Abstract
Purpose: :
Previous studies have shown that an intravitreal injection of Paraquat dichloride causes a severe retinopathy (Paraquat-Induced Retinopathy: PIR) resulting from the reactive oxygen species (ROS) that it generates. We examined how the PIR compared to the other models of oxydative retinopathy currently investigated by our group, namely: Oxygen-induced retinopathy (OIR) and Light-induced retinopathy (LIR).
Methods: :
The right eyes of Sprague-Dawley rats (N=4 per group) aged 7 (P7 group), 14 (P14 group) and 21 (P21 group) days old were injected with 1µl of 0.75mM of Paraquat dichloride diluted in 0.1M PBS. The fellow (control) eyes were injected with the vehicle (PBS) only. Scotopic (intensity:-6.3 to 0.6 log cd.sec.m-2;12 hrs dark adaptation) and photopic (intensity: 0.9 log cd.sec.m-2; background: 30 cd.m-2) ERGs and retinal histology were obtained at P30.
Results: :
There was a complete abolition of all the ERG responses noted in the P7 group, while the P14 and P21 groups yielded significant (p< .05) decrease of all ERG parameters compared to the fellow PBS injected eyes [rod a-wave (436±55 and 459±39 vs. 650±33), mix rod cone b-wave (718±153 and 1014±86 vs. 1428±99), rod Vmax (402±14 and 556± 45 vs. 776±53) and photopic cone ERG (160±34 and 177±13 vs. 290±67), respectively]. There were no significant differences (p>.05) noted between the P14 and P21 a-waves and photopic b-waves amplitudes while the amplitude of the mix rod-cone b-waves and rod Vmax were significantly larger (P<.05) in the P21 group. Retinal histology failed to reveal evidence of structural anomalies that could explain the functional impairment reported above.
Conclusions: :
Our results suggest that an intravitreal injections of Paraquat causes a severe functional but not structural retinopathy, the severity of which appearing to be inversely related to state of retinal maturation reached at time of injection. These results contrast with our OIR and LIR models where functional deficits are always accompanied with structural deficits. The absence of a significant change in a-wave amplitudes between P14 and P21 with significant changes in b-wave parameters could suggest that, although the initial insult is at the receptor level, there would also be a second site of oxydative damage in the inner retina.
Keywords: retina • oxidation/oxidative or free radical damage • electroretinography: non-clinical