Contribution of downregulation of L-type calcium currents to delayed neuronal death in rat hippocampus after global cerebral ischemia and reperfusion

Unleashing the potential: 40 Hz multisensory stimulation therapy for cognitive impairment

Cognitive impairment encompasses a spectrum of disorders marked by acquired deficits in cognitive function, potentially leading to diminished daily functioning and work capacity, often accompanied by psychiatric and behavioral disturbances. Alzheimer's disease (AD) and Post-stroke cognitive impairment (PSCI) are significant causes of cognitive decline. With the global population getting older, AD and PSCI are becoming major health concerns, underscoring the critical necessity for successful treatment options. In recent years, various non-invasive biophysical stimulation techniques, including ultrasound, light, electric, and magnetic stimulation, have been developed for the treatment of central nervous system diseases. Preliminary clinical studies have demonstrated the feasibility and safety of these techniques. This review discuss the impact of 40 Hz multisensory stimulation on cerebral function, behavioral outcomes, and disease progression in both animal models and individuals exhibiting cognitive deficits, such as AD and PSCI. Furthermore, it summarizes the potential neural pathways involved in this therapeutic modality by synthesizing evidence from a variety of studies within the field. Subsequently, it evaluates the existing constraints of this technique and underscores the potential advantages of 40 Hz multisensory stimulation therapy for individuals with cognitive deficits, with the goal of enhancing the management and care of AD and PSCI.

Cav3.2 channel regulates cerebral ischemia/reperfusion injury: a promising target for intervention

JOURNAL/nrgr/04.03/01300535-202419110-00028/figure1/v/2024-03-08T184507Z/r/image-tiff Calcium influx into neurons triggers neuronal death during cerebral ischemia/reperfusion injury. Various calcium channels are involved in cerebral ischemia/reperfusion injury. Cav3.2 channel is a main subtype of T-type calcium channels. T-type calcium channel blockers, such as pimozide and mibefradil, have been shown to prevent cerebral ischemia/reperfusion injury-induced brain injury. However, the role of Cav3.2 channels in cerebral ischemia/reperfusion injury remains unclear. Here, in vitro and in vivo models of cerebral ischemia/reperfusion injury were established using middle cerebral artery occlusion in mice and high glucose hypoxia/reoxygenation exposure in primary hippocampal neurons. The results showed that Cav3.2 expression was significantly upregulated in injured hippocampal tissue and primary hippocampal neurons. We further established a Cav3.2 gene-knockout mouse model of cerebral ischemia/reperfusion injury. Cav3.2 knockout markedly reduced infarct volume and brain water content, and alleviated neurological dysfunction after cerebral ischemia/reperfusion injury. Additionally, Cav3.2 knockout attenuated cerebral ischemia/reperfusion injury-induced oxidative stress, inflammatory response, and neuronal apoptosis. In the hippocampus of Cav3.2-knockout mice, calcineurin overexpression offset the beneficial effect of Cav3.2 knockout after cerebral ischemia/reperfusion injury. These findings suggest that the neuroprotective function of Cav3.2 knockout is mediated by calcineurin/nuclear factor of activated T cells 3 signaling. Findings from this study suggest that Cav3.2 could be a promising target for treatment of cerebral ischemia/reperfusion injury.

The Influence of Oxidative Stress Markers in Patients with Ischemic Stroke

Stroke is the second leading cause of death worldwide, and its incidence is rising rapidly. Acute ischemic stroke is a subtype of stroke that accounts for the majority of stroke cases and has a high mortality rate. An effective treatment for stroke is to minimize damage to the brain's neural tissue by restoring blood flow to decreased perfusion areas of the brain. Many reports have concluded that both oxidative stress and excitotoxicity are the main pathological processes associated with ischemic stroke. Current measures to protect the brain against serious damage caused by stroke are insufficient. For this reason, it is important to investigate oxidative and antioxidant strategies to reduce oxidative damage. This review focuses on studies assessing the concentration of oxidative stress biomarkers and the level of antioxidants (enzymatic and non-enzymatic) and their impact on the clinical prognosis of patients after stroke. Mechanisms related to the production of ROS/RNS and the role of oxidative stress in the pathogenesis of ischemic stroke are presented, as well as new therapeutic strategies aimed at reducing the effects of ischemia and reperfusion.

Ahf-Caltide, a Novel Polypeptide Derived from Calpastatin, Protects against Oxidative Stress Injury by Stabilizing the Expression of CaV1.2 Calcium Channel

Reperfusion after ischemia would cause massive myocardial injury, which leads to oxidative stress (OS). Calcium homeostasis imbalance plays an essential role in myocardial OS injury. CaV1.2 calcium channel mediates calcium influx into cardiomyocytes, and its activity is modulated by a region of calpastatin (CAST) domain L, CSL54-64. In this study, the effect of Ahf-caltide, derived from CSL54-64, on myocardial OS injury was investigated. Ahf-caltide decreased the levels of LDH, MDA and ROS and increased heart rate, coronary flow, cell survival and SOD activity during OS. In addition, Ahf-caltide permeated into H9c2 cells and increased CaV1.2, CaVβ2 and CAST levels by inhibiting protein degradation. At different Ca2+ concentrations (25 nM, 10 μM, 1 mM), the binding of CSL to the IQ motif in the C terminus of the CaV1.2 channel was increased in a H2O2 concentration-dependent manner. CSL54-64 was predicted to be responsible for the binding of CSL to CaV1.2. In conclusion, Ahf-caltide exerted a cardioprotective effect on myocardial OS injury by stabilizing CaV1.2 protein expression. Our study, for the first time, proposed that restoring calcium homeostasis by targeting the CaV1.2 calcium channel and its regulating factor CAST could be a novel treatment for myocardial OS injury.

Abnormal Spontaneous Discharges of Primary Sensory Neurons and Pain Behavior in a Rat Model of Vascular Dementia

Patients with vascular dementia experience more pain than healthy elders, potentially due to the presence of central neuropathic pain. However, the mechanisms underlying neuropathic pain in vascular dementia remain poorly understood, and there is currently a lack of effective treatment available. In this study, a rat model of vascular dementia was induced by permanently occluding the common carotid arteries bilaterally (2-VO). The cognitive impairments in the 2-VO rats were evaluated using the Morris Water Maze test, while HE and LBF staining were employed to assess brain tissue lesions in the hippocampal, cerebral cortex, and white matter regions known to be associated with severe memory and learning deficits. Furthermore, pain-related behavioral tests, including mechanical and thermal stimuli assessments, were conducted, and in vivo electrophysiological recordings of primary sensory neurons were performed. Compared to sham-operated and pre-operative rats, rats with vascular dementia exhibited mechanical allodynia and thermal hyperalgesia 30 days after surgery. Furthermore, in vivo electrophysiology revealed a significant increase in the occurrence of spontaneous activity of Aβ- and C-fiber sensory neurons in the rat model of vascular dementia. These results indicate that neuropathic pain behaviors developed in the rat model of vascular dementia, and abnormal spontaneous discharges of primary sensory neurons may play a crucial role in the development of pain after vascular dementia.

Gamma frequency entrainment rescues cognitive impairment by decreasing postsynaptic transmission after traumatic brain injury

INTRODUCTION

The relationship between oscillatory activity in hippocampus and cognitive impairment in traumatic brain injury (TBI) remains unclear. Although TBI decreases gamma oscillations and 40 Hz light flicker improves TBI prognosis, the effects and mechanism of rhythmic flicker on TBI remain unclear.

