Immunostaining of afferent and efferent fibers with TuJ1 reveals alterations in fiber fasciculation. A: Afferent fibers under the outer hair cells, running as the outer spiral bundle (OSB) and efferent fibers in the inner spiral bundle (ISB), run as tight bundles in wild type mice. The inner spiral bundle (ISB) is compact and outlines the region occupied by unstained inner hair cells (asterisk identifies one such region). B: In the SK2-/- mice, OSB fibers are de-fasciculated (arrowhead) from the main bundle, and run as individual fibers (arrows). The ISB is likewise disorganized, and IHC pockets are seldom observed.