Determination of serotonin, noradrenaline, dopamine and their metabolites in rat brain extracts and microdialysis samples by column liquid chromatography with fluorescence detection following derivatization with benzylamine and 1,2-diphenylethylenediamine

Sulfation modification of dopamine in brain regulates aggregative behavior of animals

Behavioral plasticity and the underlying neuronal plasticity represent a fundamental capacity of animals to cope with environmental stimuli. Behavioral plasticity is controlled by complex molecular networks that act under different layers of regulation. While various molecules have been found to be involved in the regulation of plastic behaviors across species, less is known about how organisms orchestrate the activity of these molecules as part of a coherent behavioral response to varying environments. Here we discover a mechanism for the regulation of animal behavioral plasticity involving molecular sulfation in the brain, a modification of substrate molecules by sulfotransferase (ST)-catalyzed addition of a sulfonate group (SO₃) from an obligate donor, 3^′-phosphoadenosine 5^′-phosphosulfate (PAPS) to the substrates. We investigated aggregation behaviors of migratory locusts, which are well-known for extreme phase change plasticity triggered by population density. The processes of PAPS biosynthesis acted efficiently on induction of locust behavioral transition: Inhibition of PAPS synthesis solicited a behavioral shift from gregarious to solitarious states; external PAPS dosage, by contrast, promoted aggregation in solitarious locusts. Genetic or pharmacological intervention in the sulfation catalyzation resulted into pronounced solitarizing effects. Analysis of substrate-specific STs suggests a widespread involvement of sulfated neurotransmitters in the behavioral response. Dopamine in the brain was finally identified to be actively sulfate conjugated, and the sulfate conjugation enhanced the free DA-mediated behavioral aggregation. Similar results in Caenorhabditis elegans and mice indicate that sulfation may be involved more broadly in the modulation of animal aggregation. These findings reveal a general mechanism that effectively regulates animal social-like behavioral plasticity, possibly through sulfation-mediated modification of neural networks.

l-Theanine ameliorates motor deficit, mitochondrial dysfunction, and neurodegeneration against chronic tramadol induced rats model of Parkinson's disease

Parkinson's disease (PD) is the second most prevalent progressive neurodegenerative disease, characterized by loss of dopaminergic neurons in substantia nigra, with deficiency of dopamine in the striatum. Tramadol is safe analgesic but long-term use confirmed to elevate oxidative stress, neuroinflammation, mitochondrial dysfunction, in brain leads to motor deficits. l-Theanine is an active constituent of green tea which prevents neuronal loss, mitochondrial failure and improves dopamine, gamma-aminobutyric acid (GABA), serotonin levels and in the central nervous system (CNS) via antioxidant, anti-inflammatory, and neuromodulatory properties. In the present study, tramadol was injected intraperitoneally to Wister rats for 28 days at a dose of 50 mg/kg. l-Theanine (25, 50, and 100 mg/kg) was administered orally 3 h before tramadol administration from day 14 to day 28. Behavioral analyses including rotarod, narrow beam walk, open field, and grip strength were used to evaluate motor coordination on a weekly basis. On the day 29, all Wistar rats were sacrificed and striatum homogenates were used for biochemical (lipid peroxidation, nitrite, glutathione, glutathione peroxidase activity, superoxide dismutase, catalase, mitochondrial complex I, IV, and cyclic adenosine monophosphate), neuroinflammatory markers (tumor necrosis factor-α, interleukin-1β, and interleukin-17), and neurotransmitters (dopamine, norepinephrine, serotonin, GABA, and glutamate) analysis. Chronic tramadol treatment caused motor deficits reduced antioxidant enzymes level, increased striatal proinflammatory cytokines release, dysbalanced neurotransmitters, and reduced mitochondrial complex activity I, IV, and cAMP activity. However, l-theanine administration attenuated behavioral, biochemical, neuroinflammatory, neurotransmitters, and mitochondrial activity indicated it as a promising neuroprotective potential against degenerative changes in experimental model of PD.

Chemometrics-assisted simultaneous voltammetric determination of multiple neurotransmitters in human serum

An electrochemical method combining chemometrics was developed for simultaneous quantification of multiple neurotransmitters including Dopamine (DA), Epinephrine (EP), Norepinephrine (NE) and serotonin (5-hydroxytryptamine, 5-HT) in human blood serum. A reduced graphene oxide modified glassy carbon electrode (RGO/GCE) was prepared via electrodeposition method. Differential pulse voltammetry (DPV) measurement of the four neurotransmitters showed that the voltammetric signals of the four targets overlapped significantly. To facilitate the simultaneous determination of the neurotransmitters, a chemometric tool of Tchebichef curve moment (TcM) method was proposed. The TcMs calculated from the voltammograms were used to establish the quantitative models by stepwise regression. The intra-day and inter-day precisions of the proposed method were less than 3.5% and 8.1%, respectively, and the recoveries were from 87.4% to 124%. The limit of detection (LOD) for DA, EP, NE and 5-HT were 74 nM, 104 nM, 84 nM and 97 nM, respectively. The above results indicated that the proposed approach is simple and reliable for the simultaneous determination of multiple neurotransmitters in human serum.

