Neurotrophins differentially stimulate the growth of cochlear neurites on collagen surfaces and in gels.

The electrodes of a cochlear implant are located far from the surviving neurons of the spiral ganglion, which results in decreased precision of neural activation compared to the normal ear. If the neurons could be induced to extend neurites toward the implant, it might be possible to stimulate more discrete subpopulations of neurons, and to increase the resolution of the device. However, a major barrier to neurite growth toward a cochlear implant is the fluid filling the scala tympani, which separates the neurons from the electrodes.

Laminin and fibronectin modulate inner ear spiral ganglion neurite outgrowth in an in vitro alternate choice assay.

Extracellular matrix (ECM) molecules have been shown to function as cues for neurite guidance in various populations of neurons. Here we show that laminin (LN) and fibronectin (FN) presented in stripe micro-patterns can provide guidance cues to neonatal (P5) inner ear spiral ganglion (SG) neurites. The response to both ECM molecules was dose-dependent.

Environmental micro-patterning for the study of spiral ganglion neurite guidance.

The projection of neuronal processes is guided by a variety of soluble and insoluble factors, which are sensed by a fiber's growth cone. It is the differential distribution of such guidance cues that determine the direction in which neurites grow. The growth cone senses these cues on a fine scale, using extensible filopodia that range from a few to tens of mum in length.