Abstract
Purpose :
The mouse retina contains rod and cone photoreceptors and begin expressing much of the molecular machinery necessary for phototransduction early in postnatal development (Wang et al. 2003, Regus-Leidig et al. 2009). However, it is not currently known when they become photoresponsive. Recently we found that the outer retina is photoresponsive to 525nm light as early as postnatal day 8 (P8), but the source of this response (rods or m-opsin expressing cones) remains unresolved (Bonezzi et al. 2018). Significant m-opsin expression levels have been detected at P7 and reach mature levels by P14, leading us to hypothesize that m-opsin drives a majority of this response. Interestingly s-opsin expression is detected much earlier (P4), but it is unknown when the outer retina becomes photoresponsive to UV light. Here we explore the developmental time-course of rods, m-opsin, and s-opsin dominant cone photoresponsivity using ex-vivo electroretinograms (ERGs).
Methods :
We recorded light evoked responses from developing wild-type mouse retinae at P7, P10 and P30. Dark-adapted retinae were isolated, mounted on a custom-designed, 3D printed ERG chamber, and perfused at 37 οC with oxygenated Ames solution. Barium chloride and LAP-4 were added to isolate the a-wave component. Pure cone-mediated responses were isolated by using a rod-adapting 525nm constant background light and superimposing 365nm or 525nm test flashes at varying intensities. A double flash protocol was used to tease apart rod and m-opsin expressing cone responses (Nymark et al. 2008). An ANOVA was used to compare responsivity across groups.
Results :
At P7 there was no detectable response to light (n=4; p>0.05). At P10 we detected rod responses (19.98 + 2.12 mV) and cone mediated responses to both UV (20.8 + 0.60 mV) and green light (15.95 + 0.85 mV; n=4; p≤0.05).
Conclusions :
Outer retinal light-evoked responses as early as P10 are driven by both rods and cones (both s-opsin and m-opsin expressing cones). Significant differences between UV and green responses seen in development become less pronounced in the adult. These differences may contribute their specific roles in promoting retinal waves and eye-specific segregation (Tiriac et al. 2018), as well as the development of synapses between cones and bipolar cells which may specifically require s or m dominant cone input (Dunn et al. 2013).
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.