Sodium Metabisulfite: Effects on Ionic Currents and Excitotoxicity

The study of the mechanism of β-N-methylamino-l-alanine (BMAA) neurotoxicity originally focused on its effects at the N-methyl-d-aspartate (NMDA) receptor. In recent years, it has become clear that its mechanism of action is more complicated. First, there are certain cell types, such as motor neurons and cholinergic neurons, where the dominate mechanism of toxicity is through action at AMPA receptors. Second, even in cortical neurons where the primary mechanism of toxicity appears to be activation of NMDA receptors, there are other mechanisms involved. We found that along with NMDA receptors, activation of mGLuR5 receptors and effects on the cystine/glutamate antiporter (system x_c-) were involved in the toxicity. The effects on system x_c- are of particular interest. System x_c- mediates the transport of cystine into the cell in exchange for releasing glutamate into the extracellular fluid. By releasing glutamate, system x_c- can potentially cause excitotoxicity. However, through providing cystine to the cell, it regulates the levels of cellular glutathione (GSH), the main endogenous intracellular antioxidant, and in this way may protect cells against oxidative stress. We have previously published that BMAA inhibits cystine uptake leading to GSH depletion and had indirect evidence that BMAA is transported into the cells by system x_c-. We now present direct evidence that BMAA is transported into both astrocytes and neurons through system x_c-. The fact that BMAA is transported by system x_c- also provides a mechanism for BMAA to enter brain cells potentially leading to misincorporation into proteins and protein misfolding.     

Alteration of Sodium Currents by New Peptide Toxins From the Venom of a Molluscivorous Conus Snail

TxIA and TxIB, peptides with 27-amino acid residues recently isolated from the molluscivorous marine snail Conus textile neovicarius , exhibit strong paralytic activity in molluscs, with no paralytic effects on arthropods and vertebrates. At concentrations of 0.25 – 0.5 μM the toxins cause spontaneous repetitive firing and dramatic broadening of the action potential of cultured Aplysia neurons. The action potential duration partially recovers within 30 min in the presence of the toxins. Under these conditions a second toxin application does not change the spike duration. TxI-induced spike broadening occurs when potassium and calcium conductances are blocked. Voltage-clamp experiments revealed that the toxins alter the kinetics of the sodium current either by slowing down the rate of sodium current inactivation or by recruiting silent sodium channels with slower activation and inactivation kinetics. The toxins shift the voltage-dependent steady-state Na⁺ current inactivation curve to more positive values by 6 mV. These changes are not associated with alteration in the rate of sodium current activation, in the peak sodium current, or the sodium current reversal potential. TxI apparently represents a new class of conotoxins with an unusual phylogenic specificity and may therefore be useful as a probe for the study of molluscan neuronal sodium channels.     

Activation of Tetrodotoxin-Resistant Sodium Channel NaV1.9 in Rat Primary Sensory Neurons Contributes to Melittin-Induced Pain Behavior

Tetrodotoxin-resistant (TTX-R) sodium channels Na_V1.8 and Na_V1.9 in dorsal root ganglion (DRG) neurons play important roles in pathological pain. We recently reported that melittin, the major toxin of whole bee venom, induced action potential firings in DRG neurons even in the presence of a high concentration (500 nM) of TTX, indicating the contribution of TTX-R sodium channels. This hypothesis is fully investigated in the present study. After subcutaneous injection of melittin, Na_V1.8 and Na_V1.9 significantly upregulate mRNA and protein expressions, and related sodium currents also increase. Double immunohistochemical results show that Na_V1.8-positive neurons are mainly medium- and small-sized, whereas Na_V1.9-positive ones are only small-sized. Antisense oligodeoxynucleotides (AS ODNs) targeting Na_V1.8 and Na_V1.9 are used to evaluate functional significance of the increased expressions of TTX-R sodium channels. Behavioral tests demonstrate that AS ODN targeting Na_V1.9, but not Na_V1.8, reverses melittin-induced heat hypersensitivity. Neither Na_V1.8 AS ODN nor Na_V1.9 AS ODN affects melittin-induced mechanical hypersensitivity. These results provide previously unknown evidence that upregulation of Na_V1.9, but not Na_V1.8, in small-sized DRG neurons contributes to melittin-induced heat hypersensitivity. Furthermore, melittin-induced biological effect indicates a potential strategy to study properties of TTX-R sodium channels.     