AIMS

In this study, we aimed to explore whether light flicker could reverse cognitive deficits, and further explore its potential mechanisms in TBI mouse model.

METHODS

The Morris water maze test (MWM), step-down test (SDT), and novel object recognition test (NOR) were applied to evaluate the cognitive ability. The local field potential (LFP) recording was applied to measure low gamma reduction of CA1 in hippocampus after TBI. And electrophysiological experiments were applied to explore effects of the gamma frequency entrainment on long-term potentiation (LTP), postsynaptic transmission, and intrinsic excitability of CA1 pyramidal cells (PCs) in TBI mice. Immunofluorescence staining and western blotting were applied to explore the effects of 40 Hz light flicker on the expression of PSD95 in hippocampus of TBI mice.

RESULTS

We found that 40 Hz light flicker restored low gamma reduction of CA1 in hippocampus after TBI. And 40 Hz, but not random or 80 Hz light flicker, reversed cognitive impairment after TBI in behavioral tests. Moreover, 40 Hz light flicker improved N-methyl-D-aspartate (NMDA) receptor-dependent LTP (LTP_NMDAR ) and L-type voltage-gated calcium channel-dependent LTP (LTP_L-VGCC ) after TBI treatment. And gamma frequency entrainment decreased excitatory postsynaptic currents (EPSCs) of CA1 PCs in TBI mice. Our results have illustrated that 40 Hz light flicker could decrease intrinsic excitability of PCs after TBI treatment in mice. Furthermore, 40 Hz light flicker decreased the expression of PSD95 in hippocampus of TBI mice.

CONCLUSION

These results demonstrated that 40 Hz light flicker rescues cognitive impairment by decreasing postsynaptic transmission in PCs after TBI treatment in mice.

Small molecules targeting cyclooxygenase/prostanoid cascade in experimental brain ischemia: Do they translate?

Acute brain ischemia accounts for most of stroke cases and constitutes a leading cause of deaths among adults and permanent disabilities in survivors. Currently, the intravenous thrombolysis is the only available medication for ischemic stroke; mechanical thrombectomy is an emerging alternative treatment for occlusion of large arteries and has shown some promise in selected subsets of patients. However, the overall narrow treatment window and potential risks largely limit the patient eligibility. New druggable targets are needed to innovate the treatment of brain ischemia. As the rate-limiting enzyme in the biosyntheses of prostanoids, cyclooxygenase (COX), particularly the inducible isoform COX-2, has long been implicated in mechanisms of acute stroke-induced brain injury and inflammation. However, the notion of therapeutically targeting COX has been diminished over the past two decades due to significant complications of the cardiovascular and cerebrovascular systems caused by long-term use of COX-2 inhibitor drugs. New treatment strategies targeting the downstream prostanoid signaling receptors regulating the deleterious effects of COX cascade have been proposed. As such, a large number of selective small molecules that negatively or positively modulate these important inflammatory regulators have been evaluated for neuroprotection and other beneficial effects in various animal models of brain ischemia. These timely preclinical studies, though not yet led to clinical innovation, provided new insights into the regulation of inflammatory reactions in the ischemic brain and could guide drug discovery efforts aiming for novel adjunctive strategies, along with current reperfusion therapy, to treat acute brain ischemia with higher specificity and longer therapeutic window.

Prostaglandin E receptors as targets for ischemic stroke: Novel evidence and molecular mechanisms of efficacy

Over the past two decades the interest has waned in therapeutically targeting cyclooxygenase-2 (COX-2) due to growing concerns over the potential cardiovascular and cerebrovascular toxicities of the long-term use of COX-2 inhibitors. Attention thus has recently been shifted downstream to the prostaglandin signaling pathways for new druggable anti-inflammatory targets aiming for higher therapeutic specificity. Prostaglandin E2 (PGE₂) is robustly synthesized in the ischemic cortex by quickly induced COX-2 and microsomal prostaglandin E synthase-1 (mPGES-1) following cerebral ischemia. The elevated PGE₂, in turn, divergently regulates the excitotoxic injury and neuroinflammation by acting on four membrane-bound G protein-coupled receptors (GPCRs), namely, EP1-EP4. Markedly, all four EP receptors have been implicated in the excitotoxicity-associated brain inflammation and injury in animal models of cerebral ischemia. However promising, these preclinical studies have not yet led to a clinical trial targeting any PGE₂ receptor for ischemic stroke. The goal of this article is to review the recent progress in understanding the pathogenic roles of PGE₂ in cerebral ischemia as well as to provide new mechanistic insights into the PGE₂ signaling via these four GPCRs in neuronal excitotoxicity and inflammation. We also discuss the feasibility of targeting EP1-EP4 receptors as an emerging delayed treatment, together with the first-line reperfusion strategy, to manage acute ischemic stroke with potentially extended window as well as improved specificity.

Rhythmic light flicker rescues hippocampal low gamma and protects ischemic neurons by enhancing presynaptic plasticity

The complex relationship between specific hippocampal oscillation frequency deficit and cognitive dysfunction in the ischemic brain is unclear. Here, using a mouse two-vessel occlusion (2VO) cerebral ischemia model, we show that visual stimulation with a 40 Hz light flicker drove hippocampal CA1 slow gamma and restored 2VO-induced reduction in CA1 slow gamma power and theta-low gamma phase-amplitude coupling, but not those of the high gamma. Low gamma frequency lights at 30 Hz, 40 Hz, and 50 Hz, but not 10 Hz, 80 Hz, and arrhythmic frequency light, were protective against degenerating CA1 neurons after 2VO, demonstrating the importance of slow gamma in cognitive functions after cerebral ischemia. Mechanistically, 40 Hz light flicker enhanced RGS12-regulated CA3-CA1 presynaptic N-type calcium channel-dependent short-term synaptic plasticity and associated postsynaptic long term potentiation (LTP) after 2VO. These results support a causal relationship between CA1 slow gamma and cognitive dysfunctions in the ischemic brain.

The Role of Selected Pro-Inflammatory Cytokines in Pathogenesis of Ischemic Stroke

Stroke is currently one of the most common causes of death and disability in the world, and its pathophysiology is a complex process, involving the oxidative stress and inflammatory reaction. Unfortunately, no biochemical factors useful in the diagnostics and treatment of stroke have been clearly established to date. Therefore, researchers are increasingly interested in the inflammatory response triggered by cerebral ischemia and its role in the development of cerebral infarction. This article gives an overview of the available literature data concerning the role of pro-inflammatory cytokines in acute stroke. Detailed analysis of their role in cerebral circulation disturbances can also suggest certain immune response regulatory mechanisms aimed to reduce damage to the nervous tissue in the course of stroke.

