Monoclonal mouse anti-peripherin antibody (Chemicon, MAB1527) was used as a marker for type II spiral ganglion neurons according to previous reports (Mou et al., 1998 (link); Reid et al., 2004 (link)). The appropriate concentration of anti-peripherin antibody was determined using a preparation in which the organ of Corti and the ganglion were cultured for 3 days in vitro, such that the type I and type II afferent innervations patterns were retained and could be distinguished using anti-peripherin antibody staining (Flores-Otero and Davis, 2011 (link)). Because anti-peripherin antibody also labels type I neurons in the apex when concentrations are too high or fails to label all type II neurons in the base when the concentrations are too low, we utilized the organ of Corti cultures to establish working concentrations that were optimized for different tonotopic regions (1:6000 for apex, 1:5000 for middle and 1:4000 for base).