Differential effects of experimental glaucoma on intrinsically photosensitive retinal ganglion cells in mice

Abstract

Glaucoma is a group of eye diseases characterized by retinal ganglion cell (RGC) loss and optic nerve damage. Studies, including this study, support that RGCs degenerate and die in a type‐specific manner following the disease insult. Here we specifically examined one RGC type, the intrinsically photosensitive retinal ganglion cell (ipRGC), and its associated functional deficits in a mouse model of experimental glaucoma. We induced chronic ocular hypertension (OHT) by laser photocoagulation and then characterized the survival of ipRGC subtypes. We found that ipRGCs suffer significant loss, similar to the general RGC population, but ipRGC subtypes are differentially affected following chronic OHT. M4 ipRGCs, which are involved in pattern vision, are susceptible to chronic OHT. Correspondingly, mice with chronic OHT experience reduced contrast sensitivity and visual acuity. By comparison, M1 ipRGCs, which project to the suprachiasmatic nuclei to regulate circadian rhythmicity, exhibit almost no cell loss following chronic OHT. Accordingly, we observed that circadian re‐entrainment and circadian rhythmicity are largely not disrupted in OHT mice. Our study demonstrates the link between subtype‐specific ipRGC survival and behavioral deficits in glaucomatous mice. These findings provide insight into glaucoma‐induced visual behavioral deficits and their underlying mechanisms.

Longitudinal analysis of retinal ganglion cell damage at individual axon bundle level in mice using visible-light optical coherence tomography fibergraphy

“…Immediately following vis-OCT imaging, mice were sacrificed, perfused, and the retinas were dissected and immunostained with rbpms, an RGC marker [43]. Flat-mounted retinas were then imaged by confocal microscopy [35, 43]. As demonstrated in the schematic representation of the flattened retina in Fig.…”

“…For example, one type of RGCs, the ipRGC, is involved in circadian functions [58], and at least one subtype, the M4 ipRGCs, has higher distribution in the superior and temporal retina [54]. It has been found that ipRGC’s are more resistant to chronic elevation of IOP [43] and ONC injury [59] than general RGCs. The retained circadian functions of the mice after chronic IOP elevation also suggest a normal function of ipRGCs.…”

“…We followed our published protocols to quantify RGC soma density [39, 43, 61, 62]. In brief, the nasal side of the eye was marked during eye dissection for orientation.…”

“…Three rectangles covering no less than 0.03mm 2 area were randomly drawn on the images, avoiding overlaps with large blood vessels. All rbpms-positive cells within the rectangles were manually counted in Zen (Zen 3.2; Oberkochen, Germany) [43]. Cell density was calculated using total cell counts divided by area for the four quadrants in each retina.…”

“…For this set of experiments, we acquired vis-OCT images from healthy wild type mice and mice at 3-d, 9-d, and 15-d pONC, respectively. Immediately following vis-OCT imaging, mice were sacrificed, perfused, and the retinas were dissected and immunostained with rbpms, an RGC marker [43]. Flat-mounted retinas were then imaged by confocal microscopy [35,43] -E).…”