In anesthetized mice, contralateral-noise suppression of DPOAEs persists after elimination of olivocochlear and middle ear reflexes

MAISON, S.F; USUBUCHI H; VETTER D; ELGOYHEN AB; THOMAS SA; LIBERMAN MC

Baltimore USA

Congreso; 34th Midwinter Meeting, Association for Research in Otolaryngology; 2011

Suppression of ipsilateral DPOAEs by contralateral noise is used to assay olivocochlear (OC) reflex strength. However, depending on species and anesthesia, contributions of other reflexes can cloud interpretation. Here, we assess the contributions of OC and middle-ear muscle (MEM) reflexes to contralateral-noise suppression in CBA/CaJ mice anesthetized with ketamine/xylazine or urethane/xylazine. Ipsilateral DPOAEs were evoked by low-level primaries (f2=16 kHz; SPLs set to evoke a DPOAE 10 dB > noise floor). After measuring baseline DPOAEs, broadband contralateral noise was presented continuously for ~8 min, at SPLs ranging from 45 to 130 dB SPL. Contralateral-noise threshold for DPOAE suppression was ~75 dB SPL. At contralateralnoise levels near cross-talk threshold (~100 dB SPL), DPOAE suppression was as great as 8-10 dB, and mean suppression was 1.2 dB. Contra-noise suppression disappeared upon contralateral cochlear destruction. Lack of MEM contribution to contra-noise suppression was suggested by: 1) lack of noise-correlated changes in ear-canal SPL of an ipsilateral 500-Hz tone interleaved among DPOAE measures, and 2) persistence of suppression after paralysis with curare or section of the facial nerve. Lack of MOC contributions to contra-noise suppression was demonstrated by persistence of the effect: 1) following strychnine (10 mg/kg, i.m.) that abolished all shock-evoked OC suppression, 2) in á9- or á10 nAChR-knockout mice where shock-evoked OC suppression is abolished, and 3) after cutting the OC bundle. Furthermore, suppression was normal in an á9 knockin line where shock-evoked OC suppression is hugely enhanced. Thus, it appears that neither MEM nor MOC reflexes are involved in contralateral-noise effects on DPOAEs in ketamine/xylazine or urethane/xylazine anesthetized mice. Further investigations will focus on possible involvement of the autonomic innervation of the inner ear in this effect.2=16 kHz; SPLs set to evoke a DPOAE 10 dB > noise floor). After measuring baseline DPOAEs, broadband contralateral noise was presented continuously for ~8 min, at SPLs ranging from 45 to 130 dB SPL. Contralateral-noise threshold for DPOAE suppression was ~75 dB SPL. At contralateralnoise levels near cross-talk threshold (~100 dB SPL), DPOAE suppression was as great as 8-10 dB, and mean suppression was 1.2 dB. Contra-noise suppression disappeared upon contralateral cochlear destruction. Lack of MEM contribution to contra-noise suppression was suggested by: 1) lack of noise-correlated changes in ear-canal SPL of an ipsilateral 500-Hz tone interleaved among DPOAE measures, and 2) persistence of suppression after paralysis with curare or section of the facial nerve. Lack of MOC contributions to contra-noise suppression was demonstrated by persistence of the effect: 1) following strychnine (10 mg/kg, i.m.) that abolished all shock-evoked OC suppression, 2) in á9- or á10 nAChR-knockout mice where shock-evoked OC suppression is abolished, and 3) after cutting the OC bundle. Furthermore, suppression was normal in an á9 knockin line where shock-evoked OC suppression is hugely enhanced. Thus, it appears that neither MEM nor MOC reflexes are involved in contralateral-noise effects on DPOAEs in ketamine/xylazine or urethane/xylazine anesthetized mice. Further investigations will focus on possible involvement of the autonomic innervation of the inner ear in this effect.á9- or á10 nAChR-knockout mice where shock-evoked OC suppression is abolished, and 3) after cutting the OC bundle. Furthermore, suppression was normal in an á9 knockin line where shock-evoked OC suppression is hugely enhanced. Thus, it appears that neither MEM nor MOC reflexes are involved in contralateral-noise effects on DPOAEs in ketamine/xylazine or urethane/xylazine anesthetized mice. Further investigations will focus on possible involvement of the autonomic innervation of the inner ear in this effect.á9 knockin line where shock-evoked OC suppression is hugely enhanced. Thus, it appears that neither MEM nor MOC reflexes are involved in contralateral-noise effects on DPOAEs in ketamine/xylazine or urethane/xylazine anesthetized mice. Further investigations will focus on possible involvement of the autonomic innervation of the inner ear in this effect.