Fig. 4.

Synaptic counts in control and ouabain ears show the massive deafferentation in the IHC area compared with minimal change in the OHC area. A High-power confocal thumbnails of all synaptic elements are used to assess whether ribbons are orphan or paired with a receptor patch. In this sample of ribbons from the IHC area, all those in the control columns are paired, whereas only three from the ouabain column are paired (arrows), and in one of those (white arrow), the two elements are abnormally far apart. B Group means (±SEMs) for synapse survival on IHCs; group sizes were control three ears from three animals, 1 week four ears from four animals, 1 month six ears from six animals, and 3 months six ears from six animals. Data are expressed as a percentage of the mean control data. All ouabain-treated ears had ABR threshold shifts of at least 30 dB; however, the shifts were smaller than those for ears with ganglion cell counts (Fig. 2C). In each cochlear region from each animal, the count is derived from ∼20 IHCs, i.e., two confocal z-stacks such as those shown in Figure 3. C Group means (±SEMs) for synapse survival on OHCs, averaged over all three rows; group sizes for both were four ears from four animals. In each cochlear region from each animal, the count is derived from ∼65 OHCs. Data are expressed as a percentage of the mean control data. All ouabain-treated ears had ABR threshold shifts of at least 30 dB and showed synaptic losses in the IHC area exceeding 95 %, except at 4 kHz where the mean losses were 90 %. Key in B also applies to C.