Biogenic amines in microdissected brain regions of Drosophila melanogaster measured with micellar electrokinetic capillary chromatography-electrochemical detection

Measurement of natural variation of neurotransmitter tissue content in red harvester ant brains among different colonies

Colonies of the red harvester ant, Pogonomyrmex barbatus, regulate foraging activity based on food availability and local conditions. Colony variation in foraging behavior is thought to be linked to biogenic amine signaling and metabolism. Measurements of differences in neurotransmitters have not been made among ant colonies in a natural environment. Here, for the first time, we quantified tissue content of 4 biogenic amines (dopamine, serotonin, octopamine, and tyramine) in single forager brains from 9 red harvester ant colonies collected in the field. Capillary electrophoresis coupled with fast-scan cyclic voltammetry (CE-FSCV) was used to separate and detect the amines in individual ant brains. Low levels of biogenic amines were detected using field-amplified sample stacking by preparing a single brain tissue sample in acetonitrile and perchloric acid. The method provides low detection limits: 1 nM for dopamine, 2 nM for serotonin, 5 nM for octopamine, and 4 nM for tyramine. Overall, the content of dopamine (47 ± 9 pg/brain) was highest, followed by octopamine (36 ± 10 pg/brain), serotonin (20 ± 4 pg/brain), and tyramine (14 ± 3 pg/brain). Relative standard deviations were high, but there was less variation within a colony than among colonies, so the neurotransmitter content of each colony might change with environmental conditions. This study demonstrates that CE-FSCV is a useful method for investigating natural variation in neurotransmitter content in single ant brains and could be useful for future studies correlating tissue content with colony behavior such as foraging. Graphical abstract.

Drosophila as a Model System for Neurotransmitter Measurements

Drosophila melanogaster, the fruit fly, is an important, simple model organism for studying the effects of genetic mutations on neuronal activity and behavior. Biologists use Drosophila for neuroscience studies because of its genetic tractability, complex behaviors, well-known and simple neuroanatomy, and many orthologues to human genes. Neurochemical measurements in Drosophila are challenging due to the small size of the central nervous system. Recently, methods have been developed to measure real-time neurotransmitter release and clearance in both larvae and adults using electrochemistry. These studies have characterized dopamine, serotonin, and octopamine release in both wild type and genetic mutant flies. Tissue content measurements are also important, and separations are predominantly used. Capillary electrophoresis, with either electrochemical, laser-induced fluorescence, or mass spectrometry detection, facilitates tissue content measurements from single, isolated Drosophila brains or small samples of hemolymph. Neurochemical studies in Drosophila have revealed that flies have functioning transporters and autoreceptors, that their metabolism is different than in mammals, and that flies have regional, life stage, and sex differences in neurotransmission. Future studies will develop smaller electrodes, expand optical imaging techniques, explore physiological stimulations, and use advanced genetics to target single neuron release or study neurochemical changes in models of human diseases.

Impact of Sampling and Cellular Separation on Amino Acid Determinations in Drosophila Hemolymph

The fruit fly is a frequently used model system with a high degree of human disease-related genetic homology. The quantitative chemical analysis of fruit fly tissues and hemolymph uniquely brings chemical signaling and compositional information to fly experimentation. The work here explores the impact of measured chemical content of hemolymph with three aspects of sample collection and preparation. Cellular content of hemolymph was quantitated and removed to determine hemolymph composition changes for seven primary amine analytes. Hemolymph sampling methods were adapted to determine differences in primary amine composition of hemolymph collected from the head, antenna, and abdomen. Also, three types of anesthesia were employed with hemolymph collection to quantitate effects on measured amino acid content. Cell content was found to be 45.4 ± 22.1 cells/nL of hemolymph collected from both adult and larvae flies. Cell-concentrated fractions of adult, but not larvae, hemolymph were found to have higher and more variable amine content. There were amino acid content differences found between all three areas indicating a robust method to characterize chemical markers from specific regions of a fly, and these appear related to physiological activity. Methods of anesthesia have an impact on hemolymph amino acid composition related to overall physiological impact to fly including higher amino acid content variability and oxygen deprivation effects. Together, these analyses identify potential complications with Drosophila hemolymph analysis and opportunities for future studies to relate hemolymph content with model physiological activity.