Astrocytic GABAB Receptors in Mouse Hippocampus Control Responses to Behavioral Challenges through Astrocytic BDNF

Major depressive disorder (MDD) is a common mood disorder that affects almost 20% of the global population. In addition, much evidence has implicated altered function of the gamma-aminobutyric acid (GABAergic) system in the pathophysiology of depression. Recent research has indicated that GABA_B receptors (GABA_BRs) are an emerging therapeutic target in the treatment of stress-related disorders such as MDD. However, which cell types with GABA_BRs are involved in this process is unknown. As hippocampal dysfunction is implicated in MDD, we knocked down GABA_BRs in the hippocampus and found that knocking down these receptors in astrocytes, but not in GABAergic or pyramidal neurons, caused a decrease in immobility in the forced swimming test (FST) without affecting other anxiety- and depression-related behaviors. We also generated astrocyte-specific GABA_BR-knockout mice and found decreased immobility in the FST in these mice. Furthermore, the conditional knockout of GABA_BRs in astrocytes selectively increased the levels of brain-derived neurotrophic factor protein in hippocampal astrocytes, which controlled the decrease in immobility in the FST. Taken together, our findings contribute to the current understanding of which cell types expressing GABA_BRs modulate antidepressant activity in the FST, and they may provide new insights into the pathological mechanisms and potential targets for the treatment of depression.

L-type Ca2+ channel-mediated Ca2+ influx adjusts neuronal mitochondrial function to physiological and pathophysiological conditions

L-type voltage-gated Ca2+ channels (LTCCs) are implicated in neurodegenerative processes and cell death. Accordingly, LTCC antagonists have been proposed to be neuroprotective, although this view is disputed, because intentional LTCC activation can also have beneficial effects. LTCC-mediated Ca2+ influx influences mitochondrial function, which plays a crucial role in the regulation of cell viability. Hence, we investigated the effect of modulating LTCC-mediated Ca2+ influx on mitochondrial function in cultured hippocampal neurons. To activate LTCCs, neuronal activity was stimulated by increasing extracellular K+ or by application of the GABAA receptor antagonist bicuculline. The activity of LTCCs was altered by application of an agonistic (Bay K8644) or an antagonistic (isradipine) dihydropyridine. Our results demonstrated that activation of LTCC-mediated Ca2+ influx affected mitochondrial function in a bimodal manner. At moderate stimulation strength, ATP synthase activity was enhanced, an effect that involved Ca2+-induced Ca2+ release from intracellular stores. In contrast, high LTCC-mediated Ca2+ loads led to a switch in ATP synthase activity to reverse-mode operation. This effect, which required nitric oxide, helped to prevent mitochondrial depolarization and sustained increases in mitochondrial Ca2+ Our findings indicate a complex role of LTCC-mediated Ca2+ influx in the tuning and maintenance of mitochondrial function. Therefore, the use of LTCC inhibitors to protect neurons from neurodegeneration should be reconsidered carefully.

EphA4 receptor regulates outwardly rectifying chloride channel in CA1 hippocampal neurons after ischemia-reperfusion

CA1 hippocampal neurons are sensitive to ischemia. The erythropoietin-producing hepatocellular carcinoma (Eph) receptors are a cell-cell contact signaling pathway for regulating neuron function and death. However, the mechanisms of EphA receptor in neuron death after ischemia remain unclear. In this study, we present evidence that outwardly rectifying chloride channels reside in CA1 hippocampal neurons. EphA4 receptor increased chloride channel currents. Moreover, the EphA4 receptor no longer had significant effects on enhanced channel currents following ischemia-reperfusion. Inhibition of EphA4 receptor with EphA4-Fc significantly decreased the channel currents after ischemia-reperfusion. These results suggest that the increased effect of the EphA4 receptor on the outwardly rectifying chloride channel activity in CA1 hippocampal neurons may provide better treatment for ischemic brain injury.

Activation of Sigma Receptors With Afobazole Modulates Microglial, but Not Neuronal, Apoptotic Gene Expression in Response to Long-Term Ischemia Exposure

Stroke continues to be a leading cause of death and serious long-term disability. The lack of therapeutic options for treating stroke at delayed time points (≥6 h post-stroke) remains a challenge. The sigma receptor agonist, afobazole, an anxiolytic used clinically in Russia, has been shown to reduce neuronal and glial cell injury following ischemia and acidosis; both of which have been shown to play important roles following an ischemic stroke. However, the mechanism(s) responsible for this cytoprotection remain unknown. Experiments were carried out on isolated microglia from neonatal rats and cortical neurons from embryonic rats to gain further insight into these mechanisms. Prolonged exposure to in vitro ischemia resulted in microglial cell death, which was associated with increased expression of the pro-apoptotic protein, Bax, the death protease, caspase-3, and reduced expression in the anti-apoptotic protein Bcl-2. Incubation of cells with afobazole during ischemia decreased the number of microglia expressing both Bax and caspase-3, and increased cells expressing Bcl-2, which resulted in a concomitant enhancement in cell survival. In similar experiments, incubation of neurons under in vitro ischemic conditions resulted in higher expression of Bax and caspase-3, while at the same time expression of Bcl-2 was decreased. However, unlike observations made in microglial cells, afobazole was unable to modulate the expression of these apoptotic proteins, but a reduction in neuronal death was still noted. The functional state of surviving neurons was assessed by measuring metabolic activity, resting membrane potential, and responses to membrane depolarizations. Results showed that these neurons maintained membrane potential but had low metabolic activity and were unresponsive to membrane depolarizations. However, while these neurons were not fully functional, there was significant protection by afobazole against long-term ischemia-induced cell death. Thus, the effects of sigma receptor activation on microglial and neuronal responses to ischemia differ significantly.

Delayed cognitive deficits can be alleviated by calcium antagonist nimodipine by downregulation of apoptosis following whole brain radiotherapy

Radiation therapy is important for the comprehensive treatment of intracranial tumors. However, the molecular mechanisms underlying the pathogenesis of delayed cognitive dysfunction are not well-defined and effective treatments or prevention measures remain insufficient. In the present study, 60 adult male Wistar rats were randomly divided into three groups, which included a control, whole brain radiotherapy (WBRT) (single dose of 30 Gy of WBRT) and nimodipine (single dose of 30 Gy of WBRT followed by nimodipine injection intraperitoneally) groups. The rats were sacrificed 7 days or 3 months following irradiation. At 3 months, the Morris water maze test was used to assess spatial learning and memory function in rats. The results demonstrated that the WBRT group demonstrated a significantly impaired cognitive performance, decreased numbers of hippocampal Cornu Ammonis (CA)1 neurons and upregulated expression of caspase-3 in the dentate gyrus compared with those in the control and nimodipine groups. Reverse transcription-quantitative polymerase chain reaction analysis demonstrated that the WBRT group exhibited increased ratio of B-cell lymphoma 2 (Bcl-2)-associated X protein (Bax)/Bcl-2 compared with that in control and nimodipine groups on day 7 following irradiation. However, the WBRT group exhibited decreased levels of brain-derived neurotrophic factor (BDNF) compared with that in control and nimodipine groups at 3 months following brain irradiation. The levels of growth-associated protein 43 and amyloid precursor protein between the nimodipine group and WBRT group were not statistically significant. The present study demonstrated that neuron apoptosis may lead to delayed cognitive deficits in the hippocampus, in response to radiotherapy. The cognitive impairment may be alleviated in response to a calcium antagonist nimodipine. The molecular mechanisms involved in nimodipine-mediated protection against cognitive decline may involve the regulation of Bax/Bcl-2 and BDNF in the hippocampus.

