression in rat hippocampal astrocytes in vitro

Brain ischaemia is a highly debilitating condition where shortage of oxygen and glucose leads to profuse cell death. Lactate is a neuroprotective metabolite whose concentrations increase up to 15-30 mmol/L during ischaemia and TREK1 is a neuroprotective potassium channel which is upregulated during ischaemia. The aim of this study was to investigate the effect of l-lactate on TREK1 expression and to evaluate the role of l-lactate-TREK1 interaction in conferring neuroprotection in ischaemia-prone hippocampus. We show that 15-30 mmol/L l-lactate increases functional TREK1 protein expression by 1.5-3-fold in hippocampal astrocytes using immunostaining and electrophysiology. Studies with transcription blocker actinomycin-D and quantitative PCR indicate that the increase in TREK1 expression is due to enhanced TREK1 mRNA transcription. We further report that l-lactate-mediated increase in TREK1 expression is via protein kinase A (PKA)-dependent pathway. This is the first report of an ischaemic metabolite affecting functional expression of an ion channel. Our studies in an in vitro model of ischaemia using oxygen glucose deprivation show that 30 mmol/L l-lactate fails to reduce cell death in rat hippocampal slices treated with TREK1 blockers, PKA inhibitors and gliotoxin. The above effects were specific to l-lactate as pyruvate failed to increase TREK1 expression and reduce cell death. l-Lactate-induced TREK1 upregulation is a novel finding of physiological significance as TREK1 channels contribute to neuroprotection by enhancing potassium buffering and glutamate clearance capacity of astrocytes. We propose that l-lactate promotes neuronal survival in hippocampus by increasing TREK1 channel expression via PKA pathway in astrocytes during ischaemia. Insufficient blood supply to the brain leads to cerebral ischaemia and increase in extracellular lactate concentrations. We incubated hippocampal astrocytes in lactate and observed increase in TREK1 channel expression via protein kinase A (PKA). Inhibition of TREK1, PKA and metabolic impairment of astrocytes prevented lactate from reducing cell death in ischaemic hippocampus. This pathway serves as an alternate mechanism of neuroprotection. Cover image for this issue: doi: 10.1111/jnc.13326.

ABCC9/SUR2 in the brain: Implications for hippocampal sclerosis of aging and a potential therapeutic target

The ABCC9 gene and its polypeptide product, SUR2, are increasingly implicated in human neurologic disease, including prevalent diseases of the aged brain. SUR2 proteins are a component of the ATP-sensitive potassium ("KATP") channel, a metabolic sensor for stress and/or hypoxia that has been shown to change in aging. The KATP channel also helps regulate the neurovascular unit. Most brain cell types express SUR2, including neurons, astrocytes, oligodendrocytes, microglia, vascular smooth muscle, pericytes, and endothelial cells. Thus it is not surprising that ABCC9 gene variants are associated with risk for human brain diseases. For example, Cantu syndrome is a result of ABCC9 mutations; we discuss neurologic manifestations of this genetic syndrome. More common brain disorders linked to ABCC9 gene variants include hippocampal sclerosis of aging (HS-Aging), sleep disorders, and depression. HS-Aging is a prevalent neurological disease with pathologic features of both neurodegenerative (aberrant TDP-43) and cerebrovascular (arteriolosclerosis) disease. As to potential therapeutic intervention, the human pharmacopeia features both SUR2 agonists and antagonists, so ABCC9/SUR2 may provide a "druggable target", relevant perhaps to both HS-Aging and Alzheimer's disease. We conclude that more work is required to better understand the roles of ABCC9/SUR2 in the human brain during health and disease conditions.

Potassium ion channels in retinal ganglion cells (review)

Retinal ganglion cells (RGCs) consolidate visual processing and constitute the last step prior to the transmission of signals to higher brain centers. RGC death is a major cause of visual impairment in optic neuropathies, including glaucoma, age‑related macular degeneration, diabetic retinopathy, uveoretinitis and vitreoretinopathy. Discharge patterns of RGCs are primarily determined by the presence of ion channels. As the most diverse group of ion channels, potassium (K+) channels play key roles in modulating the electrical properties of RGCs. Biochemical, molecular and pharmacological studies have identified a number of K+ channels in RGCs, including inwardly rectifying K+ (Kir), ATP‑sensitive K+ (KATP), tandem‑pore domain K+ (TASK), voltage‑gated K+ (Kv), ether‑à‑go‑go (Eag) and Ca2+‑activated K+ (KCa) channels. Kir channels are important in the maintenance of the resting membrane potential and controlling RGC excitability. KATP channels are involved in RGC survival and neuroprotection. TASK channels are hypothesized to contribute to the regulation of resting membrane potentials and firing patterns of RGCs. Kv channels are important regulators of cellular excitability, functioning to modulate the amplitude, duration and frequency of action potentials and subthreshold depolarizations, and are also important in RGC development and protection. Eag channels may contribute to dendritic repolarization during excitatory postsynaptic potentials and to the attenuation of the back propagation of action potentials. KCa channels have been observed to contribute to repetitive firing in RGCs. Considering these important roles of K+ channels in RGCs, the study of K+ channels may be beneficial in elucidating the pathophysiology of RGCs and exploring novel RGC protection strategies.

