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[Polygraphical study on the wakefulness-sleep cycle of the rat].

A normal wakefulness-sleep cycle of the male adult rat was observed polygraphically for 24 hrs. The male rats, albino or hooded, of 6 to 8 months, weighting over 350g, were used. There were little differences in EEG sleep patterns between the albino and hooded rats. Stainless-steel electrodes were implanted chronically in the frontal and occipital cortex and the dorsal hippocampus to record EEG monopolarly. A pair of stainless-steel electrodes were inserted into the orbit to record eye movements. Another pair of needle-electrodes were placed in the neck muscles to record the EMG. A small connector is attached to the skull with dental resin. The experiment was made about one week after operation. The rat was observed in a box placed in the soundproof and air conditioned room: the room temperature was controlled above 18°C, and the room was continuously illuminated during recording. Polygraphical recordings began between 6 and 11 p.m. and continued for 24 hrs. Daring recording, rats were free to move around in the box and were allowed to take food and water in the box. All polygraphical data were classified every 10 sec by inspection as either Awake (A), Light sleep (L), Deep sleep (D), or Paradoxical sleep (P) (Fig. 3, Table 1).Table 2 shows the appearance ratios of the four EEG patterns for all 10 rats, and Fig. 4 shows the temporal changes of EEG patterns in Rat 7 during 24 hrs. The pattern proceeds gradually A→L→D→P, and the stage of P suddenly changes to A. In the rat's EEG, there are more than ten wakefulness-sleep cycles a day. The cycle has a span of about 0.5 to 3 hrs. That is, the rat's sleep is polyphasic and it appears more frequent in day time than at night. Fig. 5-8 show the appearance ratios of the EEG patterns per hour, which indicate:1. Pattern A appears more often at night than in day time, 1. Patterns D and P appear more often in day time than at night, 3. Pattern L appears about 20% throughout the day.Table 3 shows the appearance ratios of the A, L, D and P patterns on each subject in day time (7:00 a.m.-7:00 p.m.) and at night (7:00 p.m.-7:00 a.m. next day), and matched t's between day and night. All ten subjects show a greater ratio in the Pattern A at night than in day time, and this difference is significant at the 0.1% level. 9 rats show the greater appearance ratios of Patterns D and P in day time than at night. Both differences are significant at the 1% level. In this study also activity pattern of the rat is nocturnal type as many other studies have shown.Matsumoto, et al. reported that the appearance ratio of P per day was 7.0%, and according to Jo it was 7.3%, while Michel, et al. reported 10-15%, which is more similar to our own data. Further studies are necessary to clarify these differences.