Abstract
Purpose :
Choroidal blood flow (ChBF) is adaptively controlled to maintain stable flow despite variations in systemic blood pressure, a phenomenon called baroregulation. We examined if ChBF baroregulation changes with age in both Sprague-Dawley (SD) and Fischer-344 (F344) rats, and whether any such changes were associable with changes in retinal structure and function.
Methods :
The following assessments were made in male SD rats from 120-500 days of age and male F344 rats from 140-750 days of age: 1) the flash-evoked scotopic electroretinogram (ERG); 2) ChBF as measured by Laser Doppler Flowmetry while also monitoring systemic arterial blood pressure (ABP); 3) visual acuity and contrast sensitivity as measured using optomotry (F344 only); and 4) the thickness of the retina and its individual layers in plastic-embedded sections as measured using Neurolucida morphometric analysis.
Results :
ChBF was uncorrelated with ABP (i.e. showed baroregulation) during its fluctuations above and below basal ABP in young (120-200 day old) SD rats, but became increasingly correlated with ABP as SD rats aged, so that by about a year of age ChBF tended to change linearly with ABP. Associated with the age-related progressive loss in ChBF baroregulation in SD rats was a progressive age-related decline in both the scotopic ERG b-wave amplitude and a-wave amplitude, and a thinning of the retina, particularly the inner plexiform layer and outer nuclear layer. For F344 rats, ChBF was highly correlated with ABP already in 170 day-old rats – i.e. baroregulation was already failing in young F344 rats. Acuity, contrast sensitivity and a-wave deficits and ONL thinning were evident by 400 days, and ERG b-wave deficits and additional acuity, contrast sensitivity and a-wave loss and ONL thinning were noted by 660 days.
Conclusions :
These studies indicate that ChBF compensatory baroregulation declines with age in SD rats, and its loss is correlated with functional and morphological decline in the retina. By contrast, impaired baroregulation is already evident in young F344 rats, before loss in vision and ERG is seen and before retinal thinning. This early loss of baroregulation in F344 rats may be a factor in their accelerated and severe subsequent functional decline and loss of photoreceptors. Our studies highlight the important role age-related failure in ChBF baroregulation may play in age-related disruption in retinal health and function.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.