NeuroAiD: properties for neuroprotection and neurorepair

BACKGROUND

Treatments for stroke and other brain injuries are limited. NeuroAiD has been shown to be beneficial in clinical studies. We reviewed the pharmacological effects of NeuroAiD on the normal and ischemic brain and neurons.

METHODS

In vivo and in vitro experiments using mouse model of stroke (focal ischemia), rat model of cardiac arrest (global ischemia) and cortical neurons in culture were reviewed and summarized.

RESULTS

NeuroAiD improved survival, attenuated infarct size, improved functional recovery in the model of focal ischemia, and protected neurons against glutamate-induced injury. Furthermore, it enhanced cognitive recovery by reducing hippocampal CA1 cell degeneration, DNA fragmentation, Bax expression and ma-londialdehyde release in the model of global ischemia. Activation of the Akt survival pathway and opening of KATP channels may contribute to the neuroprotective properties of NeuroAiD. NeuroAiD increased BDNF expression and induced proliferation of cells which differentiate and mature into neurons. It enhanced rosette formation of human embryonic stem cells. NeuroAiD-treated embryonic cortical neurons developed into neurons with longer neurites, denser outgrowths and networks, and more synaptic release sites.

CONCLUSIONS

NeuroAiD demonstrated both neuroprotective and neuroregenerative properties in rodent models of focal and global ischemia and in cortical cell cultures. These properties would be important for developing a treatment strategy in reducing the long-term disability of stroke, cardiac arrest and other brain injuries.

Neuroprotective role of ATP-sensitive potassium channels in cerebral ischemia

ATP-sensitive potassium (K(ATP)) channels are weak, inward rectifiers that couple metabolic status to cell membrane electrical activity, thus modulating many cellular functions. An increase in the ADP/ATP ratio opens K(ATP) channels, leading to membrane hyperpolarization. K(ATP) channels are ubiquitously expressed in neurons located in different regions of the brain, including the hippocampus and cortex. Brief hypoxia triggers membrane hyperpolarization in these central neurons. In vivo animal studies confirmed that knocking out the Kir6.2 subunit of the K(ATP) channels increases ischemic infarction, and overexpression of the Kir6.2 subunit reduces neuronal injury from ischemic insults. These findings provide the basis for a practical strategy whereby activation of endogenous K(ATP) channels reduces cellular damage resulting from cerebral ischemic stroke. K(ATP) channel modulators may prove to be clinically useful as part of a combination therapy for stroke management in the future.

Global cerebral ischemia: synaptic and cognitive dysfunction

Cardiopulmonary arrest is one of the leading causes of death and disability, primarily occurring in the aged population. Numerous global cerebral ischemia animal models induce neuronal damage similar to cardiac arrest. These global cerebral ischemia models range from vessel occlusion to total cessation of cardiac function, both of which have allowed for the investigation of this multifaceted disease and detection of numerous agents that are neuroprotective. Synapses endure a variety of alterations after global cerebral ischemia from the resulting excitotoxicity and have been a major target for neuroprotection; however, neuroprotective agents have proven unsuccessful in clinical trials, as neurological outcomes have not displayed significant improvements in patients. A majority of these neuroprotective agents have specific neuronal targets, where the success of future neuroprotective agents may depend on non-specific targets and numerous cognitive improvements. This review focuses on the different models of global cerebral ischemia, neuronal synaptic alterations, synaptic neuroprotection and behavioral tests that can be used to determine deficits in cognitive function after global cerebral ischemia.

Activation of ATP-sensitive potassium channels as an element of the neuroprotective effects of the Traditional Chinese Medicine MLC901 against oxygen glucose deprivation

NeuroAid (MLC601 and MLC901), a Traditional Medicine used in China for patients after stroke has been reported in preclinical models of ischemia to induce neuroprotection and neuroplasticity. This work shows the effects of MLC901 on an in vitro model of oxygen glucose deprivation (OGD). MLC901 prevents neuronal death induced by 120 min OGD and decreases the exaggerated Ca²⁺ entry in mature cortical neurons exposed to 120 min OGD. The neuroprotective effect of MLC901 is associated with a large hyperpolarization of ∼20 mV which is antagonized by glibenclamide, the specific inhibitor of K(ATP) channels. In addition MLC901 strengthens the activation of K(ATP) channels. MLC901 has been directly shown to act as an activator of K(ATP) channels as potent as the classical K(ATP) channel opener. The capacity of MLC901 to produce a large hyperpolarization, particularly in neurons that have suffered from energy deprivation probably plays an important role in the neuroprotective effects of this traditional medicine that comes in addition to its previously demonstrated neuroregenerative properties.

