Seasonal Variation in ATP-Induced Retinal Damage in the Cone-Dominant 13-Lined Ground Squirrel.

Purpose: To examine whether time of year (relative to hibernation emergence) influences the retinal degenerative effects of intravitreal injection of adenosine triphosphate (ATP) in the 13-lined ground squirrel (13-LGS).
Methods: Eighteen (9 male, 9 female) 13-LGS in three experimental cohorts (early season, mid-season, late season) (n = 6 each) underwent baseline imaging using scanning light ophthalmoscopy (SLO) and optical coherence tomography (OCT). Animals then received a 10-µL intravitreal injection of 0.723 M ATP, followed by OCT and SLO imaging at 3, 10, and 21 days. Adaptive optics SLO (AOSLO) was performed in animals without retinal damage after the 21-day follow-up. Retinal thickness, choroidal thickness, and cone density measures were compared to values from wild-type controls (n = 12).
Results: Five animals (four early season, one late season) showed retinal damage post-ATP injection (Fisher's exact test, P = 0.065). Animals with retinal damage displayed areas of disrupted retinal lamination on OCT. Any changes in OCT thickness were generally present on initial follow-up and resolved at later time points. Follow-up imaging with AOSLO on animals without retinal damage showed no significant differences in the cone mosaic topography from control eyes. Axial length was increased in mid-/late-season cohorts relative to early season (P = 0.0025 and P = 0.0007).
Conclusions: In this pilot study, the 13-LGS appears more susceptible to ATP-induced retinal damage during the early season. Future studies adjusting dose based on ocular biometry may help elucidate the impact of time of year on chemical response.
Translational Relevance: Consideration of ocular biometry in this and other animal models is merited when using intravitreal methods of chemical administration.