Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to study the effects of cocaine versus methylphenidate administration on both the localization and abundance of lipids in Drosophila melanogaster brain. A J105 ToF-SIMS with a 40 keV gas cluster primary ion source enabled us to probe molecular ions of biomolecules on the fly with a spatial resolution of ∼3 μm, giving us unique insights into the effect of these drugs on molecular lipids in the nervous system. Significant changes in phospholipid composition were observed in the central brain for both. Principal components image analysis revealed that changes occurred mainly for phosphatidylcholines, phosphatidylethanolamines, and phosphatidylinositols. When the lipid changes caused by cocaine were compared with those induced by methylphenidate, it was shown that these drugs exert opposite effects on the brain lipid structure. We speculate that this might relate to the molecular mechanism of cognition and memory.

For decades, “all-or-none” and “kiss-and-run” were thought to be the only major exocytotic release modes in cell-to-cell communication, while the significance of partial release has not yet been widely recognized and accepted owing to the lack of direct evidence for exocytotic partial release. Correlative imaging with transmission electron microscopy and NanoSIMS imaging and a dual stable isotope labeling approach was used to study the cargo status of vesicles before and after exocytosis; demonstrating a measurable loss of transmitter in individual vesicles following stimulation due to partial release. Model secretory cells were incubated with 13 C-labeled l -3,4-dihydroxyphenylalanine, resulting in the loading of 13 C-labeled dopamine into their vesicles. A second label, di- N -desethylamiodarone, having the stable isotope 127 I, was introduced during stimulation. A significant drop in the level of 13 C-labeled dopamine and a reduction in vesicle size, with an increasing level of 127 I – , was observed in vesicles of stimulated cells. Colocalization of 13 C and 127 I – in several vesicles was observed after stimulation. Thus, chemical visualization shows transient opening of vesicles to the exterior of the cell without full release the dopamine cargo. We present a direct calculation for the fraction of neurotransmitter release from combined imaging data. The average vesicular release is 60% of the total catecholamine. An important observation is that extracellular molecules can be introduced to cells during the partial exocytotic release process. This nonendocytic transport process appears to be a general route of entry that might be exploited pharmacologically.

Understanding FA metabolism and lipid synthesis requires a lot of information about which FAs and lipids are formed within the cells. We focused on the use of deuterated substrates of 100 μM α-linolenic acid and linoleic acid to determine the relative amounts of their converted PUFAs and specific phospholipids that are incorporated into cell plasma membranes. Time-of-flight secondary ion mass spectrometry (TOF-SIMS) was used to image and analyze lipids in model cell membranes with and without FA treatment. Because of its high spatial resolution, TOF-SIMS can be used to simultaneously provide both chemical information and distribution of various molecules in the sample surface down to the subcellular scale. Data obtained from this analysis of isotopes in the cell samples were used to calculate the relative amounts of long-chain PUFAs and phospholipids from their precursors, α-linolenic acid and linoleic acid. Our results show that the FA treatments induced an increase in the amounts of α-linolenic acid and linoleic acid and their long-chain conversion products. Moreover, an enhanced level of phospholipid turnover of these FAs in lipids such as phosphatidylcholines, phosphatidylethanolamines, and phosphatidylinositols was also observed in the cell plasma membrane.