Combined age- and trauma-related proteomic changes in rat neocortex: a basis for brain vulnerability

This proteomic study investigates the widely observed clinical phenomenon, that after comparable brain injuries, geriatric patients fare worse and recover less cognitive and neurologic function than younger victims. Utilizing a rat traumatic brain injury model, sham surgery or a neocortical contusion was induced in 3 age groups. Geriatric (21 months) rats performed worse on behavioral measures than young adults (12-16 weeks) and juveniles (5-6 weeks). Motor coordination and certain cognitive deficits showed age-dependence both before and after injury. Brain proteins were analyzed using silver-stained two-dimensional electrophoresis gels. Spot volume changes (>2-fold change, p<0.01) were identified between age and injury groups using computer-assisted densitometry. Sequences were determined by mass spectrometry of tryptic peptides. The 19 spots identified represented 13 different genes that fell into 4 general age- and injury-dependent expression patterns. Fifteen isoforms changed differentially with respect to both age and injury (p<0.05). Further investigations into the nature and function of these isoforms may yield insights into the vulnerability of older patients and resilience of younger patients in recovery after brain injuries.

Up-regulation of A-type potassium currents protects neurons against cerebral ischemia

Excitotoxicity is the major cause of many neurologic disorders including stroke. Potassium currents modulate neuronal excitability and therefore influence the pathological process. A-type potassium current (I(A)) is one of the major voltage-dependent potassium currents, yet its roles in excitotoxic cell death are not well understood. We report that, following ischemic insults, the I(A) increases significantly in large aspiny (LA) neurons but not medium spiny (MS) neurons in the striatum, which correlates with the higher resistance of LA neurons to ischemia. Activation of protein kinase Cα increases I(A) in LA neurons after ischemia. Cultured neurons from transgenic mice lacking both Kv1.4 and Kv4.2 subunits exhibit an increased vulnerability to ischemic insults. Increase of I(A) by recombinant expression of Kv1.4 or Kv4.2 is sufficient in improving the survival of MS neurons against ischemic insults both in vitro and in vivo. These results, taken together, provide compelling evidence for a protective role of I(A) against ischemia.

Protective action of endogenously generated H₂S on hypoxia-induced respiratory suppression and its relation to antioxidation and down-regulation of c-fos mRNA in medullary slices of neonatal rats

We previously reported that exogenous H(2)S played roles in protection of respiratory centers against hypoxic injury in medullary slices of neonatal rats. The protective action of endogenous H(2)S and its relation to antioxidation and down-regulation of c-fos mRNA were investigated in the present study. Perfusion of the slices with l-cysteine (Cys), substrate of cystathionine β-synthase (CBS, H(2)S synthase), could increase frequency of rhythmic respiratory discharge of the hypoglossal rootlets and prevent respiratory suppression induced by hypoxia, whereas perfusion with hydroxylamine (NH(2)OH, inhibitor of CBS) could postpone recovery of respiration from hypoxic inhibition. NH(2)OH also significantly enhanced hypoxia-induced increase in malondialdehyde (MDA) content of the slices. The hypoxia-induced up-regulation of c-fos mRNA could be markedly antagonized by S-adenosyl-l-methionine (SAM, activator of CBS), but greatly increased by NH(2)OH. Neither NH(2)OH, Cys nor SAM had any effect on expression of bcl-2 mRNA in hypoxic medullary slices. These results indicate that endogenously generated H(2)S was involved in protection of the medullary respiratory centers against hypoxic injury partly via antioxidation and down-regulation of c-fos.

