Ouabain Does Not Induce Selective Spiral Ganglion Cell Degeneration in Guinea Pigs

Figure 3

Quantification of OHC loss and SGC loss after ouabain treatment. Data are normalized and expressed as percentages of an averaged dataset from the left (untreated) cochleas (normal). (a) OHC loss accrues with increasing ouabain concentrations (1 mM: 72.6 ± 11.0% of OHCs remaining; 10 mM: 38.1 ± 4.8% of OHCs remaining). IHCs are not affected. Control (0 mM) includes right ears treated with PBS alone. Normal (100%) is 21 OHCs, the sum of OHCs counted at B1, B2, M1, M2, A1, A2, and A3. (b) SGC loss also progresses with increased ouabain concentrations. Compared to SGC packing densities in the left (nontreated) cochleas, near-normal numbers (95.3 ± 2.8%) of the SGC perikarya are present in cochleas treated with 0.01 mM and 0.1 mM ouabain. Control (0 mM) includes right ears treated with PBS alone. Normal (100%) is 1362 SGCs/mm², the average SGC packing density determined in B1, B2, M1, M2, and A1. Cochleas treated with 1 mM ouabain show a moderate loss with an average of 87.4 ± 8.7% of SGC perikarya remaining, whereas in cochleas treated with 10 mM ouabain the average number of SGC perikarya present in Rosenthal’s canal decreases to 64.6 ± 17.2%. Error bars represent SD; = p ≤ 0.01, = p ≤ 0.001. (c) OHC counts in the basal, middle, and apical turns at 1 mM and 10 mM ouabain and the average OHC count (cf. Figure 3(a)). For basal and middle turns, normal (100%) is 6 OHCs per turn, i.e., the sum of OHCs counted at B1+B2 and M1+M2, respectively, and for the apical turn normal (100%) is 9 OHCs, the sum of OHCs counted at A1+A2+A3. At a concentration of 1 mM, ouabain causes OHC loss in the basal (50.0 ± 18.9%) and middle (35.4 ± 15.6%) turns. In the apical turn, OHC counts are almost normal (93.1 ± 7.0%). A concentration of 10 mM ouabain results in loss of OHCs in all turns. In the basal turn 91.7 ± 8.4% and in the middle turn 83.3% of the OHCs are lost. In the apical turn, approximately 27.8 ± 5.5% of the OHCs is lost. (d) SGC packing densities in the basal, middle, and apical turns at 1 mM and 10 mM ouabain and the average SGC packing density (cf. Figure 3(b)). Normal (100%) is 1293 SGCs for the basal turns, 1470 SGCs for the middle turns, and 1325 SGCs for the apical turn. In the basal turn, SGC packing densities are reduced to 66.9 ± 12.6%, while they are near-normal in the middle (96.2 ± 9.2%) and apical (111.0 ± 6.5%) turns. At a concentration of 10 mM ouabain, SGC packing densities are reduced to 40.5 ± 17.0% in the basal turn and 73.1 ± 20.1% in the middle turn. The packing density in the apical turn is normal (95.8 ± 8.1%).

(a) OHC counts

(b) SGC packing densities

(c) OHC counts

(d) SGC packing densities