Characteristic patterns of feeding, drinking and motor activity under artificial twilight conditions in rats

Under natural circumstances,twilight is known to play an important role in behavioral and metabolic changes in mammals. Since experimental rooms are usually illuminated by on-off lighting system, an artificial twilight system was devised and its effect on feeding, drinking and motor activity was compared with those in on-off system. Following 10 days of on-off lighting (a 12:12 light-dark cycle), a twilight regimen was introduced. Illuminant intensity increased from 0 to 90 lumen during a 2 hr period of dawn and decreased reversely during same hour period of dusk. Three different types of twilight conditions were tested, i.e., (1) dawn: 0800-1000 hr and dusk: 1800-2000 hr, (2) dawn: 0600-0800 hr and dusk: 2000-2200 hr, (3) dawn: 0600-0800 hr and dusk: 1800-2000 hr. Total amount of 24-hr consumptions or activity was not influenced following the twilight conditions. Immediately after a period of dawn started, rats decreased food and water intake subsequent to their increase during the later periods of dark. During a dusk period, food and water intake increased markedly during twilight conditions in type 3. In type 1, however, such facilitated effects were not found.