Circadian Patterns of Rats in Their Home Cages Detected Using a Video Tracking System

The diurnal rhythm is the common event in nature and specially shows in the behavioral patterns. Using the infrared sensor or photo beam detector to detect this 24-h rhythmicity in behaviors of mammalian, including in the rats and mice, is also the common way. The photo-sensory detecting mean is friendly and its advantage is unrestricted by light density and light-dark transition. However, this kind of equipment is cost-expensive and uneasy to fit for home cage in rodents. In this study, we tried to use the video-tracking system to detect the rhythmic activity of rats in their home cages. Adult male Sprague-Dawley rats, weighing 250-280 g, were used in this study and individual was kept in its own cage. Combined with the infrared sensitive charge-coupled device (CCD) camera and with automatically lights-off sensitive infrared illuminants as the accessory device, we found that animals exhibited the circadian locomotor activity in either light-dark cycles or constant darkness conditions. Moreover, the rhythmic patterns of locomotion in animals were affected by the one-hour exposure of white light under the constant darkness condition. The phase-advanced effects were found by the video tracking system. In summary, the video tracking system is the useful way to detect the rhythmic activity, especially in long-term circadian rhythmicity, in rats.