Exosomes derived from mesenchymal stem cells repair a Parkinson's disease model by inducing autophagy

Parkinson's disease (PD) is a progressively debilitating neurodegenerative condition that leads to motor and cognitive dysfunction. At present, clinical treatment can only improve symptoms, but cannot effectively protect dopaminergic neurons. Several reports have demonstrated that human umbilical cord mesenchymal stem cells (hucMSCs) afford neuroprotection, while their application is limited because of their uncontrollable differentiation and other reasons. Stem cells communicate with cells through secreted exosomes (Exos), the present study aimed to explore whether Exos secreted by hucMSCs could function instead of hucMSCs. hucMSCs were successfully isolated and characterized, and shown to contribute to 6-hydroxydopamine (6-OHDA)-stimulated SH-SY5Y cell proliferation; hucMSC-derived Exos were also involved in this process. The Exos were purified and identified, and then labeled with PKH 26, it was found that the Exos could be efficiently taken up by SH-SY5Y cells after 12 h of incubation. Pretreatment with Exos promoted 6-OHDA-stimulated SH-SY5Y cells to proliferate and inhibited apoptosis by inducing autophagy. Furthermore, Exos reached the substantia nigra through the blood-brain barrier (BBB) in vivo, relieved apomorphine-induced asymmetric rotation, reduced substantia nigra dopaminergic neuron loss and apoptosis, and upregulated the level of dopamine in the striatum. These results demonstrate that hucMSCs-Exos have a treatment capability for PD and can traverse the BBB, indicating their potential for the effective treatment of PD.

Ethanol exposure during the brain growth spurt affects social behavior and increases susceptibility to acute ethanol effects during adolescence in male mice

The brain is particularly vulnerable to ethanol effects during its growth spurt. Outcomes of early ethanol exposure such as hyperactivity have been extensively investigated; however, persons with fetal alcohol spectrum disorder frequently have social impairments and are heavy drinkers. Despite that, scant information is available regarding the neurobiological basis of these latter behavioral issues. Here, Swiss mice exposed to ethanol (Etoh, 5 g/kg i.p., alternate days) or saline during the brain growth spurt [postnatal day (PN) 2 to 8] were used to assess social behavior after an ethanol challenging during adolescence. At PN39, animals were administered with a single ethanol dose (1 g/Kg) or water by gavage and were then evaluated in the three-chamber sociability test. We also evaluated corticosterone serum levels and the frontal cerebral cortex serotoninergic system. Etoh males showed reductions in sociability. Ethanol challenging reverted these alterations in social behavior, reduced corticosterone levels, and increased the 5-HT₂ receptor binding of male Etoh mice. No alterations were observed in 5-HT and 5-HIAA contents. These data support the idea that ethanol exposure during the brain growth spurt impacts social abilities during adolescence, alters ethanol reexposure effects, and suggests that stress response and serotoninergic system play roles in this phenomenon.

Surface-enhanced spatially-offset Raman spectroscopy (SESORS) for detection of neurochemicals through the skull at physiologically relevant concentrations

Detection techniques for neurotransmitters that are rapid, label-free, and non-invasive are needed to move towards earlier diagnosis of neurological disease.

LC-MS determination of catecholamines and related metabolites in red deer urine and hair extracted using magnetic multi-walled carbon nanotube poly(styrene-co-divinylbenzene) composite

A novel analytical methodology for the extraction and determination of catecholamines (dopamine, epinephrine and norepinephrine) and their metabolites DL-3,4-dihydroxyphenyl glycol and DL-3,4-dihydroxymandelic acid by LC-MS is developed and validated for its application to human and animal urine and hair samples. The method is based on the preliminary extraction of the analytes by a magnetic multi-walled carbon nanotube poly(styrene-co-divinylbenzene) composite. This is followed by a <9 min chromatographic separation of the target compounds in an Onyx Monolithic C₁₈ column using a mixture of 0.01% (v/v) heptafluorobutyric acid in water and methanol at 500 µL min^-1 flow rate. Detection limits within range from 0.055 to 0.093 µg mL^-1, and precision values of the response and retention times of analytes were >90%. Accuracy values comprised the range 79.5-109.5% when the analytes were extracted from deer urine samples using the selected MMWCNT-poly(STY-DVB) sorbent. This methodology was applied to real red deer urine and hair samples, and concentrations within range from 0.05 to 0.5 µg mL^-1 for norepinephrine and from 1.0 to 44.5 µg mL^-1 for its metabolite 3,4-dihydroxyphenyl glycol were calculated. Analyses of red deer hair resulted in high amounts of 3,4-dihydroxyphenyl glycol (0.9-266.9 µg mL^-1).

