Development of video analysis for home cage activity of rats during dark period

Abstract

The analyzing procedure for home cage activity of rats under dark cycle was developed. Forty-eight 4-week-old female Sprague-Dawley rats were divided into 4 groups according to a 2x2 factorial design. The first factor was dietary nickel level (no supplemental or 1 mg/kg diet). The second factor was surplus sodium chloride in diets (no additional or 4%(w/w)). Two rats were kept in a transparent acrylic cage for 10 weeks. At Day 67 or Day 68 rats were video recorded under dim red LED light (0.5-1.0 lux on the floor). Flickering and image noises were removed from the recorded videos. The 2-hour video records from 2 hours after the start of dark cycle was analyzed with both ANY-maze software and the visual observation. The freezing scores obtained with ANY-maze each second during bilateral fighting and unilateral attack visually observed were significantly higher than that during other behaviors. The freezing score indicators were positively and significantly correlated with both total fighting duration and total fighting bouts, enabling analysis of activities of two rats in a home cage under dark cycle.