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

Figure 5

Reevaluation of results using post hoc histological categorization. (a) Category 1 consists of cochleas without any OHC loss. In Category 2, average OHC loss is moderate and in Category 3 the average number of remaining OHC has even decreased more. Normal (100%) is 21 OHCs, the sum of OHCs counted at B1, B2, M1, M2, A1, A2, and A3. (b) Average SGC packing density in Category 1 cochleas is near-normal. There is on average minor loss of SGCs (i.e., <20%) in Category 2, whereas the average SGC packing density in Category 3 cochleas is approximately half of that in normal-hearing controls, i.e., the left (nontreated) cochleas. Normal (100%) is 1362 SGCs/mm², the average SGC packing density determined in B1, B2, M1, M2, and A1. (c) The wave II threshold of Category 1 remains normal, while animals in Categories 2 and 3 showed a substantial shift in wave II threshold, 4 days after treatment with ouabain. The wave II threshold shifts do not differ between Categories 2 and 3. (d) Animals in Category 1 show a slight decrease in their wave II amplitude, whereas animals in both Categories 2 and 3 show a much larger decrease, 4 days after ouabain treatment. The wave II amplitudes in Categories 2 and 3 do not significantly differ from one another. OHC counts (a) and SGC packing densities (b) are normalized and expressed as percentages of an averaged dataset from the left (untreated) cochleas (normal). Thresholds (c) and amplitudes (d) are normalized and expressed as change (in dB) from pretreatment levels. Error bars represent SEM.

(a) OHC counts

(b) SGC packing densities

(c) Wave II threshold

(d) Wave II amplitude