Traumatic brain injury in mice lacking the K channel, TREK-1

The purpose of this study was to determine whether the potassium channel, TREK-1, was neuroprotective after traumatic brain injury (TBI). Since there are no selective blockers, we used TREK-1 knockout (KO) mice for our study. Wild-type (WT) and TREK-1 KO mice were anesthetized and subjected to controlled-cortical impact injury (deformation of the brain by 1.5 mm by a 3-mm diameter rod traveling at a 3 m/s). Laser Doppler perfusion (LDP) decreased by ∼80% in the injured cortex and remained at that level in both WT and TREK-1 KO mice (n=10 and 11, respectively). Laser Doppler perfusion decreased by 50% to 60% in cortical areas directly adjacent to the site of injury. There were no statistical differences in LDP between genotype. The contusion volume, determined 15 days after the TBI using hematoxylin and eosin-stained coronal brain sections, was 4.1±0.8 (n=10) and 5.1±0.5 (n=11) mm(3) for WT and TREK-1 KO, respectively (not significant, P=0.34). Cell counts of viable neurons in the CA1 and CA3 regions of the hippocampus were similar between WT and TREK-1 KO mice (P=0.51 and 0.84 for CA1 and CA3, respectively). We conclude that TREK-1 expression does not provide brain protection after TBI.

From the background to the spotlight: TASK channels in pathological conditions

TWIK-related acid-sensitive potassium channels (TASK1-3) belong to the family of two-pore domain (K(2P) ) potassium channels. Emerging knowledge about an involvement of TASK channels in cancer development, inflammation, ischemia and epilepsy puts the spotlight on a leading role of TASK channels under these conditions. TASK3 has been especially linked to cancer development. The pro-oncogenic potential of TASK3 could be shown in cell lines and in various tumor entities. Pathophysiological hallmarks in solid tumors (e.g. low pH and oxygen deprivation) regulate TASK3 channels. These conditions can also be found in (autoimmune) inflammation. Inhibition of TASK1,2,3 leads to a reduction of T cell effector function. It could be demonstrated that TASK1(-/-) mice are protected from experimental autoimmune inflammation while the same animals display increased infarct volumes after cerebral ischemia. Furthermore, TASK channels have both an anti-epileptic as well as a pro-epileptic potential. The relative contribution of these opposing influences depends on their cell type-specific expression and the conditions of the cellular environment. This indicates that TASK channels are per se neither protective nor detrimental but their functional impact depends on the "pathophysiological" scenario. Based on these findings TASK channels have evolved from "mere background" channels to key modulators in pathophysiological conditions.

Two pore domain potassium channels in cerebral ischemia: a focus on K2P9.1 (TASK3, KCNK9)

Background

Recently, members of the two-pore domain potassium channel family (K_2P channels) could be shown to be involved in mechanisms contributing to neuronal damage after cerebral ischemia. K_2P3.1^-/- animals showed larger infarct volumes and a worse functional outcome following experimentally induced ischemic stroke. Here, we question the role of the closely related K_2P channel K_2P9.1.

Methods

We combine electrophysiological recordings in brain-slice preparations of wildtype and K_2P9.1^-/- mice with an in vivo model of cerebral ischemia (transient middle cerebral artery occlusion (tMCAO)) to depict a functional impact of K_2P9.1 in stroke formation.

Results

Patch-clamp recordings reveal that currents mediated through K_2P9.1 can be obtained in slice preparations of the dorsal lateral geniculate nucleus (dLGN) as a model of central nervous relay neurons. Current characteristics are indicative of K_2P9.1 as they display an increase upon removal of extracellular divalent cations, an outward rectification and a reversal potential close to the potassium equilibrium potential. Lowering extracellular pH values from 7.35 to 6.0 showed comparable current reductions in neurons from wildtype and K_2P9.1^-/- mice (68.31 ± 9.80% and 69.92 ± 11.65%, respectively). These results could be translated in an in vivo model of cerebral ischemia where infarct volumes and functional outcomes showed a none significant tendency towards smaller infarct volumes in K_2P9.1^-/- animals compared to wildtype mice 24 hours after 60 min of tMCAO induction (60.50 ± 17.31 mm³ and 47.10 ± 19.26 mm³, respectively).

Conclusions

Together with findings from earlier studies on K_2P2.1^-/- and K_2P3.1^-/- mice, the results of the present study on K_2P9.1^-/- mice indicate a differential contribution of K_2P channel subtypes to the diverse and complex in vivo effects in rodent models of cerebral ischemia.

Hydrogen sulfide: from brain to gut

Three hundred years have passed since the first description of the toxicity of hydrogen sulfide (H(2)S). Three papers in 1989 and 1990 described relatively high concentrations of sulfide in the brain. In 1996 we demonstrated that cystathionine beta-synthase (CBS) is a H(2)S producing enzyme in the brain and that H(2)S enhances the activity of NMDA receptors and facilitates the induction of hippocampal long-term potentiation (LTP), a synaptic model of memory. In the following year, we demonstrated that another H(2)S producing enzyme, cystathionine gamma-lyase is in the thoracic aorta, portal vein, and the ileum, and that H(2)S relaxes these tissues. Based on these observations we proposed H(2)S as a neuromodulator as well as a smooth muscle relaxant. We recently demonstrated that the third H(2)S-producing enzyme, 3-mercaptopyruvate sulfurtransferase (3MST) along with cysteine aminotransferase (CAT) produces H(2)S in the brain as well as in vascular endothelium. Various functions in many tissues have been proposed. H(2)S protects neurons and cardiac muscle from oxidative stress. H(2)S has pro- and anti-inflammatory effects, nociceptive effects, the regulatory function of insulin release, and is even involved in longevity. Recent progress in the studies of physiological functions of H(2)S in neurons and smooth muscle was described.

