Relationships between ATP depletion, membrane potential, and the release of neurotransmitters in rat nerve terminals. An in vitro study under conditions that mimic anoxia, hypoglycemia, and ischemia

The metabolic overdrive hypothesis: hyperglycolysis and glutaminolysis in bipolar mania

Evidence from diverse areas of research including chronobiology, metabolomics and magnetic resonance spectroscopy indicate that energy dysregulation is a central feature of bipolar disorder pathophysiology. In this paper, we propose that mania represents a condition of heightened cerebral energy metabolism facilitated by hyperglycolysis and glutaminolysis. When oxidative glucose metabolism becomes impaired in the brain, neurons can utilize glutamate as an alternative substrate to generate energy through oxidative phosphorylation. Glycolysis in astrocytes fuels the formation of denovo glutamate, which can be used as a mitochondrial fuel source in neurons via transamination to alpha-ketoglutarate and subsequent reductive carboxylation to replenish tricarboxylic acid cycle intermediates. Upregulation of glycolysis and glutaminolysis in this manner causes the brain to enter a state of heightened metabolism and excitatory activity which we propose to underlie the subjective experience of mania. Under normal conditions, this mechanism serves an adaptive function to transiently upregulate brain metabolism in response to acute energy demand. However, when recruited in the long term to counteract impaired oxidative metabolism it may become a pathological process. In this article, we develop these ideas in detail, present supporting evidence and propose this as a novel avenue of investigation to understand the biological basis for mania.

Endoplasmic reticular stress as an emerging therapeutic target for chronic pain: a narrative review

Chronic pain is a severely debilitating condition with enormous socioeconomic costs. Current treatment regimens with nonsteroidal anti-inflammatory drugs (NSAIDs), steroids, or opioids have been largely unsatisfactory with uncertain benefits or severe long-term side effects. This is mainly because chronic pain has a multifactorial aetiology. Although conventional pain medications can alleviate pain by keeping several dysfunctional pathways under control, they can mask other underlying pathological causes, ultimately worsening nerve pathologies and pain outcome. Recent preclinical studies have shown that endoplasmic reticulum (ER) stress could be a central hub for triggering multiple molecular cascades involved in the development of chronic pain. Several ER stress inhibitors and unfolded protein response modulators, which have been tested in randomised clinical trials or apprpoved by the US Food and Drug Administration for other chronic diseases, significantly alleviated hyperalgesia in multiple preclinical pain models. Although the role of ER stress in neurodegenerative disorders, metabolic disorders, and cancer has been well established, research on ER stress and chronic pain is still in its infancy. Here, we critically analyse preclinical studies and explore how ER stress can mechanistically act as a central node to drive development and progression of chronic pain. We also discuss therapeutic prospects, benefits, and pitfalls of using ER stress inhibitors and unfolded protein response modulators for managing intractable chronic pain. In the future, targeting ER stress to impact multiple molecular networks might be an attractive therapeutic strategy against chronic pain refractory to steroids, NSAIDs, or opioids. This novel therapeutic strategy could provide solutions for the opioid crisis and public health challenge.

Cholinergic signaling of muscarinic receptors directly involves in the neuroprotection of muscone by inducing Ca2+ antagonism and maintaining mitochondrial function

ETHNOPHARMACOLOGICAL RELEVANCE

Musk, a traditional Chinese medicine, is broadly used in inducing resuscitation and refreshing the mind, activating blood and alleviating pain. It is commonly used for the treatment of ischemic stroke, and muscone is its core medicinal component.

AIM OF THE STUDY

The aim of this study was to explore whether muscone ameliorates neuronal damage through cholinergic signaling of muscarinic receptors.

MATERIALS AND METHODS

The effects of muscone were tested in a rat model of middle cerebral artery occlusion (MCAO) as well as injured neurons induced by oxygen-glucose deprivation (OGD) in PC12 cells. Cell counting kit 8 (CCK8) assay was used to measure the cell viability, and the production of lactate dehydrogenase (LDH) and adenosine-triphosphate (ATP) were examined by kit. 2',7'-Dichlorodihydrofluorescein diacetate (DCFH-DA), tetramethylrhodamine ethyl ester (TMRE) and Fluo-4 acetoxymethyl ester (Fluo-4 AM) staining were used to demonstrate effect of muscone on the reactive oxygen species (ROS) level, mitochondria membrane potential (MMP) and intracellular Ca2+ measurement in cells respectively, in which all of those staining was visualized by laser confocal microscope. For in vivo experiments, rats' cerebral blood flow was measured using laser Doppler blood flowmetry to evaluate the MCAO model, and a modified neurological severity score (mNSS) was used to assess the recovery of neurological function. Calculate infarct rate was measured by 2,3,5-Triphenyl Tetrazolium Chloride (TTC) staining. Except DCFH-DA and Fluo-4 AM staining, 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethyl benzimidazolylcarbocyanine iodide (JC-1) staining was used to observe intracellular Ca2+ measurement in brain cells. Protein levels in cells and tissues were detected by Western blot.

RESULTS

Pretreatment with muscone significantly improved the cell viability, lactic acid production, mitochondrial membrane potential collapse and function, Ca2+ overload, ROS generation, and cell apoptosis in OGD PC12 cells. Muscone also regulated PI3K, ERK and AKT signal pathways by activating cholinergic signaling of muscarinic receptors in PC12 cells induced with OGD. More importantly, the blocking of cholinergic signaling of muscarinic receptors by atropine significantly reduces the neuroprotective effects of muscone, including the cell viability, Ca2+ efflux, and mitochondrial repair. Furthermore, muscone was found to effectively alleviate mitochondrial dysfunction and elevated levels of ROS induced by the MCAO in the brain tissue. Notably, this beneficial effect of muscone was attenuated by atropine but not by (+)-Sparteine.

CONCLUSIONS

Our study indicates that muscone exerts its neuroprotective effects by activating muscarinic receptors of cholinergic signaling, thus providing a promising therapeutic target for the treatment of OGD-induced nerve injury in stroke. The findings suggest that these treatments may hold potential benefits for stroke patients.

Neurobiochemical Disturbances in Psychosis and their Implications for Therapeutic Intervention

Psychosis, marked by the emergence of psychotic symptoms, delves into the intricate dance of neurotransmitter dynamics, prominently featuring dopamine as a key orchestrator. In individuals living with psychotic conditions, the finely tuned balance of dopamine becomes disrupted, setting off a cascade of perceptual distortions and the manifestation of psychotic symptoms. A lot of factors can impact dopamine metabolism, further complicating its effects. From genetic predispositions to environmental stressors and inflammation, the delicate equilibrium is susceptible to various influences. The sensorium, the origin of incoming information, loses its intrinsic valence in this complex interplay. The concept of the "signal-to-noise ratio" encapsulates dopamine's role as a molecular switch in neural networks, influencing the flow of information serving the basic biological functions. This nuanced modulation acts as a cognitive prism, shaping how the world is perceived. However, in psychosis, this balance is disrupted, steering individuals away from a shared reality. Understanding dopamine's centrality requires acknowledging its unique status among neurotransmitters. Unlike strictly excitatory or inhibitory counterparts, dopamine's versatility allows it to toggle between roles and act as a cognitive director in the neural orchestra. Disruptions in dopamine synthesis, exchange, and receptor representation set off a chain reaction, impacting the delivery of biologically crucial information. The essence of psychosis is intricately woven into the delicate biochemical ballet choreographed by dopamine. The disruption of this neurotransmitter not only distorts reality but fundamentally reshapes the cognitive and behavioral field of our experience. Recognizing dopamine's role as a cognitive prism provides vital insights into the multifaceted nature of psychotic conditions, offering avenues for targeted therapeutic interventions aimed at restoring this delicate neurotransmitter balance.

