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.
