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What is the earth most like? ... It is most like a single cell." -Lewis Thomas [1] Perhaps Lewis Thomas understood the struggle of exploring the earth as that of a single cell: the diverse terrain occupied by various organisms, the aqueous environment, and all the small nuances that make the world functional. To scrutinize the deepest of oceans and the highest of mountains, and to conquer every facet and function of our planet, as heterogeneous as it is, would be an accomplishment in itself.As we have better understood the overall nature of earth over time, so too have we achieved a greater understanding of many macroscopic biological processes in a variety of species. This has led scientists to ponder the purpose of increasingly smaller entities in assorted organisms. For those wishing to understand the function of a single cell in a heterogeneous environment, rapid progress in measurement technology has spawned both intriguing results and more challenging scientific queries. As we ponder on a more diminutive scale, from cellular cluster to single cell to subcellular compartment, the demands placed on analytical instrumentation are amplified, and perhaps no recent technique has greater potential for this application than single cell capillary electrophoresis (CE).Since the first assay of a single neuron from Helix aspersa by capillary liquid chromatography (cLC) and CE [2], many advances in microscale separations have been realized that improve the information obtained from single-cell assays. While chemical analysis of single cells has a long history, the range of cells and the number of chemical constituents that can be measured is rapidly growing. However, much more progress is necessary before a complete chemical inventory of a single cell can be obtained. Thus, recent and future research on single-cell CE is aimed at increasing sensitivity so that smaller quantities of a wider range of analytes can be measured. In addition, traditional sampling and detection techniques are challenged by the diminutive nature of many mammalian cells. Furthermore, the sheer number of cells in complex organisms requires improvements in the throughput of existing analytical methods. Ultimately, the desire for improved spatial, temporal, and chemical information helps to propagate advances in CE for single-cell samples.Advances in cell sampling have assisted in acquiring greater spatial information from a single cell. Efficient sampling requires small-diameter capillaries for analysis of minute cells and subcellular compartments. Many different types of sampling methodology are employed for single-cell CE, including whole-cell sampling, cytoplasmic or subcellular sampling, cell-release sampling, and extracellular sampling [3]. Whole-cell sampling requires drawing the entire cell into an etched capillary via a microscope, after which a plug of lysate is injected. As with many techniques involving single cells, sample throughput is poor, as manual injection with a microscope is necessary. However, a methodology for continuous auto...

Capillary electrophoresis (CE) enables rapid separations with high separation efficiency and compatibility with small sample volumes. Laser-induced fluorescence detection can result in extremely low limits of detection in CE. Single-channel fluorescence detection, however, furnishes little qualitative information about a species being detected, except for its CE migration time. Use of multidimensional information often enables unambiguous identification of analytes. Combination of CE with information-rich wavelength-resolved fluorescence detection is analogous with ultraviolet-visible diode-array detection and furnishes both qualitative and quantitative chemical information about target species. This review discusses recent advances in wavelength-resolved laser-induced fluorescence detection coupled with CE, with an emphasis on instrument design.

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.

The authors wish to make a correction to the above article that was published in J. Neurochem. 84, pp. 1358-1366.The following sentence appeared in the Discussion section on pp. 1365 in the second paragraph.'However, in experiments in which crude 3 ( 20 lM) was incubated with individual or homogenized pedal and abdominal de-sheathed ganglia, 2 was observed, even with ample sulfate (26 mM) available in the incubation medium for formation of the cofactor PAPS.'The correct sentence should read as follows. 'However, in experiments in which crude 3 ( 20 lM) was incubated with individual or homogenized pedal and abdominal de-sheathed ganglia, 2 was not observed, even with ample sulfate (26 mM) available in the incubation medium for formation of the cofactor PAPS.'