Scavenging of reactive oxygen species mimics the anoxic response in goldfish pyramidal neurons

Goldfish are one of a few species able to avoid cellular damage during month-long periods in severely hypoxic environments. By suppressing action potentials in excitatory glutamatergic neurons, the goldfish brain decreases its overall energy expenditure. Coincident with reductions in O2 availability is a natural decrease in cellular reactive oxygen species (ROS) generation, which has been proposed to function as part of a low-oxygen signal transduction pathway. Using live-tissue fluorescence microscopy, we found that ROS production decreased by 10% with the onset of anoxia in goldfish telencephalic brain slices. Employing whole-cell patch-clamp recording, we found that, similar to severe hypoxia, the ROS scavengers N-acetyl cysteine (NAC) and MitoTEMPO, added during normoxic periods, depolarized membrane potential (severe hypoxia -73.6 to -61.4 mV, NAC -76.6 to -66.2 mV and MitoTEMPO -71.5 mV to -62.5 mV) and increased whole-cell conductance (severe hypoxia 5.7 nS to 8.0 nS, NAC 6.0 nS to 7.5 nS and MitoTEMPO 6.0 nS to 7.6 nS). Also, in a subset of active pyramidal neurons, these treatments reduced action potential firing frequency (severe hypoxia 0.18 Hz to 0.03 Hz, NAC 0.27 Hz to 0.06 Hz and MitoTEMPO 0.35 Hz to 0.08 Hz). Neither severe hypoxia nor ROS scavenging impacted action potential threshold. The addition of exogenous hydrogen peroxide could reverse the effects of the antioxidants. Taken together, this supports a role for a reduction in [ROS] as a low-oxygen signal in goldfish brain.

Pannexin-1 Channels as Mediators of Neuroinflammation

Neuroinflammation is a major component of central nervous system (CNS) injuries and neurological diseases, including Alzheimer’s disease, multiple sclerosis, neuropathic pain, and brain trauma. The activation of innate immune cells at the damage site causes the release of pro-inflammatory cytokines and chemokines, which alter the functionality of nearby tissues and might mediate the recruitment of leukocytes to the injury site. If this process persists or is exacerbated, it prevents the adequate resolution of the inflammation, and ultimately enhances secondary damage. Adenosine 5′ triphosphate (ATP) is among the molecules released that trigger an inflammatory response, and it serves as a chemotactic and endogenous danger signal. Extracellular ATP activates multiple purinergic receptors (P2X and P2Y) that have been shown to promote neuroinflammation in a variety of CNS diseases. Recent studies have shown that Pannexin-1 (Panx1) channels are the principal conduits of ATP release from dying cells and innate immune cells in the brain. Herein, we review the emerging evidence that directly implicates Panx-1 channels in the neuroinflammatory response in the CNS.

Sex-dependent vulnerability of fetal nonhuman primate cardiac mitochondria to moderate maternal nutrient reduction

Poor maternal nutrition in pregnancy affects fetal development, predisposing offspring to cardiometabolic diseases. The role of mitochondria during fetal development on later-life cardiac dysfunction caused by maternal nutrient reduction (MNR) remains unexplored. We hypothesized that MNR during gestation causes fetal cardiac bioenergetic deficits, compromising cardiac mitochondrial metabolism and reserve capacity. To enable human translation, we developed a primate baboon model (Papio spp.) of moderate MNR in which mothers receive 70% of control nutrition during pregnancy, resulting in intrauterine growth restriction (IUGR) offspring and later exhibiting myocardial remodeling and heart failure at human equivalent ∼25 years. Term control and MNR baboon offspring were necropsied following cesarean-section, and left ventricle (LV) samples were collected. MNR adversely impacted fetal cardiac LV mitochondria in a sex-dependent fashion. Increased maternal plasma aspartate aminotransferase, creatine phosphokinase (CPK), and elevated cortisol levels in MNR concomitant with decreased blood insulin in male fetal MNR were measured. MNR resulted in a two-fold increase in fetal LV mitochondrial DNA (mtDNA). MNR resulted in increased transcripts for several respiratory chain (NDUFB8, UQCRC1, and cytochrome c) and adenosine triphosphate (ATP) synthase proteins. However, MNR fetal LV mitochondrial complex I and complex II/III activities were significantly decreased, possibly contributing to the 73% decreased ATP content and increased lipid peroxidation. MNR fetal LV showed mitochondria with sparse and disarranged cristae dysmorphology. Conclusion: MNR disruption of fetal cardiac mitochondrial fitness likely contributes to the documented developmental programming of adult cardiac dysfunction, indicating a programmed mitochondrial inability to deliver sufficient energy to cardiac tissues as a chronic mechanism for later-life heart failure.

Loss of Cervical Sympathetic Chain Input to the Superior Cervical Ganglia Affects the Ventilatory Responses to Hypoxic Challenge in Freely-Moving C57BL6 Mice

The cervical sympathetic chain (CSC) innervates post-ganglionic sympathetic neurons within the ipsilateral superior cervical ganglion (SCG) of all mammalian species studied to date. The post-ganglionic neurons within the SCG project to a wide variety of structures, including the brain (parenchyma and cerebral arteries), upper airway (e.g., nasopharynx and tongue) and submandibular glands. The SCG also sends post-ganglionic fibers to the carotid body (e.g., chemosensitive glomus cells and microcirculation), however, the function of these connections are not established in the mouse. In addition, nothing is known about the functional importance of the CSC-SCG complex (including input to the carotid body) in the mouse. The objective of this study was to determine the effects of bilateral transection of the CSC on the ventilatory responses [e.g., increases in frequency of breathing (Freq), tidal volume (TV) and minute ventilation (MV)] that occur during and following exposure to a hypoxic gas challenge (10% O₂ and 90% N₂) in freely-moving sham-operated (SHAM) adult male C57BL6 mice, and in mice in which both CSC were transected (CSCX). Resting ventilatory parameters (19 directly recorded or calculated parameters) were similar in the SHAM and CSCX mice. There were numerous important differences in the responses of CSCX and SHAM mice to the hypoxic challenge. For example, the increases in Freq (and associated decreases in inspiratory and expiratory times, end expiratory pause, and relaxation time), and the increases in MV, expiratory drive, and expiratory flow at 50% exhaled TV (EF₅₀) occurred more quickly in the CSCX mice than in the SHAM mice, although the overall responses were similar in both groups. Moreover, the initial and total increases in peak inspiratory flow were higher in the CSCX mice. Additionally, the overall increases in TV during the latter half of the hypoxic challenge were greater in the CSCX mice. The ventilatory responses that occurred upon return to room-air were essentially similar in the SHAM and CSCX mice. Overall, this novel data suggest that the CSC may normally provide inhibitory input to peripheral (e.g., carotid bodies) and central (e.g., brainstem) structures that are involved in the ventilatory responses to hypoxic gas challenge in C57BL6 mice.

Evolving relationship between respiratory functions & impairment in sleep and cognition in patients with multiple sclerosis

BACKGROUND

The most apparent source of disability in patients with multiple sclerosis (MS) is the physical and mental impact. The pathophysiological mechanisms of cognitive dysfunction are multifactorial although hypoventilation secondary to respiratory dysfunction may contribute to cognitive decline.

METHODS

This study was conducted on 146 MS patients with baseline clinical assessments including the Epworth sleepiness scale (ESS) and physical disability was assessed using the Expanded Disability Status Scale (EDSS). Cognitive testing was performed utilizing the Brief International Cognitive Assessment for Multiple Sclerosis (BICAMS) and the Perceived Deficits Questionnaire (PDQ). Respiratory functions were assessed by spirometry and the respiratory muscle functional assessment was done by maximal mouth pressure measurement.

