[Background and aims]
Feeding rhythm is an important risk factor for induction of insulin resistance, however, it is undissolved the detailed mechanism for the effect on sleep/wake regulation. We thus investigated whether different feeding schedule affects sleep/wake regulation.
[Methods]
Three groups of C57BL/6J mice were given lab chows freely during dark period (ZT12-24, Control group), first half of dark period (ZT12-18; Morning group), or second half of dark period (ZT18-24, Evening group) for 2 weeks respectively. A telemetric device for recordings of body temperature and locomotor activity was implanted in the peritoneal cavity of mice. Two stainless steel miniature screw electrodes were implanted in the skull to record the electroencephalogram (EEG). We distinguished phases of wake, rapid eye movement (REM) and non-REM (NREM) sleep by visual assessment of the EEG activities. The EEG delta and theta frequency band was set at 0.5-4.0Hz and 4.0-7.8Hz, respectively. In this study, power density of the EEG delta (ratio of delta to theta) during NREM sleep was used as a parameter of sleep pressure (slow-wave activity; SWA).
[Results]
Mice in Evening group showed lower SWA than that of other 2 groups while there were no difference an amount of NREM, REM and wake in 3 groups. We observed higher monoamine concentrations (especially in dopamine and its metabolites), which activates wake system, in cerebral cortex in Evening group. We also found increased mRNA expression of orexin in hypothalamus at ZT-1 in Evening group. There were no differences in food intake, total locomotor activity and body temperature during 24 hours among 3 groups although circadian rhythm of these parameters were shifted depending on each feeding schedule.
[Conclusion]
These results indicate that feeding schedule which only in the last half of dark period alters sleep homeostasis. This effect may be partly involved in increase of orexin expression in hypothalamus and elevated monoamine concentration in cerebral cortex.