ITH14001, a CGP37157-Nimodipine Hybrid Designed to Regulate Calcium Homeostasis and Oxidative Stress, Exerts Neuroprotection in Cerebral Ischemia

During brain ischemia, oxygen and glucose deprivation induces calcium overload, extensive oxidative stress, neuroinflammation, and, finally, massive neuronal loss. In the search of a neuroprotective compound to mitigate this neuronal loss, we have designed and synthesized a new multitarget hybrid (ITH14001) directed at the reduction of calcium overload by acting on two regulators of calcium homeostasis; the mitochondrial Na⁺/Ca²⁺ exchanger (mNCX) and L-type voltage dependent calcium channels (VDCCs). This compound is a hybrid of CGP37157 (mNCX inhibitor) and nimodipine (L-type VDCCs blocker), and its pharmacological evaluation revealed a moderate ability to selectively inhibit both targets. These activities conferred concentration-dependent neuroprotection in two models of Ca²⁺ overload, such as toxicity induced by high K⁺ in the SH-SY5Y cell line (60% protection at 30 μM) and veratridine in hippocampal slices (26% protection at 10 μM). It also showed neuroprotective effect against oxidative stress, an activity related to its nitrogen radical scavenger effect and moderate induction of the Nrf2-ARE pathway. Its Nrf2 induction capability was confirmed by the increase of the expression of the antioxidant and anti-inflammatory enzyme heme-oxygenase I (3-fold increase). In addition, the multitarget profile of ITH14001 led to anti-inflammatory properties, shown by the reduction of nitrites production induced by lipopolysaccharide in glial cultures. Finally, it showed protective effect in two acute models of cerebral ischemia in hippocampal slices, excitotoxicity induced by glutamate (31% protection at 10 μM) and oxygen and glucose deprivation (76% protection at 10 μM), reducing oxidative stress and iNOS deleterious induction. In conclusion, our hybrid derivative showed improved neuroprotective properties when compared to its parent compounds CGP37157 and nimodipine.

Bilateral Hippocampal Restricted Diffusion: Same Picture Many Causes

With some regularity, we have encountered the unusual imaging abnormality of bilateral hippocampal restricted diffusion, either in isolation or in combination with other coincident abnormalities. In this retrospective case series, we examine clinical and imaging data to explore potential etiologies and clinical implications of this imaging finding. Sixteen cases with the imaging abnormality are presented, with etiologies including hypoxemia, hypoxemia-ischemia, and seizures.

Postischemic Inflammation in Acute Stroke

Cerebral ischemia is caused by arterial occlusion due to a thrombus or an embolus. Such occlusion induces multiple and concomitant pathophysiological processes that involve bioenergetic failure, acidosis, loss of cell homeostasis, excitotoxicity, and disruption of the blood-brain barrier. All of these mechanisms contribute to neuronal death, mainly via apoptosis or necrosis. The immune system is involved in this process in the early phases after brain injury, which contributes to potential enlargement of the infarct size and involves the penumbra area. Whereas inflammation and the immune system both exert deleterious effects, they also contribute to brain protection by stimulating a preconditioning status and to the concomitant repair of the injured parenchyma. This review describes the main phases of the inflammatory process occurring after arterial cerebral occlusion, with an emphasis on the role of single mediators.

The surge of flavonoids as novel, fine regulators of cardiovascular Cav channels

Ion channels underlie a wide variety of physiological processes that involve rapid changes in cell dynamics, such as cardiac and vascular smooth muscle contraction. Overexpression or dysfunction of these membrane proteins are the basis of many cardiovascular diseases that represent the leading cause of morbidity and mortality for human beings. In the last few years, flavonoids, widely distributed in the plant kingdom, have attracted the interest of many laboratories as an emerging class of fine ion, in particular Ca_v, channels modulators. Pieces of in vitro evidence for direct as well as indirect effects exerted by various flavonoids on ion channel currents are now accumulating in the scientific literature. This activity may be responsible, at least in part, for the beneficial and protective effects of dietary flavonoids toward cardiovascular diseases highlighted in several epidemiological studies. Here we examine numerous studies aimed at analysing this feature of flavonoids, focusing on the mechanisms that promote their sometimes controversial activities at cardiovascular Ca_v channels. New methodological approaches, such as molecular modelling and docking to Ca_v1.2 channel α_1c subunit, used to elucidate flavonoids intrinsic mechanism of action, are introduced. Moreover, flavonoid-membrane interaction, bioavailability, and antioxidant activity are taken into account and discussed.

Repetitive transcranial magnetic stimulation regulates L-type Ca(2+) channel activity inhibited by early sevoflurane exposure

BACKGROUND

Sevoflurane might be harmful to the developing brain. Therefore, it is essential to reverse sevoflurane-induced brain injury.

OBJECTIVE

This study aimed to determine whether low-frequency repetitive transcranial magnetic stimulation (rTMS) can regulate L-type Ca(2+) channel activity, which is inhibited by early sevoflurane exposure.

METHODS

Rats were randomly divided into three groups: control, sevoflurane, and rTMS groups. A Whole-cell patch clamp technique was applied to record L-type Ca(2+) channel currents. The I-V curve, steady-state activation and inactivation curves were studied in rats of each group at different ages (1 week, 2 weeks, 3 weeks, 4 weeks and 5 weeks old).

RESULTS

In the control group, L-type Ca(2+) channel current density significantly increased from week 2 to week 3. Compared with the control group, L-type Ca(2+) channel currents of rats in the sevoflurane group were significantly inhibited from week 1 to week 3. Activation curves of L-type Ca(2+) channel shifted significantly towards depolarization at week 1 and week 2. Moreover, steady-state inactivation curves shifted towards hyperpolarization from week 1 to week 3. Compared with the sevoflurane group, rTMS significantly increased L-type Ca(2+) channel currents at week 2 and week 3. Activation curves of L-type Ca(2+) channel significantly shifted towards hyperpolarization at week 2. Meanwhile, steady-state inactivation curves significantly shifted towards depolarization at week 2.

CONCLUSIONS

The period between week 2 and week 3 is critical for the development of L-type Ca(2+) channels. Early sevoflurane exposure inhibits L-type Ca(2+) channel activity and rTMS can regulate L-type Ca(2+) channel activity inhibited by sevoflurane.

Voltage-gated calcium channels are abnormal in cultured spinal motoneurons in the G93A-SOD1 transgenic mouse model of ALS

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease characterized by progressive loss of motoneurons. Hyperexcitability and excitotoxicity have been implicated in the early pathogenesis of ALS. Studies addressing excitotoxic motoneuron death and intracellular Ca(2+) overload have mostly focused on Ca(2+) influx through AMPA glutamate receptors. However, intrinsic excitability of motoneurons through voltage-gated ion channels may also have a role in the neurodegeneration. In this study we examined the function and localization of voltage-gated Ca(2+) channels in cultured spinal cord motoneurons from mice expressing a mutant form of human superoxide dismutase-1 with a Gly93→Ala substitution (G93A-SOD1). Using whole-cell patch-clamp recordings, we showed that high voltage activated (HVA) Ca(2+) currents are increased in G93A-SOD1 motoneurons, but low voltage activated Ca(2+) currents are not affected. G93A-SOD1 motoneurons also have altered persistent Ca(2+) current mediated by L-type Ca(2+) channels. Quantitative single-cell RT-PCR revealed higher levels of Ca1a, Ca1b, Ca1c, and Ca1e subunit mRNA expression in G93A-SOD1 motoneurons, indicating that the increase of HVA Ca(2+) currents may result from upregulation of Ca(2+) channel mRNA expression in motoneurons. The localizations of the Ca1B N-type and Ca1D L-type Ca(2+) channels in motoneurons were examined by immunocytochemistry and confocal microscopy. G93A-SOD1 motoneurons had increased Ca1B channels on the plasma membrane of soma and dendrites. Ca1D channels are similar on the plasma membrane of soma and lower on the plasma membrane of dendrites of G93A-SOD1 motoneurons. Our study demonstrates that voltage-gated Ca(2+) channels have aberrant functions and localizations in ALS mouse motoneurons. The increased HVA Ca(2+) currents and PCCa current could contribute to early pathogenesis of ALS.