RESULTS

The respiratory muscle function test had a significant negative correlation with the score of ESS and PDQ scale and a significant positive correlation with the BICAMS scale score (p < 0.001). The ESS and PDQ scores were significantly negatively correlated with forced expiratory volume in the first second (FEV1)/ forced vital capacity (FVC) (p = 0.03, 0.02), FVC supine (p = 0.03, 0.01), FVC upright- FVC supine (ΔFVC) (p < 0.001, <0.001) FEV1 (p < 0.001) and FVC (L) (p < 0.001), respectively. While the BICAMS showed a significant positive correlation with spirometry results except FVC upright. ESS scores were significantly correlated with the BICAMS and PDQ scale score (p < 0.001).

CONCLUSION

Among MS patients, impaired respiratory functions are significantly associated with sleep disturbance and cognitive impairment. Thus the spirometry and respiratory muscle strength assessment are necessary from the early phase of MS.

Fenamates Inhibit Human Sodium Channel Nav1.2 and Protect Glutamate-Induced Injury in SH-SY5Y Cells

Voltage-gated sodium channels are crucial mediators of neuronal damage in ischemic and excitotoxicity disease models. Fenamates have been reported to have anti-inflammatory properties following a decrease in prostaglandin synthesis. Several researches showed that fenamates appear to be ion channel modulators and potential neuroprotectants. In this study, the neuroprotective effects of tolfenamic acid, flufenamic acid, and mefenamic acid were tested by glutamate-induced injury in SH-SY5Y cells. Following this, fenamates' effects were examined on both the expression level and the function of hNav1.1 and hNav1.2, which were closely associated with neuroprotection, using Western blot and patch clamp. Finally, the effect of fenamates on the expression of apoptosis-related proteins in SH-SY5Y cells was examined. The results showed that both flufenamic acid and mefenamic acid exhibited neuroprotective effects against glutamate-induced injury in SH-SY5Y cells. They inhibited peak currents of both hNav1.1 and hNav1.2. However, fenamates exhibited decreased inhibitory effects on hNav1.1 when compared to hNav1.2. Correspondingly, the inhibitory effect of fenamates was found to be consistent with the level of neuroprotective effects in vitro. Fenamates inhibited glutamate-induced apoptosis through the modulation of the Bcl-2/Bax-dependent cell death pathways. Taken together, Nav1.2 might play a part in fenamates' neuroprotection mechanism. Nav1.2 and NMDAR might take part in the neuroprotection mechanism of the fenamates. The fenamates inhibited glutamate-induced apoptosis through modulation of the Bcl-2/Bax-dependent cell death pathways.

Impact of Hypoglycemia on Brain Metabolism During Diabetes

Diabetes is a metabolic disease afflicting millions of people worldwide. A substantial fraction of world's total healthcare expenditure is spent on treating diabetes. Hypoglycemia is a serious consequence of anti-diabetic drug therapy, because it induces metabolic alterations in the brain. Metabolic alterations are one of the central mechanisms mediating hypoglycemia-related functional changes in the brain. Acute, chronic, and/or recurrent hypoglycemia modulate multiple metabolic pathways, and exposure to hypoglycemia increases consumption of alternate respiratory substrates such as ketone bodies, glycogen, and monocarboxylates in the brain. The aim of this review is to discuss hypoglycemia-induced metabolic alterations in the brain in glucose counterregulation, uptake, utilization and metabolism, cellular respiration, amino acid and lipid metabolism, and the significance of other sources of energy. The present review summarizes information on hypoglycemia-induced metabolic changes in the brain of diabetic and non-diabetic subjects and the manner in which they may affect brain function.

Regulation of Excitatory Amino Acid Transmission in the Retina: Studies on Neuroprotection

Excitotoxicity occurs in neurons due to the accumulation of excitatory amino acids such as glutamate in the synaptic and extrasynaptic locations. In the retina, excessive glutamate concentrations trigger a neurotoxic cascade involving several mechanisms, including the elevation of intracellular calcium (Ca²⁺⁾ and the activation of α-amino-3-hydroxy 5-methyl-4-iso-xazole-propionic acid/kainate (AMPA/KA) and N-methyl-d-aspartate (NMDA) receptors leading to retinal degeneration. Both ionotropic glutamate receptors (iGluRs) and metabotropic glutamate receptors (mGluRs) are present in the mammalian retina. Indeed, due to the abundant expression of GluRs, the mammalian retina is highly susceptible to excitotoxic neurodegeneration. Excitotoxicity has been postulated to present a common downstream mechanism for several stimuli, including hypoglycemia, hypoxia, ischemia, and chronic neurodegenerative diseases. Experimental approaches to the study of neuroprotection in the retina have utilized insults that trigger hypoxia, hypoglycemia, or excitotoxicity. Using these experimental approaches, the neuroprotective potential of GluR agents, including the NMDA receptor modulators (MK801, ifenprodil, memantine); AMPA/KA receptor antagonist (CNQX); Group II and III mGluR agonists (LY354740, quisqualate); and Ca²⁺-channel blockers (diltiazem, lomerizine, verapamil, ω-conotoxin), and others (pituitary adenylate cyclase activating polypeptide, neuropeptide Y, acetylcholine receptor agonists) have been elucidated. In addition to corroborating the exocytotic role of excitatory amino acids in retinal degeneration, these studies affirm that multiple mechanism/s contribute to the prevention of damage caused by excitotoxicity in the retina. Therefore, it is feasible that several pathways are involved in protecting the retina from toxic insults in ocular neurodegenerative conditions such as glaucoma and retinal ischemia. Furthermore, these experimental models are viable tools for evaluating therapeutic candidates in ocular neuropathies.

The vicious circle of hypometabolism in neurodegenerative diseases: Ways and mechanisms of metabolic correction

Hypometabolism, characterized by decreased brain glucose consumption, is a common feature of many neurodegenerative diseases. Initial hypometabolic brain state, created by characteristic risk factors, may predispose the brain to acquired epilepsy and sporadic Alzheimer's and Parkinson's diseases, which are the focus of this review. Analysis of available data suggests that deficient glucose metabolism is likely a primary initiating factor for these diseases, and that resulting neuronal dysfunction further promotes the metabolic imbalance, establishing an effective positive feedback loop and a downward spiral of disease progression. Therefore, metabolic correction leading to the normalization of abnormalities in glucose metabolism may be an efficient tool to treat the neurological disorders by counteracting their primary pathological mechanisms. Published and preliminary experimental results on this approach for treating Alzheimer's disease and epilepsy models support the efficacy of metabolic correction, confirming the highly promising nature of the strategy. © 2017 Wiley Periodicals, Inc.

Positive effects of intermittent fasting in ischemic stroke

Intermittent fasting (IF) is a dietary protocol where energy restriction is induced by alternate periods of ad libitum feeding and fasting. Prophylactic intermittent fasting has been shown to extend lifespan and attenuate the progress and severity of age-related diseases such as cardiovascular (e.g. stroke and myocardial infarction), neurodegenerative (e.g. Alzheimer's disease and Parkinson's disease) and cancerous diseases in animal models. Stroke is the second leading cause of death, and lifestyle risk factors such as obesity and physical inactivity have been associated with elevated risks of stroke in humans. Recent studies have shown that prophylactic IF may mitigate tissue damage and neurological deficit following ischemic stroke by a mechanism(s) involving suppression of excitotoxicity, oxidative stress, inflammation and cell death pathways in animal stroke models. This review summarizes data supporting the potential hormesis mechanisms of prophylactic IF in animal models, and with a focus on findings from animal studies of prophylactic IF in stroke in our laboratory.

Optical control of neuronal firing via photoinduced electron transfer in donor-acceptor conjugates

A rationally designed donor–acceptor conjugate efficiently generates a photoinduced charge-separated state in a cellular environment, achieving photoinduction of neuronal firing.