Sodium and Calcium Currents in Glial Cells of the Mouse Corpus Callosum Slice

We studied Na⁺ and Ca²⁺ currents in glial cells during the development of the corpus callosum in situ. Glioblasts and oligodendrocytes from frontal brain slices of postnatal day (P) 3 to P18 mice were identified based on morphological and ultrastructural features after characterization of the currents with the patch-clamp technique. Slices from P3-P8 mice contained predominantly glioblasts with immature morphological features. These cells showed Na⁺ and Ca²⁺ currents, but the population with these currents decreased between P3 and P8. Na⁺ currents were blocked in Na⁺-free bathing solution and in the presence of tetrodotoxin, Ca²⁺ currents were only observed when a high concentration of extracellular Ba²⁺ was present. The cells from the corpus callosum of P10 – P18 mice predominantly had morphological features of oligodendrocytes. In these cells, which in some cases were shown to form myelin, neither Na⁺ nor Ca²⁺ currents were detected. To compare these in situ results with those from the electrophysiologically and immunocytochemically well-characterized cultured glial cells, we determined the expression pattern of stage-specific antigens in the corpus callosum in situ. The first O4 antigen-positive glial precursors were observed at P1, the earliest stage examined. The oligodendrocytic antigens O7 and O10 appeared at P6 and P14, respectively, and prominent labelling with the corresponding markers was seen at P12 and P18, respectively. Despite the existence of numerous mature, O10-positive oligodendrocytes at P18, which expressed Ca²⁺ channels in vitro , we failed to detect Ca²⁺ currents in situ at this stage.     

Effect of Sodium Salicylate on Calcium Currents and Exocytosis in Cochlear Inner Hair Cells:Implications for Tinnitus Generation

Sodium salicylate is an anti-inflammatory med-ication with a side-effect of tinnitus.Here,we used mouse cochlear cultures to explore the effects of salicylate t...     

Effects of Clobazam and Its Active Metabolite on GABA-Activated Currents in Rat Cerebral Neurons in Culture

Summary: Purpose: The antiepileptic effects of clobazam, a 1,5-benzodiazepine, have been well documented in animal experiments and clinical trials. However, the drug's mechanisms of antiepileptic actions are still undetermined. The purpose of this study was to learn how clobazam and its active metabolite modulate γ-aminobutyric acid (GABA)-activated currents in rat cerebral neurons in culture. Methods: Whole-cell voltage-clamp recordings were performed on cultured cerebral neurons of the rat. Clobazam or its metabolite N-desmethylclobazam was dissolved in the extracellular solution and applied for 2 s by pressure ejection from a micropipette. To maintain GABA-activated currents, 2 mM Mg adenosine triphosphate (ATP) was added to the intracellular solution. Results: GABA elicited outward currents that were mediated by GABA_A receptor-coupled Cl^- channels. Applying clobazam with 10 μM GABA elicited enhanced outward currents. Flumazenil, an antagonist of the benzodiazepine receptor, inhibited the enhancing effect of clobazam. The enhancement ratio increased as much as 2.28-fold in a dose-dependent manner at a concentration of 3 μM clobazam. However, it started to decrease at a concentration of 10 μM clobazam. The metabolite N-desmethylclobazam was tested in the same manner, and exhibited an identical dose-dependent enhancement of GABA-activated currents. Conclusions: The antiepileptic effects of the 1,5- benzodiazepines are attributed to the enhancement of GABAergic inhibitory neurotransmission. The antiepileptic effects of clobazam are thought to depend mainly on its active metabolite N-desmethylclobazam, which is present in high concentrations in patients who receive long-term clobazam. Clobazam's enhancement of GABAactivated currents was most marked on weaker GABA currents. We therefore infer that clobazam acts more efficiently on tissues in which the release of GABA is diminished.     