Pre-treatment with metformin activates Nrf2 antioxidant pathways and inhibits inflammatory responses through induction of AMPK after transient global cerebral ischemia

Global cerebral ischemia arises in patients who have a variety of clinical conditions including cardiac arrest, shock and asphyxia. In spite of advances in understanding of the brain ischemia and stroke etiology, therapeutic approaches to improve ischemic injury still remain limited. It has been established that metformin can attenuate cell death in cerebral ischemia. One of the main functions of metformin is proposed to be conducted via AMP-activated protein kinase (AMPK)-dependent pathway in the experimental cerebral ischemia model. It is also established that metformin can suppress inflammation and activate Nuclear factor erythroid 2-related factor (Nrf2) pathways in neurons. In the current study, the role of metformin in regulating inflammatory and antioxidant pathways in the global cerebral ischemia was investigated. Our results indicated that pretreatment of rats by metformin attenuated cellular levels of nuclear factor-κB, Tumor Necrosis Factor alpha and Cyclooxygenase-2 which are considered as three important proteins involved in the inflammation pathway. Pretreatment by metformin increased the level of Nrf2 and heme oxygenase-1 in the hippocampus of ischemic rats compared with untreated ischemic group. Moreover, pretreatment by metformin enhanced the level of glutathione and catalase activities compared with them in ischemic group. Such protective changes detected by metformin pretreatment were reversed by injecting compound c, an AMPK inhibitor. These findings suggested that metformin might protect cells through modulating inflammatory and antioxidant pathways via induction of AMPK. However, more experimental and clinical trial studies regarding neuroprotective potential of metformin and the involved mechanisms, especially in the context of cerebral ischemic injuries, are necessary.

Mechanisms of gain control by voltage-gated channels in intrinsically-firing neurons

Gain modulation is a key feature of neural information processing, but underlying mechanisms remain unclear. In single neurons, gain can be measured as the slope of the current-frequency (input-output) relationship over any given range of inputs. While much work has focused on the control of basal firing rates and spike rate adaptation, gain control has been relatively unstudied. Of the limited studies on gain control, some have examined the roles of synaptic noise and passive somatic currents, but the roles of voltage-gated channels present ubiquitously in neurons have been less explored. Here, we systematically examined the relationship between gain and voltage-gated ion channels in a conductance-based, tonically-active, model neuron. Changes in expression (conductance density) of voltage-gated channels increased (Ca²⁺ channel), reduced (K⁺ channels), or produced little effect (h-type channel) on gain. We found that the gain-controlling ability of channels increased exponentially with the steepness of their activation within the dynamic voltage window (voltage range associated with firing). For depolarization-activated channels, this produced a greater channel current per action potential at higher firing rates. This allowed these channels to modulate gain by contributing to firing preferentially at states of higher excitation. A finer analysis of the current-voltage relationship during tonic firing identified narrow voltage windows at which the gain-modulating channels exerted their effects. As a proof of concept, we show that h-type channels can be tuned to modulate gain by changing the steepness of their activation within the dynamic voltage window. These results show how the impact of an ion channel on gain can be predicted from the relationship between channel kinetics and the membrane potential during firing. This is potentially relevant to understanding input-output scaling in a wide class of neurons found throughout the brain and other nervous systems.

The Protective Effects of Sufentanil Pretreatment on Rat Brains under the State of Cardiopulmonary Bypass

This study aimed to observe the protective effects of sufentanil pretreatment on rat cerebral injury during cardiopulmonary bypass (CPB) and to explore the underlying mechanism. Twenty-four male adult Sprague Dawley (SD) rats were divided into 4 groups. Then, the rat CPB model was established. A 14G trocar was inserted into the atrium dextrum. For rats in S1 and S5 groups, sufentanil (1 µgKg(-1) and 5 µgKg(-1)) were applied before CPB process. After the operation, rat brain samples were harvested for measurement of the water content of the brains, total calcium in brain tissue and the level of serum S100β. Compared with the Sham group, the water content and the total calcium of the brain tissue, and the expression of S100β in serum were significantly increased in the CPB group (P<0.05). Compared with the CPB group, sufentanil treatment significantly reduced the water content of the brains, the total calcium and S100β expression (P<0.05). The blood pressure and heart rate were significantly decreased in groups CPB, S1, and S5 compared with Sham group during CPB. Compared with the Sham group, the levels of pH and blood lactate in other groups were decreased and increased, respectively, in the post-CPB period. During the CPB and post-CPB periods, the hematocrit levels were significantly down-regulated in groups CPB, S1, and S5 compared with Sham group. In conclusion, sufentanil pretreatment was effective in reducing the cerebral injury during CPB. Reduction in calcium overload may be a potential mechanism in such process.

Neuronal injury from cardiac arrest: aging years in minutes

Cardiac arrest is a leading cause of death and permanent disability. Most victims succumb to the oxidative and inflammatory damage sustained during cardiac arrest/resuscitation, but even survivors typically battle long-term neurocognitive impairment. Although extensive research has delineated the complex mechanisms that culminate in neuronal damage and death, no effective treatments have been developed to interrupt these mechanisms. Of importance, many of these injury cascades are also active in the aging brain, where neurons and other cells are under persistent oxidative and inflammatory stress which eventually damages or kills the cells. In light of these similarities, it is reasonable to propose that the brain essentially ages the equivalent of several years within the few minutes taken to resuscitate a patient from cardiac arrest. Accordingly, cardiac arrest-resuscitation models may afford an opportunity to study the deleterious mechanisms underlying the aging process, on an accelerated time course. The aging and resuscitation fields both stand to gain pivotal insights from one another regarding the mechanisms of injury sustained during resuscitation from cardiac arrest and during aging. This synergism between the two fields could be harnessed to foster development of treatments to not only save lives but also to enhance the quality of life for the elderly.

Nuclear BK channels regulate gene expression via the control of nuclear calcium signaling

Ion channels are essential for the regulation of neuronal functions. The significance of plasma membrane, mitochondrial, endoplasmic reticulum and lysosomal ion channels in the regulation of Ca(2+) is well established. In contrast, surprisingly little is known about the function of ion channels on the nuclear envelope (NE). Here we demonstrate the presence of functional large-conductance, calcium-activated potassium channels (BK channels) on the NE of rodent hippocampal neurons. Functionally, blockade of nuclear BK channels (nBK channels) induces NE-derived Ca(2+) release, nucleoplasmic Ca(2+) elevation and cyclic AMP response element binding protein (CREB)-dependent transcription. More importantly, blockade of nBK channels regulates nuclear Ca(2+)-sensitive gene expression and promotes dendritic arborization in a nuclear Ca(2+)-dependent manner. These results suggest that the nBK channel functions as a molecular link between neuronal activity and nuclear Ca(2+) to convey signals from synapse to nucleus and is a new modulator, operating at the NE, of synaptic activity-dependent neuronal functions.

