title: Biological adaptability under seasonal variation of light/dark cycles.
abstract: 3A substantial amount of experimental models designed to understand rhythms entrainment and the effects of different regimens of light exposure on health have been proposed. However, many of them do not relate to what occurs in real life. Our objective was to evaluate the influence of "seasonal-like" variation in light/dark cycles on biological rhythms. Twenty adult male Wistar rats were assigned to three groups: control (CT), kept in 12:12 light/dark (LD) cycle; long photoperiod/short photoperiod (LP/SP), kept in 16.5:7.5 LD cycle for 18 days (phase A), then 17 days of gradual reductions in light time (phase B), then 18 days of shorter exposure (7.5:16.5 LD cycle, phase C); short photoperiod/long photoperiod (SP/LP) group, with same modifications as the LP/SP group, but in reverse order, starting phase A in 7.5:16.5 LD cycle. Activity and temperature were recorded constantly, and melatonin and cortisol concentrations were measured twice. Activity and temperature acrophases of all groups changed according to light. The correlation between activity and temperature was, overall, significantly lower for SP/LP group compared with LP/SP and CT groups. Regarding melatonin concentration, LP/SP group showed significant positive correlation between phase A and C (p = 0.018). Animals changed temperature and activity according to photoperiod and demonstrated better adaptability in transitioning from long to short photoperiod. Since this model imitates seasonal variation in light in a species that is largely used in behavioral experiments, it reveals promising methods to improve the reliability of experimental models and of further environmental health research.
authors.affiliation: a Laboratório de Cronobiologia e Sono, Hospital de Clínicas de Porto Alegre (HCPA) , Universidade Federal do Rio Grande do Sul (UFRGS) , Porto Alegre , Brasil.
authors.forename: Caroline Luísa
authors.initials: CL
authors.lastname: Quiles
authors.affiliation: a Laboratório de Cronobiologia e Sono, Hospital de Clínicas de Porto Alegre (HCPA) , Universidade Federal do Rio Grande do Sul (UFRGS) , Porto Alegre , Brasil.
authors.forename: Melissa Alves Braga
authors.initials: MA
authors.lastname: de Oliveira
authors.affiliation: a Laboratório de Cronobiologia e Sono, Hospital de Clínicas de Porto Alegre (HCPA) , Universidade Federal do Rio Grande do Sul (UFRGS) , Porto Alegre , Brasil.
authors.forename: André Comiran
authors.initials: AC
authors.lastname: Tonon
authors.affiliation: a Laboratório de Cronobiologia e Sono, Hospital de Clínicas de Porto Alegre (HCPA) , Universidade Federal do Rio Grande do Sul (UFRGS) , Porto Alegre , Brasil.|b Pós-graduação em Psiquiatria e Ciências do Comportamento, Faculdade de Medicina (FAMED) , Universidade Federal do Rio Grande do Sul (UFRGS) , Porto Alegre , Brasil.
authors.forename: Maria Paz Loayza
authors.initials: MP
authors.lastname: Hidalgo
mesh_terms: D000222:Adaptation, Physiological / Q000528:radiation effects*; D000818:Animals; D001831:Body Temperature / Q000502:physiology; D008027:Light; D008297:Male; D017440:Photoperiod; D011897:Random Allocation; D051381:Rats; D012621:Seasons
keywords: biological rhythms; chronobiology; light; light pollution; melatonin