Analysis of Catecholamines and Pterins in Inborn Errors of Monoamine Neurotransmitter Metabolism-From Past to Future

Inborn errors of monoamine neurotransmitter biosynthesis and degradation belong to the rare inborn errors of metabolism. They are caused by monogenic variants in the genes encoding the proteins involved in (1) neurotransmitter biosynthesis (like tyrosine hydroxylase (TH) and aromatic amino acid decarboxylase (AADC)), (2) in tetrahydrobiopterin (BH₄) cofactor biosynthesis (GTP cyclohydrolase 1 (GTPCH), 6-pyruvoyl-tetrahydropterin synthase (PTPS), sepiapterin reductase (SPR)) and recycling (pterin-4a-carbinolamine dehydratase (PCD), dihydropteridine reductase (DHPR)), or (3) in co-chaperones (DNAJC12). Clinically, they present early during childhood with a lack of monoamine neurotransmitters, especially dopamine and its products norepinephrine and epinephrine. Classical symptoms include autonomous dysregulations, hypotonia, movement disorders, and developmental delay. Therapy is predominantly based on supplementation of missing cofactors or neurotransmitter precursors. However, diagnosis is difficult and is predominantly based on quantitative detection of neurotransmitters, cofactors, and precursors in cerebrospinal fluid (CSF), urine, and blood. This review aims at summarizing the diverse analytical tools routinely used for diagnosis to determine quantitatively the amounts of neurotransmitters and cofactors in the different types of samples used to identify patients suffering from these rare diseases.

Novel biosensing system for the simultaneous multiplex fluorescent determination of catecholamines and their metabolites in biological liquids

A novel original biosensing system for the simultaneous multiplex determination of general markers of catecholamine-producing diseases - catecholamines (dopamine, epinephrine, norepinephrine) and their metabolites (homovanillic and vanillylmandelic acids) in biological liquids without preliminary separation of analytes, in the absence of specific antibodies and receptors and with minimum pretreatment of a samples has been developed. This outstanding approach includes the unique combination of obtaining highly fluorescent derivatives of the analytes as a result of their interaction with two different amines ̶ benzylamine and 1,2-diphenylethylenediamine in the presence of peroxidase as a catalyst, with the application of first-order derivative fluorescence spectroscopy for the resolution of their spectra. Fluorescence is measured in 96-well microplates, which wells contain a bio-recognizing film consisted of horseradish peroxidase immobilized in the polymer chitosan. Spectra of the solutions are recorded in the range 400-500 nm (λ_ex ∼ 305-356 nm). The proposed procedures provide sensitive (in the range of 3-200 nM), selective, and reproducible (RSDs ≤ 1%, n = 6) multiplex determination of the catecholamines and their metabolites in biological liquids were successfully applied for the rapid simultaneous (20 samples per 15-30 min) screening of human urine and mice blood plasma. The validated results showed good linearity, precision, accuracy and selectivity of this method.

A sensitive method for the determination of the gender difference of neuroactive metabolites in tryptophan and dopamine pathways in mouse serum and brain by UHPLC-MS/MS

Tryptophan (TRP) and dopamine (DA) pathways are of great importance for their related pathology and physiology. In the present study, a new reliable and sensitive analytical method was developed and validated for 12 neuroactive metabolites in TRP and DA pathways in mouse serum and brain by ultra-high-performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). The method exhibited good sensitivity as the lower limit of detections ranged from 0.10 to 0.50 ng/ml and the lower limit of quantifications ranged from 0.20 to 2.00 ng/ml by derivatization with dansyl chloride (DNS-Cl) following solid phase extraction (SPE) on C18 cartridges. Good linearity (R² > 0.99), intra-day precision (<9.8% in serum and <8.8% in brain), inter-day precision (<8.9% in serum and <8.5% in brain) and accuracy (90.3%-110.3% in serum and 86.5%-114.0% in brain) were obtained. The method was successfully applied in measuring 12 neuroactive metabolites in TRP and DA pathways in serum and brain samples of male and female mice to explore the differences between genders. As a result, DA and the turnover of DA to 3,4-dihydroxyphenylacetic acid (DOPAC), 5-hydroxtryptamine (5-HT) to TRP and 5-hydroxyindole acetic acid (5-HIAA) to 5-HT in the serum and norepinephrine (NE) in the brain were significantly different between genders.

Multi-metal, Multi-wavelength Surface-Enhanced Raman Spectroscopy Detection of Neurotransmitters

The development of a sensor for the rapid and sensitive detection of neurotransmitters could provide a pathway for the diagnosis of neurological diseases, leading to the discovery of more effective treatment methods. We investigate the use of surface enhanced Raman spectroscopy (SERS) based sensors for the rapid detection of melatonin, serotonin, glutamate, dopamine, GABA, norepinephrine, and epinephrine. Previous studies have demonstrated SERS detection of neurotransmitters; however, there has been no comprehensive study on the effect of the metal used as the SERS substrate or the excitation wavelength used for detection. Here, we present the detection of 7 neurotransmitters using both silver and gold nanoparticles at excitation wavelengths of 532, 633, and 785 nm. Over the range of wavelengths investigated, the SERS enhancement on the silver and gold nanoparticles varies, with an average enhancement factor of 10⁵-10⁶. The maximum SERS enhancement occurs at an excitation wavelength of 785 nm for the gold nanoparticles and at 633 nm for the silver nanoparticles.

