Electrochemical response of small organic molecules at nickel–copper alloy electrodes

Voltammetric and chronoamperometric response characteristics are summarized for glucose, cysteine and glycine over the potential range 0.00–0.70 V versus SCE at NiCu alloy electrodes in 0.10 M NaOH. The response observed for all Ni_xCu_100?x electrodes tested (x=10, 25, 50, 75) is concluded to involve a redox-mediated mechanism. It is also observed that the overpotential for O₂ evolution increases as a function of increasing x value in the alloy electrodes. Among the alloys tested, the Ni₁₀Cu₉₀ electrode yields a significantly higher response for glucose and glycine than that observed for Cu and Ni electrodes. However, the response for cysteine at the Ni₁₀Cu₉₀ electrode is similar to that observed at the Cu electrode.     

Crucial role of the 5-HT2C receptor, but not of the 5-HT2A receptor, in the down regulation of stimulated dopamine release produced by pressure exposure in freely moving rats

Helium pressure of more than 2 MPa is a well known factor underlying pressure-dependent central neuroexcitatory disorders, referred to as the high-pressure neurological syndrome. This includes an increase in both serotonin (5-HT) and dopamine (DA) release. The relationship between the increase in 5-HT transmission produced by helium pressure and its effect on DA release has been clarified in a recent study, which have first demonstrated that the helium pressure-induced increase in DA release was dependent on some 5-HT receptor activation. In the present study, we examined in freely moving rats the role of 5-HT_2A and 5-HT_2C receptors in the increase in DA release induced by 8 MPa helium pressure. We used the 5-HT_2A receptor antagonist ketanserin and the 5-HT_2C receptor agonist m-CPP which have been demonstrated to reduce DA function. Because neither ketanserin is an ideal 5-HT_2A receptor antagonist nor m-CPP an ideal 5-HT_2C receptor agonist, additional experiments were made at normal pressure to check up on the selectivity of ketanserin and m-CPP for 5-HT_2A and 5-HT_2C receptors, respectively. Administration of m-CPP reduced both DA basal level and the helium pressure-induced increase in DA release, whereas administration of ketanserin only showed a little effect on the increase in DA release produced by high helium pressure. These results suggest that the 5-HT_2C receptor, but not the 5-HT_2A receptor, would play a crucial role in the helium pressure-induced increase in DA release. This further suggests that helium pressure may simultaneously induce an increase in 5-HT transmission at the level of 5-HT_2A receptors and a decrease in 5-HT transmission at the level of 5-HT_2C receptors.     

A method for in situ auto-renewal of the surface of glassy carbon electrodes

Deposition of electrolytic products and contamination may change the surface condition of a glassy carbon electrode, the working electrode in voltammetric measurements. A method for in situ auto-renewal of the surface was developed to obtain reproducible fresh surfaces. The analytical application of this method was verified by differential pulse voltammetric determination of Fe(II). The determination exhibited a reproducibility significantly better than that with un-renewed electrodes or those renewed manually. The results of the voltammetric determination correlated well with those found by a colorimetric method (r=0.9989). The recovery of Fe(II) added to soil solution ranged from 98% to 104%. The method may find applications in the determination of reducing substances and studies on chemical reaction kinetics in closed systems.     

Wireless transmission of fast-scan cyclic voltammetry at a carbon-fiber microelectrode: proof of principle

Fast-scan cyclic voltammetry (FSCV) at a carbon-fiber microelectrode (CFM) provides exquisite temporal and spatial resolution for monitoring brain chemistry. The utility of this approach has recently been demonstrated by measuring sub-second dopamine changes associated with behavior. However, one drawback is the cable link between animal and recording equipment that restricts behavior and precludes monitoring in complex environments. As a first step towards developing new instrumentation to overcome this technical limitation, the goal of the present study was to establish proof of principle for the wireless transmission of FSCV at a CFM. Proof of principle was evaluated in terms of measurement stability, fidelity, and susceptibility to ambient electrical noise. Bluetooth digital telemetry provided bi-directional communication between remote and home-base units and stable, high-fidelity data transfer comparable to conventional, wired systems when tested using a dummy cell (i.e., a resistor and capacitor in series simulating electrical properties of a CFM), and dopamine measurements with flow injection analysis and in the anesthetized rat with electrical stimulation. The wireless system was also less susceptible to interference from ambient electrical noise. Taken together, the present findings establish proof of principle for the wireless transmission of FSCV at a CFM.     

Voltammetric assessment of dopamine clearance in the absence of the dopamine transporter: no contribution of other transporters in core or shell of nucleus accumbens

Cocaine elevates dopamine (DA) in the nucleus accumbens (NAc) by blocking the uptake of DA through the DA transporter (DAT). It is commonly believed that the reinforcing properties of cocaine depend upon interaction with the DAT, however, cocaine is still reinforcing in mice with a genetic deletion of the DAT (DAT-KO mice). Although cocaine continues being able to elevate DA in the NAc of these mice, this mechanism is unclear. The present voltammetric study in brain slices was designed to examine the role of the norepinephrine and serotonin transporters in removing DA from the extracellular space in the NAc of DAT-KO mice. We found no effects of any monoamine uptake inhibitors, including cocaine (10 μM), desipramine (10 μM) or fluoxetine (10 μM) on the clearance of DA in these mice. Therefore, it appears that there is no compensatory uptake of DA by alternative transporters either in core or shell of the nucleus accumbens of DAT-KO mice.     