Transcription factors in long-term memory and synaptic plasticity

Transcription is a molecular requisite for long-term synaptic plasticity and long-term memory formation. Thus, in the last several years, one main interest of molecular neuroscience has been the identification of families of transcription factors that are involved in both of these processes. Transcription is a highly regulated process that involves the combined interaction and function of chromatin and many other proteins, some of which are essential for the basal process of transcription, while others control the selective activation or repression of specific genes. These regulated interactions ultimately allow a sophisticated response to multiple environmental conditions, as well as control of spatial and temporal differences in gene expression. Evidence based on correlative changes in expression, genetic mutations, and targeted molecular inhibition of gene expression have shed light on the function of transcription in both synaptic plasticity and memory formation. This review provides a brief overview of experimental work showing that several families of transcription factors, including CREB, C/EBP, Egr, AP-1, and Rel, have essential functions in both processes. The results of this work suggest that patterns of transcription regulation represent the molecular signatures of long-term synaptic changes and memory formation.

In vivo administration of corticotropin-releasing hormone at remote intervals following ischemia enhances CA1 neuronal survival and recovery of spatial memory impairments: a role for opioid receptors

The contribution of corticotropin-releasing hormone (CRH) in the modulation of ischemia-induced cell death in vivo remains unclear. We characterized the impact of pre-ischemic administration of CRH (0, 0.1, 1, 5 microg, i.c.v., 15 min prior to vessel occlusion) on neuronal damage following global ischemia in rats. The injection of 5 microg CRH led to a 37% increase in CA1 neuronal survival compared to vehicle-treated ischemic animals, while pre-treatment with alpha-helical CRH (9-41) abolished this neuronal protection. A second objective aimed to determine whether CRH protection is maintained over weeks when the peptide is administered at remote time intervals following ischemia. Compared to vehicle-treated ischemic animals, administration of CRH 8h following global ischemia led to a 61% increase in CA1 neuronal survival observed 30 days post-ischemia. Neuronal protection translated into significant improvement of ischemia-induced spatial memory deficits in the radial maze. Finally, our findings demonstrated that selective blockade of kappa- and delta-opioid receptors (using nor-binaltorphimine and naltrindole, respectively) prior to CRH administration significantly reduced CA1 neuronal protection. These findings represent the first demonstration of enhanced neuronal survival following in vivo CRH administration in a global model of ischemia in rats. They also support the idea that CRH-induced neuroprotection involves opioid receptors activation.

Pinacidil reduces neuronal apoptosis following cerebral ischemia-reperfusion in rats through both mitochondrial and death-receptor signal pathways

OBJECTIVE

To investigate effect of pinacidil, an ATP sensitive potassium channel (K(ATP)) opener, on the neuronal apoptosis and its signaling transduction mechanism following focal cerebral ischemia-reperfusion in rats.

METHODS

One hundred male Wistar rats were randomly divided into four groups: A, sham-operated group; B, ischemia-reperfusion group; C, K(ATP) opener treatment group; and D, K(ATP) opener and blocker treatment group. The middle cerebral artery occlusion (MCAO) model was established by using the intraluminal suture occlusion method, neuronal apoptosis was determined by TUNEL staining, and expressions of caspase-8, caspase-9 and caspase-3 mRNA were detected by in situ hybridization.

RESULTS

(1) The numbers of apoptotic neurons at 12 h, 24 h, 48 h, and 72 h were significantly less in group C than in groups B and D (P< 0.01 or P< 0.05); and there was no difference between groups B and D at all time points (P> 0.05). (2) The expressions of caspase-3 mRNA and caspase-8 mRNA at all times and the expressions of caspase-9 mRNA at 12 h, 24 h, 48 h, 72 h were significantly lower in group C than in groups B and D (P< 0.01 or P< 0.05); and there were no differences between groups B and D at all time points (P> 0.05).

CONCLUSIONS

K(ATP) opener can significantly decrease the neuronal apoptosis and the expressions of caspase-3, caspase-8 and caspase-9 mRNAs following cerebral ischemia-reperfusion. The neuronal apoptosis may be decreased by the inhibition of both mitochondrial and death-receptor signal pathways.

