The Impact of Luminance and Temporal Frequency on S-Cone-Driven ERGs in Wildtype Mice and Mice with Long-Wavelength Absorption Spectra

Abstract

Purpose : To study S-cone-driven ERG responses recorded with the silent substitution method at different luminance and temporal frequencies in wildtype and Opn1lw^LIAIS mice expressing human L-cone pigment.

Methods : Mice were dark adapted overnight and all further handling was done under dim red light. Anesthetized animals were placed in the Ganzfeld bowl and then adapted for 2 min to the mean luminance of the following stimulus. Responses were recorded at 5 mean luminances (0.5, 5, 27.5, 55, 99 cd/m²) and 8 temporal frequencies (6, 8, 12, 14, 18, 22, 26, 30 Hz). Silent substitution stimuli achieved 49% S-cone contrast for both genotypes. Rod-isolating stimuli (0.4 cd/m², 8 Hz; Opn1lw^LIAIS: 75% contrast, wildtype: 5% contrast) were recorded as reference measurements for comparison with former studies to rod- and M-cone-driven ERGs of our lab.

Results : S-cone driven responses were measurable at all luminances and from both genotypes, but they were generally smaller at 0.5 cd/m². S-cone responses of wildtype mice were on average 30 to 60% larger than those of Opn1lw^LIAIS mice at frequencies <22 Hz. At 22 Hz and higher no differences were observed. At all mean luminance, S-cone response amplitudes had low pass characteristics, but more strongly at 0.5 cd/m². Rod-driven responses were large in Opn1lw^LIAIS mice and displayed strongly decreasing amplitudes with increasing frequency. In wildtype mice rod responses were barely above noise due to the low rod-contrast of the stimulus for wildtype mice.

Conclusions : S-cone isolation was successfully done in wildtype and Opn1lw^LIAIS mice. S-cone-driven responses displayed similar luminance and temporal frequency properties as M-cone responses (see Tsai et al, 2017 IOVS). At 0.5 cd/m² mean luminance S-cone responses show characteristics of rod-driven signals. However, in contrast to rod-driven responses, S-cone-driven responses at 0.5 cd/m² were of the same amplitude in Opn1lw^LIAIS and wildtype mice indicating the absence of rod intrusion in S-cone isolating conditions.

References: Tsai IT, A Joachimsthaler, J Kremers (2017) The effect of luminance and temporal frequency on rod and cone driven response properties in mice expressing human L-cone pigment. IOVS – Vol. 58, No. 12, 5177-5187

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.