MS/MS analysis and imaging of lipids across Drosophila brain using secondary ion mass spectrometry

Lipids are abundant biomolecules performing central roles to maintain proper functioning of cells and biological bodies. Due to their highly complex composition, it is critical to obtain information of lipid structures in order to identify particular lipids which are relevant for a biological process or metabolic pathway under study. Among currently available molecular identification techniques, MS/MS in secondary ion mass spectrometry (SIMS) imaging has been of high interest in the bioanalytical community as it allows visualization of intact molecules in biological samples as well as elucidation of their chemical structures. However, there have been few applications using SIMS and MS/MS owing to instrumental challenges for this capability. We performed MS and MS/MS imaging to study the lipid structures of Drosophila brain using the J105 and 40-keV Ar₄₀₀₀⁺ gas cluster ion source, with the novelty being the use of MS/MS SIMS analysis of intact lipids in the fly brain. Glycerophospholipids were identified by MS/MS profiling. MS/MS was also used to characterize diglyceride fragment ions and to identify them as triacylglyceride fragments. Moreover, MS/MS imaging offers a unique possibility for detailed elucidation of biomolecular distribution with high accuracy based on the ion images of its fragments. This is particularly useful in the presence of interferences which disturb the interpretation of biomolecular localization.

Graphical abstract

An Easily Fabricated Electrochemical Sensor Based on a Graphene-Modified Glassy Carbon Electrode for Determination of Octopamine and Tyramine

A simple electrochemical sensor has been developed for highly sensitive detection of octopamine and tyramine by electrodepositing reduced graphene oxide (ERGO) nanosheets onto the surface of a glassy carbon electrode (GCE). The electrocatalytic oxidation of octopamine and tyramine is individually investigated at the surface of the ERGO modified glassy carbon electrode (ERGO/GCE) by using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Several essential factors including the deposition cycle of reduced graphene oxide nanosheets and the pH of the running buffer were investigated in order to determine the optimum conditions. Furthermore, the sensor was applied to the quantification of octopamine and tyramine by DPV in the concentration ranges from 0.5 to 40 μM and 0.1 to 25 μM, respectively. In addition, the limits of detection of octopamine and tyramine were calculated to be 0.1 μM and 0.03 μM (S/N = 3), respectively. The sensor showed good reproducibility, selectivity and stability. Finally, the sensor successfully detected octopamine and tyramine in commercially available beer with satisfactory recovery ranges which were 98.5%–104.7% and 102.2%–103.1%, respectively. These results indicate the ERGO/GCE based sensor is suitable for the detection of octopamine and tyramine.

Lipid structural effects of oral administration of methylphenidate in Drosophila brain by secondary ion mass spectrometry imaging

We use time-of-flight secondary ion mass spectrometry (TOF-SIMS) imaging to investigate the effects of orally administrated methylphenidate on lipids in the brain of Drosophila melanogaster (fruit fly), a major invertebrate model system in biological study and neuroscience. TOF-SIMS imaging was carried out using a recently designed high energy 40 keV Ar4000(+) gas cluster ion gun which demonstrated improved sensitivity for intact lipids in the fly brain compared to the 40 keV C60(+) primary ion gun. In addition, correlation of TOF-SIMS and SEM imaging on the same fly brain showed that there is specific localization that is related to biological functions of various biomolecules. Different lipids distribute in different parts of the brain, central brain, optical lobes, and proboscis, depending on the length of the carbon chain and saturation level of fatty acid (FA) branches. Furthermore, data analysis using image principal components analysis (PCA) showed that methylphenidate dramatically affected both the distribution and abundance of lipids and their derivatives, particularly fatty acids, diacylglycerides, phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol in the fly brains. Our approach using TOF-SIMS imaging successfully visualizes the effects of methylphenidate on the chemical structure of the fly brain.

Quantification of histamine in various fish samples using square wave stripping voltammetric method

The objective of this study was to describe a new and simple method for the determination of histamine so that it can be used in routine food analysis. A square wave stripping voltammetric (SWSV) method has been used for the indirect determination of histamine. The method is based on accumulation copper (II) - histamine complex onto a hanging mercury drop electrode and reduction of complex. The optimum conditions include an accumulation potential of -420 mV (versus Ag/AgCl), an accumulation time of 10 s. Two linear calibration graphs were obtained with slopes of 0.078 (μM/μA) and 0.014 (μM/μA), respectively. The detection limits were found to be 3 × 10(-7) and 1 × 10(-5) M for histamine (S/N = 3), respectively. The validated SWSV method showed good linearity as well as satisfactory repeatability and immediate precision values, for both instrument and method. The effect of common excipients and metal ions on the peak height of Cu-histamine complex peak was studied. The method was successfully, applied to the determination of histamine in canned anchovy (Engraulis encrasicholus), frozen Tinca tinca (L.) and Cyprinus carpio fish samples.

