Abstract
Purpose :
We previously designed a protocol for chromatic pupillometry in mice in order to identify the different retinal inputs to the pupil light response (PLR) (Kostic et al. 2016, IOVS). We demonstrated the influence of rods and cones in the early dynamic of the response (during the first 2.5s following stimulus onset) to low and medium red stimuli and in the prolonged post-illumination response to high blue stimuli intended to bias to melanopsin contribution. Because our previous results were obtained under dark-adapted conditions, this work aims to evaluate the effect of light-adapted (LA) versus dark-adapted (DA) conditions on the PLR to this protocol and to better understand the influence of photoreceptors on the PLR.
Methods :
WT mice (C57BL6, n=16) were tested at 2 months of age, in both light- and dark-adapted conditions. For the DA condition, mice were dark-adapted overnight and testing was performed under dim-red light (<5 lux). For LA condition, testing was performed at 200 ±50 lux white light after 30 minutes of adaptation. The pupil was recorded continuously to monocularly presented red and blue light stimulations of different intensities (low, medium and high, Kostic et al, 2016, IOVS). Baseline pupil size, maximal contraction amplitude, early pupillary dynamic (diameter changes during the first 2.5s following stimulus onset) and post-illumination phase (expressed as the ratio of the sustained contraction at 9.5s to maximal contraction amplitude) were analysed.
Results :
The LA PLR is significantly different from DA PLR. For every red or blue stimulations, LA PLR have lower maximal contraction amplitude compared to DA PLR. For example, the response to low red is barely detectable in LA conditions (e.g low red mean±SEM contraction amplitude LA = 3.77 ±1.50, DA=15.14 ±1.94, P<0.001). In addition, the LA conditions decrease the ratio compared to the DA conditions in response to high blue (mean ±SEM ratio LA=0.4594 ±0.194, DA= 0.9264 ±0.044, P<0.05).
Conclusions :
In wild type mice, LA conditions mostly decrease the PLR elicited by our protocol compared to PLR in DA conditions. LA conditions favour cone input and bleach rods, thus decreased response to low and medium red suggests that mouse rod photoreceptors are a major component for this response consistently with our previous study (Kostic et al, 2016, IOVS). These results also confirm that dark adaptation is preferred to analyse the rod component of the PLR.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.