How the use of dim red-light pre-recording affects ERG responses of mice with long-wavelength shifted opsin

Abstract

Purpose : We investigated, how the ERGs of (LIAIS) mice, expressing a human L*-opsin instead of the native M-opsin, are affected by the use of visible red light, that may lead to photoisomerizations in the L*-opsin, during the preparations prior to ERG recordings.

Methods : Recordings were done on LIAIS mice, using wildtype (WT) littermates as control. Mice were dark adapted overnight and further handling was done either under dim red light or IR light with IR sensitive goggles performed in two separate sessions that were 2 weeks apart.
Anesthetized animals were placed on a heated platform in the Ganzfeld bowl and were dark adapted for 10 min before scotopic flash ERGs were recorded. Flash strengths increased from -3.7 to 0.8 log cd.s/m², with stimulus frequencies decreasing from 1 to 0.5 Hz and interstimulus intervals increasing from 10 to 120 sec.
For the following photopic flash ERG recordings the animals were adapted for 2 min to a 1.4 log cd/m² white background, before flashes with flash strengths increasing from -0.2 to 1.2 log cd.s/m² were presented upon the background.
All flash ERG responses were analyzed with regard to amplitudes and latencies of the prominent wave components.

Results : Preparation was substantially longer under IR light.
Responses to scotopic flash ERGs using red light were ≈14% smaller in LIAIS compared to WT mice. For both genotypes the use of IR light resulted in larger amplitudes of the scotopic a- and b-wave. This effect was stronger for LIAIS mice, where amplitudes increased by 22% (a-wave) and 28% (b-wave). In WT mice, a- and b-wave increased by 16% and 13%, respectively. OPs and implicit times did not depend on the light source used for preparation.
For the photopic flash ERGs, after the use of red light pre-recording the WT b-wave was 17% larger and 11% faster compared to LIAIS mice. The effect of IR light usage pre-recording was less pronounced. B-wave amplitudes were about 13% and 17% larger after IR preparation for WT and LIAIS mice, respectively.

Conclusions : The use of red light for mouse handling pre-recording has a slightly stronger effect on the red sensitive LIAIS mice compared to WT mice. However, the use of IR light resulted in larger ERG responses for both genotypes. Even though the use of IR light seems to ensure a more dark adapted state for the animals, handling is quite challenging and prolonged the total time of the experiment substantially.

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.