New dual electrochemical detector for microbore liquid chromatography. Determination of dopamine and serotonin in rat striatum dialysates

Tremella-like graphene–Au composites used for amperometric determination of dopamine

Tremella-like graphene–Au composites were synthesized by a one-step hydrothermal method for selective detection of DA.

Caffeine and a selective adenosine A2A receptor antagonist induce sensitization and cross-sensitization behavior associated with increased striatal dopamine in mice

Background

Caffeine, a nonselective adenosine A₁ and A_2A receptor antagonist, is the most widely used psychoactive substance in the world. Evidence demonstrates that caffeine and selective adenosine A_2A antagonists interact with the neuronal systems involved in drug reinforcement, locomotor sensitization, and therapeutic effect in Parkinson's disease (PD). Evidence also indicates that low doses of caffeine and a selective adenosine A_2A antagonist SCH58261 elicit locomotor stimulation whereas high doses of these drugs exert locomotor inhibition. Since these behavioral and therapeutic effects are mediated by the mesolimbic and nigrostriatal dopaminergic pathways which project to the striatum, we hypothesize that low doses of caffeine and SCH58261 may modulate the functions of dopaminergic neurons in the striatum.

Methods

In this study, we evaluated the neuroadaptations in the striatum by using reverse-phase high performance liquid chromatography (HPLC) to quantitate the concentrations of striatal dopamine and its metabolites, dihydroxylphenylacetic acid (DOPAC) and homovanilic acid (HVA), and using immunoblotting to measure the level of phosphorylation of tyrosine hydroxylase (TH) at Ser31, following chronic caffeine and SCH58261 sensitization in mice. Moreover, to validate further that the behavior sensitization of caffeine is through antagonism at the adenosine A_2A receptor, we also evaluate whether chronic pretreatment with a selective adenosine A_2A antagonist SCH58261 or a selective adenosine A₁ antagonist DPCPX can sensitize the locomotor stimulating effects of caffeine.

Results

Chronic treatments with low dose caffeine (10 mg/kg) or SCH58261 (2 mg/kg) increased the concentrations of dopamine, DOPAC and HVA, concomitant with increased TH phosphorylation at Ser31 and consequently enhanced TH activity in the striatal tissues in both caffeine- and SCH58261-sensitized mice. In addition, chronic caffeine or SCH58261 administration induced locomotor sensitization, and locomotor cross-sensitization to caffeine was observed following chronic treatment of mice with SCH58261 but not with DPCPX.

Conclusions

Our study demonstrated that low dosages of caffeine and a selective adenosine A_2A antagonist SCH58261 elicited locomotor sensitization and cross-sensitization, which were associated with elevated dopamine concentration and TH phosphorylation at Ser31 in the striatum. Blockade of adenosine A_2A receptor may play an important role in the striatal neuroadaptations observed in the caffeine-sensitized and SCH58261-sensitized mice.

Carbon Fiber/Epoxy Composite Ring-disk Electrode: Fabrication, Characterization and Application to Electrochemical Detection in Capillary High Performance Liquid Chromatography

Carbon fiber/epoxy composite materials, which are manufactured using the pultrusion process, are commercially available in various shapes and sizes at very low cost. Here we demonstrate the application of such a material as an electrochemical detector in a flow system. Cyclic voltammetry shows that the material's electrochemical behavior resembles that of glassy carbon. Using tube and rod composites, we successfully fabricated a ring-disk electrode with a 20 μm gap between the ring and the disk. The narrow gap is favorable for mass transfer in the generator-collector experiment. This composite ring-disk electrode is assembled in a thin-layer radial-flow cell and used as an electrochemical detector. The disk electrode, placed directly opposite to the flow inlet, is operated as a generator electrode with the ring electrode being a collector. The high collection efficiency on the ring electrode (0.8 for a chemically reversible species) enhances the detection selectivity.

