Promotion of neurite outgrowth and axon guidance in spiral ganglion cells by netrin-1.

OBJECTIVE To identify the expression of netrin-1, a diffusible chemoattractive molecule, and its receptor, deleted in colorectal carcinoma (DCC), in the developmentally mature inner ear, and to determine its effects on axon length and guidance in cultured auditory neurons. DESIGN Messenger RNA (mRNA) and protein expression of netrin-1 and DCC were identified in the organ of Corti and spiral ganglion cells using reverse transcription-polymerase chain reaction (RT-PCR) and fluorescence immunohistochemical analysis. In vitro experiments examined the effects of exogenous netrin-1 on spiral ganglion cell axon length. Auditory neurons were cocultured with a cell line secreting netrin-1 to determine the effect on direction of axon extension. SUBJECTS Young C57 mice and posthatched white leghorn chicks. RESULTS Netrin-1 and DCC mRNA expression were found in the mouse organ of Corti and spiral ganglion cells by RT-PCR. Application of exogenous netrin-1 led to a dosage-dependent increase in neurite length in cultured spiral ganglion cells. Chick acoustic ganglion cells cocultured with netrin-1-secreting cells demonstrated statistically significant preferential extension toward the source of netrin-1 (P = .04). CONCLUSIONS Netrin-1 and DCC are expressed in the organ of Corti and spiral ganglion cells of developmentally mature mice. Exogenous netrin-1 promotes dosage-dependent neurite growth in vitro. Mature auditory neurons preferentially direct neurite extension toward netrin-1 released in culture. These findings may lead to the development of strategies to optimize the interface between electrode arrays and spiral ganglion cells, resulting in improved cochlear implant performance.