Regenerative, Highly-Sensitive, Non-Enzymatic Dopamine Sensor and Impact of Different Buffer Systems in Dopamine Sensing

Carbon nanotube field-effect transistors are used extensively in ultra-sensitive biomolecule sensing applications. Along with high sensitivity, the possibility of regeneration is highly desired in bio-sensors. An important constituent of such bio-sensing systems is the buffer used to maintain pH and provide an ionic conducting medium, among its other properties. In this work, we demonstrate highly-sensitive regenerative dopamine sensors and the impact of varying buffer composition and type on the electrolyte gated field effect sensors. The role of the buffer system is an often ignored condition in the electrical characterization of sensors. Non-enzymatic dopamine sensors are fabricated and regenerated in hydrochloric acid (HCl) solution. The sensors are finally measured against four different buffer solutions. The impact of the nature and chemical structure of buffer molecules on the dopamine sensors is shown, and the appropriate buffer systems are demonstrated.

Differences in neurochemical profiles of two gadid species under ocean warming and acidification

Background

Exposure to future ocean acidification scenarios may alter the behaviour of marine teleosts through interference with neuroreceptor functioning. So far, most studies investigated effects of ocean acidification on the behaviour of fish, either isolated or in combination with environmental temperature. However, only few physiological studies on this issue were conducted despite the putative neurophysiological origin of the CO₂-induced behavioural changes. Here, we present the metabolic consequences of long-term exposure to projected ocean acidification (396–548 μatm PCO₂ under control and 915–1272 μatm under treatment conditions) and parallel warming in the brain of two related fish species, polar cod (Boreogadus saida, exposed to 0 °C, 3 °C, 6 °C and 8 °C) and Atlantic cod (Gadus morhua, exposed to 3 °C, 8 °C, 12 °C and 16 °C). It has been shown that B. saida is behaviourally vulnerable to future ocean acidification scenarios, while G. morhua demonstrates behavioural resilience.

Results

We found that temperature alters brain osmolyte, amino acid, choline and neurotransmitter concentrations in both species indicating thermal responses particularly in osmoregulation and membrane structure. In B. saida, changes in amino acid and osmolyte metabolism at the highest temperature tested were also affected by CO₂, possibly emphasizing energetic limitations. We did not observe changes in neurotransmitters, energy metabolites, membrane components or osmolytes that might serve as a compensatory mechanism against CO₂ induced behavioural impairments. In contrast to B. saida, such temperature limitation was not detected in G. morhua; however, at 8 °C, CO₂ induced an increase in the levels of metabolites of the glutamate/GABA-glutamine cycle potentially indicating greater GABAergic activity in G.morhua. Further, increased availability of energy-rich substrates was detected under these conditions.

Conclusions

Our results indicate a change of GABAergic metabolism in the nervous system of Gadus morhua close to the optimum of the temperature range. Since a former study showed that juvenile G. morhua might be slightly more behaviourally resilient to CO₂ at this respective temperature, we conclude that the observed change of GABAergic metabolism could be involved in counteracting OA induced behavioural changes. This may serve as a fitness advantage of this respective species compared to B. saida in a future warmer, more acidified polar ocean.

Electronic supplementary material

The online version of this article (10.1186/s12983-017-0238-5) contains supplementary material, which is available to authorized users.

In Vivo Ambient Serotonin Measurements at Carbon-Fiber Microelectrodes

The mechanisms that control extracellular serotonin levels in vivo are not well-defined. This shortcoming makes it very challenging to diagnose and treat the many psychiatric disorders in which serotonin is implicated. Fast-scan cyclic voltammetry (FSCV) can measure rapid serotonin release and reuptake events but cannot report critically important ambient serotonin levels. In this Article, we use fast-scan controlled adsorption voltammetry (FSCAV), to measure serotonin's steady-state, extracellular chemistry. We characterize the "Jackson" voltammetric waveform for FSCAV and show highly stable, selective, and sensitive ambient serotonin measurements in vitro. In vivo, we report basal serotonin levels in the CA2 region of the hippocampus as 64.9 ± 2.3 nM (n = 15 mice, weighted average ± standard error). We electrochemically and pharmacologically verify the selectivity of the serotonin signal. Finally, we develop a statistical model that incorporates the uncertainty in in vivo measurements, in addition to electrode variability, to more critically analyze the time course of pharmacological data. Our novel method is a uniquely powerful analysis tool that can provide deeper insights into the mechanisms that control serotonin's extracellular levels.

A novel multi-purpose enzymatic system and procedures for the rapid fluorescent determination of flavonoids in herbal pharmaceuticals and plant materials

The paper presents a novel multi-purpose enzymatic system and procedures for fluorescent determination of several flavonoids in herbal pharmaceuticals and plant materials after their enzyme-catalyzed oxidation by hydrogen peroxide and further derivatization with meso-1,2-diphenylethylenediamine. This system may be used for rapid (15-30min/20 samples) simultaneous screening of samples containing a certain flavonoid in a standard microplate, or as a HPLC detection system for analyzing plant extracts with uncertain composition. In the first case, this indicator system provides sensitive and reproducible microplate determination of quercetin, epicatechin, caffeic acid, and taxifolin in the ranges 0.1-5, 1-10, 0.1-10, 0.5-5μM, respectively. In the second case, quercetin, epicatechin, and caffeic acid can be determined in the ranges 0.05-0.75, 0.05-0.75, and 0.01-0.75µg/ml (0.16-2.5, 0.17-2.6, 0.06-4.2μM), respectively. We have demonstrated the application of the system for the analysis of 3 pharmaceuticals and 3 types of plants.

