Capsaicin, an agonist of transient receptor potential vanilloid receptor 1, induces axonal degeneration of peripheral sensory nerves and is commonly used to treat painful sensory neuropathies. In this study, we investigated the role of mitochondrial dynamics in capsaicin-induced axonal degeneration. In capsaicin-treated rodent sensory axons, axonal swellings, decreased mitochondrial stationary site length and reduced mitochondrial transport preceded axonal degeneration. Increased axoplasmic Ca2+ mediated the alterations in mitochondrial length and transport. While sustaining mitochondrial transport did not reduce axonal swellings in capsaicin-treated axons, preventing mitochondrial fission by overexpression of mutant dynamin-related protein 1 increased mitochondrial length, retained mitochondrial membrane potentials and reduced axonal loss upon capsaicin treatment. These results establish that mitochondrial stationary site size significantly affects axonal integrity and suggest that inhibition of Ca2+-dependent mitochondrial fission facilitates mitochondrial function and axonal survival following activation of axonal cationic channels.Electronic supplementary materialThe online version of this article (doi:10.1007/s00401-014-1354-3) contains supplementary material, which is available to authorized users.

We report plasma-enhanced chemical vapor deposition (PECVD) hydrogenated nano-crystalline silicon (nc-Si:H) thin films. In particular, the effect of hydrogen dilution ratio (R = H 2 /SiH 4) on structural and optical evolutions of the deposited nc-Si:H films were systematically investigated including Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR) and low angle X-ray diffraction spectroscopy (XRD). Measurement results revealed that the nc-Si:H structural evolution, primarily the transition of nano-crystallization from the amorphous state to the nanocrystalline state, can be carefully induced by the adjustment of hydrogen dilution ratio (R). In addition, an in situ plasma diagnostic tool of optical emission spectroscopy (OES) was used to further characterize the crystallization rate index (H α */SiH*) that increases when hydrogen dilution ratio (R) rises, whereas the deposition rate decreases. Another in situ plasma diagnostic tool of quadruple mass spectrometry (QMS) also confirmed that the "optimal" range of hydrogen dilution ratio (R = 30-40) can yield nano-crystalline silicon (n-Si:H) growth due to the depletion of higher silane radicals. A good correlation between the plasma characteristics by in situ OES/QMS and the film characteristics by XRD, Raman and FTIR, for the transition of a-Si:H to nc-Si:H film from the hydrogen dilution ratio, was obtained.

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In this study, in situ plasma diagnostic systems of optical emission spectrometry (OES) and quadrupole mass spectrometry (QMS) were used to monitor an extremely thin (5-10 nm) intrinsic amorphous/crystalline Si interface passivation film as deposited using plasma-enhanced chemical vapor deposition (PECVD). We observed a dramatic improvement in the quality of the passivation layer with a chamber background environment, even with a background pressure of 1E-6 Torr. When the chamber walls were coated (at a predeposition time of approximately 150 min) to a specified thickness of a few hundred micrometers, the minority carrier lifetime increased by more than 26 times, as compared with an insufficiently coated counterpart with a predeposition of approximately 30 min (from approximately 30 μs to 800 μs). In this predeposition process, the tendency of species to concentrate could be systematically obtained using the in situ OES system, with the chamber environment monitored using residual gas analysis and threshold ionization mass spectrometry of QMS. We found that the optimal predeposition time was 150 min, which enabled the OES intensity of Si * /SiH * , H β /Hα, and Hα/SiH * to become stable. OES and QMS were incorporated in this study and were validated using the Fourier-transform infrared spectroscopy absorbance spectra on the films. The plasma condition was stabilized and the minority carrier lifetime was improved to 800 μs. The proposed predeposition process stabilized the chamber environment and gas discharge. Therefore, the optimized value of the minority carrier lifetime could be consistently obtained. A transmission electron microscopy photograph showed a compact a-Si:H layer (of approximately 10 nm) on the c-Si substrate interface passivation layer with a void-free and crystallites-free interface after a predeposition time of 150 min.