Abstract
Purpose :
The retinal cellular mechanism of the pupillary light reflex (PLR) is still under investigation. The intrinsic photosensitive retinal ganglion cells (ipRGCs) in the retina send signals to the brain, triggering the PLR. While ipRGCs receive input from rod and cone cells, the specific contributions of these three photosensitive cell types to the PLR remain uncertain. To examine the response of ipRGCs alone, we chemically ablated rod and cone photoreceptors in several days by N-methyl-N-nitrosourea (NMU) injection. Unlike previous studies using mutant mouse models, NMU application helps prevent potential developmental changes. We conducted mouse PLR and recording electrophysiological responses through a multi-electrode array (MEA) to assess the role of ipRGCs in PLR.
Methods :
PLR was triggered by a 10-second green light flash at mesopic, low-photopic, and high-photopic levels in C57 wild type mice (WT), NMU-injected C57 mice, and rod/cone double knockout mice (Cgna3-/- & Gnat1-/-: dKO). Five to seven days after NMU injection, we recorded PLR in vivo, followed by an ex vivo light-evoked ipRGC spike recordings using an MEA.
Results :
In WT mice, pupil constriction and PLR onset speed increased with brighter light. NMU ablated photoreceptor layers in 5-7 days, but spared other retinal layers. In these mice, mesopic to low-photopic light evoked a smaller PLR than WT mice, suggesting both rods/cones contribute to PLR at these light levels. Surprisingly, a high photopic light evoked PLR similar to WT mice with a fast onset and full constriction. The dKO mice showed slower responses than NMU-injected mice at all three light levels. MEA recordings from ipRGCs in WT mice showed fast onset and long-lasting spikes, attributable to the rod/cone inputs and ipRGC responses. In the NMU-injected mice, ipRGCs overall showed slow onset. However, high-photopic light elicited fast onset spikes in a subset of ipRGCs.
Conclusions :
High photopic light induced faster PLR both in WT and NMU injected mice, as well as fast onset ipRGC responses when recorded with the MEA. Our results indicate that ipRGCs independently evoke PLR at high light conditions.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.