Numbers of surface transplanted cells and spiral ganglion cells (SGCs) in rats with and without ABR improvement. (A–C) Three months after cell transplantation, donor cells were abundant within the auditory nerve trunk (arrowheads in A and B), and at the fundus and along the wall of the internal auditory canal (IAC) (arrowheads in C) in rats with improved ABRs. These cells aggregated as observed in Rosenthal’s canal (areas 1 and 2 in C). The boxed areas in A–C are enlarged in each adjacent panel. The dotted line in C is the fundus and wall of the IAC. (D) The number of eGFP+ transplanted cells was significantly larger in the rats with improved ABRs than in those without. The survival rate of transplanted cells in the rats with ABR improvement was 13.7% of total transplanted cells. (E) Residual spiral ganglion cells in basal, middle, and apical cochlear turns of sham-treated and treated rats without ABR improvement are shown. Arrows indicate residual spiral ganglion cells in middle cochlear turns. (F) There was no significant difference in the residual numbers of endogenous SGCs between the rats with and without improved ABRs. Approximately 83–87% of SGCs degenerated after auditory nerve injury. The data are from four sham-operated rats, six rats with ABR improvement, and four rats without ABR improvement. AuN, auditory nerve. (Scale bars, 500 μm in left panels of A–C; 50 μm in right panels of C and E; and 40 μm in right panels of A and B.) *P < 0.05, ***P < 0.01, ****P < 0.001.