Laser-induced native fluorescence (LINF) imaging of serotonin depletion in depolarized neurons

Fluorescent magnetic nanoparticles with specific targeting functions for combinded targeting, optical imaging and magnetic resonance imaging

Superparamagnetic iron oxides nanoparticles possess specific magnetic properties to be an efficient contrast agent for magnetic resonance imaging (MRI) to enhance the detection and characterization of tissue lesions within the body. To endow specific properties to nanoparticles that can target cancer cells and prevent recognition by the reticuloendothelial system (RES), the surface of the nanoparticles was modified with folic-acid-conjugated poly(ethylene glycol) (FA-PEG). In this study, we investigated the multifunctional fluorescent magnetic nanoparticles (IOPFC) that can specifically target cancer cells and be monitored by both MRI and optical imaging. IOPFC consists of an iron oxide superparamagnetic nanoparticle conjugated with a layer of PEG, which was terminal modified with either Cypher5E or folic acid molecules. The core sizes of IOPFC nanoparticles are around 10 nm, which were visualized by transmission electron microscope (TEM). The hysteresis curves, generated with superconducting quantum interference device (SQUID) magnetometer analysis, demonstrated that IOPFC nanoparticles are superparamagnetic with insignificant hysteresis. IOPFC displays higher intracellular uptake into KB and MDA-MB-231 cells due to the over-expressed folate receptor. This result is confirmed by laser confocal scanning microscopy (LCSM) and atomic flow cytometry. Both in vitro and in vivo MRI studies show better IOPFC uptake by the KB cells (folate positive) than the HT1080 cells (folate negative) and, hence, stronger T 2-weighted signals enhancement. The in vivo fluorescent image recorded at 20 min post injection show strong fluorescence from IOPFC which can be observed around the tumor region. This multifunctional nanoparticle can assess the potential application of developing a magnetic nanoparticle system that combines tumor targeting, as well as MRI and optical imaging.

Paclitaxel and iron oxide loaded multifunctional nanoparticles for chemotherapy, fluorescence properties, and magnetic resonance imaging

The multifunctional nanoparticles constructed from triphenylamine-poly(lactide-co-glycolide)-poly(ethyleneglycol)-poly(lactide-co-glycolide) (TPA-PEP) and folate-poly(2-ethyl-2oxazoline)-poly(D,L-lactide) (folate-PEOz-PLA) were developed in this study. Iron oxide nanoparticles (IOP) and paclitaxel (PTX) were coencapsulated in the nanoparticles with diameter less than 200 nm. The drug-loaded nanoparticles emit fluorescence peak at 460 nm when excited with wavelength of 350 nm. The in vitro antitumor activity of the drug-loaded nanoparticles was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays against HeLa cells. When the cells were exposed to the nanoparticles with different levels of folate but the same drug loading, cell viability decreases as the level of folate increases. Confocal laser scanning microscopy (CLSM) analysis shows that cellular uptake is lower for the non-folate-nanoparticles than that for the folate-nanoparticles. The in vitro and in vivo magnetic resonance imaging (MRI) studies indicate the better T2-Weighted images can be obtained for the folate-nanoparticles. In the anticancer effect evaluation, tumor-bearing mice administered with the 30%-folate-nanoparticles showed ~50% reduction in tumor volume after 23 days. The multifunctional nanoparticles as drug carrier with capabilities of both tumor-targeting and MRI present a new direction in drug delivery system development.

Temporal characteristics of vesicular fusion in astrocytes: examination of synaptobrevin 2-laden vesicles at single vesicle resolution