In vivo autofluorescence spectrofluorometry of central serotonin

The autofluorescence properties of serotonin (5-HT) were investigated by light spectrofluorometry in in vitro, ex vivo and in vivo experiments. Ex vivo samples were prepared from rat brain regions containing serotonin (5-HT) i.e. cortex, striatum, hippocampus. Rats were untreated (controls) or previously submitted to chronic behavioural or pharmacological treatments known to affect endogenous 5-HT levels. Autofluorescence analysis (excitation: 366 nm) on hippocampus homogenates supplied with exogenous 5-HT revealed spectral alterations attributable to changes of endogenous 5-HT levels. In vivo, real time fluorescence studies were performed via a 50 microm diameter optic fiber probe stereotaxically implanted into selected brain areas of anaesthetised rats treated with fluoxetine or 5-OH-tryptophan. All autofluorescence data were consistent with those obtained in parallel experiments performed with ex vivo or in vivo voltammetry, confirming that auto-fluorescence spectroscopy is a suitable technique for the direct assessment of fluorescent neurotransmitters. This is a reliable evidence of the in vivo application of spectroscopy together with optic fiber probe for in vivo, in situ and real time measurement of 5-HT in discrete brain areas.     

Suppression of acute and chronic opioid withdrawal by a selective soluble guanylyl cyclase inhibitor

Previous studies have shown that activation of N-methyl-D-aspartate (NMDA) receptors and formation of nitric oxide (NO) contributes to the hyperactivity of locus coeruleus (LC) noradrenergic neurons and behavioural symptoms seen during opioid withdrawal. However, the role of soluble guanylyl cyclase (sGC), the 'physiological' target of NO, in this phenomenon is unclear. In this study, the effect of 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a highly selective sGC inhibitor, on the naloxone-precipitated morphine withdrawal was examined using differential normal pulse voltammetry (DNPV) to measure LC activity, in vivo microdialysis to measure glutamate/aspartate release response, and behavioural assessment to evaluate withdrawal symptoms. In halothane-anaesthetized rats, acute intracerebroventricular (i.c.v.) morphine (10 microg) reduced the catecholamine oxidation current (CA.OC) (54.5+/-4.9% of baseline). Naloxone (2 mg/kg, i.v.) reversed this action of morphine and produced a rebound increase in CA.OC (136.1+/-6.0% of baseline), representing acute morphine withdrawal. Administration of ODQ (200 nmol, i.c.v.) blocked this response without affecting acute morphine action. In animals chronically treated with morphine (15 microg/microl/h, i.c.v., 5 days), naloxone significantly increased both the CA.OC signal (270.0+/-19.6% of baseline) and the release of L-glu (193+/-30.4%) and L-asp (221.5+/-28.4%) above baseline. These responses were attenuated in animals pretreated with ODQ. In unanaesthetized chronic morphine dependent rats, ODQ treatment suppressed the signs of withdrawal precipitated by naloxone (10 mg/kg). Taken together, the results of this study suggest that sGC plays an intermediary role in the genesis of LC neuronal hyperactivity and behavioural signs of morphine withdrawal.     

A microcomputer controlled system for monitoring multiple voltammetric electrodes in vivo

An inexpensive multielectrode voltammetry system designed for in vivo neurochemical studies of the awake, unanesthetized primate has been developed. Consisting of an Apple II Plus microcomputer, parallel operational amplifier circuitry for six working electrodes, and commercially available interface boards, the system has the flexibility to implement many standard voltammetric procedures under total software control. Multielectrode monitoring is accomplished essentially simultaneously, and all channels are equipped with independent gain controls allowing for rapid amplification adjustment. An interactive chronoamperometry program, capable of making rapid 12 bit analog to digital conversions for each working electrode over four software selectable ranges, is described and system performance is evaluated.     

MCF-7细胞原位电化学检测方法研究

目的：电化学法检测原位收集获得的MCF-7细胞电化学信号,建立操作简单,快速、敏感、价廉、细胞用量少的原位细胞电化学检测方法.方法：采用循环伏安法研究原位细胞收集法对电化学信号的影响.结果：采用电化学法检测原位收集获得的MCF-7细胞质,其电化学信号高于传统收集的细胞质电化学信号.结论：原位细胞收集缩短了检测前细胞处理的准备过程,提高了细胞电化学响应强度.     

羟喜树碱在玻碳电极上的直接电化学行为研究

目的 建立直接电化学检测羟喜树碱含量的方法.方法 本文采用伏安法研究羟喜树碱在玻碳电极上的直接电化学行为.在磷酸盐缓冲液中(pH5.0),在-0.2～ 0.4 V范围内羟喜树碱在玻碳电极表面是受吸附控制,发生准可逆两电子转移电极反应过程,电子转移系数α=0.479;并以差示脉冲伏安法建立了检测羟喜树碱含量的新方法.结果 在富集电位 0.8 V,富集时间 30s,利用差示脉冲伏安法可测得其氧化峰电流Ip与浓度分别在2.0×10-7～5.0×10-6mol·L-1内呈良好的线性关系,最低检出限为5.0×10-8mol·L-1.结论 本法操作简单、快速、灵敏、准确,可为羟喜树碱药物质量的控制和检测提供了一种简便的方法.