Abstract
Purpose: :
This study is to investigate the visual function of rats with different degree of photic injury by using modified optokinetic behavior testing system.
Methods: :
All animal protocols were in accordance with ARVO guidelines. Twenty–one SD rats (200–250g) were first raised in 12–hour light/dark cycles in 14 days and then exposed to green light (580nm) with 900–1000 lux light density in a green chamber with temperature and humility control. The animals were exposure for 3, 12 and 24 hours respectively and following 24 hours dark adaptation. An optokinetic behavior testing device was designed for testing rat visual function with computerized modification. The device was set at different parameters in 0.125, 0.25 or 0.5–cycles/degree widths. The dizziness, head tracking and pre–pulse response of individual rat were recorded before and 1, 2, and 3 days after light exposure in all groups. The Total Distance of Motion (TDM) and Total Time of Motion (TTM) were recorded. The Mean Velocity of Motion (MVM) were obtained from TDM/TTM and analyzed by the computer. Seven weight–matched rats served as normal control without exposure while seven weight–matched rats with cutting optic nerve in both eye served as positive control. Histopathological study was also performed. The photoreceptor cells were marked by anti–Rhodopsin serum. The apoptotic cells were marked by TUNEL labeling.
Results: :
Histopathological and morphormetric study showed loss of photoreceptor cells in different degrees in the experimental groups. The dizziness and head tracking response of rats were gradually weakened while pre–pulse response was enhanced as the photic injury time increased. The correlation between the optokinetic behavior and number of photoreceptor cells in rats with photic injury was noted when parameter 0.5–cycles/degree was set. The MVM was no significant different among each groups before the exposure (F=1.248, p=0.315) while there was gradually decreased as the photic injury was aggravated (F=15.682, p=0.0001); to compare with each group before photic injury, there were significant changes in 12 hour–exposure (T=3.341, p=0.016) and 24 hour–exposure (T=5.469, p=0.002) groups when parameter 0.5–cycles/degree was set, respectively.
Conclusions: :
Our results show that the less value of MVM is consistently with the loss of photoreceptor cells. The motion ability of rat was various depending on the degree of retinal degeneration, suggesting that optokinetic behavior–testing device might evaluate the visual function of rat quantitatively.
Keywords: photoreceptors: visual performance • retinal degenerations: cell biology • vision and action