ABSTRACT
Adult Nothobranchius furzeri of the MZM-04/10 strain were individually kept and subjected to a "5â¯+â¯2" shifting lighting schedule (SHIFT) for 8â¯weeks in order to evaluate the desynchronizing effects of a simulated human-like shift-work schedule on the functioning of the circadian system (CS). With this aim, sixteen 21-week-old N. furzeri were placed into a Morning, Night and Evening schedule (lights on from 08:00 to 16:00, 00:00 to 08:00 and 16:00 to 00:00â¯h, respectively) and fed once a day in the middle of the corresponding photophase (12:00, 04:00 and 20:00â¯h, respectively). Then, in the weekends (2â¯days), fish were always returned to the Morning shift. As controls, 16 fish were maintained under a non-shifting LD cycle condition (CONTROL) throughout the whole experiment, with lights on from 08:00 to 16:00â¯h. Rest-activity rhythm (RAR) of fish subjected to SHIFT showed several symptoms of chronodisruption, such as a decrease in the percentage of diurnal activity and a reduction of the relative amplitude and the circadian function index with time. When a periodogram analysis was performed, RAR of N. furzeri under SHIFT conditions showed up to three separate circadian components: one longer than 24â¯h (26.5â¯h) that followed the weekly 8â¯h delays; a short-period component (~23â¯h) that was related to the weekend's phase advances, and finally, a 24â¯h component. The shifting LD schedule also affected fish CS at a molecular level, with several significant differences in the expression of core genes of the molecular clock (bmal1, clock, rorα, rev-erbα) between SHIFT and CONTROL animals. RAR impairment along with changes in clock gene expression could be associated with high stress and accelerated aging in these fish.
