Auditory event-related signals in mouse ERG recordings

In murine disease models, particularly in cases when retinal electrical activity is reduced, an event-related component becomes apparent that does not change with the stimulus intensity in electroretinogram (ERG) recordings. In this work, we show that this electric component is evoked by the sound of the flash discharge rather than the light flash itself.

Wild-type mice (C57BL/6), mice with rod function only (Cnga3 ^−/−), mice lacking any photoreceptor function (Cnga3 ^−/− rho ^−/−), and mice with no auditory function (Cdh23 ^vAlb/vAlb ) were examined with Xenon flash ERG systems. An acoustic noise generator was used to mask discharge sounds.

ERG recording modalities were identified where usually no discernible response can be elicited. These include photopic conditions in Cnga3 ^−/− mice, photopic conditions together with very low stimulus intensities in C57BL/6 mice, and both scotopic and photopic conditions in Cnga3 ^−/− rho ^−/− mice. However, in all of these cases, small signals, featuring an initial a-wave like deflection at about 20 ms and a subsequent b-wave like deflection peaking at about 40 ms after the flash, were detected. In contrast, such signals could not be detected in deaf Cdh23 ^vAlb/vAlb mice. Furthermore, masking the Xenon discharge sound by continuous acoustic noise led to a loss of the event-related signals in a reversible manner.

We could identify an auditory event-related component, presumably resembling auditory evoked potentials, as a major source of ERG signals of non-visual origin in mice. This finding may be of particular importance for the analysis and interpretation of ERG data in mice with reduced visual responses.