Suprachiasmatic Nucleus Damage Change Of Sleep Structure In Rats

The suprachiasmatic nucleus (SCN) is a master circadian pacemaker. It regulates the24h 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 out 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 SCNX 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 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 over24h. 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.Methods:1) SCNX was made by passing1mA DC current for50s at each lesion site by electronic stimulator.2) After the SCNX procedure, rats were chronically implanted with electroencephalogram (EEG) and electromyogram (EMG) electrodes for polysomnographic recordings.3) Upon completion of the EEG/EMG recordings, the brains were removed, cryoprotected in20%sucrose at4℃and then sliced into four series of30μm sections on a freezing microtome. The sections were processed for Nissl staining to confirm anatomically the success of operation. 4) Statistical analysisResults:1) Circadian rhythm of the sleep-wake cycle was almost completely eliminated after SCNX in rats. SCNX rats showed increased wakefulness with decreased NREM sleep during light period and decreased wakefulness with increased NREM sleep during dark period relative to sham groups. REM sleep was increased when the lights were on and during the late phase of the dark period in SCNX rats. Increase in REM sleep was observed only during the dark period. However, the total amount of each stage over24h was almost the same across both types of rats.2) SCNX did not change the number of bouts, mean duration of bouts, or total number of stage transitions during24h. However, when the detail was investigated in12h light and dark periods, relative to sham rats, numbers of bouts of wakefulness were decreased during the light period, the numbers of bouts of wakefulness and NREM sleep were increased during the dark period, and the number of bouts of REM sleep remained the same during both periods, The increase in the number of bouts of wakefulness and NREM sleep was accompanied by an increase in the number of transitions between NREM sleep and wakefulness during the dark period and a decrease during the light period. Correspondingly, the mean duration of wakefulness decreased.3) In SCNX rats, the power density of NREM sleep showed no obvious change during the dark or light periods.Conclusion:SCNX did not affect the total amount of sleep, but it did alter the structure of the sleep-wake cycle.