The Roman high- and low-avoidance rats respond differently to novelty in a familiarized environment

The purpose of the present study was to investigate the response to novelty in Roman high- and low-avoidance rats under non-stressful conditions. To reduce fear, a procedure of repetitive placing in the experimental chamber consisting of start, screen, and tunnel zones was applied. Each animal was placed in the experimental chamber daily for a 6min period. The first 11 sessions were the habituation sessions. In the 12th session, the novelty was introduced into the screen and tunnel zones. The subsequent two sessions were conducted under novelty conditions. Behavioral activities such as walking, object contacts, time spent in given zones, and entering the tunnels were measured. All the comparisons were made for two 3-min intervals, using a three-factor MANOVA, involving 2(sex)x2(subline)x8(3-mininterval). All subjects increased time spent in the tunnel zone, but RHA/Verh rats responded to a greater extent, especially the males. All subjects spent shorter times in the screen zone, but the RHA/Verh rats responded to a much greater extent. RHA/Verh rats, especially males responded with a substantial increase of time spent inside the tunnels. All subjects responded with an increased amount of object contacts. In general the RHA/Verh subjects showed a more pronounced response to novelty, as evidenced by a significant shift toward the tunnel zone. They spent more time in this zone than their RLA/Verh counterparts. Among the RLA/Verh rats, males tended to behave similarly to RHA/Verh rats, especially during the second 3min interval of session "12." The differences between the rat lines obtained in this study may be attributed to mechanisms specific to exploration, making them promising subjects to study the relationships between reactivity, novelty detection, adaptation, and environmental information processing.