Single neuron analysis by capillary electrophoresis with fluorescence spectroscopy

Alternative neural systems: What is a neuron? (Ctenophores, sponges and placozoans)

How to make a neuron, a synapse, and a neural circuit? Is there only one 'design' for a neural architecture with a universally shared genomic blueprint across species? The brief answer is "No." Four early divergent lineages from the nerveless common ancestor of all animals independently evolved distinct neuroid-type integrative systems. One of these is a subset of neural nets in comb jellies with unique synapses; the second lineage is the well-known Cnidaria + Bilateria; the two others are non-synaptic neuroid systems in sponges and placozoans. By integrating scRNA-seq and microscopy data, we revise the definition of neurons as synaptically-coupled polarized and highly heterogenous secretory cells at the top of behavioral hierarchies with learning capabilities. This physiological (not phylogenetic) definition separates 'true' neurons from non-synaptically and gap junction-coupled integrative systems executing more stereotyped behaviors. Growing evidence supports the hypothesis of multiple origins of neurons and synapses. Thus, many non-bilaterian and bilaterian neuronal classes, circuits or systems are considered functional rather than genetic categories, composed of non-homologous cell types. In summary, little-explored examples of convergent neuronal evolution in representatives of early branching metazoans provide conceptually novel microanatomical and physiological architectures of behavioral controls in animals with prospects of neuro-engineering and synthetic biology.

Glycine as a signaling molecule and chemoattractant in Trichoplax (Placozoa): insights into the early evolution of neurotransmitters

The origin and early evolution of neurotransmitter signaling in animals are unclear due to limited comparative information, primarily about prebilaterian animals. Here, we performed the comparative survey of signal molecules in placozoans - the simplest known free-living animals without canonical synapses, but with complex behaviors. First, using capillary electrophoresis with laser-induced fluorescence detection, we performed microchemical analyses of transmitter candidates in Trichoplax adhaerens - the classical reference species in comparative biology. We showed that the endogenous level of glycine (about 3 mM) was significantly higher than for other candidates such as L-glutamate, L-aspartate, or gamma-aminobutyric acid. Neither serotonin nor dopamine were detected. The absolute glycine concentrations in Trichoplax were even higher than we measured in ctenophores (Beroe) and cnidarians (Aequorea). We found that at millimolar concentrations of glycine (similar to the endogenous level), induced muscle-like contractions in free behaving animals. But after long incubation (24 h), 10 M of glycine could induce cytotoxicity and cell dissociation. In contrast, micromolar concentrations (10-10 M) increased Trichoplax ciliated locomotion, suggesting that glycine might act as an endogenous signal molecule. However, we showed than glycine (10 M) can also be a chemoattractant (a guiding factor for food sources), and therefore, act as the exogenous signal. These findings provide an evolutionary base for the origin of transmitters as a result of the interplay between exogenous and endogenous signaling systems early in animal evolution.

A review of the actions of Nitric Oxide in development and neuronal function in major invertebrate model systems

Ever since the late-eighties when endothelium-derived relaxing factor was found to be the gas nitric oxide, endogenous nitric oxide production has been observed in virtually all animal groups tested and additionally in plants, diatoms, slime molds and bacteria. The fact that this new messenger was actually a gas and therefore didn't obey the established rules of neurotransmission made it even more intriguing. In just 30 years there is now too much information for useful comprehensive reviews even if limited to animals alone. Therefore this review attempts to survey the actions of nitric oxide on development and neuronal function in selected major invertebrate models only so allowing some detailed discussion but still covering most of the primary references. Invertebrate model systems have some very useful advantages over more expensive and demanding animal models such as large, easily identifiable neurons and simple circuits in tissues that are typically far easier to keep viable. A table summarizing this information along with the major relevant references has been included for convenience.

NeuroSystematics and Periodic System of Neurons: Model vs Reference Species at Single-Cell Resolution

There is more than one way to develop neuronal complexity, and animals frequently use different molecular toolkits to achieve similar functional outcomes (=convergent evolution). Neurons are different not only because they have different functions, but also because neurons and circuits have different genealogies, and perhaps independent origins at the broadest scale from ctenophores and cnidarians to cephalopods and primates. By combining modern phylogenomics, single-neuron sequencing (scRNA-seq), machine learning, single-cell proteomics, and metabolomic across Metazoa, it is possible to reconstruct the evolutionary histories of neurons tracing them to ancestral secretory cells. Comparative data suggest that neurons, and perhaps synapses, evolved at least 2-3 times (in ctenophore, cnidarian and bilateral lineages) during ∼600 million years of animal evolution. There were also several independent events of the nervous system centralization either from a common bilateral/cnidarian ancestor without the bona fide neurons or from the urbilaterian with diffuse, nerve-net type nervous system. From the evolutionary standpoint, (i) a neuron should be viewed as a functional rather than a genetic character, and (ii) any given neural system might be chimeric and composed of different cell lineages with distinct origins and evolutionary histories. The identification of distant neural homologies or examples of convergent evolution among 34 phyla will not only allow the reconstruction of neural systems' evolution but together with single-cell "omic" approaches the proposed synthesis would lead to the "Periodic System of Neurons" with predictive power for neuronal phenotypes and plasticity. Such a phylogenetic classification framework of Neuronal Systematics (NeuroSystematics) might be a conceptual analog of the Periodic System of Chemical Elements. scRNA-seq profiling of all neurons in an entire brain or Brain-seq is now fully achievable in many nontraditional reference species across the entire animal kingdom. Arguably, marine animals are the most suitable for the proposed tasks because the world oceans represent the greatest taxonomic and body-plan diversity.

