Object exploration in the developing rat: methodological considerations

The current study was conducted to characterize the ontogeny of novel object recognition in rats. Initial testing (Experiment 1) was conducted in a square arena and it was observed that 21-day-old animals would often pause in the corners, greatly increasing between-subject variability and performance in this test. Significantly greater object exploration and less variability were obtained using a circular arena. In Experiment 2, we report object exploration in 21, 35, 42, and 90-day-old male and female Sprague-Dawley rats using a circular arena. The results show that measures of locomotor activity, object exploration, and within session habituation of these behaviors were surprisingly similar across all ages. Gender differences in locomotor activity were not observed until 42 days of age. Reliable recognition memory was observed at all ages. It is concluded that the novel object recognition test appears well suited for use in young rats.