Environmental light-darkness conditions induce changes in brain and peripheral pyroglutamyl-peptidase I activity

To evaluate the influence of light and darkness on brain pyroglutamyl-pepti dase I (pGluPI) activity, four experimental groups of rats were compared at the same time-point (10.00 h). Two groups were designed with a standard 12 -12 It light-dark cycle: In group A, the lights were on from 7.00 It to 19. 00 It, and the experiment was done under light conditions; in group B, the lights were on from 19.00 It to 7.00 h, and the experiment was done under d arkness conditions. Two additional groups were designed with nonstandard li ght-dark conditions: In group C, the animals were subjected to constant lig ht, and the experiment was done under light conditions. In group D, animals were subjected to constant darkness, and the experiment was done under dar kness conditions. Light (vs darkness) and standard (vs nonstandard) conditi ons produced significant changes on pGluPI activity in specific structures; the data suggested that endogenous substrates of pGluPI such as thyrotropi n-releasing hormone and gonadotropin-releasing hormone, might be modified i n parallel. There was left predominance in the retina under light condition s on a standard schedule (group A). The regional pattern of distribution of activity was similar in groups on a standard schedule (A vs B) and in grou ps tested under constant light-dark conditions (C vs D). However, this patt ern differed between groups subjected to standard vs constant light-dark co nditions (A and B vs C and D). These results support an influence of enviro nmental light and darkness on pGluPI activity, which may reflect concomitan t changes in its susceptible substrates and consequently in their functions .