The locomotory activity rhythm of the spiny mouse,Acomys spinosissimusfrom southernAfrica: light entrainment and endogenous circadian rhythms

Abstract

AbstractThe circadian rhythm of locomotor activity in the spiny mouseAcomys spinosissimusfromSouthAfrica was investigated under controlled laboratory conditions. Nine individuals were subjected to six successive light cycles of approximately 2 weeks each as follows: (1) a standard light/dark (12:12LD) cycle; (2) a period of constant darkness (DD); (3) a second standard light/dark (12L:12D) cycle; (4) an inverse of theLD(12:12DL) cycle; (5) a short day cycle (8:16LD); and (6) a long day cycle (16:8LD). All the animals exhibited entrainment of their activity to theLDandDLlighting regimes. Locomotor activity ofA. spinosissimusoccurred predominantly during the dark phases of theLD,DL, long day and short day cycles. UnderLD, the mean percentage of activity was 88.7 ± 0.07% during the dark phase. When subjected to constant darkness, all animals expressed free‐running rhythms of locomotor activity (mean ± 1 standard deviation = 23.81 ± 0.33 h; range = 23.2–24.1 h). On the reverseLDcycle, the mean percentage of activity was 81.4 ± 0.09% during the dark phase of the cycle. Mice exhibited significantly more daytime activity during the long day cycle (20.3 ± 5.8%) and no significant change in dark phase activity during the short day cycle (90.1 ± 4.01). The spiny mouse possesses a circadian rhythm of locomotor activity that entrains strongly to light. Locomotory activity occurs predominantly during the dark phase and can therefore be considered a nocturnal mammal.