A dark-light emergence test: Study at two times of the nycthemeral cycle in four-and twelve-week-old rats

The latency to emerge from a darkened compartment to a lighted one was measured twice daily in 4-and 12-week-old rats. The test was repeated on three consecutive days: at 20.00 h on the first day, at 12.00 h and 20.00 h on the second day, and at 12.00 h and 20.00 h on the third day. The latencies of the older rats were consistently longer than those of the younger ones. While the time of day had no influence on the 4-week-old rats performances, latencies of the 12-week-old rats were considerably longer at 20.00 h than at 12.00 h.