This project has been extremely fruitful and successful. We have been able to provide a causal link between biophysical properties of visual pigments, the encoding of light stimuli by the neural circuitry of the retina, and the generation of visually guided behavior. We have also developed a new behavioral assay to study the function of the neural circuits of the retina in freely behaving animals by means of the pupillary light response, in in accordance with the 3Rs principle of animal research endorsed by the European Commission (Replacement, Reduction, and Refinement).
For the development of the project, five work packages were implemented. Work package 1 focused on updating the in-house build microphotospectrophotometer of the Ala-Laurila laboratory previously developed by Professor Vicktor Govardovskii to be able to obtain reliable scans from cone visual pigments at a sufficiently fast rate. The apparatus was then used to compare the biophysical properties of wild-type s-opsin with those of S-opsin mutants and those of rhodopsin. We were able to verify a shift in the maximum wavelength of absorption of the mutant visual pigments, as well as the change in their activation kinetics. Work package 2 focused on recording the light-triggered electric responses from retinal ganglion cells to causally test if altering the kinetics of visual pigments and of cone photoreceptors produces retinal ganglion cell responses that can follow higher frequencies of flickering lights. Based on our preliminary data, we decided to implement a paired-flash protocol to test the speed of cone-mediated vision rather than a flicker-fusion-frequency protocol. Work package 3 consisted of utilizing behavioral assays to test the ability of the different mouse strains expressing various isoforms of S-opsin to perceive light stimuli at different speeds. We utilized the 6-arm water maze previously utilized by the Ala-Laurila laboratory, and a behavioral method which measured the pupillary light response of freely behaving mice. Work package 4 focused on building and developing the experimental setup required to measure the pupillary light response of freely behaving mice. We implemented single board computers and microcontrollers to control and monitor a network of custom build behavioral setups. Work package 5 consisted of the integration of the various datasets, dissemination events, and preparation of research publications. Results from this research project have been disseminated through three international meetings (Visionarium 2022, Society for Neuroscience 2022, Lindau Nobel 2023), and one national symposium (MIBS symposium 2022 at the Helsinki University). Two research publications are currently in preparation for publication. One studies the biophysical properties of mouse cone visual pigments, and the other links the biophysical properties of cone opsins to the speed of vision.
