Asymmetrical influence of a standard light/dark cycle and constant light conditions on the alanyl-aminopeptidase activity of the left and right retinas in adult male rats

Abstract

The retina acts as an independent clock informing the central pacemaker, the suprachiasmatic nucleus, under environmental light conditions, with consequences of such inputs for the central and peripheral nervous system. Differences in the behavior of the left and right retinas depending on environmental light conditions may influence the information projected to the brain hemispheres. The retina possesses neuropeptides that act as neurotransmitters or neuromodulators. Alanyl-aminopeptidase (AlaAP, EC 3.4.11.2) activity regulates some of these neuropeptides and therefore reflects their function. We analyzed AlaAP activity in the left and right retinas of adult male rats at successive time points under standard (12/12 h light/dark cycle) and nonstandard (constant light) conditions. AlaAP activity was measured fluorometrically using alanyl-beta-naphthylamide as the substrate. Under standard conditions, there were no differences in the left or right retina between time points, with the left retina predominating, particularly in the light period. In contrast, under constant light, no left versus right differences were observed, but significant differences between time points appeared. In comparison with standard conditions, constant conditions led to significantly higher AlaAP activity. Considering all the left retina data in comparison with all the right retina data, no correlation was found between the left and right retinas under standard conditions, but a significant positive correlation was observed under constant light. These results demonstrate an asymmetrical response of retinal AlaAP activity to changes in environmental light conditions, which may affect the functions in which the substrates of AlaAP are involved and the information projected to the brain hemispheres.