Nogo in the Mammalian cochlea.

Hypothesis: Different members of the Nogo system are expressed in the mammalian cochlea. Background: The protein Nogo has gained a lot of attention during the last couple of years because it inhibits neurite outgrowth in the adult central nervous system. In contrast to the central nervous system, very little is known regarding the expression and possible function of the Nogo system within the inner ear. Methods: Using reverse-transcriptase-polymerase chain reaction and immunohistochemistry, we analyzed for the expression of members of the Nogo system within the cochlea. In addition, we determined hearing levels of Nogo A knockout and wildtype mice with auditory brainstem response audiometry. Results: In this study, we demonstrate the expression of Nogo A, B, C, and of Nogo receptor mRNA in the organ of Corti, spiral ganglion, and stria vascularis. Immunohistochemistry revealed that Nogo A and Nogo receptor localize to the spiral ganglion neurons. Interestingly, Nogo A expression was also observed in the outer and inner hair cells of the organ of Corti. As revealed by light microscopy, deletion of Nogo A does not alter cochlear microanatomy. We have assessed hearing levels in 10-month old wild-type and Nogo A knockout mice, and thereby, we could not detect any differences between these 2 groups. Conclusion: Different members of the Nogo family are expressed in the mammalian cochlea. Deletion of Nogo A does not alter cochlea microanatomy or hearing levels compared with wild-type mice.