Nonexocytotic serotonin release tonically suppresses serotonergic neuron activity

The firing activity of serotonergic neurons in raphe nuclei is regulated by negative feedback exerted by extracellular serotonin (5-HT)o acting through somatodendritic 5-HT1A autoreceptors. The steady-state [5-HT]o, sensed by 5-HT1A autoreceptors, is determined by the balance between the rates of 5-HT release and reuptake. Although it is well established that reuptake of 5-HTo is mediated by 5-HT transporters (SERT), the release mechanism has remained unclear. It is also unclear how selective 5-HT reuptake inhibitor (SSRI) antidepressants increase the [5-HT]o in raphe nuclei and suppress serotonergic neuron activity, thereby potentially diminishing their own therapeutic effect. Using an electrophysiological approach in a slice preparation, we show that, in the dorsal raphe nucleus (DRN), continuous nonexocytotic 5-HT release is responsible for suppression of phenylephrine-facilitated serotonergic neuron firing under basal conditions as well as for autoinhibition induced by SSRI application. By using 5-HT1A autoreceptor-activated G protein-gated inwardly rectifying potassium channels of patched serotonergic neurons as 5-HTo sensors, we show substantial nonexocytotic 5-HT release under conditions of abolished firing activity, Ca(2+) influx, vesicular monoamine transporter 2-mediated vesicular accumulation of 5-HT, and SERT-mediated 5-HT transport. Our results reveal a cytosolic origin of 5-HTo in the DRN and suggest that 5-HTo may be supplied by simple diffusion across the plasma membrane, primarily from the dense network of neurites of serotonergic neurons surrounding the cell bodies. These findings indicate that the serotonergic system does not function as a sum of independently acting neurons but as a highly interdependent neuronal network, characterized by a shared neurotransmitter pool and the regulation of firing activity by an interneuronal, yet activity-independent, nonexocytotic mechanism.

3D plasmonic nanoantennas integrated with MEA biosensors

Neuronal signaling in brain circuits occurs at multiple scales ranging from molecules and cells to large neuronal assemblies. However, current sensing neurotechnologies are not designed for parallel access of signals at multiple scales. With the aim of combining nanoscale molecular sensing with electrical neural activity recordings within large neuronal assemblies, in this work three-dimensional (3D) plasmonic nanoantennas are integrated with multielectrode arrays (MEA). Nanoantennas are fabricated by fast ion beam milling on optical resist; gold is deposited on the nanoantennas in order to connect them electrically to the MEA microelectrodes and to obtain plasmonic behavior. The optical properties of these 3D nanostructures are studied through finite elements method (FEM) simulations that show a high electromagnetic field enhancement. This plasmonic enhancement is confirmed by surface enhancement Raman spectroscopy of a dye performed in liquid, which presents an enhancement of almost 100 times the incident field amplitude at resonant excitation. Finally, the reported MEA devices are tested on cultured rat hippocampal neurons. Neurons develop by extending branches on the nanostructured electrodes and extracellular action potentials are recorded over multiple days in vitro. Raman spectra of living neurons cultured on the nanoantennas are also acquired. These results highlight that these nanostructures could be potential candidates for combining electrophysiological measures of large networks with simultaneous spectroscopic investigations at the molecular level.

Convergent evolution of neural systems in ctenophores

Neurons are defined as polarized secretory cells specializing in directional propagation of electrical signals leading to the release of extracellular messengers - features that enable them to transmit information, primarily chemical in nature, beyond their immediate neighbors without affecting all intervening cells en route. Multiple origins of neurons and synapses from different classes of ancestral secretory cells might have occurred more than once during ~600 million years of animal evolution with independent events of nervous system centralization from a common bilaterian/cnidarian ancestor without the bona fide central nervous system. Ctenophores, or comb jellies, represent an example of extensive parallel evolution in neural systems. First, recent genome analyses place ctenophores as a sister group to other animals. Second, ctenophores have a smaller complement of pan-animal genes controlling canonical neurogenic, synaptic, muscle and immune systems, and developmental pathways than most other metazoans. However, comb jellies are carnivorous marine animals with a complex neuromuscular organization and sophisticated patterns of behavior. To sustain these functions, they have evolved a number of unique molecular innovations supporting the hypothesis of massive homoplasies in the organization of integrative and locomotory systems. Third, many bilaterian/cnidarian neuron-specific genes and 'classical' neurotransmitter pathways are either absent or, if present, not expressed in ctenophore neurons (e.g. the bilaterian/cnidarian neurotransmitter, γ-amino butyric acid or GABA, is localized in muscles and presumed bilaterian neuron-specific RNA-binding protein Elav is found in non-neuronal cells). Finally, metabolomic and pharmacological data failed to detect either the presence or any physiological action of serotonin, dopamine, noradrenaline, adrenaline, octopamine, acetylcholine or histamine - consistent with the hypothesis that ctenophore neural systems evolved independently from those in other animals. Glutamate and a diverse range of secretory peptides are first candidates for ctenophore neurotransmitters. Nevertheless, it is expected that other classes of signal and neurogenic molecules would be discovered in ctenophores as the next step to decipher one of the most distinct types of neural organization in the animal kingdom.

The ctenophore genome and the evolutionary origins of neural systems

The origins of neural systems remain unresolved. In contrast to other basal metazoans, ctenophores, or comb jellies, have both complex nervous and mesoderm-derived muscular systems. These holoplanktonic predators also have sophisticated ciliated locomotion, behaviour and distinct development. Here, we present the draft genome of Pleurobrachia bachei, Pacific sea gooseberry, together with ten other ctenophore transcriptomes and show that they are remarkably distinct from other animal genomes in their content of neurogenic, immune and developmental genes. Our integrative analyses place Ctenophora as the earliest lineage within Metazoa. This hypothesis is supported by comparative analysis of multiple gene families, including the apparent absence of HOX genes, canonical microRNA machinery, and reduced immune complement in ctenophores. Although two distinct nervous systems are well-recognized in ctenophores, many bilaterian neuron-specific genes and genes of “classical” neurotransmitter pathways either are absent or, if present, are not expressed in neurons. Our metabolomic and physiological data are consistent with the hypothesis that ctenophore neural systems, and possibly muscle specification, evolved independently from those in other animals.

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.

