Figure 2

Innervations of vestibular and cochlear sensory epithelia are highly compromised in mice lacking both the PLCγ and the SHC docking sites of TrkB. The pattern of afferent (A, D) and efferent (B-C, E-F) innervations of newborn control (C, F) and Trkb^D/D mutant mice (A-B, D-E) is revealed by filling afferent or efferent from specific areas of the brainstem. Note that many afferent (A) and efferent (B) fibers reach the utricle (u) but only few fibers reach the canal cristae (A, B), whereas canal cristae are densely innervated in control mice (C). Trkb^D/D mutant mice show wider spacing between radial fiber bundles (RF), both afferent (D) and efferent (E), compared to control (F). Schematic diagrams show the changes in innervation density of afferents (red) and efferent fibers (green) to the various sensory epithelia. Note that in Trkb^D/D mutant mice compared to controls (Trkb^WT/WT) the fiber density to canal cristae is reduced (AC, HC) or lost (PC) and that the density of innervation of utricle, saccule and cochlear apex is also reduced (larger green/red boxes), whereas the basal turn organ of corti innervation density is similar to controls. Innervation density in the schematic diagrams is indicated by green/red squares. AC, anterior cristae; HC, horizontal cristae; U, utricle; S, saccule; OC, organ of Corti; RF, radial fibers; Spgl, spiral ganglion. Scale bars, 100 μm.