A series of porphyrin–fullerene linked molecules has been synthesized to evaluate the effects of substituents and molecular structures on their charge-separation yield and the lifetime of a final charge-separated state in various hydrophilic environments. The selected high-performance molecule effectively achieved depolarization in a plasma cell membrane by visible light as well as two-photon excitation using a near-infrared light laser. Moreover, it was revealed that the depolarization can trigger neuronal firing in rat hippocampal neurons, demonstrating the potential and versatility for controlling cell functions using light.

Functional impairment of endothelial cells by the antimycotic amphotericin B

We set out to determine the membrane potential (Vm) of the endothelial cell line EA.hy926 and its sensitivity to the antimycotic amphotericin B (AmB), a commonly used antifungal component in cell culture media. We measured the endothelial Vm under various experimental conditions by patch clamp technique and found that Vm of AmB-treated cells is (-12.1 ± 9.3) mV, while in AmB-untreated (control) cells it is (-57.1 ± 4.1) mV. In AmB-free extracellular solutions, Vm recovered toward control levels and this gain in Vm rapidly dissipated upon re-addition of AmB, demonstrating a rapid and reversible effect of AmB on endothelial Vm. The consequences of AmB dependent alterations in endothelial transmembrane potential were tested at the levels of Ca(2+) signaling, of nucleotide concentrations, and energy metabolism. In AmB-treated cells we found substantially reduced Ca(2+) entry (to about 60% of that in control cells) in response to histamine induced endoplasmic reticulum (ER) Ca(2+) depletion, and diminished the ATP-to-ADP ratio (by >30%). Our data demonstrate a marked and experimentally relevant dependence of basic functional parameters of cultured endothelial cells on the presence of the ionophoric antimycotic AmB. The profound and reversible effects of the widely used culture media component AmB need careful consideration when interpreting experimental data obtained under respective culture conditions.

Presynaptic Molecular Determinants of Quantal Size

The quantal hypothesis for the release of neurotransmitters at the chemical synapse has gained wide acceptance since it was first worked out at the motor endplate in frog skeletal muscle in the 1950’s. Considering the morphological identification of synaptic vesicles (SVs) at the nerve terminals that appeared to be homogeneous in size, the hypothesis proposed that signal transduction at synapses is mediated by the release of neurotransmitters packed in SVs that are individually uniform in size; the amount of transmitter in a synaptic vesicle is called a quantum. Although quantal size—the amplitude of the postsynaptic response elicited by the release of neurotransmitters from a single vesicle—clearly depends on the number and sensitivity of the postsynaptic receptors, accumulating evidence has also indicated that the amount of neurotransmitters stored in SVs can be altered by various presynaptic factors. Here, I provide an overview of the concepts and underlying presynaptic molecular underpinnings that may regulate quantal size.

Deciphering of mitochondrial cardiolipin oxidative signaling in cerebral ischemia-reperfusion

It is believed that biosynthesis of lipid mediators in the central nervous system after cerebral ischemia-reperfusion starts with phospholipid hydrolysis by calcium-dependent phospholipases and is followed by oxygenation of released fatty acids (FAs). Here, we report an alternative pathway whereby cereberal ischemia-reperfusion triggered oxygenation of a mitochondria-specific phospholipid, cardiolipin (CL), is followed by its hydrolysis to yield monolyso-CLs and oxygenated derivatives of fatty (linoleic) acids. We used a model of global cerebral ischemia-reperfusion characterized by 9 minutes of asphyxia leading to asystole followed by cardiopulmonary resuscitation in postnatal day 17 rats. Global ischemia and cardiopulmonary resuscitation resulted in: (1) selective oxidation and hydrolysis of CLs, (2) accumulation of lyso-CLs and oxygenated free FAs, (3) activation of caspase 3/7 in the brain, and (4) motor and cognitive dysfunction. On the basis of these findings, we used a mitochondria targeted nitroxide electron scavenger, which prevented CL oxidation and subsequent hydrolysis, attenuated caspase activation, and improved neurocognitive outcome when administered after cardiac arrest. These data show that calcium-independent CL oxidation and subsequent hydrolysis represent a previously unidentified pathogenic mechanism of brain injury incurred by ischemia-reperfusion and a clinically relevant therapeutic target.

Inducible glutamate oxaloacetate transaminase as a therapeutic target against ischemic stroke

SIGNIFICANCE

Glutamate serves multi-faceted (patho)physiological functions in the central nervous system as the most abundant excitatory neurotransmitter and under pathological conditions as a potent neurotoxin. Regarding the latter, elevated extracellular glutamate is known to play a central role in ischemic stroke brain injury.

RECENT ADVANCES

Glutamate oxaloacetate transaminase (GOT) has emerged as a new therapeutic target in protecting against ischemic stroke injury. Oxygen-sensitive induction of GOT expression and activity during ischemic stroke lowers glutamate levels at the stroke site while sustaining adenosine triphosphate levels in brain. The energy demands of the brain are among the highest of all organs underscoring the need to quickly mobilize alternative carbon skeletons for metabolism in the absence of glucose during ischemic stroke. Recent work builds on the important observation of Hans Krebs that GOT-mediated metabolism of glutamate generates tri-carboxylic acid (TCA) cycle intermediates in brain tissue. Taken together, outcomes suggest GOT may enable the transformative switch of otherwise excitotoxic glutamate into life-sustaining TCA cycle intermediates during ischemic stroke.

CRITICAL ISSUES

Neuroprotective strategies that focus solely on blocking mechanisms of glutamate-mediated excitotoxicity have historically failed in clinical trials. That GOT can enable glutamate to assume the role of a survival factor represents a paradigm shift necessary to develop the overall significance of glutamate in stroke biology.

FUTURE DIRECTIONS

Ongoing efforts are focused to develop the therapeutic significance of GOT in stroke-affected brain. Small molecules that target induction of GOT expression and activity in the ischemic penumbra are the focus of ongoing studies.

Validation of [(11) C]ORM-13070 as a PET tracer for alpha2c -adrenoceptors in the human brain

This study explored the use of the α2C -adrenoceptor PET tracer [(11) C]ORM-13070 to monitor α2C -AR occupancy in the human brain. The subtype-nonselective α2 -AR antagonist atipamezole was administered to eight healthy volunteer subjects to determine its efficacy and potency (Emax and EC50 ) at inhibiting tracer uptake. We also explored whether the tracer could reveal changes in the synaptic concentrations of endogenous noradrenaline in the brain, in response to several pharmacological and sensory challenge conditions. We assessed occupancy from the bound-to-free ratio measured during 5-30 min post injection. Based on extrapolation of one-site binding, the maximal extent of inhibition of striatal [(11) C]ORM-13070 uptake (Emax ) achievable by atipamezole was 78% (95% CI 69-87%) in the caudate nucleus and 65% (53-77%) in the putamen. The EC50 estimates of atipamezole (1.6 and 2.5 ng/ml, respectively) were in agreement with the drug's affinity to α2C -ARs. These findings represent clear support for the use of [(11) C]ORM-13070 for monitoring drug occupancy of α2C -ARs in the living human brain. Three of the employed noradrenaline challenges were associated with small, approximately 10-16% average reductions in tracer uptake in the dorsal striatum (atomoxetine, ketamine, and the cold pressor test; P < 0.05 for all), but insulin-induced hypoglycemia did not affect tracer uptake. The tracer is suitable for studying central nervous system receptor occupancy by α2C -AR ligands in human subjects. [(11) C]ORM-13070 also holds potential as a tool for in vivo monitoring of synaptic concentrations of noradrenaline, but this remains to be further evaluated in future studies.