Signals from the brainstem sleep/wake centers regulate behavioral timing via the circadian clock

Sleep-wake cycling is controlled by the complex interplay between two brain systems, one which controls vigilance state, regulating the transition between sleep and wake, and the other circadian, which communicates time-of-day. Together, they align sleep appropriately with energetic need and the day-night cycle. Neural circuits connect brain stem sites that regulate vigilance state with the suprachiasmatic nucleus (SCN), the master circadian clock, but the function of these connections has been unknown. Coupling discrete stimulation of pontine nuclei controlling vigilance state with analytical chemical measurements of intra-SCN microdialysates in mouse, we found significant neurotransmitter release at the SCN and, concomitantly, resetting of behavioral circadian rhythms. Depending upon stimulus conditions and time-of-day, SCN acetylcholine and/or glutamate levels were augmented and generated shifts of behavioral rhythms. These results establish modes of neurochemical communication from brain regions controlling vigilance state to the central circadian clock, with behavioral consequences. They suggest a basis for dynamic integration across brain systems that regulate vigilance states, and a potential vulnerability to altered communication in sleep disorders.

Automated method for analysis of tryptophan and tyrosine metabolites using capillary electrophoresis with native fluorescence detection

Capillary electrophoresis (CE) with laser-induced native fluorescence (LINF) detection offers the ability to characterize low levels of selected analyte classes, depending on the excitation and emission wavelengths used. Here a new automated CE-LINF system that provides deep ultraviolet (DUV) excitation (224 nm) and variable emission wavelength detection was evaluated for the analysis of small molecule tryptophan- and tyrosine-related metabolites. The optimized instrument design includes several features that increase throughput, lower instrument cost and maintenance, and decrease complexity when compared with earlier systems using DUV excitation. Sensitivity is enhanced by using an ellipsoid detection cell to increase the fluorescence collection efficiency. The limits of detection ranged from 4 to 30 nmol/L for serotonin and tyrosine, respectively. The system demonstrated excellent linearity over several orders of magnitude of concentration and intraday precision from 1-11 % relative standard deviation (RSD). The instrument's performance was validated via tryptophan and serotonin characterization using tissue extracts from the mammalian brain stem, with RSDs of less than 10 % for both metabolites. The flexibility and sensitivity offered by DUV laser excitation and tunable emission enables a broad range of small-volume measurements.

Single-neuron transcriptome and methylome sequencing for epigenomic analysis of aging

Enormous heterogeneity in transcription and signaling is the feature that slows down progress in our understanding of the mechanisms of normal aging and age-related diseases. This is critical for neurobiology of aging where the enormous diversity of neuronal populations presents a significant challenge in experimental design. Here, we introduce Aplysia as a model for genomic analysis of aging at the single-cell level and provide protocols for integrated transcriptome and methylome profiling of individually identified neurons during the aging process. These single-cell RNA-seq and DNA methylation assays (methyl-capture/methyl enrichment) are compatible with all major next generation sequencing platforms (we used Roche/454 and SOLiD/Life Technologies as illustrative examples) and can be used to integrate an epigenetic signature with transcriptional output. The described sequencing library construction protocol provides both quantitative and directional information from transcriptional profiling of individual cells. Our results also confirm that different copies of DNA in polyploid Aplysia neurons behave similarly with respect to their DNA methylation.

Single-cell metabolomics: changes in the metabolome of freshly isolated and cultured neurons

Metabolites are involved in a diverse range of intracellular processes, including a cell’s response to a changing extracellular environment. Using single-cell capillary electrophoresis coupled to electrospray ionization mass spectrometry, we investigated how placing individual identified neurons in culture affects their metabolic profile. First, glycerol-based cell stabilization was evaluated using metacerebral neurons from Aplysia californica; the measurement error was reduced from ∼24% relative standard deviation to ∼6% for glycerol-stabilized cells compared to those isolated without glycerol stabilization. In order to determine the changes induced by culturing, 14 freshly isolated and 11 overnight-cultured neurons of two metabolically distinct cell types from A. californica, the B1 and B2 buccal neurons, were characterized. Of the more than 300 distinctive cell-related signals detected, 35 compounds were selected for their known biological roles and compared among each measured cell. Unsupervised multivariate and statistical analysis revealed robust metabolic differences between these two identified neuron types. We then compared the changes induced by overnight culturing; metabolite concentrations were distinct for 26 compounds in the cultured B1 cells. In contrast, culturing had less influence on the metabolic profile of the B2 neurons, with only five compounds changing significantly. As a result of these culturing-induced changes, the metabolic composition of the B1 neurons became indistinguishable from the cultured B2 cells. This observation suggests that the two cell types differentially regulate their in vivo or in vitro metabolomes in response to a changing environment.

A hyphenated optical trap capillary electrophoresis laser induced native fluorescence system for single-cell chemical analysis

Single-cell measurements allow a unique glimpse into cell-to-cell heterogeneity; even small changes in selected cells can have a profound impact on an organism's physiology. Here an integrated approach to single-cell chemical sampling and assay are described. Capillary electrophoresis (CE) with laser-induced native fluorescence (LINF) has the sensitivity to characterize natively fluorescent indoles and catechols within individual cells. While the separation and detection approaches are well established, the sampling and injection of individually selected cells requires new approaches. We describe an optimized system that interfaces a single-beam optical trap with CE and multichannel LINF detection. A cell is localized within the trap and then the capillary inlet is positioned near the cell using a computer-controlled micromanipulator. Hydrodynamic injection allows cell lysis to occur within the capillary inlet, followed by the CE separation and LINF detection. The use of multiple emission wavelengths allows improved analyte identification based on differences in analyte fluorescence emission profiles and migration time. The system enables injections of individual rat pinealocytes and quantification of their endogenous indoles, including serotonin, N-acetyl-serotonin, 5-hydroxyindole-3-acetic acid, tryptophol and others. The amounts detected in individual cells incubated in 5-hydroxytryptophan ranged from 10(-14) mol to 10(-16) mol, an order of magnitude higher than observed in untreated pinealocytes.