Analysis of neurotransmitter tissue content of Drosophila melanogaster in different life stages

Drosophila melanogaster is a widely used model organism for studying neurological diseases with similar neurotransmission to mammals. While both larva and adult Drosophila have central nervous systems, not much is known about how neurotransmitter tissue content changes through development. In this study, we quantified tyramine, serotonin, octopamine, and dopamine in larval, pupal, and adult fly brains using capillary electrophoresis coupled to fast-scan cyclic voltammetry. Tyramine and octopamine content varied between life stages, with almost no octopamine being present in the pupa, while tyramine levels in the pupa were very high. Adult females had significantly higher dopamine content than males, but no other neurotransmitters were dependent on sex in the adult. Understanding the tissue content of different life stages will be beneficial for future work comparing the effects of diseases on tissue content throughout development.

Selected recent in vivo studies on chemical measurements in invertebrates

Review ofin vivoanalysis of brain chemicals in invertebrates.

ToF-SIMS imaging of lipids and lipid related compounds in Drosophila brain

Drosophila melanogaster (fruit fly) has a relatively simple nervous system but possesses high order brain functions similar to humans. Therefore, it has been used as a common model system in biological studies, particularly drug addiction. Here, the spatial distribution of biomolecules in the brain of the fly was studied using time-of flight secondary ion mass spectrometry (ToF-SIMS). Fly brains were analyzed frozen to prevent molecular redistribution prior to analysis. Different molecules were found to distribute differently in the tissue, particularly the eye pigments, diacylglycerides, and phospholipids, and this is expected to be driven by their biological functions in the brain. Correlations in the localization of these molecules were also observed using principal components analysis of image data, and this was used to identify peaks for further analysis. Furthermore, consecutive analyses following 10 keV Ar₂₅₀₀⁺ sputtering showed that different biomolecules respond differently to Ar₂₅₀₀⁺ sputtering. Significant changes in signal intensities between consecutive analyses were observed for high mass molecules including lipids.

Small-volume analysis of cell-cell signaling molecules in the brain

Modern science is characterized by integration and synergy between research fields. Accordingly, as technological advances allow new and more ambitious quests in scientific inquiry, numerous analytical and engineering techniques have become useful tools in biological research. The focus of this review is on cutting edge technologies that aid direct measurement of bioactive compounds in the nervous system to facilitate fundamental research, diagnostics, and drug discovery. We discuss challenges associated with measurement of cell-to-cell signaling molecules in the nervous system, and advocate for a decrease of sample volumes to the nanoliter volume regimen for improved analysis outcomes. We highlight effective approaches for the collection, separation, and detection of such small-volume samples, present strategies for targeted and discovery-oriented research, and describe the required technology advances that will empower future translational science.

Freeze-drying as sample preparation for micellar electrokinetic capillary chromatography-electrochemical separations of neurochemicals in Drosophila brains

Micellar electrokinetic capillary chromatography with electrochemical detection has been used to quantify biogenic amines in freeze-dried brains of Drosophila melanogaster. Freeze-drying samples offers a way to preserve the biological sample while making dissection of these tiny samples easier and faster. Fly samples were extracted in cold acetone and dried in a rotary evaporator. Extraction and drying times were optimized in order to avoid contamination by red pigment from the fly eyes and still have intact brain structures. Single freeze-dried fly brain samples were found to produce representative electropherograms as a single hand-dissected brain sample. With utilization of the faster dissection time that freeze-drying affords, the number of brains in a fixed homogenate volume can be increased to concentrate the sample. Thus, concentrated brain samples containing five or fifteen preserved brains were analyzed for their neurotransmitter content, and four analytes; N-acetyloctopamine, N-acetylserotonin, N-acetyltyramine, and N-acetyldopamine were found to correspond well with previously reported values.

Rethinking data collection and signal processing. 1. Real-time oversampling filter for chemical measurements

Minimizing noise in chemical measurements is critical to achieve low limits of detection and accurate measurements. We describe a real-time oversampling filter that offers a method to reduce stochastic noise in a time-dependent chemical measurement. The power of this technique is demonstrated in its application to the separation of dopamine and serotonin by micellar electrokinetic chromatography with amperometric detection. Signal-to-noise ratios were increased by almost an order of magnitude, allowing for limits of detection of 100 and 120 amol, respectively. Real-time oversampling filters can be implemented using simple software algorithms and require no change to existing experimental apparatus. The application is not limited to analytical separations, and this technique can be used to improve the signal-to-noise ratio in any experiment where the necessary sampling rate is less than the maximum sampling rate of the analog-to-digital converter. Theory, implementation, and the performance of this filter are described. We propose that this technique should be the default mode of operation for an analog-to-digital converter.

Recent progress for capillary electrophoresis with electrochemical detection

Capillary electrophoresis (CE) is an attractive technique in separation science because of its high separation performance, short analysis time and low cost. Electrochemical detection (EC) is a powerful tool for CE because of its high sensitivity. In this review, developments of CE-EC from 2008 to August, 2011 are reviewed. We choose papers of innovative and novel results to demonstrate the newest and most important progress in CE-EC.

