A–F Vglut1 immunoreactivity (A,B), Calb1 immunoreactivity (C,D), or Nissl stained sections (E,F) in the superior olivary complex of adult (P22– P30) wild type (A,C,E) or Dicer1Egr2 mice (B,D,F). Only weak Vglut1 staining is observed in the SOC of Dicer1Egr2 mice and principal nuclei such as the MNTB or the U-shaped LSO cell group are absent in these animals. Calb1 labeling is observed in somata of MNTB neurons and in the neuropil of the LSO, MSO, and SPN in wild type mice. No labeling is observed in Dicer1Egr2 mice. In Nissl stained sections, the cell groups of the MNTB and LSO are recognizable in control mice, but not in Dicer1Egr2 mice. The cell group at the ventral part in Dicer1Egr2 mice corresponds to the olivocochlear neurons. G–J Vglut1 immunoreactivity (G,H), or Nissl stained sections (I,J) in the superior olivary complex of P0 wild type (G,I) or Dicer1Egr2 mice (H,J). Vglut1 staining is restricted to the olivocochlear neurons in the SOC of Dicer1Egr2 mice, and principal nuclei such as the MNTB or the LSO cell group are absent in these animals. In Nissl stained sections, the cell groups of the MNTB and LSO are recognizable in wild type mice, but not in Dicer1Egr2 mice. The cell group at the ventral part in Dicer1Egr2 mice corresponds to the olivocochlear neurons. LSO, lateral superior olive; MNTB, medial nucleus of the trapezoid body; MSO, medial superior olive; OCN, olivocochlear neurons; SPN, superior paraolivary nucleus. Dorsal is up, lateral is to the right.