Cell shrinkage and monovalent cation fluxes: role in apoptosis

The loss of cell volume or cell shrinkage has been a morphological hallmark of the programmed cell death process known as apoptosis. This isotonic loss of cell volume has recently been term apoptotic volume decrease or AVD to distinguish it from inherent volume regulatory responses that occurs in cells under anisotonic conditions. Recent studies examining the intracellular signaling pathways that result in this unique cellular characteristic have determined that a fundamental movement of ions, particularly monovalent ions, underlie the AVD process and plays an important role on controlling the cell death process. An efflux of intracellular potassium was shown to be a critical aspect of the AVD process, as preventing this ion loss could protect cells from apoptosis. However, potassium plays a complex role as a loss of intracellular potassium has also been shown to be beneficial to the health of the cell. Additionally, the mechanisms that a cell employs to achieve this loss of intracellular potassium vary depending on the cell type and stimulus used to induce apoptosis, suggesting multiple ways exist to accomplish the same goal of AVD. Additionally, sodium and chloride have been shown to play a vital role during cell death in both the signaling and control of AVD in various apoptotic model systems. This review examines the relationship between this morphological change and intracellular monovalent ions during apoptosis.

Local potassium signaling couples neuronal activity to vasodilation in the brain

The mechanisms by which active neurons, via astrocytes, rapidly signal intracerebral arterioles to dilate remain obscure. Here we show that modest elevation of extracellular potassium (K+) activated inward rectifier K+ (Kir) channels and caused membrane potential hyperpolarization in smooth muscle cells (SMCs) of intracerebral arterioles and, in cortical brain slices, induced Kir-dependent vasodilation and suppression of SMC intracellular calcium (Ca2+) oscillations. Neuronal activation induced a rapid (<2 s latency) vasodilation that was greatly reduced by Kir channel blockade and completely abrogated by concurrent cyclooxygenase inhibition. Astrocytic endfeet exhibited large-conductance, Ca2+-sensitive K+ (BK) channel currents that could be activated by neuronal stimulation. Blocking BK channels or ablating the gene encoding these channels prevented neuronally induced vasodilation and suppression of arteriolar SMC Ca2+, without affecting the astrocytic Ca2+ elevation. These results support the concept of intercellular K+ channel-to-K+ channel signaling, through which neuronal activity in the form of an astrocytic Ca2+ signal is decoded by astrocytic BK channels, which locally release K+ into the perivascular space to activate SMC Kir channels and cause vasodilation.

Hydrogen sulfide protects HT22 neuronal cells from oxidative stress

Hydrogen sulfide (H2S) is a neuromodulator in the brain and a relaxant for smooth muscle. H2S protects primary cortical neurons from oxidative stress by increasing the intracellular concentrations of glutathione, the major antioxidant in cells. However, changes in glutathione alone are not sufficient to account for full protection in all types of nerve cells. H2S is here shown to protect an immortalized mouse hippocampal cell line from oxidative glutamate toxicity by activating ATP-dependent K+ (KATP) and Cl- channels, in addition to increasing the levels of glutathione. The present study therefore identifies a novel pathway for H2S protection from oxidative stress.

K(ATP) channel therapeutics at the bedside

The family of potassium channel openers regroups drugs that share the property of activating adenosine triphosphate-sensitive potassium (K(ATP)) channels, metabolic sensors responsible for adjusting membrane potential-dependent functions to match cellular energetic demands. K(ATP) channels, widely represented in metabolically-active tissue, are heteromultimers composed of an inwardly rectifying potassium channel pore and a regulatory sulfonylurea receptor subunit, the site of action of potassium channel opening drugs that promote channel activity by antagonizing ATP-induced pore inhibition. The activity of K(ATP) channels is critical in the cardiovascular adaptive response to stress, maintenance of neuronal electrical stability, and hormonal homeostasis. Thereby, K(ATP) channel openers have a unique therapeutic spectrum, ranging from applications in myopreservation and vasodilatation in patients with heart or vascular disease to potential clinical use as bronchodilators, bladder relaxants, islet cell protector, antiepileptics and promoters of hair growth. While the current experience in practice with potassium channel openers remains limited, multitude of ongoing investigations aims at defining the benefit of this emerging family of therapeutics in diverse disease conditions associated with metabolic distress.

Late preconditioning with isoflurane in cultured rat cortical neurones

BACKGROUND

We tested the hypothesis that isoflurane induces late preconditioning in cultured rat cortical neurones and preconditioning elicits changes in expression of Kir6.2 (the ion-conducting subunit of the metabolically responsive ATP-sensitive potassium (K(ATP)) channel) and EAAC1 (neuronal glutamate transporter).