Capillary electrophoresis and small molecule drug discovery: a perfect match?

Capillary electrophoresis (CE) is an analytical technique based on the separation of the analytes within a capillary owing to their different electrophoretic mobilities. It is widely used in pharmaceutical analyses owing to its versatility and high separation power. However, its penetration into the drug discovery scene has been relatively limited until recent years. Several factors have contributed to this low implementation, including the maturity of liquid chromatography, the scarcity of experienced CE practitioners, and certain limitations intrinsic to the technique. Recently, instrumental improvements and the growing demand for analytical information have lead to a continuously expanding range of routine electrophoretic applications throughout pharmaceutical discovery and development. In this article we review CE fundamentals, review well-established CE methodologies in drug discovery of small molecules and discuss trends that, in our opinion, might emerge in the coming years.

Role of salsolinol in the regulation of pituitary prolactin and peripheral dopamine release

(R)-Salsolinol (SAL), a dopamine (DA)-related tetrahydroisoquinoline, has been found in extracts of the neuro-intermediate lobes (NIL) of pituitary glands and in the median eminence of the hypothalamus obtained from intact male rats and from ovariectomized and lactating female rats. Moreover, analysis of SAL concentrations in NIL revealed parallel increases with plasma prolactin (PRL) in lactating rats exposed to a brief (10 min) suckling stimulus after 4-h separation. SAL is sufficiently potent in vivo to account for the massive discharge of PRL that occurs after physiological stimuli (i.e. suckling). At the same time, it was without effect on the secretion of other pituitary hormones. It has been also shown that another isoquinoline derivative, 1-methyldihydroisoquinoline (1MeDIQ), which is a structural analogue of SAL, can dose-dependently inhibit the in-vivo PRL-releasing effect of SAL. Moreover, 1MeDIQ can inhibit the elevation of plasma PRL induced by physiological stimuli, for example suckling, or in different stressful situations also. 1MeDIQ also has a psycho-stimulant action, which is fairly similar to the effect of amphetamine, i.e. it induces an increase in plasma catecholamine concentrations. It is clear from these data that this newly discovered endogenous compound could be involved in regulation of pituitary PRL secretion. It has also been observed that SAL is present in peripheral, sympathetically innervated organs, for example the atrium, spleen, liver, ovaries, vas deferens, and salivary gland. Furthermore, SAL treatment of rats results in dose-dependent and time-dependent depletion of the DA content of the organs listed above without having any effect on the concentration of norepinephrine. More importantly, this effect of SAL can be completely prevented by amphetamine and by 1MeDIQ pretreatment. It is clear there is a mutual interaction between SAL, 1MeDIQ, and amphetamine or alcohol, not only on PRL release; their interaction with catecholamine "synthesis/metabolism" of sympathetic nerve terminals is also obvious.

Analysis of biogenic amines in a single Drosophila larva brain by capillary electrophoresis with fast-scan cyclic voltammetry detection

Drosophila, the fruit fly, is a common model organism in biology; however, quantifying neurotransmitters in Drosophila is challenging because of the small size of the central nervous system (CNS). Here, we develop neurotransmitter quantification by capillary electrophoresis with fast-scan cyclic voltammetry (CE-FSCV) detection, which allows peak identification by both migration time and the cyclic voltammogram, in contrast to traditional amperometric detection which provides no chemical identification. Tissue content of biogenic amine neurotransmitters was determined in a single CNS dissected from a Drosophila larva. Low detection limits, 1 nM for dopamine and serotonin, 2.5 nM for tyramine, and 4 nM for octopamine, were achieved using field-amplified sample stacking by diluting the homogenized tissue with percholoric acid and acetonitrile. Two different strains of wild-type flies, Oregon R and Canton S, have similar dopamine and serotonin levels but different octopamine content. When flies are fed NSD-1015, which inhibits dopamine decarboxylase (Ddc) a synthesis enzyme in the dopamine and serotonin pathways, dopamine significantly decreases by 52%. A genetically altered driver line, Ddc-GAL4, had lower serotonin and dopamine content as did w(118) flies. When the Ddc-GAL4 line was used to produce flies overexpressing the serotonin synthesis enzyme tryptophan hydroxylase (Ddc-GAL4;UAS-Trh), the serotonin tissue content was greater than for Ddc-GAL4 but not significantly different than the wild-type. These results show that CE-FSCV is useful for monitoring the impact of genetic and pharmacological manipulations on the content of multiple neurotransmitters in a CNS from a Drosophila larva.