Developmental effects of Tityus serrulatus scorpion venom on the rat offspring

Scorpion envenomation is a public health problem. Extensive research has been conducted to describe the systemic effects of scorpion venoms and their toxins, however, few reports are available about their effects on pre- and post-natal periods. Whole venom of the Tityus serrulatus scorpion was administered to rats on the 10th and 16th days of pregnancy to determine the effect on physical, reflexive and behavioral development of offspring. Thirty female Wistar rats were mated and distributed into three groups with one control group (C) and two experimental groups that were injected with venom (1 mg/kg) on the 10th (GD10) or the 16th day (GD16) of pregnancy. After birth, the litter was standardized (eight pups for dam) and the rat pups were submitted to physical and behavioral analysis. A greater weight gain was observed on the 20th day of life (PN20) in the female and male pups of the two experimental groups compared to controls. In the GD16 group, a delay in ear opening and acceleration in ear unfolding were observed. In relation to reflexive development, an increased time for palmar grasp reflex was observed on PN8 in GD16. For this group, there was a decrease in the time of righting reflex on PN4 and PN6, and of negative geotaxis on PN6, PN8 and PN10. In conclusion, scorpion venom administered to pregnant rats on specific gestational days and at a dose that simulates a small accident, results in alterations in some reflex and physical parameters in their offspring.     

全蝎醇提物对氯化锂-毛果芸香碱诱导癫痫持续状态模型大鼠海马神经细胞caspase-3表达的影响

目的：探讨全蝎醇提物（EES）对氯化锂-毛果芸香碱诱导癫痫持续状态模型鼠的疗效及对癫痫持续状态后海马神经细胞caspase-3表达的影响。方法：156只成年雄性大鼠除6只设为正常对照组外,其余均建立氯化锂-毛果芸香碱癫痫持续状态大鼠模型,造模成功后随机分为模型组、丙戊酸钠干预组和EES低（EESL组）、中（EESM组）、高（EESH组）剂量干预组（均n=30）,观察各组大鼠癫痫持续状态发作情况,用免疫组化方法观察各组大鼠癫痫持续状态后6、24、48、72h和7d各时点海马神经细胞caspase-3表达的变化。结果：癫痫持续状态模型鼠的造模成功率为95．2％。经EESM、EESH和丙戊酸钠冶疗后,大鼠发作癫痫持续状态级别及持续时间较模型组显著改善（P〈0．01）。各观察时点CA1区和CA3区caspase-3阳性细胞数较模型组显著减少（P〈0．05）,其中以EESH和丙戊酸钠疗效最好（两者疗效相当,P〉0．05）;EESL疗效不明显,与模型组比差异无统计学意义（P〉0．05）。结论：一定剂量的EES能显著对抗癫痫持续状态发作,疗效与caspase-3细胞的减少相对应,说明EES具有抗凋亡作用。对caspase-3表达的抑制可能是其发挥抗凋亡作用的机制之一。     

Sodium Valproate and Valpromide: Differential Interactions with Carbamazepine in Epileptic Patients

