Optical stimulation of auditory neurons: effects of acute and chronic deafening.
In developing neural prostheses, particular success has been realized with cochlear implants. These devices bypass damaged hair cells in the auditory system and electrically stimulate the auditory nerve directly. In contemporary cochlear implants, however, the injected electric current spreads widely along the scala tympani and across turns. Consequently, stimulation of spatially discrete spiral ganglion cell populations is difficult. In contrast to electrical stimulation, it has been shown that extremely spatially selective stimulation is possible using infrared radiation (e.g. [Izzo, A.D., Su, H.S., Pathria, J., Walsh Jr., J.T., Whitlon, D.S., Richter, C.-P., 2007a. Selectivity of neural stimulation in the auditory system: a comparison of optic and electric stimuli. J. Biomed. Opt. 12, 1-7]). Here, we explore the correlation between surviving spiral ganglion cells, following acute and chronic deafness induced by neomycin application into the middle ear, and neural stimulation using optical radiation and electrical current. In vivo experiments were conducted in gerbils. Before the animals were deafened, acoustic thresholds were obtained and neurons were stimulated with optical radiation at various pulse durations, radiation exposures, and pulse repetition rates. In one group of animals, measurements were made immediately after deafening, while the other group was tested at least four weeks after deafening. Deafness was confirmed by measuring acoustically evoked compound action potentials. Optically and electrically evoked compound action potentials and auditory brainstem responses were determined for different radiation exposures and for different electrical current amplitudes, respectively. After completion of the experiments, the animals were euthanized and the cochleae were harvested for histology. Acoustically evoked compound action potential thresholds were elevated by more than 40 dB after neomycin application in acutely deaf and more than 60 dB in chronically deaf animals. Compound action potential thresholds, which were determined with optical radiation pulses, were not significantly elevated in acutely deaf animals. However, in chronically deaf animals optically evoked CAP thresholds were elevated. Changes correlated with the number of surviving spiral ganglion cells and the optical parameters that were used for stimulation.
Richter
Claus-Peter
CP
Department of Otolaryngology, Northwestern University, 303 E. Chicago Avenue, Searle 12-561, Chicago, IL 60611, USA. cri529@northwestern.edu
Bayon
Rodrigo
R
Izzo
Agnella D
AD
Otting
Margarete
M
Suh
Eul
E
Goyal
Sheila
S
Hotaling
Jeffrey
J
Walsh
Joseph T
JT
D000208:Acute Disease; D000818:Animals; D002908:Chronic Disease; D003056:Cochlear Nerve / Q000473:pathology / Q000503:physiopathology*; D003638:Deafness / Q000473:pathology / Q000503:physiopathology* / Q000628:therapy*; D004558:Electric Stimulation; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D005849:Gerbillinae; D008027:Light; D023421:Models, Animal; D009355:Neomycin / Q000009:adverse effects; D009410:Nerve Degeneration / Q000139:chemically induced; D011500:Protein Synthesis Inhibitors / Q000009:adverse effects; D013136:Spiral Ganglion / Q000473:pathology / Q000503:physiopathology
D011500:Protein Synthesis Inhibitors; D009355:Neomycin