Sleep and wake in rhythmic vs arrhythmic chronotypes of a microphthalmic species of African mole rat (Cryptomys mechowi)

Abstract

The giant Zambian molerat (Cryptomys mechowi) is a subterranean African rodent noted for its regressed visual system and unusual patterns of circadian rhythmicity – within this species some individuals exhibit distinct regular circadian patterns while others have arrhythmic circadian patterns. The current study was aimed at understanding whether differences in circadian chronotypes in this species affects the patterns and proportions of the different phases of the sleep-wake cycle. Physiological parameters of sleep (EEG and EMG) and behaviour (video recording) were recorded continuously for 72 h from six mole rats (three rhythmic and three arrhythmic) using a telemetric system and a low light CCTV camera connected to a DVD recorder. The telemetric data was scored (in both 5 s and 1 min epochs) as wake, nonREM sleep (NREM) and rapid eye movement (REM) stages subject to the correlation between EEG, EMG and behaviour. Spectral power was calculated for EEG in each implanted individual, which assisted in understanding the sleep phases and the intensity of NREM between the chronotypes. In addition REM periodicity was calculated from which sleep cycle length was inferred. The results indicate that the arrhythmic individuals spend more time in waking with a longer average duration of a waking episode, less time in NREM with a shorter average duration of a NREM episode though a greater nonREM sleep intensity, and similar sleep cycle lengths. The time spent in REM and the average duration of a REM episode was similar between the chronotypes.