Mitochondria: a multimodal hub of hypoxia tolerance

Decreased oxygen availability impairs cellular energy production and, without a coordinated and matched decrease in energy consumption, cellular and whole organism death rapidly ensues. Of particular interest are mechanisms that protect brain from low oxygen injury, as this organ is not only the most sensitive to hypoxia, but must also remain active and functional during low oxygen stress. As a result of natural selective pressures, some species have evolved molecular and physiological mechanisms to tolerate prolonged hypoxia with no apparent detriment. Among these mechanisms are a handful of responses that are essential for hypoxia tolerance, including (i) sensors that detect changes in oxygen availability and initiate protective responses; (ii) mechanisms of energy conservation; (iii) maintenance of basic brain function; and (iv) avoidance of catastrophic cell death cascades. As the study of hypoxia-tolerant brain progresses, it is becoming increasingly apparent that mitochondria play a central role in regulating all of these critical mechanisms. Furthermore, modulation of mitochondrial function to mimic endogenous neuroprotective mechanisms found in hypoxia-tolerant species confers protection against otherwise lethal hypoxic stresses in hypoxia-intolerant organs and organisms. Therefore, lessons gleaned from the investigation of endogenous mechanisms of hypoxia tolerance in hypoxia-tolerant organisms may provide insight into clinical pathologies related to low oxygen stress.

Insulin-associated neuroinflammatory pathways as therapeutic targets for traumatic brain injury

Traumatic brain injury (TBI) is characterized by an abrupt blow or exchange of force against the head and can be categorized as mild, moderate, and severe. The secondary cell death after TBI displays ischemic-like patterns including neuroinflammation. The scavenger receptor cluster of differentiation (CD) 36 is a lipid-associated protein capable of transducing intracellular signals to promote inflammatory mechanisms within different cell types. Expression and activation of CD36 is closely related to dyslipidemia secondary to diabetes. Diabetes mellitus (DM) has been documented as a co-morbidity factor in TBI, in that patients with a history of diabetes present with more severe brain damage and slower recovery from TBI than non-diabetic patients. Indeed, a strict regulation of blood serum glucose by the use of insulin promotes a better outcome for TBI patients. Based on these recent findings, we now advance the hypothesis that CD36 via DM insulin-associated pathways is closely involved in TBI chronic pathology.

Modulation of crucial adenosinetriphosphatase activities due to U-74389G administration in a porcine model of intracerebral hemorrhage

Spontaneous intracerebral hemorrhage (ICH) represents a partially-understood cerebrovascular disease of high incidence, morbidity and mortality. We, herein, report the findings of our study concerning the role of two important adenosinetriphosphatases (ATPases) in a porcine model of spontaneous ICH that we have recently developed (by following recent references as well as previously-established models and techniques), with a focus on the first 4 and 24 h following the lesion's induction, in combination with a study of the effectiveness of the lazaroid antioxidant U-74389G administration. Our study demonstrates that the examined ICH model does not cause a decrease in Na(+),K(+)-ATPase activity (the levels of which are responsible for a very large part of neuronal energy expenditure) in the perihematomal basal ganglia territory, nor a change in the activity of Mg(2+)-ATPase. This is the first report focusing on these crucial ATPases in the experimental setting of ICH and differs from the majority of the findings concerning the behavior of these (crucial for central nervous system cell survival) enzymes under stroke-related ischemic conditions. The administration of U-74389G (an established antioxidant) in this ICH model revealed an injury specific type of behavior, that could be considered as neuroprotective provided that one considers that Na(+),K(+)- and Mg(2+)-ATPase inhibition might in this case diminish the local ATP consumption.

The early activation of PI3K strongly enhances the resistance of cortical neurons to hypoxic injury via the activation of downstream targets of the PI3K pathway and the normalization of the levels of PARP activity, ATP, and NAD⁺

Phosphatidylinositol 3-kinase (PI3K) plays several important roles in neuronal survival. Activation of the pathway is essential for the neuroprotective mechanisms of materials that shield neuronal cells from many stressful conditions. However, there have been no reports to date about the effect of the direct activation of the pathway in hypoxic injury of neuronal cells. We investigated whether the direct activation of the PI3K pathway inhibits neuronal cell death induced by hypoxia. Primary cultured cortical neurons (PCCNs) were exposed to hypoxic conditions (less than 1 mol% O2) and/or treated with PI3K activator. Hypoxia reduced the viability of PCCNs in a time-dependent manner, but treatment with PI3K significantly restored viability in a concentration-dependent manner. Among the signaling proteins involved in the PI3K pathway, those associated with survival, including Akt and glycogen synthase kinase-3β, were decreased shortly after exposure to hypoxia and those associated with cell death, including BAX, apoptosis-induced factor, cytochrome c, caspase-9, caspase-3, and poly(ADP-ribose) polymerase (PARP), were increased. However, treatment with PI3K activator normalized the expression levels of those signaling proteins. PARP activity and levels of ATP and NAD(+) altered by hypoxia were also normalized with direct PI3K activation. All these findings suggest that direct and early activation is important for protecting neuronal cells from hypoxic injury.

Cognitive effects of NSAIDs in cerebral ischemia: a hypothesis exploring mechanical action mediated pharmacotherapy

Cerebral ischemia is associated with altered neuronal mechanics leading to dynamic reshaping of neuronal structures, giving rise to a cascade of biological pathways leading to many deleterious consequences and cognitive deficits. Memory and learning specifically are mediated by neurotransmitter release from vesicles clustered at the synapse. Mechanical tension is an important factor governing the amount of vesicular neurotransmitter release in response to an action potential. Neuroinflammation in cerebral ischemia leads to altered mechanical/physical forces on neurons which gives rise to abnormal mechanical tension along the neuron resulting in neurotransmitter imbalance leading to cognitive dysfunction. We consider the possibility that modulation of mechanical forces on neurons may be a therapeutic strategy to help prevent cognitive deficit in cerebral ischemia. Here we show how NSAIDs may act as candidate pharmacological molecules which have the ability to inhibit neuroinflammation and which can alter neuronal mechanics by their COX-2 inhibiting property.

Mitochondria, oligodendrocytes and inflammation in bipolar disorder: evidence from transcriptome studies points to intriguing parallels with multiple sclerosis

Gene expression studies of bipolar disorder (BPD) have shown changes in transcriptome profiles in multiple brain regions. Here we summarize the most consistent findings in the scientific literature, and compare them to data from schizophrenia (SZ) and major depressive disorder (MDD). The transcriptome profiles of all three disorders overlap, making the existence of a BPD-specific profile unlikely. Three groups of functionally related genes are consistently expressed at altered levels in BPD, SZ and MDD. Genes involved in energy metabolism and mitochondrial function are downregulated, genes involved in immune response and inflammation are upregulated, and genes expressed in oligodendrocytes are downregulated. Experimental paradigms for multiple sclerosis demonstrate a tight link between energy metabolism, inflammation and demyelination. These studies also show variabilities in the extent of oligodendrocyte stress, which can vary from a downregulation of oligodendrocyte genes, such as observed in psychiatric disorders, to cell death and brain lesions seen in multiple sclerosis. We conclude that experimental models of multiple sclerosis could be of interest for the research of BPD, SZ and MDD.

High-level inhibition of mitochondrial complexes III and IV is required to increase glutamate release from the nerve terminal

Background

The activities of mitochondrial complex III (ubiquinol-cytochrome c reductase, EC 1.10.2.2) and complex IV (cytochrome c oxidase EC 1.9.3.1) are reduced by 30-70% in Huntington's disease and Alzheimer's disease, respectively, and are associated with excitotoxic cell death in these disorders. In this study, we investigated the control that complexes III and complex IV exert on glutamate release from the isolated nerve terminal.

Results

Inhibition of complex III activity by 60-90% was necessary for a major increase in the rate of Ca²⁺-independent glutamate release to occur from isolated nerve terminals (synaptosomes) depolarized with 4-aminopyridine or KCl. Similarly, an 85-90% inhibition of complex IV activity was required before a major increase in the rate of Ca²⁺-independent glutamate release from depolarized synaptosomes was observed. Inhibition of complex III and IV activities by ~ 60% and above was required before rates of glutamate efflux from polarized synaptosomes were increased.