Astrocytes can release various gliotransmitters in response to stimuli that cause increases in intracellular Ca(2+) levels; this secretion occurs via a regulated exocytosis pathway. Indeed, astrocytes express protein components of the vesicular secretory apparatus. However, the detailed temporal characteristics of vesicular fusions in astrocytes are not well understood. In order to start addressing this issue, we used total internal reflection fluorescence microscopy (TIRFM) to visualize vesicular fusion events in astrocytes expressing the fluorescent synaptobrevin 2 derivative, synapto-pHluorin. Although our cultured astrocytes from visual cortex express synaptosome-associated protein of 23 kDa (SNAP23), but not of 25 kDa (SNAP25), these glial cells exhibited a slow burst of exocytosis under mechanical stimulation; the expression of SNAP25B did not affect bursting behaviour. The relative amount of two distinct types of events observed, transient and full fusions, depended on the applied stimulus. Expression of exogenous synaptotagmin 1 (Syt1) in astrocytes endogenously expressing Syt4, led to a greater proportion of transient fusions when astrocytes were stimulated with bradykinin, a stimulus otherwise resulting in more full fusions. Additionally, we studied the stability of the transient fusion pore by measuring its dwell time, relation to vesicular size, flickering and decay slope; all of these characteristics were secretagogue dependent. The expression of SNAP25B or Syt1 had complex effects on transient fusion pore stability in a stimulus-specific manner. SNAP25B obliterated the appearance of flickers and reduced the dwell time when astrocytes were mechanically stimulated, while astrocytes expressing SNAP25B and stimulated with bradykinin had a reduction in decay slope. Syt1 reduced the dwell time when astrocytes were stimulated either mechanically or with bradykinin. Our detailed study of temporal characteristics of astrocytic exocytosis will not only aid the general understanding of this process, but also the interpretation of the events at the tripartite synapse, both in health and disease.

Gliotransmission: Exocytotic release from astrocytes

Gliotransmitters are chemicals released from glial cells fulfilling a following set of criteria: (i) they are synthesized by and/or stored in glia; (ii) their regulated release is triggered by physiological and/or pathological stimuli; (iii) they activate rapid (milliseconds to seconds) responses in neighboring cells; and (iv) they play a role in (patho)physiological processes. Astrocytes can release a variety of gliotransmitters into the extracellular space using several different mechanisms. In this review, we focus on exocytotic mechanism(s) underlying the release of three classes of gliotransmitters: (i) amino acids, such as, glutamate and d-serine; (ii) nucleotides, like adenosine 5'-triphosphate; and (iii) peptides, such as, atrial natriuretic peptide and brain-derived neurotrophic factor. It is becoming clear that astrocytes are endowed with elements that qualify them as cells communicating with neurons and other cells within the central nervous system by employing regulated exocytosis.

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.

Chemical cytometry: fluorescence-based single-cell analysis

Cytometry deals with the analysis of the composition of single cells. Flow and image cytometry employ antibody-based stains to characterize a handful of components in single cells. Chemical cytometry, in contrast, employs a suite of powerful analytical tools to characterize a large number of components. Tools have been developed to characterize nucleic acids, proteins, and metabolites in single cells. Whereas nucleic acid analysis employs powerful polymerase chain reaction-based amplification techniques, protein and metabolite analysis tends to employ capillary electrophoresis separation and ultrasensitive laser-induced fluorescence detection. It is now possible to detect yoctomole amounts of many analytes in single cells.

Two-photon excited fluorescence detection at 420 nm for label-free detection of small aromatics and proteins in microchip electrophoresis

Two photon excited (TPE) fluorescence detection was applied to native fluorescence detection of aromatics in microchip electrophoresis (MCE). This technique was evaluated as an alternative to common one photon excitation in the deep UV spectral range. TPE enables fluorescence detection of unlabeled aromatic compounds, even in non-deep UV-transparent microfluidic chips. In this study, we demonstrate the proof of concept of native TPE fluorescence detection of small aromatics in commercial microfluidic glass chips. Label-free TPE fluorescence detection of native proteins and small aromatics in MCE was achieved within the micromolar concentration range, utilising 420 nm excitation light.

Vesicular transmitter release from astrocytes

Astrocytes can release a variety of transmitters, including glutamate and ATP, in response to stimuli that induce increases in intracellular Ca(2+) levels. This release occurs via a regulated, exocytotic pathway. As evidence of this, astrocytes express protein components of the vesicular secretory apparatus, including synaptobrevin 2, syntaxin, and SNAP-23. Additionally, astrocytes possess vesicular organelles, the essential morphological elements required for regulated Ca(2+)-dependent transmitter release. The location of specific exocytotic sites on these cells, however, remains to be unequivocally determined.

