Abstract
BackgroundAn endogenous circadian clock controls locomotor activity in common spiny mice (Acomys cahirinus). However, little is known about the effects of constant light (LL) on this activity or about the existence of an additional food entrainable clock. A series of experiments were performed to investigate the effects of LL and DD on tau and activity levels.MethodsSpiny mice were housed individually and their running wheel activity monitored. One group of mice was exposed to LD, DD and several intensities of LL. Another group was exposed to a restricted feeding (RF) paradigm in light: dark (LD) during one hour before the L to D transition. Significance of rhythmicity was assessed using Lomb-Scargle periodograms.ResultsIn LD all animals exhibited nocturnal activity rhythms that persisted in DD. When animals were exposed to RF (during L), all of these animals (n = 11) demonstrated significant food anticipatory activity as well as an increase in diurnal activity. This increase in diurnal activity persisted in 4/11 animals during subsequent ad libitum conditions. Under LL conditions, the locomotor rhythms of 2/11 animals appeared to entrain to RF. When animals were exposed to sequentially increasing LL intensities, rhythmicity persisted and, while activity decreased significantly, the free-running period was relatively unaffected. In addition, the period in LL was significantly longer than the period in DD. Exposure to LL also induced long-term changes (after-effects) on period and activity when animals were again exposed to DD.ConclusionsOverall these studies demonstrate clear and robust circadian rhythms of wheel-running in A. cahirinus. In addition, LL clearly inhibited activity in this species and induced after-effects. The results also confirm the presence of a food entrainable oscillator in this species.
Highlights
An endogenous circadian clock controls locomotor activity in common spiny mice (Acomys cahirinus)
Despite clear evidence from other species, the presence of food anticipatory activity (FAA) or a food-entrainable oscillator (FEO) has yet to be demonstrated in A. cahirinus
Wheel turns were monitored with a physical switch and the activity stored on a computer (Effects of Constant light (LL): DAM System, Trikinetics, Waltham, MA or Effects of restricted feeding (RF): ClockLab, Actimetrics, Evanston, IL) for later analysis
Summary
An endogenous circadian clock controls locomotor activity in common spiny mice (Acomys cahirinus). All organisms exhibit circadian rhythms that can be entrained by a light-dark (LD) cycle [1]. These LD cycles entrain the primary circadian pacemaker, which is often called the light-entrainable oscillator (LEO) This oscillator has been well studied in many mammalian species including rats [2], flying squirrels [3], weasels and mink [4]. Rats exposed to restricted daily feeding schedules exhibit increased activity and lever-pressing just before the scheduled feeding time(s) in both LD and LL. This activity can even persist for up to five days when food availability is completely eliminated [8]. Despite clear evidence from other species, the presence of FAA or a FEO has yet to be demonstrated in A. cahirinus
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