Photopic Electroretinogram in Cynomolgus Monkeys: Effects of Short–Term Hyperglycemia.

Abstract

Abstract: : Purpose: To evaluate the effects of short–term hyperglycemia on electroretinogram (ERG) under photopic conditions in cynomolgus monkeys. Methods: Binocular, full field ERGs were recorded from 4 fully anesthetized cynomolgus monkeys (2 males and 2 females) before, immediately after and 20 minutes after an intravenous administration of 200 mg/kg glucose. Glycemia was measured on each of the 3 occasions. The flicker retinal responses were evoked to 4 different temporal frequencies (6, 12, 20 and 30 Hz) in photopic conditions. The flash retinal responses were evoked to 20 different increasing intensities presented in the same photopic conditions in order to assess (from the derived luminance–response curves) both Vmax and log K parameters. Results: Marked hyperglycemia was obtained immediately (2.57+0.42 g/l) and 20 minutes (2.18+0.33 g/l) after the glucose injection when compared to the baseline mean value (0.91+0.17 g/l). The mean photopic Vmax calculated before (137.1+29.0 µV), immediately after (136.9+35.0 µV) and 20 minutes after (132.6+40.1 µV) glucose injection did not yield a significant modification with hyperglycemia. No changes were observed in log K values. Interestingly however, for flicker frequencies above 12 Hz, hyperglycemia resulted in a significant reduction in ERG amplitudes. Conclusions: There was a hyperglycemia–induced reduction in ERG amplitudes evoked with high (>12 Hz) temporal frequencies, but the origin remains undetermined. Interestingly however, previous studies have shown that hyperglycemia can reduce the flicker–induced retinal vasodilation, which could impair the normal functioning of the retina at a time when its metabolic activity must be increased in order to respond to the flickering stimulus.

Keywords: electroretinography: non–clinical • photoreceptors • diabetes