Colorimetric Fingerprints of Gold Nanorods for Discriminating Catecholamine Neurotransmitters in Urine Samples

Catecholamine neurotransmitters, generally including dopamine (DA), epinephrine (EP) and norepinephrine (NE) are known as substantial indicators of various neurological diseases. Simultaneous detection of these compounds and their metabolites is highly recommended in early clinical diagnosis. To this aim, in the present contribution, a high performance colorimetric sensor array has been proposed for the detection and discrimination of catecholamines based on their reducing ability to deposit silver on the surface of gold nanorods (AuNRs). The amassed silver nanoshell led to a blue shift in the longitudinal localized surface plasmon resonance (LSPR) peak of AuNRs, creating a unique pattern for each of the neurotransmitters. Hierarchical cluster analysis (HCA) and linear discriminate analysis (LDA) pattern recognition techniques were employed to identify DA, EP and NE. The proposed colorimetric array is able to differentiate among individual neurotransmitters as well as their mixtures, successfully. Finally, it was shown that the sensor array can identify these neurotransmitters in human urine samples.

Escitalopram reversed the traumatic stress-induced depressed and anxiety-like symptoms but not the deficits of fear memory

RATIONALE

Posttraumatic stress disorder (PTSD) is a trauma-induced mental disorder characterised by fear extinction dysfunction in which fear circuit monoamines are possibly associated. PTSD often coexists with depressive/anxiety symptoms, and selective serotonin reuptake inhibitors (SSRIs) are recommended to treat PTSD. However, therapeutic mechanisms of SSRIs underlying the PTSD fear symptoms remain unclear.

OBJECTIVES

Using a rodent PTSD model, we examined the effects of early SSRI intervention in mood and fear dysfunctions with associated changes of monoamines within the fear circuit areas.

METHODS

A 14-day escitalopram (ESC) regimen (5 mg/kg/day) was undertaken in two separate experiments in rats which previously received a protocol of single prolonged stress (SPS). In experiment 1, sucrose preference and elevated T-maze were used to index anhedonia depression and avoidance/escape anxiety profiles. In experiment 2, the percentage of freezing time was measured in a 3-day fear conditioning paradigm. At the end of our study, tissue levels of serotonin (5-HT) in the medial prefrontal cortex, amygdala, hippocampus, and striatum were measured in experiment 1, and the efflux levels of infralimbic (IL) monoamines were measured in experiment 2.

RESULTS

In experiment 1, ESC corrected both behavioural (depression/anxiety) and neurochemical (reduced 5-HT tissue levels in amygdala/hippocampus) abnormalities. In experiment 2, ESC was unable to correct the SPS-impaired retrieval of fear extinction. In IL, ESC increased the efflux level of 5-HT but failed to reverse SPS-reduced dopamine (DA) and noradrenaline (NA).

CONCLUSIONS

PTSD-induced mood dysfunction is psychopathologically different from PTSD-induced fear disruption in terms of disequilibrium of monoamines within the fear circuit areas.

Quantitative analysis of drugs in biological matrices by HPLC hyphenated to fluorescence detection

An overview of the state-of-the art in HPLC coupled with fluorescence detection is presented. Over the last 20 years, the increasing number of methodological papers on this topic (4082 between 1994 and 2004 and 7725 between 2004 and 2014) is testament to its utility in bioanalytical applications. Compared with conventional UV absorbance detection used in HPLC, fluorescence detection can greatly enhance the sensitivity leading to limits of detection similar to those obtained with mass spectrometry, offering researchers a sensitive, robust and relatively inexpensive instrumental method. This work will focus on the analysis of pharmaceutical compounds in different biological matrices, either naturally fluorescent or derivatized with a fluorescent agent, and some of them chiral. Therapeutic applications, sample preparation and derivatization, sensitivity for each example are described.

Highly sensitive isotope-dilution liquid-chromatography-electrospray ionization-tandem-mass spectrometry approach to study the drug-mediated modulation of dopamine and serotonin levels in Caenorhabditis elegans

Dopamine (DA) and serotonin (SRT) are monoamine neurotransmitters that play a key role in regulating the central and peripheral nervous system. Their impaired metabolism has been implicated in several neurological disorders, such as Parkinson's disease and depression. Consequently, it is imperative to monitor changes in levels of these low-abundant neurotransmitters and their role in mediating disease. For the first time, a rapid, specific and sensitive isotope-dilution liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated for the quantification of DA and SRT in the nematode Caenorhabditis elegans (C. elegans). This model organism offers a unique approach for studying the effect of various drugs and environmental conditions on neurotransmitter levels, given by the conserved DA and SRT biology, including synaptic release, trafficking and formation. We introduce a novel sample preparation protocol incorporating the usage of sodium thiosulfate in perchloric acid as extraction medium that assures high recovery of the relatively unstable neurotransmitters monitored. Moreover, the use of both deuterated internal standards and the multiple reaction monitoring (MRM) technique allows for unequivocal quantification. Thereby, to the best of our knowledge, we achieve a detection sensitivity that clearly exceeds those of published DA and SRT quantification methods in various matrices. We are the first to show that exposure of C. elegans to the monoamine oxidase B (MAO-B) inhibitor selegiline or the catechol-O-methyltransferase (COMT) inhibitor tolcapone, in order to block DA and SRT degradation, resulted in accumulation of the respective neurotransmitter. Assessment of a behavioral output of the dopaminergic system (basal slowing response) corroborated the analytical LC-MS/MS data. Thus, utilization of the C. elegans model system in conjunction with our analytical method is well-suited to investigate drug-mediated modulation of the DA and SRT system in order to identify compounds with neuroprotective or regenerative properties.

