Horseradish peroxidase dye tracing and embryonic statoacoustic ganglion cell transplantation in the rat auditory nerve trunk

At present severe damage to hair cells and sensory neurons in the inner ear results in non-treatable auditory disorders. Cell implantation is a potential treatment for various neurological disorders and has already been used in clinical practice. In the inner ear, delivery of therapeutic substances including neurotrophic factors and stem cells provide strategies that in the future may ameliorate or restore hearing impairment. In order to describe a surgical auditory nerve trunk approach, in the present paper we injected the neuronal tracer horseradish peroxidase (HRP) into the central part of the nerve by an intra cranial approach. We further evaluated the applicability of the present approach by implanting statoacoustic ganglion (SAG) cells into the same location of the auditory nerve in normal hearing rats or animals deafened by application of β-bungarotoxin to the round window niche. The HRP results illustrate labeling in the cochlear nucleus in the brain stem as well as peripherally in the spiral ganglion neurons in the cochlea. The transplanted SAGs were observed within the auditory nerve trunk but no more peripheral than the CNS-PNS transitional zone. Interestingly, the auditory nerve injection did not impair auditory function, as evidenced by the auditory brainstem response. The present findings illustrate that an auditory nerve trunk approach may well access the entire auditory nerve and does not compromise auditory function. We suggest that such an approach might compose a suitable route for cell transplantation into this sensory cranial nerve.

Research Highlights
► Auditory nerve trunk approach injections do not impair auditory function.
► HRP injected to the AN can be distributed both anteriogradely and retrogradely.
► SAGs implanted to the auditory nerve trunk survive for up to 5 weeks.