METHODS

Primary cultures of rat cortical neurones were exposed to non-lethal oxygen-glucose deprivation (OGD), i.e. ischaemic preconditioning, for 30 min, 100 microM of diazoxide, a potent opener of the mitochondrial K(ATP) (mitoK(ATP)) channels, for 60 min or 1.4% isoflurane for 3 h. Lethal OGD was performed for 120 min 24 h after preconditioning stimuli. Neuronal injury was assessed by measurement of lactate dehydrogenase (LDH) efflux into the medium 24 h after lethal OGD, and neural viability was determined by proliferation assay. Gene and protein expression was confirmed by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and western blot analysis 24 h after preconditioning stimuli.

RESULTS

All preconditioning stimuli resulted in a significant decrease in LDH activity and maintained neuronal viability. These effects were abolished by 5-hydroxydecanoate, a selective inhibitor of the mitoK(ATP) channel. Quantitative RT-PCR and Western blot analysis demonstrated that there was no significant difference between Kir6.2 mRNA and protein levels. All preconditioning stimuli resulted in > or =2-fold increases in EAAC1 mRNA and protein compared with control.

CONCLUSIONS

Isoflurane induced late preconditioning in cultured rat cortical neurones. Ischaemic and pharmacological preconditioning with diazoxide and isoflurane induced ischaemic tolerance in the cultured neurones via mitoK(ATP) channels without an increase in Kir6.2 expression, and induced upregulation of EAAC1 expression.

Heat shock protein modulation of KATPand KCachannel cerebrovasodilation after brain injury

Fluid percussion brain injury (FPI) impairs pial artery dilation to activators of the ATP-sensitive (KATP) and calcium-activated (KCa) K+channels. This study investigated the role of heat shock protein (HSP) in the modulation of K+channel-induced pial artery dilation after FPI in newborn pigs equipped with a closed cranial window. Under nonbrain injury conditions, topical coadministration of exogenous HSP-27 (1 μg/ml) blunted dilation to cromakalim, CGRP, and NS-1619 (10−8and 10−6M; cromakalim and CGRP are KATPagonists and NS-1619 is a KCaagonist). In contrast, coadministration of exogenous HSP-70 (1 μg/ml) potentiated dilation to cromakalim, CGRP, and NS-1619. FPI increased the cerebrospinal fluid (CSF) concentration of HSP-27 from 0.051 ± 0.012 to 0.113 ± 0.035 ng/ml but decreased the CSF concentration of HSP-70 from 50.42 ± 8.96 to 30.9 ± 9.9 ng/ml at 1 h postinsult. Pretreatment with topical exogenous HSP-70 (1 μg/ml) before FPI fully blocked injury-induced impairment of cromakalim and CGRP dilation and partially blocked injury-induced impairment of dilation to NS-1619. These data indicate that HSP-27 and HSP-70 contribute to modulation of K+channel-induced pial artery dilation. These data suggest that HSP-70 is an endogenous protectant of which its actions may be unmasked and/or potentiated with exogenous administration before brain injury.

Protective preconditioning by transient global ischemia in the rat: components of delayed injury progression and lasting protection distinguished by comparisons of depolarization thresholds for cell loss at long survival times

Robust ischemic preconditioning has been shown in rodent brain, but there are concerns regarding the persistence of neuron protection. This issue was examined in rat hippocampus following 4-vessel occlusion (4-VO) ischemia, using DC shifts characteristic of ischemic depolarization to reproducibly define insult severity. Preconditioning ischemia producing 2 to 3.5 mins depolarization was followed at intervals of 2, 5, or 7 days by test insults of varied duration, after which CA1 counts were obtained at 1, 2, 4, or 12 weeks. Neuron loss in naive animals increased with depolarization time longer than 4 mins regardless of postischemic survival interval. Preconditioning 2, 5, or 7 days before test insults prolonged the injury threshold evaluated at 1 week survival to 15, 9, or 6 mins, respectively, showing robust protection and a rapid decay of the protected state. However, by 2 weeks survival after preconditioning at a 2-day interval, the injury threshold dramatically regressed from 15 to 9 mins. Thereafter protection remained relatively stable through 1 month, but slight progression of neuron injury was evident at 3 months. Inflammatory responses were seen in both naive and preconditioned hippocampi throughout this interval, appropriate to the extent of neuron injury. These studies show distinct components of transient and lasting protection after ischemic preconditioning. Finally, it was found that ischemic depolarization was delayed by approximately 1 min in optimally preconditioned rat hippocampus, in contrast to previous results in the gerbil, identifying one specific mechanism by which insult severity is reduced in this model.