Permeation of Dopamine Sulfate through the Blood-Brain Barrier

Dopamine sulfate (DA-3- and DA-4-S) have been determined in the human brain, but it is unclear whether they are locally formed in the central nervous system (CNS), or transported into the CNS from peripheral sources. In the current study, permeation of the blood-brain barrier (BBB) by DA-S was studied by injecting ¹³C₆-labelled regioisomers of DA-S (¹³DA-3-S and ¹³DA-4-S) and dopamine (DA) subcutaneously (s.c.) in anesthetized rats, then analyzing brain microdialysis and plasma samples by UPLC-MS/MS. The results in the microdialysis samples demonstrated that brain concentrations of ¹³DA-S regioisomers clearly increased after the s.c. injections. The concentration of DA did not change, indicating the permeation of DA-S through an intact BBB. The analysis of plasma samples, however, showed that DA-S only permeates the BBB to a small extent, as the concentrations in plasma were substantially higher than in the microdialysis samples. The results also showed that the concentrations of DA-3-S were around three times higher than the concentrations of DA-4-S in rat brain, as well as in the plasma samples after the s.c. injections, indicating that DA-3-S and DA-4-S permeate the BBB with similar efficiency. The fate of ¹³DA-S in brain was followed by monitoring ¹³C₆-labelled DA-S hydrolysis products, i.e. ¹³DA and its common metabolites; however, no ¹³C₆-labelled products were detected. This suggests that DA-S either permeates through the BBB back to the peripheral circulation or is dissociated or metabolized by unexpected mechanisms.

The effects of LPM570065, a novel triple reuptake inhibitor, on extracellular serotonin, dopamine and norepinephrine levels in rats

Triple reuptake inhibitors (TRIs) are currently being developed as a new class of promising antidepressants that block serotonin (5-HT), dopamine (DA) and norepinephrine (NE) transporters, thereby increasing extracellular monoamine concentrations. The purpose of this study was to investigate the effects of LPM570065, a novel TRI and a desvenlafaxine prodrug, on extracellular 5-HT, DA and NE levels in the rat striatum after acute and chronic administration relative to desvenlafaxine, using High Performance Liquid Chromatography (HPLC) and microdialysis. Acute administration was performed by providing rodents with oral solutions (0.06 mmol·kg(-1) p.o.), oral suspensions (0.06 mmol·kg(-1) p.o.) and intravenous solutions (0.04 mmol·kg(-1) i.v.) of LPM570065 and desvenlafaxine. Oral suspensions (0.06 mmol·kg(-1)·day(-1)) of the two drugs were also administered for a 14-day chronic period. HPLC analysis revealed that LPM570065 rapidly penetrated the rat striatum, converted into desvenlafaxine and exhibited larger total exposure compared with the administration of desvenlafaxine. Microdialysis revealed that acute and chronic administration of oral suspension of LPM570065 increased the 5-HT, DA and NE levels more than the relative administration of desvenlafaxine. Unlike desvenlafaxine, acute administration of an intravenous LPM570065 solution did not induce the undesirable 90% decrease in extracellular 5-HT levels. In contrast to the fully dose-dependent elevation of 5-HT induced by desvenlafaxine, the acute administration of LPM570065 showed a capped increase in extracellular 5-HT levels when combined with WAY-100635. Additionally, forced swim test demonstrated that acute and chronic administration of LPM570065 reduced the immobility time more than the relative administration of desvenlafaxine. These data suggest that LPM570065 may have greater efficacy and/or a more rapid onset of antidepressant action than desvenlafaxine and also counterbalance the harmful effects of desvenlafaxine on 5-HT neurotransmission related to 5-HT1A autoreceptors. Thus, this new class of drugs, TRIs has the potential to provide a new therapeutic mechanism for treating depression.