Evaluation of anti-Fas ligand-induced apoptosis and neural differentiation of PC12 cells treated with nerve growth factor using small interfering RNA method and sampling by microdialysis

The small interfering RNA (siRNA) method is an effective technique for silencing gene expression and is a useful tool for screening the gene functions in drug discovery. Our study found that nerve growth factor (NGF) can increase the cell viability of PC12 cells and that NGF induction up-regulates the expression of Bcl-2 detected by real-time reverse transcription-polymerase chain reaction (RT-PCR). To further investigate the role of Bcl-2 expression in NGF-treated PC12 cells, the plasmid of Bcl-2 siRNA was then transfected into PC12 cells. Moreover, to investigate and continuously monitor the real-time dynamic neurotransmitter release, and to compare with the time course of Bcl-2 expression, a liquid chromatography coupled with electrochemical detection (LC-ED) and with a microdialysis device was used. After 6h of NGF being added to the PC12 cell culture medium, the dopamine (DA) concentrations were significantly increased (P<0.05). This result is simultaneously compatible with the up-regulated messenger RNA (mRNA) expressions of tyrosine hydroxylase (TH), aromatic acid decarboxylase (AADC), and Bcl-2 by RT-PCR. Using the Bcl-2 siRNA method, our data revealed that NGF can inhibit Fas ligand (FasL)-induced apoptosis in PC12 cells through the activation of Bcl-2. The in vitro observation further demonstrated that NGF can stimulate the neurite development in PC12 cells through the activation of Bcl-2. Moreover, the DA concentrations of NGF induction were decreased specifically by Bcl-2 siRNA (P<0.05). In sum, our data support that NGF prevents Fas-induced apoptosis, facilitates neural differentiation, promotes dendritic formation, and increases DA release in PC12 cells through activation of Bcl-2.

Derivatization chemistries for determination of serotonin, norepinephrine and dopamine in brain microdialysis samples by liquid chromatography with fluorescence detection

The present paper provides an overview on currently developed derivatization chemistries and techniques for determination of monoamine neurotransmitters serotonin (5-HT), norepinephrine (NE) and dopamine (DA) in microdialysis samples by microbore liquid chromatography with fluorescence detection. In mild alkaline conditions, 5-hydroxyindoles and catecholamines react with benzylamine (BA), forming highly fluorescent 2-phenyl-4,5-pyrrolobenzoxazoles and 2-phenyl(4,5-dihydropyrrolo) [2,3-f]benzoxazoles, respectively. However, for derivatization of DA a higher fluorescence intensity was achieved for reaction with 1,2-diphenylethylenediamine (DPE) rather than with BA, therefore for simultaneous determination of 5-HT, NE and DA in brain microdialysates, a two-step derivatization with BA followed by DPE was developed. The detection limits for 5-HT, NE and DA were 0.2, 0.08 and 0.13 fmol, respectively, in an injection volume of 20 microL, which corresponds to concentrations of 30, 12 and 19.5 pm, respectively in standard solution prior to derivatization. The experimental data presented demonstrate the ability of the technique to simultaneously monitor neuronally releasable pools of monoamine neurotransmitters in the rat and mouse brains at basal conditions and following pharmacological treatments or physiological stimuli. These techniques play an important role in drug discovery and clinical investigation of psychiatric and neurological diseases such as depression, schizophrenia and Parkinson's disease.

