Efeitos agudo e crônico de uma exposição ao claro constante no ritmo circadiano de atividade locomotora, na memória e no comportamento tipo-ansioso em ratos Wistar adultos

Abstract

Adult rats exposed to constant light (LL) shows a free running rhythm of locomotor activity. In some rats, the permanent exposure to LL induces an arrhythmic pattern of locomotor activity due to uncoupling between multiple circadian oscillators in the suprachiasmatic nucleus of the hypothalamus. In addition, exposure to LL causes deficits in memory and alters emotional state. The aim of this study was to evaluate the acute and chronic effect of exposure to LL in the circadian rhythmicity of locomotor activity, cognitive performance and the anxiety like-behavior in adult rats. 35 Wistar male rats were used in this study. In the postnatal day (P) 22, after the weaning, the animals were housed individually in cages in a 12:12 light and dark cycle (LD); locomotor activity was recorded continually, and both food consumption and body mass was recorded weekly. On P60, animals were submitted to LL and kept until the end of the experiment. Control animals were kept under LD. The open field and novel object recognition tests were performed after 3 weeks for the animals in LD (n = 11) and in LL (n = 11) tested in a short-term, and after 7 weeks by the animals in LD (n = 7) and in LL (n = 6) for longterm effects. The object-in-place test was performed one week after the previous tasks. Compared to LD animals, LL animals showed a free-running rhythm of locomotor activity rhythm with a longer period and a lower percentage of variance explained by the rhythm. Additionally, LL animals showed object recognition memory in a short-, but not in a long-, term. However, the object-in-place memory was disturbed in the LL animals tested in both times. In the open field test, the long-term LL animals spent more time in the central area of, and left more fecal boli. In addition, compared to short-term animals, long-term animals show a higher travelled total distance and increased parameters of grooming behavior in the open field. Finally, LL animals consumed more chow immediately after the exposure to LL compared to the LD animals. Together, these results suggests that the effects of the exposure to LL in memory worsen over time of exposure. In conclusion, the results suggest that the negative effects of the exposure to constant light on the memory increase according to the length of stay under constant light condition, however the effects on the anxiety-like behavior are not clear.