Effects of continuous light exposure on the rat retina and pineal gland

Developmental effects of constant light on circadian behaviour and gene expressions in zebra finches: Insights into mechanisms of metabolic adaptation to aperiodic environment in diurnal animals

A most crucial feature of biological adaptation is the maintenance of a close temporal relationship of behaviour and physiology with prevailing 24-h light-dark environment, which is rapidly changing with increasing nighttime illumination. This study investigated developmental effects of the loss of night on circadian behaviour, metabolism and gene expressions in diurnal zebra finches born and raised under LL, with controls on 12L:12D. Birds under LD were entrained, and showed normal body mass and a significant 24-h rhythm in both activity-rest pattern and mRNA expression of candidate genes that we measured. But, under LL, birds gained weight and accumulated lipid in the liver. Intriguingly, at the end of the experiment, the majority (4/5th) of birds under LL were rhythmic in activity despite arrhythmic expression in the hypothalamus of c-Fos (neuronal activity), Rhodopsin and Mel1-a genes (light perception), and clock genes (Bmal1, Per2 and Rev-erb β). In peripheral tissues, LL induced variable clock gene expressions. Whereas 24-h mRNA rhythm was abolished for Bmal1 in both liver and gut, it persisted for Per2 and Rev-erb β in liver, and for Per2 in gut. Further, we found under LL, the loss of 24-h rhythm in hepatic expression of Fasn and Cd36/Fat (biosynthesis and its uptake), and gut expression of Sglt1, Glut5, Cd36 and Pept1 (nutrient absorption) genes. As compared to LD, baseline mRNA levels of Fasn and Cd36 genes were attenuated under LL. Among major transporter genes, Sglt1 (glucose) and Cd36 (fat) genes were arrhythmic, while Glut5 (glucose) and Pept1 (protein) genes were rhythmic but with phase differences under LL, compared to LD. These results demonstrate dissociation of circadian behaviour from clock gene rhythms, and provide molecular insights into possible mechanisms at different levels (behaviour and physiology) that diurnal animals might employ in order to adapt to an emerging overly illuminated-night urban environment.

Epiphysis morphology under light and radiation exposure in experiment

Epiphysis is an organ of the control of biorhythms and adaptogenesis connected with photoperiodism. To evaluate photoradiomodificating effect and conarium plasticity using the methods of light and electron microscopy, there have been analyzed changes in morphological indices of pineal secretion activity in white rat males after 48-hour bright light exposure, general X-ray exposure and its combination. The received results have been handled by the method of variation statistics. It has been revealed that the decrease of light pinealocyte part, its protein-synthesizing system reduction, reparative activity decrease and the increase of degenerating pinealocyte part after combined exposure were expressed more significantly as compared to the light and X-ray exposures.