• circadian rhythm;
  • sleep;
  • suprachiasmatic nucleus


The suprachiasmatic nucleus (SCN) is a master circadian pacemaker. It regulates the 24 h timing of many physiological processes, including sleeping and waking. After bilateral SCN lesions, the circadian rhythm of the sleep–wake cycle was completely eliminated, but the characteristics of the sleep–wake profile were not well clarified. In the present study, bilateral suprachiasmatic nucleus lesions (SCNX) were created in rats to determine the effects of SCNX on the sleep–wake profile in terms of number of episodes, mean duration of each stage and number of transitions between stages. Although bilateral SCN lesions completely eliminated the circadian rhythm in the sleep–wake cycle, there was no significant change in the total amount of daily sleep or wakefulness before and after lesions. However, the SCN-lesioned rats exhibited an increased episode number of wake and non-rapid eye movement (NREM) sleep during dark period and a decreased one during light period. The mean duration of wakefulness decreased significantly during the dark period and increased during the light period. The number of transitions between NREM sleep and wakefulness increased during the dark period and decreased during the light period. The NREM sleep power density and total number of episodes, number of transitions, and mean duration were not significantly different from those of sham controls when viewed over 24 h. These results indicate that lesions of suprachiasmatic nucleus did not alter the total amount of daily sleep but did modify the structure of sleep–wake profiles in rats.