Assaying neurotransmitters in and around single neurons with information-rich detectors

Lab-on-a-plate: extending the functionality of MALDI-MS and LDI-MS targets

We review the literature that describes how (matrix-assisted) laser desorption/ionization (MA)LDI target plates can be used not only as sample supports, but beyond that: as functional parts of analytical protocols that incorporate detection by MALDI-MS or matrix-free LDI-MS. Numerous steps of analytical procedures can be performed directly on the (MA)LDI target plates prior to the ionization of analytes in the ion source of a mass spectrometer. These include homogenization, preconcentration, amplification, purification, extraction, digestion, derivatization, synthesis, separation, detection with complementary techniques, data storage, or other steps. Therefore, we consider it helpful to define the "lab-on-a-plate" as a format for carrying out extensive sample treatment as well as bioassays directly on (MA)LDI target plates. This review introduces the lab-on-plate approach and illustrates it with the aid of relevant examples from the scientific and patent literature.

Bioanalytical profile of the L-arginine/nitric oxide pathway and its evaluation by capillary electrophoresis

This review briefly summarizes recent progress in fundamental understanding and analytical profiling of the L-arginine/nitric oxide (NO) pathway. It focuses on key analytical references of NO actions and the experimental acquisition of these references in vivo, with capillary electrophoresis (CE) and high-performance capillary electrophoresis (HPCE) comprising one of the most flexible and technologically promising analytical platform for comprehensive high-resolution profiling of NO-related metabolites. Another aim of this review is to express demands and bridge efforts of experimental biologists, medical professionals and chemical analysis-oriented scientists who strive to understand evolution and physiological roles of NO and to develop analytical methods for use in biology and medicine.

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.

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.

Matrix-Assisted Laser Desorption/Ionization Fourier Transform Mass Spectrometry for the Identification of Orcokinin Neuropeptides in Crustaceans Using Metastable Decay and Sustained Off-Resonance Irradiation

Vacuum UV matrix-assisted laser desorption/ionization (MALDI) Fourier transform ion cyclotron resonance mass spectrometry (FTMS) has been applied to the direct analysis of crustacean neuronal tissues using in-cell accumulation techniques to improve sensitivity. In an extension of previous work by Li and co-workers (Kutz, K. K.; Schmidt, J. J.; Li, L. Anal. Chem. 2004, 76, 5630-5640), and with a focus on the Maine lobster, Homarus americanus, we report that many peaks appearing in direct tissue spectra from crustaceans result from the metastable decay of aspartate-containing neuropeptides with localized protonation sites. We report on mass spectral characteristics of crustacean neuropeptides under MALDI-FTMS conditions and show how fragments formed by Asp-Xxx cleavages can be used to advantage for the identification of orcokinin peptides, a ubiquitous family of crustacean neuropeptides with a highly conserved N-terminus sequence. We show that predicted fragment ion fingerprints (FIFs) can be used to screen internally calibrated direct tissue spectra to provide high-confidence identification of previously identified orcokinin peptides. We use FIFs, identified based upon characteristic neutral losses, to screen for new members of the orcokinin family. Sustained off-resonance irradiation of y-series fragment ions is used to sequence the variable C-terminus. We apply these techniques to the analysis of CoG tissues from Cancer borealis and Panulirus interruptus and show that orcokinins in P. interruptus were misidentified in a previous MALDI-TOF study.

Recent advances in the application of capillary electrophoresis to neuroscience

With fast separation times (seconds to minutes), minimal sample requirements (nanoliters to femtoliters), and excellent mass detection limits (femtomole to zeptomole), capillary electrophoresis (CE) is ideally suited for in vitro and in vivo sampling of neurological samples with a high degree of spatial resolution. Advances in extracellular fluid analysis employing improved microdialysis and push-pull perfusion sampling methodologies has enabled the resolution of neurotransmitters present in limited amounts using CE. Great progress has been made to resolve complex neuropeptides, amino acids, and biogenic amines in tissue and cell cultures. Finally, owing largely to the small volume sampling abilities of CE, investigations of single nerve cells, both invertebrate and mammalian, have been accomplished. These applications of CE to the advancement of neuroscience are presented.

Ascorbic acid assays of individual neurons and neuronal tissues using capillary electrophoresis with laser-induced fluorescence detection

Ascorbic acid is an important cellular metabolite involved in many biochemical pathways. A method to quantitate ascorbic acid and dehydroascorbic acid in individual neurons and neuronal tissues is described with detection limits of 320 pM (430 zmol). The method uses microvial sampling, derivatization with 4,5-dimethyl-1,2-phenylenediamine, capillary electrophoresis separation, and laser-induced fluorescence detection and quantifies the ascorbic acid and dehydroascorbic acid levels with less than a 15-min total analysis time including sample preparation and derivatization. Ascorbic acid and dehydroascorbic acid levels are measured using functionally characterized and identified neurons of Aplysia californica, Pleurobranchaea californica, and Lymnaea stagnalis -three well-recognized models in cellular and system neuroscience. Multiple assays of a particular identified neuron (e.g., metacerebral cells from Aplysia) show a high level of reproducibility, while endogenous intracellular concentrations of ascorbate are neuron-specific. Ascorbic acid concentrations in the neurons studied range from 0.19 to 6.2 mM for Aplysia and 0.12 to 0.22 mM for Lymnaea. In contrast, concentrations of ascorbic acid observed in heterogeneous tissues such as ganglia (with connective tissues, glia, blood vessels, neuropile, and areas with intercellular spaces), 4-190 microM, are significantly lower than the single-cell values.

Recent advances in capillary electrophoresis of peptides

The article gives a comprehensive review on the recent developments in the applications of high-performance capillary electromigration methods, including zone electrophoresis, isotachophoresis, isoelectric focusing, affinity electrophoresis, electrokinetic chromatography and electrochromatography, to analysis, preparation and physicochemical characterization of peptides. The article presents new approaches to the theoretical description and experimental verification of electromigration behavior of peptides, and covers the methodological aspects of capillary electroseparations of peptides, such as strategy and rules for the rational selection of separation mode and experimental conditions, sample treatment, suppression of peptide adsorption to the inner capillary wall, new developments in individual separation modes and new designs of detection systems. Several types of applications of capillary electromigration methods to peptide analysis are presented: conventional qualitative and quantitative analysis for determination of purity, determination in biomatrices, monitoring of physical and chemical changes and enzymatic conversions, amino acid and sequence analysis and peptide mapping of proteins. Some examples of micropreparative peptide separations are given and capabilities of capillary electromigration techniques to provide important physicochemical characteristics of peptides are demonstrated.

Single-cell MALDI: a new tool for direct peptide profiling

Matrix-assisted laser desorption-ionization (MALDI) mass spectrometry (MS) is a rapid and sensitive analytical approach that is well suited for obtaining molecular weights of peptides and proteins from complex samples. MALDI-MS can profile the peptides and proteins from single-cell and small tissue samples without the need for extensive sample preparation, except for the cell isolation and matrix application. Strategies for peptide identification and characterization of post-translational modifications are presented. Furthermore, several recent enhancements in MALDI-MS technology, including in situ peptide sequencing as well as the direct spatial mapping of peptides in cells and tissues are discussed.