Targeted therapy of the inner ear.
BACKGROUND
There is experimental evidence that targeted delivery of steroids to the inner ear can protect hearing during cochlear implant surgery. The best protection appears to be achieved through pre-treatment of the cochlea, but the time period required for treatment is long compared with the duration of surgery, and needs further optimization. The stability of hearing thresholds is determined over a 3-month period after hearing preservation cochlear implantation.


METHODS
Adult guinea pigs were implanted with a miniature cochlear implant electrode, and pure tone auditory brainstem response (ABR) thresholds were estimated in response to pure tones of 2-32 kHz immediately after surgery and at 1 week, 1 month and 3 months. Spiral ganglion cell (SGC) densities were estimated from mid-modular histological sections of the cochlea. Thirty minutes prior to implantation, a polymeric sponge (Seprapack, Genzyme) was loaded with either a 2% solution of dexamethasone phosphate or normal saline (control) and placed onto the round window.


RESULTS
Implantation was associated with an immediate elevation in thresholds across frequencies, with a full recovery below 2 kHz over the next week and a partial recovery of thresholds at higher frequencies. These thresholds remained unchanged for the next 3 months. There was an immediate and sustained reduction in the elevation of thresholds at 32 kHz in dexamethasone-treated animals. SGC densities were greater in steroid-treated animals than controls in the basal turn of the cochlea (at the region of implantation) 3 months after implantation.


CONCLUSIONS
It is concluded that ABR thresholds remain stable for 3 months after cochlear implantation in the guinea pig, and that local application of steroids to the inner ear prior to implantation is an effective method of preserving SGC populations when there is residual hearing at the time of implantation.
Maini
Sangeeta
S
Department of Otolaryngology, University of Melbourne, Melbourne, Victoria, Australia.
Lisnichuk
Halina
H
Eastwood
Hayden
H
Pinder
Darren
D
James
David
D
Richardson
Rachael T
RT
Chang
Andrew
A
Connolly
Tim
T
Sly
David
D
Kel
Gordana
G
O'Leary
Stephen J
SJ
D000704:Analysis of Variance; D000818:Animals; D001301:Audiometry, Pure-Tone; D001309:Auditory Threshold / Q000502:physiology; D002452:Cell Count; D019929:Cochlear Implantation; D003054:Cochlear Implants; D003907:Dexamethasone / Q000008:administration & dosage*; D004333:Drug Administration Routes; D007758:Ear, Inner / Q000187:drug effects* / Q000502:physiology / Q000601:surgery; D004567:Electrodes, Implanted; D004594:Electrophysiology; D016057:Evoked Potentials, Auditory, Brain Stem / Q000187:drug effects / Q000502:physiology; D006168:Guinea Pigs; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D013136:Spiral Ganglion / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D013997:Time Factors
D003907:Dexamethasone