Activation of AMP-activated protein kinase by metformin protects against global cerebral ischemia in male rats: interference of AMPK/PGC-1α pathway

Here, we have investigated the effect of metformin pretreatment in the rat models of global cerebral ischemia. Cerebral ischemia which leads to brain dysfunction is one of the main causes of neurodegeneration and death worldwide. Metformin is used in clinical drug therapy protocols of diabetes. It is suggested that metformin protects cells under hypoxia and ischemia in non-neuronal contexts. Protective effects of metformin may be modulated via activating the AMP activated protein kinase (AMPK). Our results showed that induction of 30 min global cerebral I/R injury using 4-vesseles occlusion model led to significant cell death in the rat brain. Metformin pretreatment (200 mg kg/once/day, p.o., 2 weeks) attenuated apoptotic cell death and induced mitochondrial biogenesis proteins in the ischemic rats, analyzed using histological and Western blot assays. Besides, inhibition of AMPK by compound c showed that metformin resulted in apoptosis attenuation via AMPK activation. Interestingly, AMPK activation was also involved in the induction of mitochondrial biogenesis proteins using metformin, inhibition of AMPK by compound c reversed such effect, further supporting the role of AMPK upstream of mitochondrial biogenesis proteins. In summary, Metformin pretreatment is able to modulate mitochondrial biogenesis and apoptotic cell death pathways through AMPK activation in the context of global cerebral ischemia, conducting the outcome towards neuroprotection.

Early exposure to sevoflurane inhibits Ca(2+) channels activity in hippocampal CA1 pyramidal neurons of developing rats

Sevoflurane is one of inhalation anesthetics and has been commonly used in obstetric and pediatric anesthesia. The widespread use of sevoflurane in newborns and infants has made its safety a health issue of concern. Voltage-gated Ca(2+) channels (VGCCs) play an important role in neuronal excitability and are essential for normal brain development. However, the role of sevoflurane on regulating Ca(2+) channels during the period of rapid brain development is still not well understood. The aim of this study is to explore the effects of sevoflurane on voltage-gated Ca(2+) channels for hippocampal CA1 pyramidal neurons during the period of rapid brain development. 1-week-old Sprague-Dawley rats were randomly divided into 3 groups: control group, 2.1% sevoflurane group (exposed to 2.1% sevoflurane for 6h) and 3% sevoflurane group (exposed to 3% sevoflurane for 6h). Whole-cell patch clamp technique was used. I-V curve, steady-state activation and inactivation curves of Ca(2+) channels were studied in rats of the both 3 treated groups at 5 different ages (1 week, 2 weeks, 3 weeks, 4 and 5 weeks old). After anesthesia with sevoflurane at 1-week-old rats, Ca(2+) channels current density was significantly decreased at week 1 and week 2 (p<0.01). And 3% sevoflurane exposure resulted in a rightward shift in steady-state activation curve at week 1 and week 2, as well as the inactivation curve from week 1 to week 3. However, the 2.1% sevoflurane-induced rightward shift was only found in steady-state inactivation curve of Ca(2+) channels at week 1 and week 2. Both the slope factor (k) of Ca(2+) channels activation and inactivation curves increased by 3% sevoflurane at week 1 (p<0.05). Therefore, early exposure to sevoflurane persistently inhibits Ca(2+) channels activity in hippocampal CA1 pyramidal neurons of developing rats but the development of Ca(2+) channels recovers to normal level at juvenile age. Moreover, the inhibition of 3% sevoflurane on VGCCs is greater than that of 2.1% sevoflurane.

The changing landscape of voltage-gated calcium channels in neurovascular disorders and in neurodegenerative diseases

It is a common belief that voltage-gated calcium channels (VGCC) cannot carry toxic amounts of Ca²⁺ in neurons. Also, some of them as L-type channels are essential for Ca²⁺-dependent regulation of prosurvival gene-programs. However, a wealth of data show a beneficial effect of drugs acting on VGCCs in several neurodegenerative and neurovascular diseases. In the present review, we explore several mechanisms by which the “harmless” VGCCs may become “toxic” for neurons. These mechanisms could explain how, though usually required for neuronal survival, VGCCs may take part in neurodegeneration. We will present evidence showing that VGCCs can carry toxic Ca²⁺ when: a) their density or activity increases because of aging, chronic hypoxia or exposure to β-amyloid peptides or b) Ca²⁺-dependent action potentials carry high Ca²⁺ loads in pacemaker neurons. Besides, we will examine conditions in which VGCCs promote neuronal cell death without carrying excess Ca²⁺. This can happen, for instance, when they carry metal ions into the neuronal cytoplasm or when a pathological decrease in their activity weakens Ca²⁺-dependent prosurvival gene programs. Finally, we will explore the role of VGCCs in the control of nonneuronal cells that take part to neurodegeneration like those of the neurovascular unit or of microglia.

Pathogenesis of acute stroke and the role of inflammasomes

Inflammation is an innate immune response to infection or tissue damage that is designed to limit harm to the host, but contributes significantly to ischemic brain injury following stroke. The inflammatory response is initiated by the detection of acute damage via extracellular and intracellular pattern recognition receptors, which respond to conserved microbial structures, termed pathogen-associated molecular patterns or host-derived danger signals termed damage-associated molecular patterns. Multi-protein complexes known as inflammasomes (e.g. containing NLRP1, NLRP2, NLRP3, NLRP6, NLRP7, NLRP12, NLRC4, AIM2 and/or Pyrin), then process these signals to trigger an effector response. Briefly, signaling through NLRP1 and NLRP3 inflammasomes produces cleaved caspase-1, which cleaves both pro-IL-1β and pro-IL-18 into their biologically active mature pro-inflammatory cytokines that are released into the extracellular environment. This review will describe the molecular structure, cellular signaling pathways and current evidence for inflammasome activation following cerebral ischemia, and the potential for future treatments for stroke that may involve targeting inflammasome formation or its products in the ischemic brain.

The alterations of Ca2+/calmodulin/CaMKII/CaV1.2 signaling in experimental models of Alzheimer's disease and vascular dementia

The two critical forms of dementia are Alzheimer's disease (AD) and vascular dementia (VD). The alterations of Ca(2+)/calmodulin/CaMKII/CaV1.2 signaling in AD and VD have not been well elucidated. Here we have demonstrated changes in the levels of CaV1.2, calmodulin, p-CaMKII, p-CREB and BDNF proteins by Western blot analysis and the co-localization of p-CaMKII/CaV1.2 by double-labeling immunofluorescence in the hippocampus of APP/PS1 mice and VD gerbils. Additionally, expression of these proteins and intracellular calcium levels were examined in cultured neurons treated with Aβ1-42. The expression of CaV1.2 protein was increased in VD gerbils and in cultured neurons but decreased in APP/PS1 mice; the expression of calmodulin protein was increased in APP/PS1 mice and VD gerbils; levels of p-CaMKII, p-CREB and BDNF proteins were decreased in AD and VD models. The number of neurons in which p-CaMKII and CaV1.2 were co-localized, was decreased in the CA1 and CA3 regions in two models. Intracellular calcium was increased in the cultured neurons treated with Aβ1-42. Collectively, our results suggest that the alterations in CaV1.2, calmodulin, p-CaMKII, p-CREB and BDNF can be reflective of an involvement in the impairment in memory and cognition in AD and VD models.