Sampling techniques for single-cell electrophoresis

Cells are extraordinarily complex, containing thousands of different analytes with concentrations spanning at least nine orders of magnitude. Analyzing single cells instead of tissue homogenates provides unique insights into cell-to-cell heterogeneity and aids in distinguishing normal cells from pathological ones. The high sensitivity and low sample consumption of capillary and on-chip electrophoresis, when integrated with fluorescence, electrochemical, and mass spectrometric detection methods, offer an ideal toolset for examining single cells and even subcellular organelles; however, the isolation and loading of such small samples into these devices is challenging. Recent advances have addressed this issue by interfacing a variety of enhanced mechanical, microfluidic, and optical sampling techniques to capillary and on-chip electrophoresis instruments for single-cell analyses.

Serotonin of mast cell origin contributes to hippocampal function

In the central nervous system, serotonin, an important neurotransmitter and trophic factor, is synthesized by both mast cells and neurons. Mast cells, like other immune cells, are born in the bone marrow and migrate to many tissues. We show that they are resident in the mouse brain throughout development and adulthood. Measurements based on capillary electrophoresis with native fluorescence detection indicate that a significant contribution of serotonin to the hippocampal milieu is associated with mast cell activation. Compared with their littermates, mast cell-deficient C57BL/6 Kit(W-sh/W-sh) mice have profound deficits in hippocampus-dependent spatial learning and memory and in hippocampal neurogenesis. These deficits are associated with a reduction in cell proliferation and in immature neurons in the dentate gyrus, but not in the subventricular zone - a neurogenic niche lacking mast cells. Chronic treatment with fluoxetine, a selective serotonin reuptake inhibitor, reverses the deficit in hippocampal neurogenesis in mast cell-deficient mice. In summary, the present study demonstrates that mast cells are a source of serotonin, that mast cell-deficient C57BL/6 Kit(W-sh/W-sh) mice have disrupted hippocampus-dependent behavior and neurogenesis, and that elevating serotonin in these mice, by treatment with fluoxetine, reverses these deficits. We conclude that mast cells contribute to behavioral and physiological functions of the hippocampus and note that they play a physiological role in neuroimmune interactions, even in the absence of inflammatory responses.

Metabolite analyses of single cells

Single-cell analysis is a promising method for understanding not only cellular physiology but also biological mechanisms of multicellular organisms. Although neighboring cells in multicellular organisms originate from the same genomic information, different circumstances around cells or epigenetic differences have different influences on each cell, leading to differing expression of genes, and thus differing levels and dynamics of metabolites, in single cells. However, single-cell analysis is a tough challenge, even with recent technologies, because of the small size of single cells. Unlike genes, metabolites cannot be amplified, and therefore metabolite analysis is another issue. To analyze such a tiny quantity of metabolites in a single cell, various techniques have been tried and developed. Especially in mass spectrometry, marked improvements in both detection sensitivity and ionization techniques have opened up the challenge for the analysis of metabolites in single cells. In this review, we discuss the method for metabolite detection at the level of single cells and recent advancements in technology.

Telore R, Sekar N. Synthesis of novel fluorescent 1,3,5-trisubstituted triazine derivatives and photophysical property evaluation of fluorophores and their BSA conjugates

Cyanuric chloride was allowed to react with

Synthesis and characterization of novel 2, 2'-bipyrimidine fluorescent derivative for protein binding

Background

Fluorescent dyes with biocompatible functional group and good fluorescence behavior are used as biosensor for monitoring different biological processes as well as detection of protein assay. All reported fluorophore used as sensors are having high selectivity and sensitivity but till there is more demand to synthesized new fluorophore which have improved fluorescence properties and good biocompatibility.

Results

Novel 4, 4'-(1, 1'-(5-(2-methoxyphenoxy)-[2, 2'-bipyrimidine]-4, 6-diyl)bis(1H-pyrazol-3, 1-diyl)) dianiline fluorescent dye was synthesized by multistep synthesis from 2-phenylacetonitrile, 2-chloropyrimidine and 2-methoxyphenol. This dye has absorption at 379 nm with intense single emission at 497 nm having fairly good quantum yield (0.375) and Stokes shift. The intermediates and dye were characterized by FT-IR, ¹H NMR, ¹³C NMR and Mass spectral analysis. The pyrazole bipyrimidine based fluorescent dye possessing two amino groups suitable for binding with protein is reported. Its utility as a biocompatible conjugate was explained by conjugation with bovine serum albumin. The method is based on direct fluorescence detection of fluorophore-labelled protein before and after conjugation. Purified fluorescent conjugate was subsequently analyzed by fluorimetry. The analysis showed that the tested conjugation reaction yielded fluorescent conjugates of the dye through carbodiimide chemistry.

Conclusion

In summery synthesized fluorophore pyrazole-bipyrimidine has very good interaction towards protein bovine serum albumin and it acts as good candidate for protein assay.

Profiling metabolites and peptides in single cells

The intracellular levels and spatial localizations of metabolites and peptides reflect the state of a cell and its relationship to its surrounding environment. Moreover, the amounts and dynamics of metabolites and peptides are indicative of normal or pathological cellular conditions. Here we highlight established and evolving strategies for characterizing the metabolome and peptidome of single cells. Focused studies of the chemical composition of individual cells and functionally defined groups of cells promise to provide a greater understanding of cell fate, function and homeostatic balance. Single-cell bioanalytical microanalysis has also become increasingly valuable for examining cellular heterogeneity, particularly in the fields of neuroscience, stem cell biology and developmental biology.

Parallel detection of intrinsic fluorescence from peptides and proteins for quantification during mass spectrometric analysis

Direct mass spectrometric quantification of peptides and proteins is compromised by the wide variabilities in ionization efficiency which are hallmarks of both the MALDI and ESI ionization techniques. We describe here the implementation of a fluorescence detection system for measurement of the UV-excited intrinsic fluorescence (UV-IF) from peptides and proteins just prior to their exit and electrospray ionization from an ESI capillary. The fluorescence signal provides a quantifiable measure of the amount of protein or peptide present, while direct or tandem mass spectrometric analysis (MS/MS) on the ESI-generated ions provides information on identity. We fabricated an inexpensive, modular fluorescence excitation and detection device utilizing an ultraviolet light-emitting diode for excitation in a ∼300 nL fluorescence detection cell integrated into the fused-silica separation column. The fluorescence signal is linear over 3 orders of magnitude with on-column limits of detection in the low femtomole range. Chromatographically separated intact proteins analyzed using UV-IF prior to top-down mass spectrometry demonstrated sensitive detection of proteins as large as 77 kDa.

