The circadian system is a mechanism designed to generate circadian time and to synchronize it with the solar cycle. Its function is to adjust to behavioral and physiological function with the 24-hour period. The adjustment is performed using a so-called zeitgeber or synchronizer. The main circadian clock is in the suprachiasmatic nuclei (SCN) in the hypothalamus. Prolonged exposure of the organism to constant light conditions results in desynchronization of the circadian clock, which can lead to many pathologies. The impact of light at night on the organism has been studied for a long time, but the question of the impact of constant light on the development of the circadian system of the organism has been less studied. My thesis deals with this issue. Using RT-qPCR I investigated how the rhytm changes in the expression of selected clock genes in selected parts of the rat's brain, which has been kept in constant light sice birth. I also tested the impact of exposure to constant light on the early development of rhytm in locomotor activity later in the rat's life. Keywords: circadian system, photic entrainment, desynchronization under constant light, development, rat

Les yeux forment des avant-postes visuels importants du cerveau. Comme les autres organes, la rétine sensorielle des yeux est vulnérable aux effets nocifs des facteurs environnementaux, tels que la lumière et l'oxygène. Dans ce travail, nous nous sommes concentrés sur l’impact de l’exposition à une lumière constante et l’hyperoxie prolongée sur l'architecture et la fonction rétinienne. Dans la première partie de notre étude, nous avons montré qu’ une exposition de sept jours à une lumière constante perturbe la phagocytose des bâtonnets et cônes et régule négativement leur renouvellement dans la « rétine riche en cônes " d’Arvicanthis ansorgei. Notre étude donne un aperçu sur la physiopathologie des cônes, ce qui représente la principale source de handicap visuel dans une variété de pathologies rétiniennes, y compris la rétinite pigmentaire (RP) et la dégénérescence maculaire liée à l'âge (DMLA). Dans la deuxième partie de notre étude, nous avons montré qu’ une exposition de cinq jours à l’hyperoxie entraîne chez les souris néonatales une perte significative de cellules ganglionnaires dans les régions périphériques de la rétine, et de cellules à mélanopsine (ipRGC). L’exposition prolongée à l’hyperoxie perturbe également la capacité de photoentrainment des animaux probablement due à la perte des ipRGC et la perte de la rhodopsine dans les segments externes des bâtonnets chez les animaux traités. / Eyes form important visual outposts of the brain. Just like other organs, sensory retina in the eyes is also vulnerable to the injurious effects of environmental factors; such as light and oxygen. In this work, we have focused on the impacts of constant prolonged light and hyperoxia on the retinal architecture and function. In the first part of our study, we show that seven days of constant light disrupts rod and cone phagocytosis and downregulates their turnover in the “cone rich retina” of Arvicanthis ansorgei. The study gives an insight on the cone pathophysiology, which represents the major source of visual handicap in a variety of retinal pathologies, including retinitis pigmentosa (RP) and age-related macular degeneration (AMD). In the second part of our study, we show that five days of hyperoxia treatment in the neonatal mice results in the significant loss of retinal ganglion cells in the peripheral regions; the loss of melanopsin expressing retinal ganglion cells (ipRGC) was found to be significant. Hyperoxia also affects the photoentrainment capability of the animals probably because of the loss of ipRGC and the loss of rhodopsin in the outer segments of the photoreceptors in the treated animals.