Alpha9alpha10 knockout mice show altered physiological and behavioral responses to signals in masking noise

Medial olivocochlear (MOC) efferents modulate outer hair cell motility through specialized nicotinic acetylcholine receptors to support encoding of signals in noise. Transgenic mice lacking the alpha9 subunits of these receptors (9KOs) have normal hearing in quiet and noise, but lack classic cochlear suppression effects and show abnormal temporal, spectral, and spatial processing. Mice deficient for both the alpha9 and alpha10 receptor subunits (910KOs) may exhibit more severe MOC-related phenotypes. Like 9KOs, 910KOs have normal auditory brainstem response (ABR) thresholds and weak MOC reflexes. Here, we further characterized auditory function in 910KO mice. Wildtype and 910KO mice had similar ABR thresholds and acoustic startle response (ASR) amplitudes in quiet and noise, and similar frequency and intensity difference sensitivity. 910KO mice had larger ABR Wave I amplitudes than wildtypes in quiet and noise, but the noise:quiet amplitude ratio suggested 910KOs were more susceptible to masking effects for some stimuli. 910KO mice also had larger startle amplitudes in tone backgrounds than wildtypes. Overall, 910KO mice had grossly normal auditory function in quiet and noise, though their larger ABR amplitudes and hyperreactive startles suggest some auditory processing abnormalities. These findings contribute to the growing literature showing mixed effects of MOC dysfunction on hearing.