ENHANCED PRESERVATION OF THE AUDITORY-NERVE FOLLOWING COCHLEAR PERFUSION WITH NERVE GROWTH-FACTOR

Survival of auditory neurons in the cochlea is thought to be an import ant factor in the success of cochlear implantations. Damage to the coc hlear end-organ often produces loss of dendrites in the osseous spiral lamina. The authors have established a method that delivers water sol uble pharmacologic agents to the cochlea using a mini osmotic pump wit h a polyethylene cannula that is inserted into the scala tympani via c ochleostomy. The cannula is filled with an ototoxic agent, neomycin, t hat destroys the end-organ over the first 24 hours after insertion. Ne rve growth factor (NGF), or a control substance, is placed in the pump reservoir and is pumped into the cochlea over a 2-week period. In thi s study, auditory nerve fibers in the osseous spiral lamina were count ed in the apical, middle, and basal turns of the cochlea in 16 guinea pigs. At each location, fiber counts were significantly higher when ne omycin was followed by perfusion with NGF, than when it was followed b y infusion with control substances. The study demonstrates that NGF co nfers some protection against ototoxic induced degeneration of the aud itory nerve in vivo.