Early pathogenesis in the adult-onset neurodegenerative disease amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a devastating paralytic disorder caused by dysfunction and degeneration of motor neurons starting in adulthood. Most of our knowledge about the pathophysiological mechanisms of ALS comes from transgenic mice models that emulate a subgroup of familial ALS cases (FALS), with mutations in the gene encoding superoxide dismutase (SOD1). In the more than 15 years since these mice were generated, a large number of abnormal cellular mechanisms underlying motor neuron degeneration have been identified, but to date this effort has led to few improvements in therapy, and no cure. Here, we consider that this surfeit of mechanisms is best interpreted by current insights that suggest a very early initiation of pathology in motor neurons, followed by a diversity of secondary cascades and compensatory mechanisms that mask symptoms for decades, until trauma and/or aging overloads their protective function. This view thus posits that adult-onset ALS is the consequence of processes initiated during early development. In fact, motor neurons in neonatal mutant SOD mice display important alterations in their intrinsic electrical properties, synaptic inputs and morphology that are accompanied by subtle behavioral abnormalities. We consider evidence that human mutant SOD1 protein in neonatal hSOD1(G93A) mice instigates motor neuron degeneration by increasing persistent sodium currents and excitability, in turn altering synaptic circuits that control excessive motor neuron firing and leads to excitotoxicity. We also discuss how therapies that are aimed at suppressing abnormal neuronal activity might effectively mitigate or prevent the onset of irreversible neuronal damage in adulthood. J. Cell. Biochem. 113: 3301-3312, 2012. © 2012 Wiley Periodicals, Inc.

Calcium and potassium channels in experimental subarachnoid hemorrhage and transient global ischemia

Healthy cerebrovascular myocytes express members of several different ion channel families which regulate resting membrane potential, vascular diameter, and vascular tone and are involved in cerebral autoregulation. In animal models, in response to subarachnoid blood, a dynamic transition of ion channel expression and function is initiated, with acute and long-term effects differing from each other. Initial hypoperfusion after exposure of cerebral vessels to oxyhemoglobin correlates with a suppression of voltage-gated potassium channel activity, whereas delayed cerebral vasospasm involves changes in other potassium channel and voltage-gated calcium channels expression and function. Furthermore, expression patterns and function of ion channels appear to differ between main and small peripheral vessels, which may be key in understanding mechanisms behind subarachnoid hemorrhage-induced vasospasm. Here, changes in calcium and potassium channel expression and function in animal models of subarachnoid hemorrhage and transient global ischemia are systematically reviewed and their clinical significance discussed.

Hippocampal magnetic resonance imaging abnormalities in cardiac arrest are associated with poor outcome

BACKGROUND

The role of neuroimaging in assessing prognosis in comatose cardiac survivors appears promising, but little is known regarding the import of particular spatial patterns. We report a specific spatial imaging abnormality on magnetic resonance imaging (MRI) that portends a poor prognosis: bilateral hippocampal hyperintensities on diffusion-weighted imaging (DWI) and fluid-attenuated inversion recovery (FLAIR) sequences.

METHODS

Eighty sequential comatose cardiac arrest patients underwent MRI scans. Qualitative and quantitative regional analyses were performed. Patients were categorized as HIPPO(+) (n = 18) or HIPPO(-) (n = 62) based on whether they had bilateral hippocampal hyperintensities. Poor outcome was defined by a modified Rankin Scale (mRS) score ≥4 at 6 months.

RESULTS

Patients with bilateral hippocampal abnormalities had a higher frequency of poor outcome (P = .032). HIPPO(+) patients suffered more severe cerebral injury, with lower whole brain apparent diffusion coefficient values (P = .043) and a greater number of affected regions on DWI (P = .001) and FLAIR (P = .001) than HIPPO(-) patients. The hippocampal approach was 100% specific for a poor prognosis; only 1 patient survived and remained in a vegetative state.

CONCLUSIONS

Bilateral hippocampal hyperintensities on MRI may be a specific imaging finding that is indicative of poor prognosis in patients who suffer global hypoxic-ischemic injury. More research on the prognostic significance of this and similar neuroimaging patterns is indicated.

Inhibition of EphA4 signaling after ischemia-reperfusion reduces apoptosis of CA1 pyramidal neurons

Hippocampal CA1 pyramidal neurons are sensitive to ischemic damage. However, the cellular and molecular mechanisms underlying neuronal cell death caused by ischemia-reperfusion (I/R) are not completely clear. Here, we report that the ephrinA/EphA cell-cell interaction signaling pathway plays an important role in the apoptosis of hippocampal CA1 pyramidal neurons induced by I/R. We found that the expression of ephrinA3 and EphA4 is increased in the CA1 region following transient forebrain ischemia. Blocking ephrinA3/EphA4 interaction by EphA4-Fc, an inhibitor of EphA4, attenuated apoptotic neuronal cell death, likely through the inhibition of caspase-3 activation. These results reveal a novel function of ephrin/Eph signaling in the regulation of apoptosis in CA1 pyramidal neurons after I/R.

Hypoxia enhances high-voltage-activated calcium currents in rat primary cortical neurons via calcineurin

Hypoxia regulates neuronal ion channels, sometimes resulting in seizures. We evaluated the effects of brief sustained hypoxia (1% O(2), 4h) on voltage-gated calcium channels (VGCCs) in cultured rat primary cortical neurons. High-voltage activated (HVA) Ca(2+) currents were acquired immediately after hypoxic exposure or after 48h recovery in 95% air/5% CO(2). Maximal Ca(2+) current density increased 1.5-fold immediately after hypoxia, but reverted to baseline after 48h normoxia. This enhancement was primarily due to an increase in L-type VGCC activity, since nimodipine-insensitive residual Ca(2+) currents were unchanged. The half-maximal potentials of activation and steady-state inactivation were unchanged. The calcineurin inhibitors FK-506 (in the recording pipette) or cyclosporine A (during hypoxia) prevented the post-hypoxic increase in HVA Ca(2+) currents, while rapamycin and okadaic acid did not. L-type VGCCs were the source of Ca(2+) for calcineurin activation, as nimodipine during hypoxia prevented post-hypoxic enhancement. Hypoxia transiently potentiated L-type VGCC currents via calcineurin, suggesting a positive feedback loop to amplify neuronal calcium signaling that may contribute to seizure generation.

The flavonoid scaffold as a template for the design of modulators of the vascular Ca(v) 1.2 channels

BACKGROUND AND PURPOSE

Previous studies have pointed to the plant flavonoids myricetin and quercetin as two structurally related stimulators of vascular Ca(v) 1.2 channel current (I(Ca1.2) ). Here we have tested the proposition that the flavonoid structure confers the ability to modulate Ca(v) 1.2 channels.

EXPERIMENTAL APPROACH

Twenty-four flavonoids were analysed for their effects on I(Ca1.2) in rat tail artery myocytes, using the whole-cell patch-clamp method.

KEY RESULTS

Most of the flavonoids stimulated or inhibited I(Ca1.2) in a concentration- and voltage-dependent manner with EC(50) values ranging between 4.4 µM (kaempferol) and 16.0 µM (myricetin) for the stimulators and IC(50) values between 13.4 µM (galangin) and 100 µM [(±)-naringenin] for the inhibitors. Key structural requirements for I(Ca1.2) stimulatory activity were the double bond between C2 and C3 and the hydroxylation pattern on the flavonoid scaffold, the latter also determining the molecular charge, as shown by molecular modelling techniques. Absence of OH groups in the B ring was key in I(Ca1.2) inhibition. The functional interaction between quercetin and either the stimulator myricetin or the antagonists resokaempferol, crysin, genistein, and 5,7,2'-trihydroxyflavone revealed that quercetin expressed the highest apparent affinity, in the low µM range, for Ca(v) 1.2 channels. Neither protein tyrosine kinase nor protein kinase Cα were involved in quercetin-induced stimulation of I(Ca1.2).