Conclusions

These results suggest that nerve terminal mitochondria possess high reserves of complex III and IV activity and that high inhibition thresholds must be reached before excess glutamate is released from the nerve terminal. The implications of the results in the context of the relationship between electron transport chain enzyme deficiencies and excitotoxicity in neurodegenerative disorders are discussed.

Impact of STZ-induced hyperglycemia and insulin-induced hypoglycemia in plasma amino acids and cortical synaptosomal neurotransmitters

In this work, we evaluated the effects of streptozotocin (STZ)-induced hyperglycemia and an acute episode of insulin-induced hypoglycemia in plasma amino acids and cortical neurotransmitters. For that purpose, we used citrate (vehicle)-treated Wistar rats, STZ-treated rats [i.p., 50 mg/kg body weight], and STZ-treated rats injected with insulin [s.c., dose adjusted with blood glucose levels] 1 h prior to sacrifice to induce an acute episode of hypoglycemia. Plasma was collected for determination of amino acids levels. In addition, cortical synaptosomal preparations were obtained and the total levels of neurotransmitters, levels of aspartate, glutamate, taurine, and GABA released by the action of KCl, iodoacetic acid (IAA), ouabain, and veratridine, membrane potential and ATP levels were evaluated. Compared with control rats, plasma from hypoglycemic rats presented increased levels of aspartate, glutamate, glutamine, and taurine whereas GABA levels were decreased in STZ and hypoglycemic rats. Similarly, glutamate and taurine levels were increased in hypoglycemic synaptosomes while GABA decreased in hypoglycemic and STZ-diabetic synaptosomes. The depolarizing agent KCl promoted an increase in aspartate, glutamate, and taurine release from hypoglycemic synaptosomes. The highest release of neurotransmitters occurred in the presence of veratridine and ouabain, two other depolarizing agents, in all groups of experimental animals. However, a higher release of glutamate was observed in the diabetic and hypoglycemic synaptosomes. No alterations were observed in synaptosomal membrane potential and ATP levels. These results show that in the presence of a metabolic insult a higher release of excitatory amino acids occurs, which may underlay the neuronal injury observed in type 1 diabetic patients under insulin therapy.

The anti-inflammatory and neuroprotective effects of ghrelin in subarachnoid hemorrhage-induced oxidative brain damage in rats

To elucidate the putative neuroprotective effects of ghrelin in subarachnoid hemorrhage (SAH)-induced brain injury, Wistar albino rats (n = 54) were divided into sham-operated control, saline-treated SAH, and ghrelin-treated (10 microg/kg/d IP) SAH groups. The rats were injected with blood (0.3 mL) into the cisterna magna to induce SAH, and were sacrificed 48 h after the neurological examination scores were recorded. In plasma samples, neuron-specific enolase (NSE), S-100beta protein, TNF-alpha, and IL-1beta levels were evaluated, while forebrain tissue samples were taken for the measurement of malondialdehyde (MDA), glutathione (GSH), reactive oxygen species levels, myeloperoxidase (MPO), Na(+)-K(+)-ATPase activity, and DNA fragmentation ratio. Brain tissue samples containing the basilar arteries were obtained for histological examination, while cerebrum and cerebellum were removed for the measurement of blood-brain barrier (BBB) permeability and brain water content. The neurological scores were impaired at 48 h after SAH induction, and SAH caused significant decreases in brain GSH content and Na(+)-K(+)-ATPase activity, and increases in chemiluminescence, MDA levels, and MPO activity. Compared with the control group, the protein levels of NSE, S-100beta, TNF-alpha, and IL-1beta in plasma were also increased, while ghrelin treatment prevented all SAH-induced alterations observed both biochemically and histopathologically. The results demonstrate that ghrelin alleviates SAH-induced oxidative brain damage, and exerts neuroprotection by maintaining a balance in oxidant-antioxidant status, by inhibiting proinflammatory mediators, and preventing the depletion of endogenous antioxidants evoked by SAH.

Cognition and chronic hypoxia in pulmonary diseases

Lung disease with chronic hypoxia has been associated with cognitive impairment of the subcortical type.

Trolox ameliorates 3-nitropropionic acid-induced neurotoxicity in rats

3-nitropropionic acid (3-NPA) is a naturally occurring neurotoxin produced by legumes of the genus Astragalus and Arthrium fungi. Acute exposure to 3-NPA results in striatal astrocytic death and variety of behavior dysfunction in rats. Oxidative stress has been reported to play an important role in 3-NPA-induced neurotoxicity. Trolox is a potent free radical chain breaking antioxidant which has been shown to restore structure and function of the nervous system following oxidative stress. This rapid and efficient antioxidant property of trolox was attributed to its enhanced water solubility as compared with alpha-tocopherol. This investigation was aimed to study the effect of trolox against 3-NPA-induced neurotoxicity in female Wistar rats. The animals received trolox (0, 40 mg, 80 mg and 160 mg/kg, orally) daily for 7 days. 3-NPA (25mg/kg, i.p.) was administered daily 30 min after trolox for the same duration. One additional group of rats served as control (vehicle only). On day 8, the animals were observed for neurobehavioral performance. Immediately after behavioral studies, the animal's brains were dissected out for histological studies. Lesions in the striatal dopaminergic neurons were assessed by immunohistochemical method using tyrosine hydroxylase immunostaining. Administration of 3-NPA alone caused significant depletion of striatal dopamine and glutathione, whereas, the levels of thiobarbituric acid reactive substance (TBARS) and nitric oxide (NO) were significantly increased suggesting an elevated level of oxidative stress. Trolox significantly and dose-dependently protected animals against 3-NPA-induced neurobehavioral, neurochemical and structural abnormalities. These results clearly suggest that protective effect of trolox against 3-NPA-induced neurotoxicity is mediated through its free radical scavenging activity.

Evidence for neuroprotection by the fenamate NSAID, mefenamic acid

Fenamate NSAIDs are inhibitors of cyclooxygenases, antagonists of non-selective cation channels, subtype-selective modulators of GABA(A) receptors, weak inhibitors of glutamate receptors and activators of some potassium channels. These pharmacological actions are all implicated in the pathogenesis of ischemic stroke. The aim of this study was to investigate the hypothesis that the fenamate, mefenamic acid, is neuroprotective in an in vitro and in vivo model of stroke. Embryonic rat hippocampal neurons were cultured and maintained for up to 14 days in vitro. At 9 or 14 days, cells were exposed to glutamate (5microM) or glutamate (5microM) plus mefenamic acid (10-100microM) or the control agent, MK-801 (10microM) for 10min. 24h later, cell death was determined by measuring lactate dehydrogenase (LDH) levels in the culture media. In vivo, male Wistar rats (300-350g) were subjected to 2h middle cerebral artery occlusion (MCAO) followed by 24h reperfusion. Animals received either a single i.v. dose of MFA (10mg/kg or 30mg/kg), or MK-801 (2mg/kg) or saline prior to MCAO or, four equal doses of MFA (20mg/kg) at 1h intervals beginning 1h prior to MCAO. Ischemic damage was then assessed 24h after MCAO. In vitro, mefenamic acid (10-100microM) and MK-801 (10microM) significantly reduced glutamate-evoked cell death compared with control cultures. In vivo, MFA (20mg/kgx4) significantly reduced infarct volume, total ischemic brain damage and edema by 53% (p< or =0.02), 41% (p< or =0.002) and 45% (p< or =0.002) respectively. Furthermore, mefenamic acid reduced cerebral edema when measured as a function of brain water content. MK-801 was also neuroprotective against MCAO brain injury. This study demonstrates a significant neuroprotective effect by a fenamate NSAID against glutamate-induced cell toxicity, in vitro and against ischemic stroke in vivo. Further experiments are currently addressing the mechanism(s) of this neuroprotection.

