Poly(allylamine) (a mimic of biopolyamines) and the R5 peptide (a repeat unit of a silaffin protein isolated from a diatom) induce the formation of mineralized titanium from soluble titanium(IV) precursors. These reactions proceed under mild aqueous conditions. Scanning electron microscopy shows that the nanometer to micrometer diameter particles induced by poly(allylamine) are spherical under a range of conditions, while those induced by the R5 peptide include spheres and fused structures. Dynamic light scattering experiments confirm the SEM results and reveal that the particles range in size from 2 nm to 5 μm. The surface charge is negative at neutral pH. Energy dispersive X-ray spectroscopy shows the composition to be primarily titanium, oxygen, and phosphorus. The solids are amorphous at room temperature by powder X-ray diffraction but the material induced by poly(allylamine) converts to cubic crystalline TiP2O7 with annealing to 800 °C. Infrared spectroscopy suggests that the biomolecule mineralization inducers are encapsulated in the solid. Discrete poly(allylamine)-induced spheres are formed only between pH 7−9.5, with polydispersity strongly dependent on pH. The surface of the poly(allylamine)-induced spheres becomes smoother at higher reaction temperatures. Green fluorescent protein can be immobilized in the solid induced by poly(allylamine) but not R5 peptide under the conditions examined.
Huntington’s disease is a fatal, neurodegenerative movement disorder characterized by preferential and extensive striatal degeneration. Here, we used fast-scan cyclic voltammetry to study the mobilization and efflux of reserve pool dopamine in striatal brain slices from Huntington’s disease model R6/2 mice. When applying stimulus trains of 120 pulses, evoked dopamine release in wild-type slices was greater than that in R6/2 slices at the higher frequencies (50 and 60 Hz). To quantify cytosolic and reserve pool dopamine levels, amphetamine-induced dopamine efflux was measured after pre-treatment with either tetrabenazine or alpha-methyl-p-tyrosine. Slices from 12-week old R6/2 mice released less dopamine than slices from wild-type mice, while no difference was noted in slices from 6-week old mice. The vesicular release of reserve pool dopamine, mobilized by treatment with cocaine, was shorter lived in R6/2 slices compared to wild-type slices even though peak dopamine release was the same. Moreover, the number of dopamine reserve pool vesicles in R6/2 mice was less than half of that in wild-type. Therefore, our data suggest that the same number of dopamine molecules are present in each reserve pool vesicle in WT and R6/2 mice and that these vesicles are readily mobilized in both genotypes; however, R6/2 mice have fewer dopamine reserve pool vesicles available for mobilization.
Huntington’s disease (HD) is a progressive, neurodegenerative movement disorder. Here, we used fast-scan cyclic voltammetry to measure dopamine release and uptake in striatal brain slices from R6/1 HD model mice. Peak dopamine release ([DA]max) was significantly diminished in R6/1 mice (52% of wild-type at 24 weeks of age). Similarly, dopamine released per locally applied electrical stimulus pulse ([DA]p), which is [DA]max corrected for uptake and electrode performance, was also diminished in R6/1 mice (43% of wild-type by 24 weeks of age). Moreover, Vmax, the maximum rate of dopamine uptake, obtained by modeling the stimulated release plots, was decreased at 16 and 24 weeks of age in R6/1 mice (51 and 48% of wild-type, respectively). Thus, impairments in both dopamine release and uptake appear to progress in an age-dependent manner in R6/1 mice.
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