Microelectrophoresis platform for fast serial analysis of single cells

A capillary-based microelectrophoresis platform for fast serial analysis of single cells is described. In this system, the capillary remains fixed and a two-channel flow system is used to rapidly switch the buffer surrounding the capillary inlet from a physiological buffer to an electrophoretic buffer. Single cells are retained in the physiologic buffer channel utilizing an array of cell microwells patterned into the channel floor. The defined addresses of the cells on the array enable the sequential delivery of individual cells to the inlet of the capillary, where a focused laser pulse lyses the cell. The cell chamber is moved along a preordained route so that the inlet of the capillary is located in the electrophoresis buffer for separation and the physiological buffer during cell sampling. The throughput of the current system is limited by peak overlap between successive samples. Key characterizations of this system including the fluid flow rates, the cell array dimensions, and laser energies were performed. To demonstrate this system, 28 cells loaded with Oregon green and fluorescein were serially analyzed in under 16 min, a rate of 1.8 cells/min.

Serotonin and its metabolism in basal deuterostomes: insights from Strongylocentrotus purpuratus and Xenoturbella bocki

Serotonin (5-HT), an important molecule in metazoans, is involved in a range of biological processes including neurotransmission and neuromodulation. Both its creation and release are tightly regulated, as is its removal. Multiple neurochemical pathways are responsible for the catabolism of 5-HT and are phyla specific; therefore, by elucidating these catabolic pathways we glean greater understanding of the relationships and origins of various transmitter systems. Here, 5-HT catabolic pathways were studied in Strongylocentrotus purpuratus and Xenoturbella bocki, two organisms occupying distinct positions in deuterostomes. The 5-HT-related compounds detected in these organisms were compared with those reported in other phyla. In S. purpuratus, 5-HT-related metabolites include N-acetyl serotonin, gamma-glutamyl-serotonin and 5-hydroxyindole acetic acid; the quantity and type were found to vary based on the specific tissues analyzed. In addition to these compounds, varying levels of tryptamine were also seen. Upon addition of a 5-HT precursor and a monoamine oxidase inhibitor, 5-HT itself was detected. In similar experiments using X. bocki tissues, the 5-HT-related compounds found included 5-HT sulfate, gamma-glutamyl-serotonin and 5-hydroxyindole acetic acid, as well as 5-HT and tryptamine. The sea urchin metabolizes 5-HT in a manner similar to both gastropod mollusks, as evidenced by the detection of gamma-glutamyl-serotonin, and vertebrates, as indicated by the presence of 5-hydroxyindole acetic acid and N-acetyl serotonin. In contrast, 5-HT metabolism in X. bocki appears more similar to common protostome 5-HT catabolic pathways.

Bioanalytical applications of capillary electrophoresis with laser-induced native fluorescence detection

In this article we describe recent developments and applications of capillary electrophoresis (CE) coupled with laser-induced native fluorescence (LINF) detection in the analysis of biological, pharmaceutical and environmental samples. Compared with traditional UV absorbance detection used in CE, the LINF technique can greatly improve the concentration sensitivity of CE without the need for derivatization; the only requirement being that the analyte must have native fluorescence. Instrumentation and laser sources used in CE–LINF are summarized and specific applications of CE–LINF to small-biomolecule analysis, profiling of human biofluids, detection of native fluorescent peptides and proteins, single-cell analysis and the use of online sample preconcentration methods are also reviewed in detail.

Capillary electrophoresis with electrospray ionization mass spectrometric detection for single-cell metabolomics

A method that enables metabolomic profiling of single cells and subcellular structures is described using capillary electrophoresis coupled to electrospray ionization time-of-flight mass spectrometry. A nebulizer-free coaxial sheath-flow interface completes the circuit and provides a stable electrospray, yielding a signal with a relative standard deviation of under 5% for the total ion electropherogram. Detection limits are in the low nanomolar range (i.e., <50 nM (<300 amol)) for a number of cell-to-cell signaling molecules, including acetylcholine (ACh), histamine, dopamine, and serotonin. The instrument also yields high-efficiency separations, e.g., approximately 600,000 for eluting ACh bands. The utility of this setup for single-cell metabolomic profiling is demonstrated with identified neurons from Aplysia californica--the R2 neuron and metacerebral cell (MCC). Single-cell electropherograms are reproducible, with a large number of metabolites detected; more than 100 compounds yield signals of over 10(4) counts from the injection of only 0.1% of the total content from a single MCC. Expected neurotransmitters are detected within the cells (ACh in R2 and serotonin in MCC), as are compounds that have molecular masses consistent with all of the naturally occurring amino acids (except cysteine). Tandem MS using a quadrupole time-of-flight tandem mass spectrometer distinguishes ACh from isobaric compounds in the R2 neuron and demonstrates the ability of this method to characterize and identify metabolites present within single cells.

Label-free fluorescence detection in capillary and microchip electrophoresis

Herein, we summarize the current status of native fluorescence detection in microchannel electrophoresis, with a strong focus on chip-based systems. Fluorescence detection is a powerful technique with unsurpassed sensitivity down to the single-molecule level. Accordingly fluorescence detection is attractive in combination with miniaturised separation techniques. A drawback is, however, the need to derivatize most analytes prior to analysis. This can often be circumvented by utilising excitation light in the UV spectral range in order to excite intrinsic fluorescence. As sensitive absorbance detection is challenging in chip-based systems, deep-UV fluorescence detection is currently one of the most general optical detection techniques in microchip electrophoresis, which is especially attractive for the detection of unlabelled proteins. This review gives an overview of research on native fluorescence detection in capillary (CE) and microchip electrophoresis (MCE) between 1998 and 2008. It discusses material aspects of native fluorescence detection and the instrumentation used, with particular focus on the detector design. Newer developments, featured techniques, and their prospects in the future are also included. In the last section, applications in bioanalysis, drug determination, and environmental analysis are reviewed with regard to limits of detection.

