and perhaps irritability or aggression (Everson, 1997; Horne, 1985; Naitoh et al., 1990).

Another relatively common approach to inducing sleep loss in animals is the so-called “flowerpot” technique. This approach produces REMS deprivation by taking advantage of the muscle atony that develops during REMS (Cohen and Dement, 1965; Jouvet et al., 1964). The animals (typically rats) are placed on a small platform (historically an inverted flowerpot) in a tank of water. The platform is large enough to allow the rat to engage in slow-wave sleep, in which residual muscle tone allows it to retain a stable sleeping posture. However, as the animal enters REMS and develops skeletal-muscle atony, it slips from the platform into the water and awakens.

A third approach to causing sleep loss in animals is called the “disk-over-water” technique; it can be used to deprive animals of REMS alone or of both NREMS and REMS (Bergmann et al., 1989; Rechtschaffen et al., 1983). The animals are housed on a rotating platform, or disk, that is positioned over a pan of water. When the electroencephalogram indicates that an animal is entering a state of sleep, a computer algorithm causes the disk to rotate at a low speed. The animal then generally awakens and walks to avoid contacting the water.

A fourth approach is forced locomotion, usually in a slowly revolving drum (Frank et al., 1998; Mistlberger et al., 1987; Rechtschaffen et al., 1999). Animal-welfare considerations relevant to this method are similar to those mentioned previously for exercise models. Interpretation of data collected with this method is confounded by the effect of continuous locomotion or exercise as opposed to the effects of sleep loss itself (Rechtschaffen et al., 1999).

In contrast with the gentle-handling method, the flowerpot and disk-over-water techniques can be easily imposed for long periods, and these approaches create some animal-use concerns. The flowerpot method of REMS deprivation causes alterations in several biochemical indexes of stress (Suchecki et al., 2002). In a refinement of the flowerpot and disk-over-water methods, multiple platforms are used in one large pool so that animals can engage in locomotor activity (Suchecki et al., 2002). Several animals can be housed together in these conditions. Social interactions may reduce some of the nonspecific stress associated with the environment and the physiologic challenge (Suchecki et al., 2002).

Sleep deprivation of over 7 days with the disk-over-water system results in the development of ulcerative skin lesions, hyperphagia, loss of body mass, hypothermia, and eventually septicemia and death in rats (Everson, 1995; Rechtschaffen et al., 1983). The duration of sleep deprivation must be well justified scientifically, particularly if it will be continuous for more than a few days. However, relatively few studies have imposed sleep deprivation long enough to cause those signs. In general, animals that are maintained on chronic sleep-deprivation schedules should be closely monitored for injury and general well-being, and observations should be recorded. The task is simplified by the fact that research teams typically monitor such animals very closely to ensure that they are

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