1 2 1 A I nside a neuron, clusters of molecules shuttle toward a cell membrane tightly packaged within vesicles. The vesicles fuse with the cell membrane, expelling the molecules into the extracellular space. As the molecules reach their targets, electrical currents fly, and the brain hums along.Without these chemical and electrical transformations, we would not remember the smell of coffee, recognize our child's face, or appreciate a delicate melody. The intricate signals and cascades induce thought, behavior, and memory. Analytical chemists are in on the act of understanding the compounds that drive human contemplation, including the reading of this sentence; what will be remembered after reading it; and even what emotions it will evoke. The goal of this article is to provide a general overview of the methods used to characterize neurotransmission in the brain, update recent specialized articles on brain chemistry, and complement articles about imaging MS and new electroanalytical methods that examine the role of dopamine in addiction (1-3).The brain is composed of nervous system cells, or neurons, which communicate with one another through ports called synapses. Cell-cell communication, or neurotransmission, is embodied through electrical impulses or chemical messengers. Although electrophysiological signaling is an important facet of brain function, we will focus on chemical signaling in the brain and the analytical methods used to study it.The Chemistry of Thought:

We report the detection and characterization of the Ni(III) intermediates generated by reaction of (1,4,8,11-tetraazacyclotetradecane)nickel(II) perchlorate with KHSO5. Four Ni(III) intermediates can be trapped or detected through variation in Cl- or KHSO5 concentrations. Upon oxidation of [Ni(cyclam)]2+ by 2.5 equiv of KHSO5, deprotonation of the cyclam ligand generates two red Ni(III) species with lambda max = 530 nm and g perpendicular = 2.20 and g parallel = 2.02 or g perpendicular = 2.16 and g parallel = 2.01 for the axial 4-coordinate or 6-coordinate dichloride species, respectively. These forms decay to Ni(II) products via complex ligand oxidation mechanisms. The Ni(III) dichloride species can be reprotonated and subsequently binds to DNA via an outer-sphere interaction as evidenced by the inverted sign of the CD signal near 400 nm. Cumulatively, the results indicate that the Ni(III) center is coordinately saturated under excess chloride conditions but is still able to interact with DNA substrates. This suggests alternative mechanistic pathways for DNA modification by reaction of [Ni(cyclam)]2+ with KHSO5 and possibly other Ni(II) complexes as well.

Significant research efforts have focused on advancing our understanding of serotonin (5-HT) 2 function and its mechanism of release, uptake, and metabolism. The majority of this research has involved the central nervous system, where imbalances in 5-HT levels have been linked to various diseases, including Parkinson, Huntington, Alzheimer, Alzheimer-like dementia, anxiety, and depression (1), and its regulation depends on a multitude of 5-HT receptors and neurochemical pathways (2). Other 5-HT functions within the brain involve learning and memory (3, 4) and regulation of various stages of development (5). However, neither 5-HT nor its effects are limited to the central nervous system; 5-HT is found in most smooth muscles in the body and is responsible for the induction of the contractile responses of the gastrointestinal, pulmonary, and genito-urinary systems (6). Specifically, researchers estimate that 95% of the approximate 10 mg of 5-HT in the human body is produced in the enteric nervous system, which includes both the peripheral nervous system of the gastrointestinal tract, as well as the 5-HT-secreting enterochromaffin cells of the gut lining (7). In the enteric nervous system, 5-HT fulfills all criteria necessary for classification as a neurotransmitter (8). Imbalances in 5-HT levels within the enteric nervous system have been observed in association with various disorders, including irritable bowel syndrome, functional dyspepsia, non-cardiac chest pain, and gastric ulcer formation (6, 9). Our focus is to gain insight into the pathways by which 5-HT is catabolized and the compounds into which it is converted. Because of its high biological potency, tight regulation of 5-HT levels in specific nervous system regions is necessary, and 5-HT catabolism plays an important role in this regulation. Because 5-HT conversion into these other compounds affects the overall levels of 5-HT, formation of these conversion products can be a fundamental factor in 5-HT regulation.Scheme 1 represents the main 5-HT metabolic pathways and enzymes; however, these represent only a subset of the pathways of 5-HT metabolism, as other lower abundance serotonin metabolites, such as 5-HT sulfate, are known. In immune response pathways, compounds such as formyl 5-HT and 5-hydroxykynuremine (10) are additional serotonin metabolic products. Research performed in the 1950s to track the metabolism of radiolabeled tryptophan demonstrated a number of unknown 5-HT metabolites, proposed to result from additional branches of the monoamine oxidase (MAO) pathway (11). MAO exists in two forms, MAOa and MAOb (12); the former is the primary form of the enzyme responsible for the conversion of 5-HT, although, in the absence of MAOa, MAOb takes over the 5-HT conversion process. With a more in-depth understanding of this, and other potential tissue-specific 5-HT catabolic pathways, it may be possible to develop methods for controlling serotonergic levels in a tissue-specific manner.In this study, we identify unique 5-HT metabolites by analyzing 5-HTp...