Defined Growth Factor Combination of BDNF and NT-3 Increased Neurite Outgrowth in a Postnatal Day 7 Murine In Vitro Spiral Ganglion Explant Model

Cochlea implants (CI) are the method of choice for patients suffering sensorineural hearing loss. A major obstacle is the spatial distance between the electrode array of the CI in scala tympani and the stimulated region of the auditory nerve. This anatomical gap restricts the number of information channels provided by the implant. To increase frequency selectivity, a direct coupling between the CI electrodes and the cochlear nerve fibers should be achieved. Therefore, the neurite outgrowth from the spiral ganglia neurons (SGNs) towards and onto the electrode should be induced. The regulation of outgrowth, maintenance and survival of nerve fibers in the inner ear is crucially linked to factors like BDNF (brain-derived neurotrophic factor) and NT-3 (neurotrophin 3). In the cochlea, an opposing NT-3 and BDNF gradient from base to apex and in addition a reversal of the gradient during development was described.

We tested SGN outgrowth in vitro by applying BDNF and NT-3 either individually or both in combination of various compositions. For better comparison to the adult situation and to account for the switch from embryonic to adult phenotype, we established a mouse organotypic in vitro spiral ganglion explant model at postnatal day 7 (P7) utilizing 96-well plates. Effective stimulation of neurite outgrowth was quantified using an adapted Sholl analysis (ImageJ plugin).

Under control conditions (no growth factor added) the P7 spiral ganglion explant model shows substantial neurite outgrowth, BDNF or NT-3 enhanced this outgrowth. This could be even potentiated by combining BDNF and NT-3.

The presented new model, more resembling the adult situation, is suitable for the evaluation of compounds affecting the SGN neurite outgrowth in vitro.

Publication History

Publication Date:
23 April 2019 (online)