To evaluate the comparative effects of valproic acid (VPA) and valpromide (VPM) on plasma levels and protein binding of carbamazepine (CBZ) and CBZ-10,11-epoxide (CBZ-E), 12 adult epileptic patients stabilized on CBZ monotherapy were divided into two groups. One group (n = 6) received sodium valproate (1,100 mg/day) for 2 weeks, while the other group (n = 6) was given, for the same period, a dosage of VPM (1,200 mg/day) expected to produce VPA levels equivalent to those achieved with valproate. Plasma CBZ levels were not affected by either treatment. In the valproate-treated group, plasma CBZ-E levels increased by 101% (range, 29-238%) within 1 week of combined therapy (p less than 0.02) and returned to baseline values after VPA treatment was stopped. In the VPM-treated patients, the elevation of plasma CBZ-E levels was much greater. In this group, plasma CBZ-E increased by 330% (range, 110-864%), and this was associated in two patients with the appearance of adverse effects which subsided after reducing the VPM dosage. The plasma protein binding of CBZ and CBZ-E was not affected significantly by VPM or valproate therapy. Plasma VPA levels were similar in the two groups. It is concluded that VPM is not simply a prodrug of VPA. Although both VPA and VPM increase CBZ-E levels--probably by inhibiting the enzyme epoxide hydrolase--the interaction caused by VPM is of much greater magnitude and potential clinical significance.     

Differential Effects of Endogenous and Exogenous Attention on Sensory Tuning

Covert spatial attention (without concurrent eye movements) improves performance in many visual tasks (e.g., orientation discrimination and visual search). However, both covert attention systems—endogenous (voluntary) and exogenous (involuntary)—exhibit differential effects on performance in tasks mediated by spatial and temporal resolution suggesting an underlying mechanistic difference. We investigated whether these differences manifest in sensory tuning by assessing whether and how endogenous and exogenous attention differentially alter the representation of two basic visual dimensions—orientation and spatial frequency (SF). The same human observers detected a grating embedded in noise in two separate experiments (with endogenous or exogenous attention cues). Reverse correlation was used to infer the underlying neural representation from behavioral responses, and we linked our results to established neural computations via a normalization model of attention. Both endogenous and exogenous attention similarly improved performance at the attended location by enhancing the gain of all orientations without changing tuning width. In the SF dimension, endogenous attention enhanced the gain of SFs above and below the target SF, whereas exogenous attention only enhanced those above. Additionally, exogenous attention shifted peak sensitivity to SFs above the target SF, whereas endogenous attention did not. Both covert attention systems modulated sensory tuning via the same computation (gain changes). However, there were differences in the strength of the gain. Compared with endogenous attention, exogenous attention had a stronger orientation gain enhancement but a weaker overall SF gain enhancement. These differences in sensory tuning may underlie differential effects of endogenous and exogenous attention on performance.SIGNIFICANCE STATEMENT Covert spatial attention is a fundamental aspect of cognition and perception that allows us to selectively process and prioritize incoming visual information at a given location. There are two types: endogenous (voluntary) and exogenous (involuntary). Both typically improve visual perception, but there are instances where endogenous improves perception but exogenous hinders perception. Whether and how such differences extend to sensory representations is unknown. Here we show that both endogenous and exogenous attention mediate perception via the same neural computation—gain changes—but the strength of the orientation gain and the range of enhanced spatial frequencies depends on the type of attention being deployed. These findings reveal that both attention systems differentially reshape the tuning of features coded in striate cortex.     

长期应用托吡酯、丙戊酸钠对于血脂水平的影响

目的 观察长期应用托吡酯、丙戊酸钠单药治疗对癫痫患者血脂水平的影响。 方法 连续入组长期单药应用丙戊酸钠控制良好的癫痫患者28例、单药应用托吡酯控制良好的癫痫患者30例,并选取健康对照60例,观察各组间血脂代谢指标的差异。 结果 丙戊酸钠组血清脂蛋白（a）水平显著高于托吡酯组（P<0.001）及健康对照组（P=0.003）,而总胆固醇、低密度脂蛋白胆固醇、高密度脂蛋白胆固醇、甘油三酯水平较其他两组无明显差异。托吡酯组的总胆固醇、低密度脂蛋白胆固醇、高密度脂蛋白胆固醇、脂蛋白（a）、甘油三酯水平较对照组均未有显著差异。 结论 长期单药应用丙戊酸钠有可能增加癫痫患者脂蛋白（a）的水平,而长期单药应用托吡酯对于血脂水平影响并不明显。     

