title: Post-treatment effects of local GDNF administration to the inner ears of deafened guinea pigs.
abstract: For patients with profound hearing loss, a cochlear implant is the only treatment available today. The function of a cochlear implant depends in part on the function and survival of spiral ganglion neurons. Following deafferentation, glial cell-derived neurotrophic factor (GDNF) is known to affect spiral ganglion neuron survival. The purpose of this study was to assess delayed GDNF treatment after deafening, the effects of cessation of GDNF treatment, and the effects of subsequent antioxidants on responsiveness and survival of the spiral ganglion neurons. Three-week deafened (by local neomycin administration) guinea pigs were implanted in the scala tympani with a combined cochlear implant electrode and cannula. GDNF (1 μg/mL) or artificial perilymph was then delivered for 4 weeks, following which the animals received systemic ascorbic acid  +  Trolox or saline for an additional 4 weeks. Thresholds for electrically-evoked auditory brain stem responses (eABRs) were significantly elevated at 3 weeks with deafness, stabilized with GDNF, and showed no change with GDNF cessation and treatment with antioxidants or saline. The populations of spiral ganglion neurons were reduced with deafness (by 40% at 3 weeks and 70% at 11 weeks), and rescued from cell death by GDNF with no further reduction at 8 weeks following 4 weeks of cessation of GDNF treatment equally in both the antioxidant- and saline-treated groups. Local growth factor treatment of the deaf ear may prevent deterioration in electrical responsiveness and rescue auditory nerve cells from death; these effects outlast the period of treatment, and may enhance the benefits of cochlear implant therapy for the deaf.
authors.affiliation: Center for Hearing and Communication Research and Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.
authors.forename: Anette
authors.initials: A
authors.lastname: Fransson
authors.forename: Jun
authors.initials: J
authors.lastname: Maruyama
authors.forename: Josef M
authors.initials: JM
authors.lastname: Miller
authors.forename: Mats
authors.initials: M
authors.lastname: Ulfendahl
mesh_terms: D000161:Acoustic Stimulation / Q000379:methods; D000818:Animals; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D003638:Deafness / Q000188:drug therapy* / Q000473:pathology / Q000503:physiopathology; D007758:Ear, Inner / Q000187:drug effects* / Q000502:physiology; D005072:Evoked Potentials, Auditory / Q000187:drug effects* / Q000502:physiology; D005260:Female; D051100:Glial Cell Line-Derived Neurotrophic Factor / Q000008:administration & dosage*; D006168:Guinea Pigs; D008297:Male; D016896:Treatment Outcome
chemical_list: D051100:Glial Cell Line-Derived Neurotrophic Factor