Cone photoreceptor reflectance variation in the northern tree shrew and thirteen-lined ground squirrel

Abstract

In vivo images of human cone photoreceptors have been shown to vary in their reflectance both spatially and temporally. While it is generally accepted that the unique anatomy and physiology of the photoreceptors themselves drives this behavior, the exact mechanisms have not been fully elucidated as most studies on these phenomena have been limited to the human retina. Unlike humans, animal models offer the ability to experimentally manipulate the retina and perform direct in vivo and ex vivo comparisons. The thirteen-lined ground squirrel and northern tree shrew are two emerging animal models being used in vision research. Both models feature cone-dominant retinas, overcoming a key limitation of traditional rodent models. Additionally, each possesses unique but well-documented anatomical differences in cone structure compared to human cones, which can be leveraged to further constrain theoretical models of light propagation within photoreceptors. Here we sought to characterize the spatial and temporal reflectance behavior of cones in these species. Adaptive optics scanning light ophthalmoscopy (AOSLO) was used to non-invasively image the photoreceptors of both species at 5 to 10 min intervals over the span of 18 to 25 min. The reflectance of individual cone photoreceptors was measured over time, and images at individual time points were used to assess the variability of cone reflectance across the cone mosaic. Variability in spatial and temporal photoreceptor reflectance was observed in both species, with similar behavior to that seen in human AOSLO images. Despite the unique cone structure in these animals, these data suggest a common origin of photoreceptor reflectance behavior across species. Such data may help constrain models of the cellular origins of photoreceptor reflectance signals. These animal models provide an experimental platform to further explore the morphological origins of light capture and propagation.

Human iPSC-derived photoreceptor transplantation in the cone dominant 13-lined ground squirrel

“…A high-resolution image of the cone mosaic of transplanted cells was captured using our previously described custom AOSLO system ( Gaffney et al., 2021 ; Sajdak et al. 2016 , 2019 ).…”

A Novel Tree Shrew Model of Chronic Experimental Autoimmune Uveitis and Its Disruptive Application

“…Experimental autoimmune uveitis (EAU) in nocturnal rodents with sparse cone is utilized in research to investigate human diseases, but such animal models cannot reflect the effect of fovea on vision loss in human disorders, so it is necessary to develop a variety of animal models to represent the distinct aspects and diverse findings of uveitis in humans.Tree shrews are a diurnal species with cone-dominated retina and immune systems similar to those of both primates and humans ( 5 , 6 ). They have been widely used as a model animal for studying glaucoma, myopia, refractive development, and central visual processing and are becoming a crucial model animal in vision research ( 7 – 9 ).…”

Emerging imaging developments in experimental vision sciences and ophthalmology

“…55 Gaffney et al demonstrate AO-SLO to investigate cone photoreceptor reflectance variation in the northern tree shrew and 13-lined ground squirrel. 56 Ansari et al illustrate polarized infrared retinal imaging of pathognomonic macular ripples in patients with foveal hypoplasia. 57 Jiao et al highlight a comparative study of OCT angiography algorithms for rodent retinal imaging.…”