Fig. 5. Reduced size of efferent synapses in the absence of Bdnf and TrkB signalling. Cochleae of adult TrkB^shc/+, TrkB^shc/-, Bdnf^+/+ and Bdnf^-/- mice at P19 were isolated, sectioned, and double-immunostained with anti-synaptophysin and anti-SK2 antibodies as described under Materials and methods. (A) Representative micrographs illustrating synaptophysin (Syn; green) and SK2 (red) staining at the outer hair cell (OHC) level of the basal cochlear turn in mice with the indicated genotypes. Note the severe reduction of synaptophysin-positive boutons and of SK2 staining opposite the synaptic bouton in TrkB^shc/- and Bdnf^-/- mutant mice compared with their respective controls. (B) Higher magnification view of a representative OHC from A. Area outlined by dotted line represents the position of the OHC body. Scale bars: 10 µm in A; 5 µm in B.