Fig. 3. Rescue of neuronal numbers, target innervation and function in the cochlea in BDNF^NT3/NT3 mice. (A) BDNF and NT3 expression in the cochlea during development and in adult animals. BDNF (red) is expressed in the hair cells during development while NT3 (blue) is expressed in both hair cells and supporting cells. In adult animals NT3 is only expressed in the IHC. (B) Auditory brainstem response in BDNF^–/– (green), BDNF^NT3/NT3 (red) and wild-type (blue) mice. Note that the BDNF^–/– mice suffer from a hearing loss that is completely rescued in the BDNF^NT3/NT3 mice. (C,D) Afferent innervation in sections from the apical to middle part of the cochlea stained with an antibody directed against p75^NTR (red) counterstained with phalloidin (green) to visualise the hair cells. Scale bars: 20 µm. The arrows indicate the OHC. Note innervation of the three rows of OHCs in the BDNF^NT3/NT3 mice. (E) Spiral ganglion neurons (SGN) were counted at P0 and P17. At P0 25% (n=3) and at P17 29% (n=4) of the neurons were lost in BDNF^–/– mice compared to wild-type mice. This loss was rescued at P0 in BDNF^NT3/NT3 mice (n=3) and at P17 there was still no significant difference between the wild-type (n=4) and BDNF^NT3/NT3 mice (n=3). ANOVA Fischer's ***P<0.001; ±s.e.m.

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