Intermolecular association provides specific optical and NMR signatures for serotonin at intravesicular concentrations

Neurotransmitter vesicles contain biomolecules at extraordinarily high concentrations (hundreds of millimoles/liter). Such concentrations can drive intermolecular associations, which may affect vesicular osmolarity and neuronal signaling. Here we investigate whether aqueous serotonin (a monoamine neurotransmitter) forms oligomers at intravesicular concentrations and whether these oligomers have specific spectroscopic signatures that can potentially be used for monitoring neuronal storage and release. We report that, as serotonin concentration is increased from 60 microM to 600 mM, the normalized fluorescence spectrum of serotonin displays a growing long-wavelength tail, with an isoemissive point at 376 nm. The fluorescence decay is monoexponential with a lifetime of 4 ns at low concentrations but is multiexponential with an average lifetime of 0.41 ns at 600 mM. A 600 mM serotonin solution has 30% less osmolarity than expected for monomeric serotonin, indicating oligomer formation. The proton NMR chemical shifts move upfield by as much as 0.3 ppm at 600 mM compared to those at 10 mM, indicating a stacking of the serotonin indole moieties. However, no intermolecular crosspeak is evident in the two-dimensional NMR rotating frame Overhauser effect spectroscopy spectrum even at 600 mM, suggesting that oligomeric structures are possibly weakly coupled. The appearance of a single peak for each proton suggests that the rate of interconversion between the monomeric and the oligomeric structures is faster than 240 Hz. A stopped-flow kinetic experiment also confirms that the rate of dissociation is faster than 100 ms. We conclude that serotonin forms oligomers at intravesicular concentrations but becomes monomeric quickly on dilution. NMR signatures of the oligomers provide potential contrast agents for monitoring the activity of serotonergic neurons in vivo.

Chemical analysis of single cells

Chemical analysis of single cells requires methods for quickly and quantitatively detecting a diverse array of analytes from extremely small volumes (femtoliters to nanoliters) with very high sensitivity and selectivity. Microelectrophoretic separations, using both traditional capillary electrophoresis and emerging microfluidic methods, are well suited for handling the unique size of single cells and limited numbers of intracellular molecules. Numerous analytes, ranging from small molecules such as amino acids and neurotransmitters to large proteins and subcellular organelles, have been quantified in single cells using microelectrophoretic separation techniques. Microseparation techniques, coupled to varying detection schemes including absorbance and fluorescence detection, electrochemical detection, and mass spectrometry, have allowed researchers to examine a number of processes inside single cells. This review also touches on a promising direction in single cell cytometry: the development of microfluidics for integrated cellular manipulation, chemical processing, and separation of cellular contents.

5-HT and 5-HT-SO4, but not tryptophan or 5-HIAA levels in single feeding neurons track animal hunger state

Serotonin (5-HT) is an intrinsic modulator of neural network excitation states in gastropod molluscs. 5-HT and related indole metabolites were measured in single, well-characterized serotonergic neurons of the feeding motor network of the predatory sea-slug Pleurobranchaea californica. Indole amounts were compared between paired hungry and satiated animals. Levels of 5-HT and its metabolite 5-HT-SO4 in the metacerebral giant neurons were observed in amounts approximately four-fold and two-fold, respectively, below unfed partners 24 h after a satiating meal. Intracellular levels of 5-hydroxyindole acetic acid and of free tryptophan did not differ significantly with hunger state. These data demonstrate that neurotransmitter levels and their metabolites can vary in goal-directed neural networks in a manner that follows internal state.

Serotonin catabolism in the central and enteric nervous systems of rats upon induction of serotonin syndrome

Serotonin, a well-known neurotransmitter in mammals, has been linked to a number of neurological and gastrointestinal disorders. One of these disorders, serotonin syndrome, is a potentially deadly condition caused by increased levels of serotonin in the extracellular space. Information on the neurochemical effects of serotonin syndrome on serotonin catabolism is lacking, particularly in relation to the enteric system of the gastrointestinal tract. Here the catabolism of serotonin is monitored in rats with pharmacologically induced serotonin syndrome, with the catabolites characterized using a specialized capillary electrophoresis system with laser-induced native fluorescence detection. Animals induced with serotonin syndrome demonstrate striking increases in the levels of serotonin and its metabolites. In the brain, levels of serotonin increased 2- to 3-fold in animals induced with serotonin syndrome. A major serotonin metabolite, 5-hydroxyindole acetic acid, increased 10- to 100-fold in experimental animals. Similar results were observed in the gastrointestinal tissues; in the small intestines, serotonin levels increased 4- to 5-fold. Concentrations of 5-hydroxyindole acetic acid increased 32- to 100-fold in the intestinal tissues of experimental animals. Serotonin sulfate showed surprisingly large increases, marking what may be the first time the compound has been reported in rat intestinal tissues.

Contributions of capillary electrophoresis to neuroscience

Capillary electrophoresis (CE) is a small-volume separation approach amenable to the analysis of complex samples for their small molecule, peptide and protein content. A number of the features of CE make it a method of choice for addressing questions related to neurochemistry. The figures of merit inherent to CE that make it well suited for studying cell-to-cell and intracellular signaling include small sample volumes, high separation efficiency, the ability for online analyte concentration, and compatibility with sensitive and high-information content detection methods. A variety of instrumental aspects are detailed, including detection methods and sampling techniques that are particularly useful for the analysis of signaling molecules. Studies that have used these techniques to increase our understanding of neurobiology are emphasized throughout. One notable application is single neuron chemical analysis, a research area that has been greatly advanced by CE.

