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This study aimed at examining the effects on the subjective symptoms in nurses of both timing and length of a 2-h nap during a 16-h night shift. Compared to pre-nap levels, sleepiness, fatigue, and dullness increased immediately after napping. Afterwards, sleepiness decreased significantly, and the other symptoms returned to the pre-nap values. The nurses' subjective symptoms after napping were not associated with the timing of the nap and post-nap fatigue lasted longer as the nap time increased (> 1.5 h). These results suggest that for effective napping during long night shifts, the nap length should be determined carefully to avoid persistent sleep inertia.

Acute effects of a single i.p. injection of toluene on circadian rhythms of sleep-wakefulness were investigated in rats which were chronically implanted with EEG and EMG electrodes for polygraphic recordings. The toluene injection produced an initial increase in wakefulness (W) and a subsequent increase in slow-wave sleep (SWS) during the dark period. In an attempt to clarify mechanisms of these biphasic effects of toluene on sleep-wakefulness rhythms, brain monoamines and their metabolites were determined at the times of the initial increase in W and the increased SWS. The initial increase in W was associated with an increase in cortical NA, MHPG and 5-HT together with a decrease in cortical 5-hydroxyindoleacetic acid (5-HIAA), while the increased SWS during the dark period was associated with an increase in 5-HIAA and a concomitant decrease in 3-methoxy-4-hydroxyphenylglycol (MHPG). The toluene-induced changes in sleep-wakefulness seemed to be manifested at lower blood levels of toluene than the behavioral signs of central nervous system (CNS) depression. These biphasic effects of toluene on circadian sleep-wakefulness rhythms are discussed in terms of the reciprocal interactions between central 5-HT and NA neurons.