Scanning laser optical tomography in a neuropathic mouse model: Visualization of structural changes

Background In the field of hearing research a variety of imaging techniques are available to study molecular and cellular structures of the cochlea. Most of them are based on decalcifying, embedding, and cutting of the cochlea. By means of scanning laser optical tomography (SLOT), the complete cochlea can be visualized without cutting. The Ca v 1.3 −/− mice have already been extensively characterized and show structural changes in the inner ear. Therefore, they were used in this study as a model to investigate whether SLOT can detect structural differences in the murine cochlea. Materials and methods Whole undissected cochleae from Ca v 1.3 −/− and wild-type mice of various postnatal stages were immunostained and analyzed by SLOT. The results were compared to cochlea preparations that were immunostained and analyzed by fluorescence microscopy. In addition, cochlea preparations were stained with osmium tetraoxide. Results Visualization by SLOT showed that the staining of nerve fibers at P27 in Ca v 1.3 −/− mice was almost absent compared to wild-type mice and earlier timepoints (P9). The analysis of cochlea preparations confirmed a reduction of the radial nerve fibers. In addition, a significantly reduced number of ribbon synapses per inner hair cell (IHC) at P20 and P27 in the apical part of the cochlea of Ca v 1.3 −/− mice was detected. Conclusion The visualization of whole non-dissected cochleae by SLOT is a suitable tool for the analysis of gross phenotypic changes, as demonstrated by means of the Ca v 1.3 −/− mouse model. For the analysis of finer structures of the cochlea, however, further methods must be used.