Traumatic brain injury: cause or risk of Alzheimer's disease? A review of experimental studies

Traumatic Brain Injury is the leading cause of death and disability among young individuals in our society. Moreover, according to some epidemiological studies, head trauma is one of the most potent environmental risk factors for subsequent development of Alzheimer's disease. Interestingly, pathological features that are present also in Alzheimer's disease (in particular deposition of beta-amyloid protein) were observed in traumatised brains already a few hours after the initial insult. The primary objective of this review is to present methodology and results of numerous recent human and animal studies dealing with this issue. Special emphasis was placed on head trauma experiments in transgenic mouse models of Alzheimer's disease. We further evaluate the connection between traumatic brain insults and subsequent development of dementia and try to differentiate between primary and secondary pathological mechanisms.

Activation of ATP-sensitive potassium channels prevents the cleavage of cytosolic mu-calpain and abrogates the elevation of nuclear c-Fos and c-Jun expressions after hypoxic-ischemia in neonatal rat brain

The purpose of this study was to determine whether activation of ATP-sensitive K+ (KATP) channels with diazoxide (DIZ) is able to prevent the cleavage of cytosolic mu-calpain and abrogate the elevation of nuclear c-Fos and c-Jun protein (c-Fos, c-Jun) expressions after hypoxic-ischemia (HI) in brain. The model of hypoxic-ischemic brain injury (HIBI) was made in the 7-day-old Sprague-Dawley (SD) rats by left carotid arterial ligation and hypoxia (8% oxygen). DIZ was injected into the left lateral ventricle (5 microl, 1 mg/ml) before or post-hypoxic-ischemia (HI) insults. Western blot and computer image processing were used to detect the integrated density of nuclear c-Fos and c-Jun at 4 h and cleavage of cytosolic mu-calpain at 24 h after HI insults from cerebral cortical and hippocampal samples. Compared with HI controls (c-Fos=30.37+/-7.39 from cortical samples, 58.61+/-3.64 from hippocampal samples; c-Jun=52.48+/-14.23 from cortical samples, 35.55+/-4.73 from hippocampal samples), there was a significant down-regulation of c-Fos and c-Jun expressions from cortical and hippocampal samples in rats treated with DIZ before (c-Fos=11.10+/-4.64 from cortical samples, 4.82+/-3.38 from hippocampal samples; c-Jun=19.01+/-5.29 from cortical samples, 35.55+/-4.73 from hippocampal samples) or post- (c-Fos=18.81+/-7.93 from cortical samples, 11.33+/-7.05 from hippocampal samples; c-Jun=24.64+/-10.01 from cortical samples, 19.75+/-3.47 from hippocampal samples) HI insults. Furthermore, the ratio of 76 kD/80 kD of mu-calpain was down-regulated from cortical and hippocampal samples in rats treated with DIZ before or post-HI insults, demonstrating a significant difference compared with that observed in HI controls. Finally, the increase in DNA fragments caused by the HI injury was decreased or eliminated by the treatment with DIZ. These data suggests that activation of KATP channels by DIZ reduces the degree of mu-calpain proteolysis, and c-Fos and c-Jun expressions in immature brain may contribute to the neuroprotection of K(ATP) channel openers against HIBI.

Increase of delayed rectifier potassium currents in large aspiny neurons in the neostriatum following transient forebrain ischemia

Large aspiny (LA) neurons in the neostriatum are resistant to cerebral ischemia whereas spiny neurons are highly vulnerable to the same insult. Excitotoxicity has been implicated as the major cause of neuronal damage after ischemia. Voltage-dependent potassium currents play important roles in controlling neuronal excitability and therefore influence the ischemic outcome. To reveal the ionic mechanisms underlying the ischemia-resistance, the delayed rectifier potassium currents (Ik) in LA neurons were studied before and at different intervals after transient forebrain ischemia using brain slices and acute dissociation preparations. The current density of Ik increased significantly 24 h after ischemia and returned to control levels 72 h following reperfusion. Among currents contributing to Ik, the margatoxin-sensitive currents increased 24 h after ischemia while the KCNQ/M current remained unchanged after ischemia. Activation of protein kinase A (PKA) down-regulated Ik in both control and ischemic LA neurons, whereas inhibition of PKA only up-regulated Ik and margatoxin-sensitive currents 72 h after ischemia, indicating an active PKA regulation on Ik at this time. Protein tyrosine kinases had a tonic inhibition on Ik to a similar extent before and after ischemia. Compared with that of control neurons, the spike width was significantly shortened 24 h after ischemia due to facilitated repolarization, which could be reversed by blocking margatoxin-sensitive currents. The increase of Ik in LA neurons might be one of the protective mechanisms against ischemic insult.