We applied electrochemical techniques with nano-tip electrodes to show that micromolar concentrations of zinc not only trigger changes in the dynamics of exocytosis, but also vesicle content in a model cell line. The vesicle catecholamine content in PC12 cells is significantly decreased after 100 μM zinc treatment, but, catecholamine release during exocytosis remains nearly the same. This contrasts the number of molecules stored in the exocytosis vesicles, which decreases, and we find that the amount of catecholamine released from zinc-treated cells reaches nearly 100 percent content being expelled. Further investigation shows that zinc slows down exocytotic release allowing time for this to occur. Our results provide the missing link between zinc and the regulation of neurotransmitter release processes, which might be important in memory formation and storage.

Imaging mass spectrometry has shown to be a valuable method in medical research and can be performed using different instrumentation and sample preparation methods, each one with specific advantages and drawbacks. Time-of-flight-secondary ion mass spectrometry (TOF-SIMS) has the advantage of high spatial resolution imaging but is often restricted to low mass molecular signals and can be very sensitive to sample preparation artifacts. In this report we demonstrate the advantages of using gas cluster ion beams (GCIBs) in combination with trifluoracetic acid (TFA) vapor exposure for the imaging of lipids in mouse brain sections. There is an optimum exposure to TFA that is beneficial for increasing high mass signal as well as producing signal from previously unobserved species in the mass spectrum. Cholesterol enrichment and crystallization on the sample surface is removed by TFA exposure uncovering a wider range of lipid species in the white matter regions of the tissue, greatly expanding the chemical coverage and the potential application of TOF-SIMS imaging in neurological studies. Ar4000(+) (40 keV) in combination with TFA treatment facilitates high resolution, high mass imaging closing the gap between TOF-SIMS and matrix-assisted laser desorption ionization (MALDI).

Laser desorption ionization mass spectrometry (LDI-MS) is used to image brain lipids in the fruit fly, Drosophila, a common invertebrate model organism in biological and neurological studies. Three different sample preparation methods, including sublimation with two common organic matrixes for matrix-assisted laser desorption ionization (MALDI) and surface-assisted laser desorption ionization (SALDI) using gold nanoparticles, are examined for sample profiling and imaging the fly brain. Recrystallization with trifluoroacetic acid following matrix deposition in MALDI is shown to increase the incorporation of biomolecules with one matrix, resulting in more efficient ionization, but not for the other matrix. The key finding here is that the mass fragments observed for the fly brain slices with different surface modifications are significantly different. Thus, these approaches can be combined to provide complementary analysis of chemical composition, particularly for the small metabolites, diacylglycerides, phosphatidylcholines, and triacylglycerides, in the fly brain. Furthermore, imaging appears to be beneficial using modification with gold nanoparticles in place of matrix in this application showing its potential for cellular and subcellular imaging. The imaging protocol developed here with both MALDI and SALDI provides the best and most diverse lipid chemical images of the fly brain to date with LDI.

Am icromolar concentrationo fz inc has been shown to significantly change the dynamics of exocytosis as well as the vesicle contentsi namodel cell line, providing direct evidencet hat zinc regulates neurotransmitter release.T op rovide insight into how zinc modulates these exocytotic processes, neurotransmitter releasea nd vesicle contentw erec ompared with single cell amperometry and intracellular impact vesicle cytometry with ar ange of zinc concentrations.A dditionally,t ime-of-flight secondary ion mass spectrometry (ToF-SIMS) images of lipid distributions in the cell membranea fter zinc treatment correlatet o changes in exocytosis. By combining electrochemical techniques andm ass spectrometry imaging, we proposed a mechanism by which zinc changes the fusion pore and the rate of neurotransmitter release by changing lipid distributions and results in the modulation of synaptic strength and plasticity.

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