High-sensitive liquid chromatographic method for determination of neuronal release of serotonin, noradrenaline and dopamine monitored by microdialysis in the rat prefrontal cortex

A high-sensitive liquid chromatographic method based on precolumn derivatization and fluorescence detection allowing simultaneous determination of serotonin (5-HT), noradrenaline (NA) and dopamine (DA) in brain microdialysis samples is described. 5-HT, NA and DA were derivatized with benzylamine and 1,2-diphenylethylenediamine in the presence of potassium hexacyanoferrate(III) and glycine, which yielded to highly fluorescent and stable benzoxazoles. The derivatized samples were separated on a microbore column (150 mm x 1.0mm i.d., packed with C18 silica, 5 microm) within 60 min. The mobile phase consisted of acetonitrile-Briton-Robinson buffer (pH 7.2) (32:68, v/v) containing 5 mM Na2EDTA and 5 mM octanesulfonic acid sodium salt. The detection limits (signal-to-noise ratio of 3) for 5-HT, NA and DA were 76, 42 and 95 amol/10 microl injected on-column, respectively. Microdialysis samples were collected at 10-min intervals from the probes implanted in the prefrontal cortex of awake rats. The basal levels of 5-HT, NA and DA were 7.3 +/- 0.7, 5.3 +/- 0.31 and 8.1 +/- 0.47 fmol/5 microl (mean +/- S.E.M., n = 5). Following 90-min perfusion with tetrodotoxin (1 microM) or calcium-free Ringer solution, the DA and NA levels were reduced to about 15 and 20%, respectively and the 5-HT levels to 45 and 60% of the basal levels, respectively. Reserpine, 12h after a dose of 5mg/kg i.p., reduced the extracellular 5-HT, NA and DA concentrations to about 34, 39 and 32% of the basal levels, respectively. In conclusion, the preset microdialysis/analytical method enables simultaneous monitoring of basal and pharmacologically reduced neuronal release of 5-HT, NA and DA in the rat brain.

Simultaneous determination of norepinephrine, serotonin, and 5-hydroxyindole-3-acetic acid in microdialysis samples from rat brain by microbore column liquid chromatography with fluorescence detection following derivatization with benzylamine

A microbore column liquid chromatographic method for the simultaneous determination of norepinephrine (NE), serotonin (5-HT), and 5-hydroxyindole-3-acetic acid (5HIAA) in microdialysis samples from rat brain is described. The method is based on precolumn derivatization of NE, 5HT, and 5HIAA with benzylamine in the presence of potassium hexacyanoferrate(III) resulting in the corresponding highly fluorescent and stable benzoxazole derivatives. A 15-microl sample was mixed with 15 microl derivatization reagent solution containing 0.3M 3-cyclohexylaminopropanesulfonic acid buffer (pH 12.0), 0.5M benzylamine, 10mM potassium hexacyanoferrate(III), and methanol (1/1/1/12, v/v/v/v). The derivatization was carried out at 50 degrees C for 20 min. The benzylamine derivatives of NE, 5HT, and 5HIAA were separated on a reversed-phase column (100 x 1.0mm i.d., packed with C18 silica, 5 microm) within 30 min. The mobile phase consisted of 15 mM acetate buffer (pH 5.0) and acetonitrile (31%, v/v); the flow rate was 50 microl/min. The detection limits (signal-to-noise ratio of 3) for NE, 5HT, and 5HIAA in the injection volume of 20 microl were 90, 210, and 260 amol, respectively. Microdialysis samples were collected in 7.5-min intervals from the probes implanted in the hippocampus and prefrontal cortex of awake rats. The basal levels of NE, 5HT, and 5HIAA in the dialysates from the hippocampus were 4.2+/-0.5, 4.9+/-0.6, and 934.1 +/- 63.4 fmol/20 microl, and those from the prefrontal cortex were 6.0+/-1.2,5.51.3, and 669.1 +/- 96.0 fmol/20 microl (mean +/- SE, n=25), respectively. The NE and 5HT levels were altered by perfusion of high-potassium or low-calcium solution and following antidepressant drugs imipramine and desipramine. It is concluded that the new fluorescence derivatization method in combination with microbore column liquid chromatography allows the simultaneous determination of NE, 5HT, and 5HIAA in the microdialysis samples at higher sensitivity, providing easier maintenance in routine use than that achieved by high-performance liquid chromatographic methods with electrochemical detection.

