Figure 4-6921.

Western blot quantification of reduced TrkB but elevated p75NTR proteins in cochlear homogenates from deafened animals. Cochlear proteins from normal hearing and deafened animals experiencing two distinct durations of deafness (6 to 7 weeks versus 9 weeks or longer) were immunoblotted with pan-TrkB, Ab 9992 (p75NTR), and GAPDH antibodies. The intensity of the full-length TrkB immunoreactive band was progressively reduced after 6 and 9 weeks of deafness (A, TrkB, full-length), whereas the intensity of the truncated fragment did not vary considerably (A, TrkB, truncated). On the contrary, in the same blot, there was an up-regulation of p75NTR-immunoreactive band (A, p75), whereas GAPDH levels remained relatively constant between samples (A, GAPDH). The intensity of the full-length (fl)-TrkB band was normalized to the GAPDH band in three independent experiments, and the mean ratio for each group was then expressed as a relative percentage of the control group of normal hearing animals (B). Statistical significance between each deafness cohort and the control group is indicated by asterisks. There was a significant reduction in this ratio in the two deafness cohorts (B, **P < 0.01). Similarly, the intensity of the p75NTR-band was normalized to the GAPDH band in four independent experiments, and the mean ratio for each group was again expressed as a relative percentage of the control group of normal hearing animals (C). Comparison between the control group and each of the deafened cohorts showed a significant increase in this ratio in animals deafened for 6 to 7 weeks (C, *P < 0.05) and animals experiencing more than 9 weeks of deafness (C, **P < 0.01). Numerical data indicate means ± SEM.