Chromatic Flash Electroretinograms in Mice

Abstract

Abstract: : Purpose: To investigate the properties of scotopic flash electroretinograms (ERGs) elicited by chromatic stimuli in mice. Methods: A stimulator was designed that uses a Xenon flash source input to a monochromator with variable wavelength. Recordings were performed by variation of the flash wavelength from 650 to 250 nm in steps of 20 nm, keeping flash intensity and ISI constant. To analyze rod and cone system responses separately, mice with specific functional properties, namely Rho^–/– (rod opsin knockout, cone function only), Cngb1^–/– (rod CNG channel deficient, cone function only), and Cnga3^–/– (cone CNG channel deficient, rod function only), were used. Amplitudes and implicit times from each response were calculated. The study was performed in accordance with the ARVO Statement for the Use of Animals in Ophthalmic and Vision Research. Results: The stimulator was so far used with scotopic single flash and flicker protocols. In Cnga3^–/– mice, the spectral sensitivity had a rather broad peak between approx. 390nm and 570nm, with a max. sensitivity of around 490–510nm consistent with previous studies on the rod system. Similarly, the M and UV cone peaks were present in the sensitivity spectra of the Rho^–/– and Cngb1^–/– mice. The spectrum of the wt mice could roughly be obtained by addition of the rod– and cone–specific ones, suggesting a linear superposition of signals for the protocols used. This will be investigated in more detail. Conclusions: In this study, we could demonstrate the feasibility of a tunable chromatic Xenon flash stimulator for use in mice. The spectral properties of chromatic flash ERGs in functionally normal, all–cone, and all–rod mice were investigated, and were found to be consistent with current knowledge about photoreceptor sensitivity. This technique will thus be very valuable in the detailed phenotyping of mutant mice with unknown visual defects.

Keywords: electroretinography: non-clinical • photoreceptors • retina: distal (photoreceptors, horizontal cells, bipolar cells)