Antioxidant, antiinflammatory and antiapoptotic effects of dapsone in a model of brain ischemia/reperfusion in rats

Although dapsone (4,4'-diaminodiphenylsulfone) has been described as a neuroprotective agent in occlusive focal ischemia in rats, its mechanism of action is still unknown. To explore this mechanism, oxidative, inflammatory and apoptotic processes were evaluated in the striatum of adult rats using a model of ischemia-reperfusion (I/R), either with or without dapsone treatment. Male Wistar rats were submitted to transient middle cerebral artery occlusion for 2 hr, followed by reperfusion. Rats were dosed either with dapsone (12.5 mg/kg i.p.) or vehicle 30 min before or 30 min after the ischemia onset. Lipid peroxidation (LP) and nitrotyrosine contents were measured 22 hr after reperfusion, and myeloperoxidase activity was evaluated 46 hr after I/R. Different markers for apoptosis and necrosis were also evaluated both at 24 and 72 hr after I/R experimental procedure. LP increased by 37% in ischemic animals vs controls, and this effect was reversed by dapsone treatments. A similar effect was observed regarding nitrotyrosine striatal contents. Myeloperoxidase activity, a marker of inflammatory response, increased 3.7-fold in ischemic animals vs. control rats, and dapsone treatment antagonized that effect. Although apoptosis was increased by the effect of ischemia at both evaluation times, dapsone antagonized that effect only at 72 hr after surgery. Dapsone antagonized all of the I/R end points measured, showing a remarkable ability to decrease markers of damage through antioxidant, antiinflammatory, and anti-apoptotic effects.

3-Nitropropionic acid depresses spinal reflexes involving GABAergic and glycinergic transmission in neonatal rat spinal cord in vitro

AIMS

3-Nitropropionic acid (3-NPA) is a naturally occurring fungal toxin that leads to ATP-depletion by inhibiting mitochondrial succinate dehydrogenase and produces chemical anoxia. The present study was conducted to identify the involvement of inhibitory system in 3-NPA-induced depression of spinal reflexes.

METHODS

The monosynaptic (MSR) and polysynaptic reflex (PSR) potentials were recorded at ventral root by stimulating the corresponding dorsal root in hemisected (sagitally) spinal cord from 4-8 day old rats. Effect of 3-NPA in the absence and presence of antagonists was evaluated on the reflexes.

KEY FINDINGS

Superfusion of 3-NPA (3.4 mM) depressed the reflexes in a time-dependent manner abolishing them by 35 min. The T-50 values were around 18 and 16 min for MSR and PSR, respectively. An NMDA receptor antagonist, DL-2-amino-5-phosphonovaleric acid (10 microM) failed to block the 3-NPA (3.4 mM)-induced depression of reflexes. Superfusion of bicuculline (GABAA receptor antagonist; 1 microM), or strychnine (glycineA receptor antagonist; 1 microM) antagonized the 3-NPA-induced depression of reflexes significantly. The T-50 values were 26 and 30 min in bicuculline and strychnine pretreated groups, respectively and were significantly greater than 3-NPA only group.

SIGNIFICANCE

The results indicate that 3-NPA-induced depression of spinal reflexes is partially mediated by GABAergic and glycinergic inhibitory transmission.

Na(+)/H(+) exchanger inhibition modifies dopamine neurotransmission during normal and metabolic stress conditions

Na(+)/H(+) exchanger (NHE) proteins are involved in intracellular pH and volume regulation and may indirectly influence neurotransmission. The abundant NHE isoform 1 (NHE1) has also been linked to brain cell damage during metabolic stress. It is not known, however, whether NHE1 or other NHE isoforms play a role in striatal dopamine (DA) neurotransmission under normal or metabolic stress conditions. Our study tested the hypothesis that NHE inhibition with cariporide mesilate (HOE-642) modifies striatal DA overflow and DAergic terminal damage in mice caused by the mitochondrial inhibitor malonate. We also explored the expression of NHE1-5 in the striatum and substantia nigra. Reverse microdialysis of HOE-642 elicited a transient elevation followed by a reduction in DA overflow accompanied by a decline in striatal DA content. HOE-642 pre-treatment diminished the malonate-induced DA overflow without reducing the intensity of the metabolic stress or subsequent DAergic axonal damage. Although NHE isoforms 1-5 are expressed in the striatum and midbrain, NHE1 protein was not co-located on nigrostriatal DAergic neurons. The absence of NHE1 co-location on DAergic neurons suggests that the effects of HOE-642 on striatal DA overflow are either mediated via NHE1 located on other cell types or that HOE-642 is acting through multiple NHE isoforms.

Neuroprotective effects of the novel glutamate transporter inhibitor (-)-3-hydroxy-4,5,6,6a-tetrahydro-3aH-pyrrolo[3,4-d]-isoxazole-4-carboxylic acid, which preferentially inhibits reverse transport (glutamate release) compared with glutamate reuptake

(+/-)-3-Hydroxy-4,5,6,6a-tetrahydro-3aH-pyrrolo [3,4 -d]-isoxazole-4-carboxylic acid (HIP-A) and (+/-)-3-hydroxy-4,5,6, 6a-tetrahydro-3aH-pyrrolo[3,4-d]isoxazole-6-carboxylic acid (HIP-B) are selective inhibitors of excitatory amino acid transporters (EAATs), as potent as DL-threo-beta-benzyloxyaspartic acid (TBOA). We report here that the active isomers are (-)-HIP-A and (+)-HIP-B, being approximately 150- and 10-fold more potent than the corresponding enantiomers as inhibitors of [3H]aspartate uptake in rat brain synaptosomes and hEAAT1-3-expressing cells. Comparable IC(50) values were found on the three hEAAT subtypes. (-)-HIP-A maintained the remarkable property, previously reported with the racemates, of inhibiting synaptosomal glutamate-induced [3H]D-aspartate release (reverse transport) at concentrations significantly lower than those inhibiting [3H]L-glutamate uptake. New data suggest that the noncompetitive-like interaction described previously is probably the consequence of an insurmountable, long-lasting impairment of EAAT's function. Some minutes of preincubation are required to induce this impairment, the duration of preincubation having more effect on inhibition of glutamate-induced release than of glutamate uptake. In organotypic rat hippocampal slices and mixed mouse brain cortical cultures, TBOA, but not (-)-HIP-A, had toxic effects. Under ischemic conditions, a neuroprotective effect was found with 10 to 30 microM (-)-HIP-A, but not with 10 to 30 microM TBOA or 100 microM (-)-HIP-A. The effect of (-)-HIP-A suggests that, under ischemia, EAATs mediate both release (reverse transport) and uptake of glutamate. The neuroprotection with the lower (-)-HIP-A concentrations may indicate a selective inhibition of the reverse transport confirming the data obtained in synaptosomes. The selective interference with glutamate-induced glutamate release might offer a new strategy for neuroprotective action.

Partial inhibition of complex I activity increases Ca-independent glutamate release rates from depolarized synaptosomes

Mitochondria have been implicated in the pathogenesis of several neurodegenerative disorders and, in particular, complex I (NADH:ubiquinone oxidoreductase, EC 1.6.5.3) activity has been shown to be partially reduced in postmortem studies of the substantia nigra of Parkinson's disease patients. The present study examines the effect of partial inhibition of complex I activity on glutamate release from rat brain synaptosomes. Following a 40% inhibition of complex I activity with rotenone, it was found that Ca(2+)-independent release of glutamate increased from synaptosomes depolarized with 4-aminopyridine. Highest rates of glutamate release were found to occur between 60-90% complex I inhibition. A similar pattern of increase was shown to occur in synaptosomes depolarized with KCl. The increase in glutamate release was found to correlate to a significant decrease in ATP. Inhibition of complex I activity by 40% was also shown to cause a significant collapse in mitochondrial membrane potential (Deltapsi(m)). These results suggest that partial inhibition of complex I activity in in situ mitochondria is sufficient to significantly increase release of glutamate from the pre-synaptic nerve terminal. The relevance of these results in the context of excitotoxicity and the pathogenesis of neurodegenerative disorders is discussed.

