A laboratory animal model of human shift work.

The purpose of this study was to develop a laboratory animal model of human shift work. Two methods of monitoring circadian rhythms in rats were employed: an activity wheel cage, where number of wheel revolutions (WR) were counted, and an internal radio transmitter, which recorded gross motor activity (GMA) and body temperature (BT). Rats were implanted with biotelemetry transmitters that detected GMA and BT and were placed in activity wheel cages. A 12 hour/12 hour light/dark cycle was maintained. Subjects were subdivided into two groups: control and experimental. Following a habituation period of 15 days, in which animals had ad-libitum access to food and water and unlimited access to the running wheel, the experimental period ensued for 22 days. Control animals were food restricted and their activity wheels were locked during the light; experimental animals were food restricted and their activity wheels were locked during the dark. At the end of the experimental period, animals were returned to the habituation paradigm for 15 days. Recordings of WR, GMA and BT, as well as daily monitoring of body weight and food intake, indicated that experimental animals resembled humans employed in a shift work schedule. In the experiment, the light entrainable oscillator and the food entrainable oscillator were uncoupled in experimental animals, producing alterations in activity/rest cycles, consummatory behavior, and overt behavior. Since similar alterations occur in shift workers, it is proposed that the experimental paradigm presented in this manuscript is a useful model of shift work and provides a framework upon which future experiments may be conducted.