Monitoring real-time release of ATP from the molluscan central nervous system

The further understanding of neuronal function is imperative for the prevention and treatment of neurofunctional disorders. To aid in this realization, novel methods for monitoring neuronal cell function must be developed and characterized. In this study, we report the application of real-time imaging of luciferase-catalyzed ATP chemiluminescence for the investigation of ATP release from whole central nervous systems of the freshwater snail Lymnaea stagnalis. Release of ATP from Lymnaea ganglia varied among the different ganglia as well as within individual ganglia. Furthermore, the magnitude of ATP release varied following the stimulation of neurons with common neurotransmitters.

Statistical and Generalized Two-Dimensional Correlation Spectroscopy of Multiple Ionization States. Fluorescence of Neurotransmitter Serotonin

Fluorescence spectra of neurotransmitter serotonin are analyzed with generalized and statistical two-dimensional correlation spectroscopy. A comparison is provided for these two emerging data analysis techniques. Both methods reveal correlations between spectral variables and demonstrate enhanced sensitivity in detecting the dynamic spectral changes over conventional one-dimensional spectroscopy. Both statistical and generalized 2D correlation analysis emphasize simultaneous spectral changes in response to external perturbations. Generalized 2D correlation spectroscopy further reveals the difference in rates of these dynamic changes. Using 2D correlation analysis, a third ionization species of serotonin is identified using pH and excitation wavelength perturbation. This species is a doubly deprotonated serotonin with very low fluorescence quantum yield, confirmed by using a laser excitation at longer wavelength and at higher pH. Taking advantage of the spectral differences between excitation of serotonin and tryptophan, as low as 3.8 nM serotonin can be detected in the presence of 20 microM tryptophan, with long-wavelength excitation. This represents the sensitive detection of serotonin in 5000-fold excess of tryptophan.

Imaging ofl-Glutamate Fluxes in Mouse Brain Slices Based on an Enzyme-Based Membrane Combined with a Difference-Image Analysis

A time-resolved imaging method for visualizing L-glutamate release in mammalian brain slices is proposed by using an enzyme membrane combined with a difference-image analysis. The enzyme membrane is composed of L-glutamate oxidase and horseradish peroxidase incorporated into a bovine serum albumin matrix. L-Glutamate triggers an enzyme-coupling reaction to convert a redox substrate (DA-64) to Bindschedler's Green, which gives a green color signal. The difference-image analysis is based on calculating slopes of a signal versus time (t) plot in the time range from (t - 40 s) to (t + 40 s) for visualizing L-glutamate release in terms of its flux (in mol min(-1) cm(-2)). The method was applied to a time-resolved imaging of hippocampal distribution of ischemia-induced L-glutamate release in mouse brain slices. The image of L-glutamate distribution showed that the level and time courses of L-glutamate fluxes were neuronal region-dependent. The maximum flux of L-glutamate at CA1 was observed at 7.7 min after ischemia. The flux at 7.7 min increased in the order of CA1 approximately CA3 > DG. The time course of the L-glutamate flux in the CA1 region was biphasic and that in the DG region was modestly biphasic. In the CA3 region, such biphasic release of L-glutamate was not seen. The ischemia-induced L-glutamate flux was accelerated when Mg2+ was omitted from an extracellular solution. The present enzyme membrane-based approach provides a useful method for visualizing distribution of L-glutamate release in the brain slices during ischemia.

Detection of secretion from single pancreatic beta-cells using extracellular fluorogenic reactions and confocal fluorescence microscopy

Confocal microscopy with Zinquin, a fluorogenic Zn(2+)-specific indicator, was used for spatially and temporally resolved measurement of Zn2+ efflux from single pancreatic beta-cells. When cells were incubated in buffer containing Zinquin, application of insulin secretagogues evoked an increase in fluorescence around the surface of the cell, indicative of detection of Zn2+ efflux from the cell. The fluorescence increases corresponded spatially and temporally with measurements of exocytosis obtained simultaneously by amperometry. When images were taken at 266-ms intervals, the detection limit for Zn2+ was approximately 0.5 microM. With this image frequency, it was possible to observe bursts of fluorescence which were interpreted as fluctuations of Zn2+ level due to exocytosis. The average intensity of these fluorescence bursts corresponded to a Zn2+ concentration of approximately 7 microM. Since insulin is co-stored with Zn2+ in secretory vesicles, it was concluded that the Zn2+ efflux corresponded to exocytosis of insulin/Zn(2+)-containing granules from the beta-cell. Exocytosis sites identified by this technique were frequently localized to one portion of the cell, indicative of active areas of release.