Differential Effects of Phenobarbital and Pentobarbital on Isolated Nervous Tissue

Epileptiform after discharges evoked by repetitive electrical stimulation of chronically isolated cortical slabs (cat) were shortened by low doses of phenobarbital but not affected by hypnotic doses of pentobarbital. Both pentobarbital and phenobarbital raised threshold and lowered spike amplitude in isolated sciatic nerves. The action of both drugs was increased by reducing Na in the medium and by decreasing the Ringer's pH. Similar to the action of other general anesthetics, the axonal effect of pentobarbital was enhanced by D2O replacement for H2O in the Ringer's (suggesting that tissue water is involved in pentobarbital action), whereas D2O replacement did not modify the action of phenobarbital or of local anesthetics. These results suggest that the varying in vivo effects of pentobarbital and phenobarbital may be due to a difference in their action upon excitable membranes (rather than to a different regional distribution in brain).     

Differential Effects of Fondaparinux and Bemiparin on Angiogenic and Vasculogenesis-like processes

Introduction

Conventional therapy for venous thromboembolism or acute coronary syndrome involves the administration of glycoanticoagulants (heparins) or oligosaccharides (fondaparinux). We evaluated the effects of such drugs on angiogenesis and vasculogenesis-like models.

Materials and Methods

Human umbilical vein endothelial cells or human endothelial progenitor cells were treated with bemiparin, fondaparinux or unfractionated heparin, at concentrations reflecting the doses used in clinical practice. After 24 h, cell viability, proliferation, tubule formation and angiogenic molecular mechanisms, such as activation of the serine/threonine kinase AKT, were assessed. In vivo angiogenesis was studied using a Matrigel sponge assay in mice.

Results

Bemiparin gave a significant decrease of in vitro angiogenesis as shown by the reduction of endothelial cell tubule network, while both fondaparinux and unfractionated heparin did not show any significant effect. In assays of Matrigel sponge invasion in mice, unfractionated heparin was able to stimulate angiogenesis and, conversely, bemiparin inhibited angiogenesis. Furthermore, both bemiparin and fondaparinux caused a significant reduction in an in vitro vasculogenesis-like model, as demonstrated by the decrease of tubule network after co-seeding of endothelial progenitor cells and human umbilical vein endothelial cells. In addition, unfractionated heparin but not bemiparin was able to increase AKT phosphorylation.

Conclusions

In in vitro experiments, bemiparin was the only drug to show an anti-angiogenic and vasculogenic-like effect, unfractionated heparin showed only a trend to increase in angiogenesis assay and fondaparinux affected only the vasculogenesis-like model. Notably, the in vivo experiments corroborated these data. Such results are important for the choice of a patient-tailored therapy.     

Differential Cognitive Effects of Carbamazepine and Gabapentin

PURPOSE: The cognitive effects of the newer antiepileptic drugs (AEDs) compared with the older standard AEDs are uncertain. METHODS: We directly compared the cognitive effects of carbamazepine (CBZ) and gabapentin (GBP) in 35 healthy subjects by using a double-blind, randomized crossover design with two 5-week treatment periods. During each treatment condition, subjects received either GBP, 2,400 mg/day, or CBZ (mean, 731 mg/day) adjusted to a dose to achieve midrange standard therapeutic blood levels (mean, 8.3 microg/ml). Subjects were tested at the end of each AED treatment period and in four drug-free conditions [two pretreatment baselines and two post-treatment washout periods (1 month after each AED)]. The neuropsychological test battery included 17 measures yielding 31 total variables. RESULTS: Direct comparison of the two AEDs revealed significantly better performance on eight variables for GBP, but none for CBZ. Comparison of CBZ and GBP to the nondrug average revealed significant statistical differences for 15 (48%) of 31 the variables. Pairwise follow-up analyses of the 15 variables revealed significantly better performance for nondrug average on 13 variables compared with CBZ, and on four compared with GBP. GBP was better than nondrug average on one variable. CONCLUSIONS: Although both CBZ and GBP produced some effects, GBP produced significantly fewer untoward cognitive effects compared with CBZ at the dosages used in this study.     

