The study on the targets of the optical evoked auditory brainstem response on the cochlea of guinea pig stimulating by infrared laser

Abstract

Objective: To identify the targets of the infrared laser stimulating on the cochlea of guinea pig which evoked auditory brainstem response (oABR), and explore the mechanisms of the infrared neurostimulation. Methods: A polished optical fiber with 200 μm diameter (NA=0.22) was planted into the scala tympani of guinea pigs to stimulate the cochlea of both the normal hearing and acute deafened guinea pigs. The direction of the fiber distal was changed to radiate different regions of the scala tympani, recording the oABR respectively. Differences of energy thresholds and amplitudes of oABR between normal hearing and acute deafened animals was concerned, and different responses were recorded as the optical path of laser fiber being changed to investigate the targets of the infrared laser stimulation. Immunofluorescence was used to detect the changes of inner and outer hair cells, and spiral ganglion neurons 7 days post-deafening, to looking for the probable association with the oABR changes at the same stimulus. SPSS 18.0 software was used to analyze the data. Results: Inner and outer hair cells were damaged in basal and middle turn, butresidual hair cells were observed in apical turn.Only when the optical fiber pointed to Rosenthal's canal stimulated the spiral ganglion region directly could the oABR be evoked. No response was recorded while the fiber pointed to other directions. Conclusion: Infrared laser stimulates cochlea evoked oABR generats from the response of spiral ganglion directly, the spiral ganglion neurons are the target of infrared stimulation.