Abstract
Purpose :
To characterize stimulus-driven intrinsic optical signal imaging (R-IOI) in the rat retina, as compared with other, previously studied species (cat, monkey, human, mouse, etc). It is further hypothesized that imaged signals from an albino strain of rat would be larger than those found in a pigmented strain.
Methods :
Intrinsic optical signals of anesthetized (K/X) adult rat retina were recorded and imaged in vivo with a cooled CCD camera attached to a custom optical rig with a front-end endoscope/otoscope -- a setup previously used for R-IOI of mice (Begum et al, 2020). Retinal images under near-infrared (700-900nm) illumination were collected at 2Hz for 10-20secs while a brief (300msec) visible (505nm) LED stimulus was delivered to the retina.
Results :
Stimulus-driven intrinsic signals were observed in the rat retina, similar to those previously describe in other species (cat, monkey, human, mouse). In comparison to R-IOI of (pigmented) adult C57BL/6J wild-type mouse retina performed under the same stimulated and recording conditions using the same equipment, imaged signals from pigmented Long-Evans adult rats were preliminarily similar in time course, but larger in amplitude (0.24% vs 0.060%). However R-IOI under the same conditions recorded in albino Sprague-Dawley adult rats revealed signals greater in amplitude (0.58% +- 0.16% vs 0.24% +- 0.067%). One major difference is that the retinal return, the amount of NIR illumination reflected back into the camera was also substantially greater in the albino vs pigmented rat -- typically 6-7 times greater.
While the larger retinal return likely contributed to the observed greater signal amplitude in the albino rat, another hypothesis is that a greater contribution of the choriocapillaris is observed in the albino rat. This may be expected due to our previous work demonstrating a dominant hemodynamic component of the R-IOI signal that is driven by rod activity. For comparison, the cat has exhibited the largest signal (1-2%) while the macaque monkey is at 0.25%.
Conclusions :
These findings confirm the expectation that R-IOI reveals imaged signals similar to those observed in other species.
Furthermore, the greater signal amplitudes observed in the albino rat coincide with previous evidence of a significant component of the observed R-IOI signal originating from outer retinal sources (rod photoreceptors).
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.