A,B: Electron micrographs of endbulb of Held (EB) profiles (yellow) ipsilateral to the cochlear implant placed in 3-month-old congenitally deaf cats. Note that the PSDs (*) are restored to their normal dome shape. A′,B′: The 3-D reconstructions illustrate the return of PSDs to their normal size and distribution. The red area highlights the sections of the EB series shown in the electron micrographs, and the horizontal lines indicate section edges. SBC, spherical bushy cell. Scale bar = 0.5 μm in A (applies to A,B) and A′ (applies to A′,B′).