Temporary Neurotrophin Treatment Prevents Deafness-Induced Auditory Nerve Degeneration and Preserves Function.
After substantial loss of cochlear hair cells, exogenous neurotrophins prevent degeneration of the auditory nerve. Because cochlear implantation, the current therapy for profound sensorineural hearing loss, depends on a functional nerve, application of neurotrophins is being investigated. We addressed two questions important for fundamental insight into the effects of exogenous neurotrophins on a degenerating neural system, and for translation to the clinic. First, does temporary treatment with brain-derived neurotrophic factor (BDNF) prevent nerve degeneration on the long term? Second, how does a BDNF-treated nerve respond to electrical stimulation? Deafened guinea pigs received a cochlear implant, and their cochleas were infused with BDNF for 4 weeks. Up to 8 weeks after treatment, their cochleas were analyzed histologically. Electrically evoked compound action potentials (eCAPs) were recorded using stimulation paradigms that are informative of neural survival. Spiral ganglion cell (SGC) degeneration was prevented during BDNF treatment, resulting in 1.9 times more SGCs than in deafened untreated cochleas. Importantly, SGC survival was almost complete 8 weeks after treatment cessation, when 2.6 times more SGCs were observed. In four eCAP characteristics (three involving alteration of the interphase gap of the biphasic current pulse and one involving pulse trains), we found large and statistically significant differences between normal-hearing and deaf controls. Importantly, for BDNF-treated animals, these eCAP characteristics were near normal, suggesting healthy responsiveness of BDNF-treated SGCs. In conclusion, clinically practicable short-term neurotrophin treatment is sufficient for long-term survival of SGCs, and it can restore or preserve SGC function well beyond the treatment period. Significance statement: Successful restoration of hearing in deaf subjects by means of a cochlear implant requires a healthy spiral ganglion cell population. Deafness-induced degeneration of these cells can be averted with neurotrophic factors. In the present study in deafened guinea pigs, we investigated the long-term effects of temporary (i.e., clinically practicable) treatment with brain-derived neurotrophic factor (BDNF). We show that, after treatment cessation, the neuroprotective effect remains for at least 8 weeks. Moreover, for the first time, it is shown that the electrical responsiveness of BDNF-treated spiral ganglion cells is preserved during this period as well. These findings demonstrate that treatment of the auditory nerve with neurotrophic factors may be relevant for cochlear implant users.
Department of Otorhinolaryngology and Head & Neck Surgery and Brain Center Rudolf Magnus, University Medical Center Utrecht, 3508 GA, Utrecht, The Netherlands, and.
Dyan
D
Ramekers
Department of Otorhinolaryngology and Head & Neck Surgery and Brain Center Rudolf Magnus, University Medical Center Utrecht, 3508 GA, Utrecht, The Netherlands, and h.versnel@umcutrecht.nl.
Huib
H
Versnel
Research and Development, MED-EL Medical Electronics, 6020 Innsbruck, Austria.
Stefan B
http://orcid.org/0000-0002-7770-6146
SB
Strahl
Department of Otorhinolaryngology and Head & Neck Surgery and Brain Center Rudolf Magnus, University Medical Center Utrecht, 3508 GA, Utrecht, The Netherlands, and.
Sjaak F L
SF
Klis
Department of Otorhinolaryngology and Head & Neck Surgery and Brain Center Rudolf Magnus, University Medical Center Utrecht, 3508 GA, Utrecht, The Netherlands, and.
Wilko
W
Grolman
D000200:Action Potentials; D000818:Animals; D019208:Brain-Derived Neurotrophic Factor / Q000494:pharmacology* / Q000627:therapeutic use; D003056:Cochlear Nerve / Q000187:drug effects* / Q000473:pathology / Q000502:physiology; D003638:Deafness / Q000188:drug therapy* / Q000473:pathology; D005260:Female; D006168:Guinea Pigs; D018696:Neuroprotective Agents / Q000494:pharmacology* / Q000627:therapeutic use; D013136:Spiral Ganglion / Q000166:cytology / Q000187:drug effects / Q000502:physiology
D019208:Brain-Derived Neurotrophic Factor; D018696:Neuroprotective Agents
BDNF; cochlear implant; eCAP; guinea pig; hearing loss; spiral ganglion cell