Chronic jet lag (CJL) model

To induce chronic jet lag by advances (ChrA^6/2), mice were exposed to a schedule of 6-h advances of the LD cycle every 2 days (+6/2). This was achieved by reducing the duration of every second dark phase by 6 h (Figure 1A). Consequently, mice went through a pattern of alternating “short-nights” (only 6 h of darkness) and “long-nights” (12 h of darkness). This chronic jet lag model with the alternating short and long nights was originally reproduced from an already published protocol (Filipski et al., 2004). Our group has previously reported that this protocol of ChrA induces forced desynchronization of locomotor activity rhythms (Casiraghi et al., 2012), altered metabolism (Casiraghi et al., 2016) and tumorigenesis (Aiello et al., 2020) in mice. The control group was housed under 12:12-h LD cycles throughout the experiments, while being subjected to identical conditions to the CJL group in all other aspects.

Schematic illustration of experimental groups and timeline. (A) Male mice were randomly assigned into control (LD, 12:12 light/dark cycle, N = 8) or chronic jet lag of 6 h advances of the LD cycle every 2 days (CJL +6/2, N = 12) groups. In this kind of chronic phase advances, animals alternate between two nights, a long night of 12 h and a short one of 6 h. Behavioral experiments were conducted during the night, 2 h after lights OFF, as indicated by a blue star in the LD group. For the CJL group, performance during the long night (CJL-LN, pink star) and the short night (CJL-SN, orange star) were compared. (B) Behavioral experiments started at week 8 of CJL. Mice were evaluated in the following order: sucrose preference test (SPT, week 8), elevated plus maze (EPM, week 9), open field (OF, week 10), motivation for food reward (MFR, weeks 12–14), and tail suspension test (TST, week 15).