Resveratrol protects rat striatal slices against anoxia-induced dopamine release

Incubation of rat striatal slices in anoxic medium caused significant alterations in dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) outputs; while DA release increased several times, 50% decline in DOPAC output was observed under this condition. Tissue ATP level, on the other hand, was decreased 40% by anoxia. Presence of resveratrol in the medium decreased anoxia-induced DA release in a concentration-dependent manner. Enhanced DA output, however, was declined slightly by epicatechine and catechine, and not altered significantly by morin hydrate and quercetin dehydrate which are other penolic compounds present in the red wine. In contrary to DA output, anoxia-induced decline in tissue ATP level was not ameliorated by resveratrol. In addition to anoxia, resveratrol, as observed with DA uptake blocker nomifensine, also reduced DA release stimulated by ouabain. Efficiencies of both resveratrol and nomifensine to attenuate ouabain-induced DA output, however, were closely dependent on ouabain concentration in the medium. These results indicate that some phenolic compounds, particularly resveratrol decrease anoxia-induced DA output and appear promising agents to improve the alterations occurred under anoxic-ischemic conditions.

Mannosylglycerate is essential for osmotic adjustment in Thermus thermophilus strains HB27 and RQ-1

We disrupted the mpgS encoding mannosyl-3-phosphoglycerate synthase (MpgS) of Thermus thermophilus strains HB27 and RQ-1, by homologous recombination, to assess the role of the compatible solute mannosylglycerate (MG) in osmoadaptation of the mutants, to examine their ability to grow in NaCl-containing medium and to identify the intracellular organic solutes. Strain HB27 accumulated only MG when grown in defined medium containing 2% NaCl; mutant HB27M9 did not grow in the same medium containing more than 1% NaCl. When trehalose or MG was added, the mutant was able to grow up to 2% of NaCl and accumulated trehalose or MG, respectively, plus amino acids. T. thermophilus RQ-1 grew in medium containing up to 5% NaCl, accumulated trehalose and lower amounts of MG. Mutant RQ-1M1 lost the ability to grow in medium containing more than 3% NaCl and accumulated trehalose and moderate levels of amino acids. Exogenous MG did not improve the ability of the organism to grow above 3% NaCl, but caused a decrease in the levels of amino acids. Our results show that MG serves as a compatible solute primarily during osmoadaptation at low levels of NaCl while trehalose is primarily involved in osmoadaptation during growth at higher NaCl levels.

Reactive oxygen species generation by the ethylene-bis-dithiocarbamate (EBDC) fungicide mancozeb and its contribution to neuronal toxicity in mesencephalic cells

Previous in vitro studies in our laboratory have shown that mancozeb (MZ) and maneb (MB), both widely used EBDC fungicides, are equipotent neurotoxicants that produce cell loss in mesencephalic dopaminergic and GABAergic cells after an acute 24h exposure. Mitochondrial uncoupling and inhibition were associated with fungicide exposure. Inhibition of mitochondrial respiration is known to increase free radical production. Here the mechanism(s) of neuronal damage associated with MZ exposure was further explored by determining the role that reactive oxygen species (ROS) played in toxicity. Damage to mesencephalic dopamine and GABA cell populations were significantly attenuated when carried out in the presence of ascorbate or SOD, indicative of a free radical-mediated contribution to toxicity. ROS generation monitored by hydrogen peroxide (H(2)O(2)) production using Amplex Red increased in a dose-dependent manner in response to MZ. Inhibition of intracellular catalase with aminotriazole had little effect on H(2)O(2) generation, whereas exogenously added catalase significantly reduced H(2)O(2) production, demonstrating a large extracellular contribution to ROS generation. Conversely, cells preloaded with the ROS indicator dye DCF showed significant MZ-induced ROS production, demonstrating an increase in intracellular ROS. Both the organic backbone of MZ as well as its associated Mn ion, but not Zn ion, were responsible and required for H(2)O(2) generation. The functionally diverse NADPH oxidase inhibitors, diphenylene iodonium chloride, apocynin, and 4-(2-aminoethyl)benzene-sulfonyl fluoride hydrochloride significantly attenuated H(2)O(2) production by MZ. In growth medium lacking cells, MZ produced little H(2)O(2), but enhanced H(2)O(2) generation when added with xanthine plus xanthine oxidase whereas, in cultured cells, allopurinol partially attenuated H(2)O(2) production by MZ. Minocycline, an inhibitor of microglial activation, modestly reduced H(2)O(2) formation in mesencephalic cells. In contrast, neuronal-enriched cultures or cultures treated with MAC-1-SAP to kill microglia, did not show an attenuation of ROS production. These findings demonstrate that Mn-containing EBDC fungicides such as MZ and MB can produce robust ROS generation that likely occurs via redox cycling with extracellular and intracellular oxidases. The findings further show that microglia may contribute to but are not required for ROS production by MZ.

Mitochondrial stress-induced dopamine efflux and neuronal damage by malonate involves the dopamine transporter

Endogenous striatal dopamine (DA) overflow has been associated with neuropathological conditions resulting from ischemia, psychostimulants, and metabolic inhibition. Malonate, a reversible inhibitor of succinate dehydrogenase, models the effects of energy impairment in neurodegenerative disorders. We have previously reported that the striatal DA efflux and damage to DA nerve terminals resulting from intrastriatal malonate infusions is prevented by prior DA depletion, suggesting that DA plays a role in the neuronal damage. We presently report that the malonate-induced DA efflux is partially mediated by reverse transport of DA from the cytosol to the extracellular space via the DA transporter (DAT). Pharmacological blockade of the DAT with a series of structurally different inhibitors [cocaine, mazindol, 1-(2-(bis(4-fluophenyl methoxy) ethyl)-4-(3-(4-fluorophenyl)-propyl)piperazine) dimethane sulfonate (GBR 13098) and methyl(-)-3beta-(p-fluorophenyl)-1alphaH,5alphaH-tropane-2beta-carboxylate1,5-naphthalene (Win 35,428)] attenuated malonate-induced DA overflow in vivo and protected mice against subsequent damage to DA nerve terminals. Consistent with these findings, the DAT inhibitors prevented malonate-induced damage to DA neurons in mesencephalic cultures and also protected against the loss of GABA neurons in this system. The DAT inhibitors did not modify malonate-induced formation of reactive oxygen species or lactate production, indicating that the DAT inhibitors neither exert antioxidant effects nor interfere with the actions of malonate. Taken together, these findings provide direct evidence that mitochondrial impairment and metabolic stress cause striatal DA efflux via the DAT and suggest that disruptions in DA homeostasis resulting from energy impairment may contribute to the pathogenesis of neurodegenerative diseases.

ATP dependence of the non-specific ion channel in Torpedo synaptic vesicles

Synaptic vesicles of Torpedo electromotor neurons contain a high amount of ATP. The concentration of total ATP is around 120 mM, whereas the free [ATP] is about 5-6 mM. We examined the effect of intravesicular ATP on the non-specific ion channel in Torpedo-fused synaptic vesicles. It was found that this channel is closed when the ATP concentration is above 2 mM, but it is very frequently open at lower ATP concentrations. Unmasking this ion channel at a low ATP concentration may be significant for post-fusion control of transmitter release by the 'kiss and run' mechanism in normal conditions, while during metabolic stress it may underlie dissipation of important gradients across the vesicle membrane.