Effects of Acetazolamide on Transient K+ Currents and Action Potentials in Nodose Ganglion Neurons of Adult Rats

The aim of the present study was to determine whether acetazolamide (AZ) contributes to the inhibition of the fast inactivating transient K⁺ current (I_A) in adult rat nodose ganglion (NG) neurons. We have previously shown that pretreatment with either AZ or 4‐AP attenuated or blocked the CO₂‐induced inhibition of slowly adapting pulmonary stretch receptors in in vivo experiments. The patch‐clamp experiments were performed by using the isolated NG neurons. In addition to this, the RT‐PCR of mRNA and the expression of voltage‐gated K⁺ (Kv) 1.4, Kv 4.1, Kv 4.2, and Kv 4.3 channel proteins from nodose ganglia were examined. We used NG neurons sensitive to the 1 mM AZ application. The application of 1 mM AZ inhibited the I_A by approximately 27% and the additional application of 4‐AP (1 mM) further inhibited I_A by 48%. The application of 0.1 μM α‐dendrotoxin (α‐DTX), a slow inactivating transient K⁺ current (I_D) blocker, inhibited the baseline I_A by approximately 27%, and the additional application of 1 mM AZ further decreased the I_A by 51%. In current clamp experiments, AZ application (1 mM) increased the number of action potentials due to the decreased duration of the depolarizing phase of action potentials and/or due to a reduction in the resting membrane potential. Four voltage‐gated K⁺ channel proteins were present, and most (80–90%) of the four Kv channels immunoreactive neurons showed the co‐expression of carbonic anhydrase‐II (CA‐II) immunoreactivity. These results indicate that the application of AZ causes the reduction in I_A via the inhibition of four voltage‐gated K⁺ channel (Kv) proteins without affecting I_D.     

Differential Effects of Unilateral Temporal Lobectomy on Visuospatial Memory and Attention

Abstract

We investigated free recall of visuospatial arrays in a free-field format in epileptic patients following unilateral temporal lobectomy (TL) (left = 15, right = 17). TL patients exhibited leftward deviation in right hemispace, but more variable response in left hemispace, a pattern that has been observed in healthy adults. This finding is postulated to result from combined preferential right cerebral activation and a tendency to err toward peri-personal space. Temporal lobectomy affected overall leftward deviation by initially shifting deviation more toward the side of lesion. The initial directional shift in immediate memory dissipated over time suggesting that these subtle attentional shifts may be compensated by learning. Consistent with differential cerebral hemispheric mechanisms, absolute vertical errors were greater in right than left TL patients, and absolute horizontal errors were worse in right hemispace.     

Differential Long-lasting Potentiation of the NMDA and Non-NMDA Synaptic Currents Induced by Metabotropic and NMDA Receptor Coactivation in Cerebellar Granule Cells

Whole-cell patch-clamp recordings in rat cerebellar slices were used to investigate the effect of metabotropic glutamate receptor activation on mossy fibre-granule cell synaptic transmission. Transient application of 20 μM 1 S , 3 R -1 -aminocyclopentane-1,3-dicarboxylic acid simultaneously with low-frequency NMDA receptor activation induced long-lasting non-decremental potentiation of both NMDA and non-NMDA receptor-mediated synaptic transmission. Potentiation could be prevented by application of the metabotropic glutamate receptor antagonist (+)- O -methyl-4-carboxyphenyl-glycine at 500 μM. Characteristically, NMDA potentiation was two to three times as large as non-NMDA current potentiation, occurred only in a slow subcomponent, and was voltage independent. This result demonstrates a pivotal role of NMDA receptors in the metabotropic potentiation of transmission, which may be important in regulating cerebellar information processing.