CONCLUSIONS AND IMPLICATIONS

Quercetin-like plant flavonoids were active on vascular Ca(v)1.2 channels. Thus, the flavonoid scaffold may be a template for the design of novel modulators of vascular smooth muscle Ca(v)1.2 channels, valuable for the treatment of hypertension and stroke.

Neuroprotective effects of valproic acid following transient global ischemia in rats

AIMS

A growing number of studies demonstrate that valproic acid (VPA), an anti-convulsant and mood-stabilizing drug, is neuroprotective against various insults. This study investigated whether treatment of ischemic stroke with VPA ameliorated hippocampal cell death and cognitive deficits. Possible mechanisms of action were also investigated.

MAIN METHODS

Global cerebral ischemia was induced to mimic ischemia/reperfusion (I/R) damage. The pyramidal cells within the CA1 field were stained with cresyl violet. Cognitive ability was measured 7 days after I/R using a Morris water maze. The anti-inflammatory effects of VPA on microglia were also investigated by immunohistochemistry. Pro-inflammatory cytokine production was determined using enzyme-linked immunosorbent assays (ELISA). Western blot analysis was performed to determine the levels of acetylated H3, H4 and heat shock protein 70 (HSP70) in extracts from the ischemic hippocampus.

KEY FINDINGS

VPA significantly increased the density of neurons that survived in the CA1 region of the hippocampus on the 7th day after transient global ischemia. VPA ameliorated severe deficiencies in spatial cognitive performance induced by transient global ischemia. Post-insult treatment with VPA also dramatically suppressed the activation of microglia but not astrocytes, reduced the number of microglia, and inhibited other inflammatory markers in the ischemic brain. VPA treatment resulted in a significant increase in levels of acetylated histones H3 and H4 as well as HSP70 in the hippocampus.

SIGNIFICANCE

Our results indicated that VPA protected against hippocampal cell loss and cognitive deficits. Treatment with VPA following cerebral ischemia probably involves multiple mechanisms of action, including inhibition of ischemia-induced cerebral inflammation, inhibition of histone deacetylase (HDAC) and induction of HSP.

Activity-dependent survival of developing neocortical neurons depends on PI3K signalling

Spontaneous electrical network activity plays a major role in the control of cell survival in the developing brain. Several intracellular pathways are implicated in transducing electrical activity into gene expression dependent and independent survival signals. These include activation of phosphatidylinositol 3-kinase (PI3K) and its downstream effector Akt, activation of Ras and subsequently MAPK/extracellular signal-regulated kinase (MEK) and extracellular signal-regulated kinase and signalling via calcium/calmodulin-dependent protein kinase (CaMK). In the present study, we analyzed the role of these pathways for the control of neuronal survival in different extracellular potassium concentrations ([K(+) ](ex) ). Organotypic neocortical slice cultures prepared from newborn mice were kept in 5.3, 8.0 and 25.0mM [K(+) ](ex) and treated with specific inhibitors of PI3K, MEK1, CaMKK and a broad spectrum CaMK inhibitor. After 6h of incubation, slices were immunostained for activated caspase 3 (a-caspase 3) and the number of apoptotic cells was quantified by computer based analysis. We found that in 5.3 and 8.0mM [K(+) ](ex) only PI3K was important for neuronal survival. When [K(+) ](ex) was raised to 25.0mM, a concentration above the depolarization block, we found no influence of PI3K on neuronal survival. Our data demonstrate that only the PI3K pathway, and not the MEK1, CaMKK or CaMKs pathway, plays a central role in the regulation of activity-dependent neuronal survival in the developing cerebral cortex.

Ca(2+) channel currents of cortical neurons from pure and mixed cultures

Voltage-gated Ca(2+) channels (VGCCs) are key regulators of many neuronal functions, and involved in multiple central nervous system diseases. In the last 30 years, a large number of injury and disease models have been established based on cultured neurons. Culture with serum develops a mixture of neurons and glial cells, while culture without serum develops pure neurons. Both of these neuronal-culture methods are widely used. However, the properties of Ca(2+) currents in neurons from these two cultures have not been compared. In this study, we cultured rat cortical neurons in serum-containing or -free medium and then recorded the Ca(2+) channel currents using patch-clamp technique. Our results showed that there were significant differences in the amplitude and activation properties of whole-cell Ca(2+) channel currents, and of non-L-type Ca(2+) channel currents between the neurons from these two culture systems. Our data suggested that the difference of whole-cell Ca(2+) currents may result from the differences in non-L-type currents. Understanding of these properties will considerably advance studies of VGCCs in neurons from pure or mixed culture.

Nonarteritic anterior ischemic optic neuropathy (NAION) and its experimental models

Anterior ischemic optic neuropathy (AION) can be divided into nonarteritic (NAION) and arteritic (AAION) forms. NAION makes up ~85% of all cases of AION, and until recently was poorly understood. There is no treatment for NAION, and its initiating causes are poorly understood, in part because NAION is not lethal, making it difficult to obtain fresh, newly affected tissue for study. In-vivo electrophysiology and post-mortem studies reveal specific responses that are associated with NAION. New models of NAION have been developed which enable insights into the pathophysiological events surrounding this disease. These models include both rodent and primate species, and the power of a 'vertically integrated' multi-species approach can help in understanding the common cellular mechanisms and physiological responses to clinical NAION, and to identify potential approaches to treatment. The models utilize laser light to activate intravascular photoactive dye to induce capillary vascular thrombosis, while sparing the larger vessels. The observable optic nerve changes associated with rodent models of AION (rAION) and primate NAION (pNAION) are indistinguishable from that seen in clinical disease, including sectoral axonal involvement, and in-vivo electrophysiological data from these models are consistent with clinical data. Early post-infarct events reveal an unexpected inflammatory response, and changes in intraretinal gene expression for both stress response, while sparing outer retinal function, which occurs in AAION models. Histologically, the NAION models reveal an isolated loss of retinal ganglion cells by apoptosis. There are changes detectable by immunohistochemistry suggesting that other retinal cells mount a brisk response to retinal ganglion cell distress without themselves dying. The optic nerve ultimately shows axonal loss and scarring. Inflammation is a prominent early histological feature. This suggests that clinically, specific modulation of inflammation may be a useful approach to NAION treatment early in the course of the disease.

Modes of Neuronal Calcium Entry and Homeostasis following Cerebral Ischemia

One of the major instigators leading to neuronal cell death and brain damage following cerebral ischemia is calcium dysregulation. The neuron's inability to maintain calcium homeostasis is believed to be a result of increased calcium influx and impaired calcium extrusion across the plasma membrane. The need to better understand the cellular and biochemical mechanisms of calcium dysregulation contributing to neuronal loss following stroke/cerebral ischemia is essential for the development of new treatments in order to reduce ischemic brain injury. The aim of this paper is to provide a concise overview of the various calcium influx pathways in response to ischemia and how neuronal cells attempts to overcome this calcium overload.