A multichannel native fluorescence detection system for capillary electrophoretic analysis of neurotransmitters in single neurons

A laser-induced native fluorescence detection system optimized for analysis of indolamines and catecholamines by capillary electrophoresis is described. A hollow-cathode metal vapor laser emitting at 224 nm is used for fluorescence excitation, and the emitted fluorescence is spectrally distributed by a series of dichroic beam-splitters into three wavelength channels: 250-310 nm, 310-400 nm, and >400 nm. A separate photomultiplier tube is used for detection of the fluorescence in each of the three wavelength ranges. The instrument provides more information than a single-channel system, without the complexity associated with a spectrograph/charge-coupled device-based detector. With this instrument, analytes can be separated and identified not only on the basis of their electrophoretic migration time but also on the basis of their multichannel signature, which consists of the ratios of relative fluorescence intensities detected in each wavelength channel. The 224-nm excitation channel resulted in a detection limit of 40 nmol L-1 for dopamine. The utility of this instrument for single-cell analysis was demonstrated by the detection and identification of the neurotransmitters in serotonergic LPeD1 and dopaminergic RPeD1 neurons, isolated from the central nervous system of the well-established neurobiological model Lymnaea stagnalis. Not only can this system detect neurotransmitters in these individual neurons with S/N>50, but analyte identity is confirmed on the basis of spectral characteristics.

Analysis of mitochondria isolated from single cells

Bulk studies are not suitable to describe and study cell-to-cell variation, which is of high importance in biological processes such as embryogenesis, tissue differentiation, and disease. Previously, capillary electrophoresis with laser-induced fluorescence detection (CE-LIF) was used to measure the properties of organelles isolated from millions of cells. As such, these bulk measurements reported average properties for the organelles of cell populations. Similar measurements for organelles released from single cells would be highly relevant to describe the subcellular variations among cells. Toward this goal, here we introduce an approach to analyze the mitochondria released from single mammalian cells. Osteosarcoma 143B cells are labeled with either the fluorescent mitochondrion-specific 10-N-nonyl acridine orange (NAO) or via expression of the fluorescent protein DsRed2. Subsequently, a single cell is introduced into the CE-LIF capillary where the organelles are released by a combined treatment of digitonin and trypsin. After this treatment, an electric field is applied and the released organelles electromigrate toward the LIF detector. From an electropherogram, the number of detected events per cell, their individual electrophoretic mobilities, and their individual fluorescence intensities are calculated. The results obtained from DsRed2 labeling, which is retained in intact mitochondria, and NAO labeling, which labels all mitochondria, are the basis for discussion of the strengths and limitations of this single-cell approach.

Serotonin Catabolism and the Formation and Fate of 5-Hydroxyindole Thiazolidine Carboxylic Acid

Serotonin (5-HT) functions as a neurotransmitter and neuromodulator in both the central and enteric nervous systems of mammals. The dynamic degradation of 5-HT metabolites in 5-HT-containing nervous system tissues is monitored by capillary electrophoresis with wavelength-resolved laser-induced native fluorescence detection in an effort to investigate known and novel 5-HT catabolic pathways. Tissue samples from wild type mice, genetically altered mice, Long Evans rats, and cultured differentiated rat pheochromocytoma PC-12 cells, are analyzed before and after incubation with excess 5-HT. From these experiments, several new compounds are detected. One metabolite, identified as 5-hydroxyindole thiazoladine carboxylic acid (5-HITCA), has been selected for further study. In 5-HT-incubated central and enteric nervous system tissue samples and differentiated PC-12 cells, 5-HITCA forms at levels equivalent to 5-hydroxyindole acetic acid, via a condensation reaction between L-cysteine and 5-hydroxyindole acetaldehyde. In the enteric nervous system, 5-HITCA is detected without the addition of 5-HT. The levels of L-cysteine and homocysteine in rat brain mitochondria are measured between 80 and 140 microm and 1.9 and 3.4 microm, respectively, demonstrating that 5-HITCA can be formed using available, free L-cysteine in these tissues. The lack of significant accumulation of 5-HITCA in the central and enteric nervous systems, along with data showing the degradation of 5-HITCA into 5-hydroxyindole acetaldehyde, suggests that an equilibrium coupled to the enzyme, aldehyde dehydrogenase type 2, prevents the accumulation of 5-HITCA. Even so, the formation of 5-HITCA represents a catabolic pathway of 5-HT that can affect the levels of 5-HT-derived compounds in the body.

d-Aspartate as a putative cell-cell signaling molecule in theAplysia californicacentral nervous system

The content, synthesis and transport of D-aspartate (D-Asp) in the CNS of Aplysia californica is investigated using capillary electrophoresis (CE) with both laser-induced fluorescence and radionuclide detection. Millimolar concentrations of D-Asp are found in various regions of the CNS. In the cerebral ganglion, three adjacent neuronal clusters have reproducibly different D-Asp levels; for example, in the F- and C-clusters, up to 85% of the free Asp is present in the D-form. Heterogeneous distribution of D-Asp is also found in the individual identified neurons tested, including the optical ganglion top-layer neurons, metacerebral cells, R2 neurons, and F-, C- and G-cluster neurons. The F-cluster neurons have the highest percentage of D-Asp (approximately 58% of the total Asp), whereas the lowest value of approximately 8% is found in R2 neurons. In pulse-chase experiments with radiolabeled D-Asp, followed by CE with radionuclide detection, the synthesis of D-Asp from L-aspartate (L-Asp) is confirmed. Is D-Asp in the soma, or is it transported to distantly located release sites? D-Asp is clearly detected in the major nerves of A. californica, including the pleuroabdominal and cerebrobuccal connectives and the anterior tentacular nerves, suggesting it is transported long distances. In addition, both D-Asp and L-Asp are transported in the pleuroabdominal connectives in a colchicine-dependent manner, whereas several other amino acids are not. Finally, d-Asp produces electrophysiological effects similar to those induced by L-Asp. These data are consistent with an active role for D-Asp in cell-to-cell communication.

