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We tested the hypothesis that the obese (fa/fa) Zucker rat has a sleep organization that differs from that of lean Zucker rats. We used the polygraphic technique to identify and to quantify the distribution of the three main states of the rat: wakefulness (W), non-rapid-eye-movement (NREM), and rapid-eye movement (REM) sleep states. Assessment of states was made with light present (1000-1600), at the rats thermoneutral temperature of 29 degrees C. Obese rats, compared with lean ones, did not show significant differences in the total time spent in the three main states. Whereas the mean durations of W and REM states did not differ statistically, that of NREM did (P = 0.046). However, in the obese rats, the frequencies of switching from NREM sleep to W, which increased, and from NREM to REM sleep, which decreased, were statistically significantly different (P = 0.019). Frequency of switching from either REM or W state was not significantly different. We conclude that sleep organization differs between lean and obese Zucker rats and that it is due to a disparity in switching from NREM sleep to either W or REM sleep and the mean duration of NREM sleep.

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