Differential alteration of catecholamine release during chemical hypoxia is correlated with cell toxicity and is blocked by protein kinase C inhibitors in PC12 cells

Release of neurotransmitters, including dopamine and glutamate, has been implicated in hypoxia/ischemia-induced alterations in neuronal function and in subsequent tissue damage. Although extensive studies have been done on the mechanism underlying the changes in glutamate release, few have examined the mechanism that is responsible for the changes in catecholamines. Rat pheochromocytoma-12 (PC12) cells synthesize, store, and release catecholamines including DA and NE. Therefore, we used HPLC and ED to evaluate extracellular DA and NE concentrations in a medium during chemical hypoxia in PC12 cells. Chemical hypoxia produced by KCN induced differential release of DA and NE. Under normal glucose conditions, KCN induced release of NE, but not DA. Under glucose-free conditions, KCN-induced release of DA was elevated transiently, whereas the release of NE increased progressively. Under parallel conditions, KCN biphasically elevated the level of cytosolic free calcium ([CA(2+)](i)) in glucose-free DMEM, peaking at 95 +/- 18 nM at 1,107 +/- 151 s, followed by a new plateau level at 249 +/- 24 nM sustained from 4,243 +/- 466 to 5,263 +/- 440 s. Cell toxicity, as measured by LDH release, was increased significantly by KCN in glucose-free DMEM but was diminished in the presence of glucose, and was correlated with DA release by chemical hypoxia. The protein kinase C (PKC) inhibitor GO6976 or staurosporine inhibited KCN-induced LDH release as well as the release of NE and DA. Taken together, selective activation of DA but not NE was correlated with the LDH release by chemical hypoxia, and was diminished with GO6976 or staurosporine. These results suggest that selective activation of PKC isoforms is involved in the chemical hypoxia-induced DA release, which may lead to neuronal cell toxicity.

A dual-probe microdialysis study in simultaneously monitoring extracellular pyruvate, lactate, and biogenic amines in gerbil striata during unilateral cerebral ischemia

A dual-probe microdialysis technique coupled with liquid chromatographic assays was developed for the simultaneous monitoring of neurochemicals in gerbil striata during cerebral ischemia. Isocratic separation of lactate and pyruvate was achieved within 5 min whereas the separation of biogenic amines was completed within 30 min. An unilateral ligation was produced by occlusion of the right common carotid artery for 30 mins in anesthetized gerbils to perform a typical focal cerebral ischemia. Microdialysis probes were inserted in both sides of the striata to simultaneously monitor biogenic amines, lactate and pyruvate during cerebral ischemia. Dynamic and comparative changes of these analytes in ipsilateral and contralateral sides of the brain can be simultaneously measured by the assay. The present assay can be used as a research tool to explore neurochemical substances and their relationships during cerebral ischemia.

Determination of catecholamines in pheochromocytoma cell (PC-12) culture medium by microdialysis-microbore liquid chromatography

An in vitro microdialysis system was constructed for the measurement of catecholamines in pheochromocytoma cell culture medium. The novel microdialysis device is composed of a petri dish, a dialysis membrane and two transmission tubes. The dialysis membrane is located in the space of a petri dish such that it is immersed in the culture medium. Catecholamines contained in the culture medium diffused into a designed dialysis membrane with sufficient recovery (about 60%). Dialysates were collected by a sampling loop and introduced by an on-line injector to a microbore liquid chromatographic system for analysis of catecholamines. This assay yielded a detection limit of 0.2-0.5 pg/injection with acceptable intra- and inter-assay reproducibilities in 5 microl of dialysates. To evaluate the on-line microdialysis system, PC-12 cells were cultured in a petri dish within an incubator. The baseline concentration of dopamine in PC-12 cell culture medium was about 0.29 ng/ml which was elevated to 2.43 ng/ml after treatment with 0.5 mM potassium cyanide. In conclusion, the present microassay provides for the sensitive, direct measurement of catecholamines in culture medium while minimizing pretreatment procedures for sample preparation.