An interface for sensitive analysis of monoamine neurotransmitters by ion-pair chromatography-electrospray ionization-mass spectrometry with continuous online elimination of ion-pair reagents

A challenge in coupling ion-pair chromatography (IPC) online with electrospray ionization-mass spectrometry (ESI-MS) is that the nonvolatile ion-pair reagent (e.g., alkyl sulfate for amines or tetrabutylammonium for carboxylic acids) in the mobile phase suppresses the ESI-MS signals in the gas phase and their accumulation can clog the MS sampling interface. Consequently, IPC-ESI-MS is conducted either with a volatile ion-pair reagent, which could compromise the analyte separation efficiency, or with a downstream ion-exchange column to rid the ion-pair reagents of the mobile phase. In the latter approach, the limited capacity of ion-exchange columns requires frequent off-line column regeneration, which affects the separation throughput and prohibits long separations from being performed. A dual-valve, dual-ion exchange column interface of IPC-ESI-MS is designed for undisrupted separations and simultaneous column regeneration. Owing to the efficacy in removing the ion-pair reagent, the detection of eluents of monoamine neurotransmitters by an ion trap MS results in the limits of detection of 0.03 μM for dopamine or DA and 0.01 μM for 5-hydroxytryptamine or 5-HT. These values are lower than those obtained with ion trap MS of similar sensitivity when combined with the use of specialized chromatographic columns or sample preconcentration. Excellent reproducibility was attained with repeatedly regenerated ion-exchange columns (RSD = 4-6%) for an extended period of time (RSD < 6% for 6 days). DA and 5-HT in rat straital extracts were analyzed, and our data demonstrate that interferences inherent in the tissues and the ion-pair reagent have been successfully eliminated. This simple interface should be readily amenable to the separation and MS analysis of other types of polar compounds in complex sample media.

Investigation on the co-luminescence effect of europium (III)-lanthanum(III)-dopamine-sodium dodecylbenzene sulfonate system and its application

A novel luminescence, enhancement phenomenon in the europium(III)-dopamine-sodium dodecylbenzene sulfonate system was observed when lanthanum(III) was added. Based on this, a sensitive co-luminescence method was established for the determination of dopamine. The luminescence signal for the europium (III)-lanthanum(III)-dopamine-sodium dodecylbenzene sulfonate system was monitored at λ(ex) = 300 nm, λ(em) = 618 nm and pH 8.3. Under optimized conditions, the enhanced luminescence signal responded linearly to the concentration of dopamine in the range 1.0 × 10(-10)-5.0 × 10(-7) mol/L with a correlation coefficient of 0.9993 (n = 11). The detection limit (3σ) was 2.7 × 10(-11) mol/L and the relative standard deviation for 11 parallel measurements of 3.0 × 10(-8) mol/L dopamine was 1.9%. The presented method was successfully applied for the estimation of dopamine in samples of pharmaceutical preparations, human serum and urine. The possible luminescence enhancement mechanism of the system is discussed briefly.

Behavioral correlates of cerebrospinal fluid amino acid and biogenic amine neurotransmitter alterations in dementia

BACKGROUND

Behavioral and psychological signs and symptoms of dementia (BPSD) are a heterogeneous group of behavioral and psychiatric disturbances occurring in dementia patients of any etiology. Research suggests that altered activities of dopaminergic, serotonergic, (nor)adrenergic, as well as amino acid neurotransmitter systems play a role in the etiopathogenesis of BPSD. In this study we attempted to identify cerebrospinal fluid (CSF) neurochemical correlates of BPSD to provide further insight into its underlying neurochemical pathophysiological mechanisms.

METHODS

Patients with probable Alzheimer's disease (AD; n = 202), probable AD with cerebrovascular disease (n = 37), probable frontotemporal dementia (FTD; n = 32), and probable dementia with Lewy bodies (DLB; n = 26) underwent behavioral assessment and lumbar puncture. CSF levels of six amino acids and several biogenic amines and metabolites were analyzed using ultraperformance liquid chromatography with fluorescence detection and reversed-phase high-performance liquid chromatography with fluorescence detection.

RESULTS

In the AD patients, CSF homovanillic acid/5-hydroxyindoleacetic acid (HVA/5HIAA) ratios correlated positively with anxieties/phobias, whereas CSF levels of taurine correlated negatively with depression and behavioral disturbances in general. In FTD patients, CSF levels of glutamate correlated negatively with verbally agitated behavior. In DLB patients, CSF levels of HVA correlated negatively with hallucinations.

CONCLUSIONS

Several neurotransmitter systems can be linked to one specific behavioral syndrome depending on the dementia subtype. In addition to biogenic amines and metabolites, amino acids seem to play a major role in the neurochemical etiology of BPSD as well.

Investigation on the downregulation of dopamine by acetaminophen administration based on their simultaneous determination in urine

A highly sensitive and selective method is developed for the simultaneous detection of dopamine (DA) and acetaminophen (AP) by reactive blue-4 (RB4) dye entrapped poly1,5-diaminonaphthalne (polyDAN) composite film layer. The polyDAN-RB4 composite is electrochemically developed at glassy carbon electrode. The polymeric film, characterized by XPS and SEM is able to catalyze the oxidation of DA and AP. Two well-defined oxidation peaks are observed in the differential pulse voltammogram (DPV). The experimental parameters affecting the analytical performance are optimized in terms of RB4 concentration, temperature, and pH. The dynamic range for DA and AP analysis is between 0.1-150 and 0.2-164μM with a detection limit of 0.061±0.002 and 0.083±0.003μM, respectively. The anionic form of the polyDAN-RB4 composite repels common metabolites present in serum and urine, and hence no interference is observed. The effect of AP on the DA concentrations in urine is also studied after the oral administration of a single as well as multiple doses. The DA concentrations have been found to decrease nearly 50±3% after prolonged AP administration.