Quantitative measurement of serotonin synthesis and sequestration in individual live neuronal cells

Synthesis and subsequent sequestration into vesicles are essential steps that precede neurotransmitter exocytosis, but neither the total neurotransmitter content nor the fraction sequestered into vesicles have been measured in individual live neurons. We use multiphoton microscopy to directly observe intracellular and intravesicular serotonin in the serotonergic neuronal cell line RN46A. We focus on how the relationship between synthesis and sequestration changes as synthesis is up-regulated by differentiation or down-regulated by chemical inhibition. Temperature-induced differentiation causes an increase of about 60% in the total serotonin content of individual cells, which goes up to about 10 fmol. However, the number of vesicles per cell increases by a factor of four and the proportion of serotonin sequestered inside the vesicles increases by a factor of five. When serotonin synthesis is inhibited in differentiated cells and the serotonin content goes down to the level present in undifferentiated cells, the sequestered proportion still remains at this high level. The total neurotransmitter content of a cell is, thus, an unreliable indicator of the sequestered amount.

Confirmation of peak assignments in capillary electrophoresis using immunoprecipitation. Application to D-aspartate measurements in neurons

Capillary electrophoresis (CE) with laser-induced fluorescence (LIF) detection is a powerful tool for analysis of samples ranging from tissue extracts to single cells. However, accurate peak identification in electropherograms is challenging when complex biological samples are analyzed, as often matching a migration time between an analyte and corresponding standard may be insufficient to confirm the peak's identity. A method which combines single-step immunoprecipitation and CE-LIF analysis for investigation of the chiral amino acids in single cells and small tissue samples is demonstrated. D-Aspartate (D-Asp) has been reported in the central nervous system of the invertebrate neurobiological model Aplysia californica. In order to confirm the identity of D-Asp signal in the complex electropherograms of nerve tissue extracts and individual neurons, anti-D-Asp serum, preincubated with L-Asp conjugate, is added to the sample. This selectively binds the free D-Asp, creating an antibody-antigen complex with a migration time similar to that of antibody alone, but not that of D-Asp. The complete disappearance of the putative D-Asp peak confirms its identity and validates that there are no other detectable analytes co-migrating with D-Asp in the electropherogram.

Pharmacological manipulation of serotonin levels in the nervous system of the opisthobranch mollusc Tritonia diomedea

Serotonin-related disorders can be treated by manipulating serotonin synthesis with the serotonin precursor 5-hydroxytryptophan (5-HTP) or other pharmacological agents. The mollusc Tritonia diomedea is a model for investigating the effects of altering serotonin content on the functions of identified neurons. We used high-performance liquid chromatography and immunohistochemistry to examine the amount and localization of 5-HTP, serotonin, and the serotonin breakdown product 5-hydroxyindolacetic acid (5-HIAA) in the Tritonia brain after various pharmacological treatments. Exposure to 5-HTP (2 mM for 30 min-1 h) caused an immediate and massive increase in total 5-HTP content, which lasted more than 20 h, and the widespread appearance of 5-HTP immunoreactivity in neurons. Serotonin levels rose gradually, but only a restricted number of additional neurons displayed serotonin immunoreactivity. 5-HTP treatment also caused an increase in the total amount of 5-HIAA and the appearance of 5-HIAA immunoreactivity throughout the brain. Treatment with the synthesis cofactor tetrahydrobiopterin, the initial precursor tryptophan, or serotonin itself had no persistent effect on total serotonin content. The amino acid decarboxylase inhibitor hydroxybenzylhydrazine (NSD-1015) also had no effect on the total serotonin content, although it caused an accumulation of 5-HTP. Thus, serotonin levels in the brain of T. diomedea appear to be maintained by a homeostatic mechanism that can be disrupted by 5-HTP.

Direct single cell determination of nitric oxide synthase related metabolites in identified nitrergic neurons

The biochemical characterization of individual nitrergic (NO releasing) neurons is a non-trivial task both in vertebrate and invertebrate preparations. In spite of numerous efforts, there are limited data related to intracellular concentrations of essential metabolites involved in NO synthesis and degradation. This situation creates controversies in both identification of nitrergic neurons and the selection of reliable reporters of NOS activity in heterogeneous cell populations. We take advantage of identified neurons from the pulmonate mollusc Lymnaea stagnalis to perform direct single cell microanalysis of intracellular concentrations of the major nitric oxide synthase (NOS) related metabolites such as arginine, citrulline, argininosuccinate, NO(2)(-),and NO(3)(-). Capillary electrophoresis protocols have been developed to quantitate levels of these metabolites in single identified neurons from the buccal, cerebral, and pedal ganglia using laser-induced fluorescence and conductivity detection. The limits of detection (LODs) for arginine (Arg) and citrulline (Cit) are 84 amol (11nM) and 110 amol (15 nM), respectively, and LODs for NO(2)(-)and NO(3)(-) are <200 amol (<10nM) each. We report that intracellular concentrations of NOS related metabolites are in the millimolar range and less than 1% of a single cell is required for microchemical analysis. From four cell types tested, only the esophageal motoneuron B2 contains active NOS, and they also contain surprisingly high nitrite levels (up to 5mM) compared to other neurons tested (peptidergic B4, dopaminergic RPeD1, and serotonergic CGC). These B2 neurons also exhibit an Arg/Cit ratio susceptible to the selective NOS inhibitor l-iminoethyl-N-ornithine whereas others neurons do not even though they all may contain NOS transcripts. On the contrary, we found that absolute concentrations of other NOS related metabolites including nitrates are not reliable markers of NOS activity and demonstrate the need for multiple assays for NOS activity.

Fundamentals and practice for ultrasensitive laser-induced fluorescence detection in microanalytical systems

Laser-induced fluorescence is an extremely sensitive method for detection in chemical separations. In addition, it is well-suited to detection in small volumes, and as such is widely used for capillary electrophoresis and microchip-based separations. This review explores the detailed instrumental conditions required for sub-zeptomole, sub-picomolar detection limits. The key to achieving the best sensitivity is to use an excitation and emission volume that is matched to the separation system and that, simultaneously, will keep scattering and luminescence background to a minimum. We discuss how this is accomplished with confocal detection, 90 degrees on-capillary detection, and sheath-flow detection. It is shown that each of these methods have their advantages and disadvantages, but that all can be used to produce extremely sensitive detectors for capillary- or microchip-based separations. Analysis of these capabilities allows prediction of the optimal means of achieving ultrasensitive detection on microchips.