Spiral ganglion cell survival after round window membrane application of brain-derived neurotrophic factor using gelfoam as carrier.

Several studies have shown that treatment with various neurotrophins protects spiral ganglion cells (SGCs) from degeneration in hair-cell deprived cochleas. In most of these studies the neurotrophins are delivered by means of intracochlear delivery methods. Recently, other application methods that might be more suited in cochlear implant patients have been developed. We have examined if round window membrane application of gelfoam infiltrated with a neurotrophin resulted in SGC survival in deafened guinea pigs. Two weeks after deafening, gelfoam cubes infiltrated with 6 μg of brain-derived neurotrophic factor (BDNF) were deposited onto the round window membrane of the right cochleas. Electric pulses were delivered through an electrode positioned within the round window niche to electrically evoke auditory brainstem responses (eABRs). Two or four weeks after deposition of the gelfoam all cochleas were histologically examined. We found that local BDNF treatment enhances the survival of SGCs in the basal cochlear turn after two and four weeks. The treatment had no effect on SGC size or shape. In animals treated with BDNF, eABR amplitudes were smaller than in normal-hearing control animals and similar to those in deafened controls. We conclude that BDNF delivered by means of local gelfoam application provides a protective effect, which is limited compared to intracochlear delivery methods.