Toward the understanding of the metabolism of levodopa I. DFT investigation of the equilibrium geometries, acid-base properties and levodopa-water complexes

Levodopa (LD) is used to increase dopamine level for treating Parkinson’s disease. The major metabolism of LD to produce dopamine is decarboxylation. In order to understand the metabolism of LD; the electronic structure of levodopa was investigated at the Density Functional DFT/B3LYP level of theory using the 6-311+G** basis set, in the gas phase and in solution. LD is not planar, with the amino acid side chain acting as a free rotator around several single bonds. The potential energy surface is broad and flat. Full geometry optimization enabled locating and identifying the global minimum on this Potential energy surface (PES). All possible protonation/deprotonation forms of LD were examined and analyzed. Protonation/deprotonation is local in nature, i.e., is not transmitted through the molecular framework. The isogyric protonation/deprotonation reactions seem to involve two subsequent steps: First, deprotonation, then rearrangement to form H-bonded structures, which is the origin of the extra stability of the deprotonated forms. Natural bond orbital (NBO) analysis of LD and its deprotonated forms reveals detailed information of bonding characteristics and interactions across the molecular framework. The effect of deprotonation on the donor-acceptor interaction across the molecular framework and within the two subsystems has also been examined. Attempts to mimic the complex formation of LD with water have been performed.

Quantum dot-enhanced chemiluminescence detection for simultaneous determination of dopamine and epinephrine by capillary electrophoresis

A sensitive method based on quantum dot (QD)-enhanced capillary electrophoresis-chemiluminescence (CE-CL) detection was developed for simultaneous determination of dopamine (DA) and epinephrine (E). In this work, CdTe QD was added into the running buffer of CE to catalyze the post-column CL reaction between luminol and hydrogen peroxide, achieving higher CL emission. Negative peaks were produced due to the inhibitory effects on CL emission from DA and E eluted from the electrophoretic capillary. The decrease in CL intensity was proportional to the concentration of DA and E in the range of 8.0 × 10(-8)-5.0 × 10(-6)M and 4.0 × 10(-8)-5.0 × 10(-6)M, respectively. Detection limits for DA and E were 2.3 × 10(-8)M and 9.3 × 10(-9)M, respectively. Using this method, the levels of DA and E in human urine from healthy donors were determined.

A cyclodextrin host-guest recognition approach to an electrochemical sensor for simultaneous quantification of serotonin and dopamine

An electrochemical sensor for simultaneous quantification of serotonin (5-hydroxytryptamine, 5-HT) and dopamine (DA) using a β-cyclodextrin/poly(N-acetylaniline)/carbon nanotube composite modified carbon paste electrode has been developed. Synergistic effect of multi-walled carbon nanotube (MWCNT) in addition to the pre-concentrating effect of β-cyclodextrin (β-CD) as well as its different inclusion complex stability with 5-HT and DA was used to construct an electrochemical sensor for quantification of these important neurotransmitters. The overlapping anodic peaks of 5-HT and DA at 428 mV on bare electrode resolved in two well-defined voltammetric peaks at 202 and 363 mV vs. Ag/AgCl respectively. The oxidation mechanism of 5-HT and DA on the surface of the electrode was investigated by cyclic voltammetry and it was found that the electrode processes are pH dependent and electrochemical oxidation of 5-HT is totally irreversible while the electrode gave a more reversible process to DA. Under optimized conditions, linear calibration curves were obtained in the range of about 4-200 μM with a detection limits down to sub-μM levels (S/N=3) after 20-s accumulation, for both. The proposed sensor was shown to be remarkably selective for 5-HT and DA in matrices containing different species including ascorbic acid and uric acid. The suitability of the developed method was tested for the determination of 5-HT and DA in the Randox Synthetic Plasma samples and acceptable recoveries were obtained for a set of spiked samples.

Simultaneous determination of catecholamines and their metabolites related to Alzheimer's disease in human urine

A simple and specific high-performance liquid chromatography method coupled with fluorescence detection (HPLC-FL) has been developed for the simultaneous determination of L-3,4-dihydroxyphenylalanine, norepinephrine, dopamine, epinephrine and 3,4-dihydroxyphenylacetic acid in human urine. The samples were derivatized by 1,2-diphenylethylenediamine with isoprenaline as internal standard. The factors affecting the fluorescence yield were investigated, including the reaction and separation conditions. The catecholamine derivatives were separated on a Kromasil C(18) column with methanol and sodium acetate buffer as mobile phase. The limits of detection for all catecholamines ranged from 0.2 to 1.1 ng/mL. The linear ranges were from 2.5 to 200 ng/mL except 3,4-dihydroxyphenylacetic acid from 5 to 200 ng/mL. The intra- and interday RSDs for all catecholamines were 1.0-8.0 and 2.1-14%, respectively. The method was successfully applied to determine the catecholamines in human urine from 14 Alzheimer's disease patients and 14 healthy volunteers. It was concluded that the mean levels of catecholamines in urine of Alzheimer's disease patients were all lower than those in healthy volunteers. The cluster analysis and independent samples T-test were used to distinguish the Alzheimer's disease patients and healthy volunteers.