Simultaneous measurement of dopamine, serotonin, their metabolites and tryptophan in mouse brain homogenates by high-performance liquid chromatography with dual coulometric detection

A new rapid and sensitive high-performance liquid chromatography (HPLC) method for the simultaneous determination of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine, 5-hydroxytryptamine (serotonin), 5-hydroxyindoleacetic acid (5-HIAA), homovanillic acid and tryptophan has been developed and applied to mouse frontal cortex, caudate nucleus and dorsal raphe assays. A dual coulometric detector was used with detection at +0.25 and +0.55 V, which allowed the determination of tryptophan. Detection limits for all compounds (0.8-9.0 pg per injection, depending on the compounds) were useful for this application. Owing to great sensitivity of the method, the brain tissue samples can be very small, less than 2 mg. Linearity of standards was excellent (r > 0.999 in all cases). Intraday and interday precisions for samples analytes were generally acceptable (intraday assay CV < 8.7% and interday assay CV < 7.0% except for DOPAC and 5-HIAA, which was 11.4% for the low concentrations). Average recoveries of standard additions to sample analytes were > 90%. Attention was paid to stability of standard and sample analytes when stored at +4 degrees C or at -70 degrees C with two different homogenizing agents (0.1 M HClO4 with 10(-7) M ascorbic acid and 0.05 M HClO4 without ascorbic acid). This simple, rapid and efficient method can be used as a basic research tool for modification of brain neurotransmitters in experimental pharmacological protocols for following psychotropic drug treatments in animals.

In vivo on-line HPLC-microdialysis: simultaneous detection of monoamines and their metabolites in awake freely-moving rats

An on-line microbore high performance liquid chromatographic--electrochemical (HPLC--EC) detection method has been developed for the simultaneous measurement of dopamine (3,4-dihydroxyphenethylamine, DA), its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (3-methoxy-4-hydroxyphenylacetic acid, HVA), as well as serotonin (5-hydroxytryptamine, 5-HT) and its metabolise 5-hydroxyindole-3-acetic acid (5-HIAA) in the striatum of awake and freely moving rats. Our method was capable of detecting DOPAC, 5-HIAA, HVA, DA and 5-HT at retention time of 3, 5, 6.5, 9, and 24 min, respectively, in repeated on-line microdialysis sampling. Analysis was performed using a 150 x 1 mm 5 microm C18 microbore column attached directly to a thin-layer radial flow electrochemical cell (UniJet) comprising a 6 mm glassy carbon working electrode. In order to accommodate signal outputs (due to a varying level in the neurochemicals under investigation), an amperometric detector was equipped with a sensitivity programmable controlling software for automatically switching sensitivity inattentively and repeatedly for each collection cycle.

Pharmacokinetic and pharmacodynamic analyses of trazodone in rat striatum by in vivo microdialysis

The aim of this study was to investigate the brain pharmacokinetics and pharmacodynamics of trazodone. Sensitive microbore high-performance liquid chromatographic methods with electrochemical detection (LC-ED) were developed for the determination of trazodone, serotonin (5-HT), and their respective metabolites. The feasibility of microdialysis coupled with LC-ED system for direct analysis of these compounds in the rat striatum was investigated. Striatal dialysates were automatically injected onto a cyano microbore column, through an on-line injector, for the determination of trazodone and its metabolite or onto a reversed phase microbore column for the determination of 5-HT and its metabolite. A monophase phenomenon with a first-order elimination rate constant was observed for trazodone. The brain pharmacokinetics of trazodone appear to conform to a one-compartment model. Surprisingly, no significant changes in striatal 5-HT or its metabolite were observed following the same dosage and time course. The present results suggest that brain microdialysis methods may be applicable to pharmacokinetic and pharmacodynamic studies of psychotrophic agents.