Retinal ganglion cell dendritic pruning has been reported in association with a 50% reduction in Opa1 transcript and protein in retinal and neural tissue, which manifests as visual dysfunction in the heterozygous mutant mouse, B6;C3-Opa1(Q285STOP). Here we report a marked reduction in retinal ganglion cell synaptic connectivity in the absence of soma loss and explore the mechanism and relationship between mitochondrial integrity and synaptic connectivity. We observed decreased levels of postsynaptic density protein 95 in Opa1(+/-) mutant mice consistent with synaptic loss in the inner plexiform layer. Glutamatergic but not γ-aminobutyric acid-ergic synaptic sites were reduced in Opa1(+/-) mice. We observed increased synaptic vesicle number in bipolar cell terminal arbours assessed by immunohistochemistry, electron microscopy and western blot analysis. These changes occur without significant loss of mitochondrial membrane potential in retina and optic nerve. Analysis of biolistically transfected retinal ganglion cells shows the retraction of mitochondria towards the soma, and mitochondrial fragmentation, preceding dendritic loss. These processes cast light on the intimate relationship between normal mitochondrial fusion and fission balances, as influenced by the OPA1 protein, in neural cell connectivity in the mammalian retina.

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Raman and Fourier transform infrared (FT-IR) spectroscopic imaging techniques can be used to characterize bone composition. In this study, our objective was to validate the Raman mineral:matrix ratios (ν PO:amide III, ν PO:amide I, ν PO:Proline + hydroxyproline, ν PO:Phenylalanine, ν PO:δ CH peak area ratios) by correlating them to ash fraction and the IR mineral:matrix ratio (ν PO:amide I peak area ratio) in chemical standards and native bone tissue. Chemical standards consisting of varying ratios of synthetic hydroxyapatite (HA) and collagen, as well as bone tissue from humans, sheep, and mice, were characterized with confocal Raman spectroscopy and FT-IR spectroscopy and gravimetric analysis. Raman and IR mineral:matrix ratio values from chemical standards increased reciprocally with ash fraction (Raman ν PO/Amide III: P < 0.01, R= 0.966; Raman ν PO/Amide I: P < 0.01, R= 0.919; Raman ν PO/Proline + Hydroxyproline: P < 0.01, R= 0.976; Raman ν PO/Phenylalanine: P < 0.01, R= 0.911; Raman ν PO/δ CH: P < 0.01, R= 0.894; IR P < 0.01, R= 0.91). Fourier transform infrared mineral:matrix ratio values from native bone tissue were also similar to theoretical mineral:matrix ratio values for a given ash fraction. Raman and IR mineral:matrix ratio values were strongly correlated ( P < 0.01, R= 0.82). These results were confirmed by calculating the mineral:matrix ratio for theoretical IR spectra, developed by applying the Beer-Lambert law to calculate the relative extinction coefficients of HA and collagen over the same range of wavenumbers (800-1800 cm). The results confirm that the Raman mineral:matrix bone composition parameter correlates strongly to ash fraction and to its IR counterpart. Finally, the mineral:matrix ratio values of the native bone tissue are similar to those of both chemical standards and theoretical values, confirming the biological relevance of the chemical standards and the characterization techniques.