Paradoxical differences in animal models of anxiety among the Roman rat lines

The Roman high-avoidance (RHA) and low-avoidance (RLA) rat lines have been selected upon their divergent active avoidance behaviours. On the basis of open-field behavioural analyses, it has been suggested that RLA rats display more emotionality than RHA rats. Herein, we have analysed the behaviours of male RHA and RLA rats in three tests putatively related to anxiety, namely the elevated plus-maze, the black/white box, and the social interaction test. In the elevated plus-maze, neither the number of total arm entries nor the percent number of open arm entries were different between the Roman lines. Alternatively, RLA rats spent more time on the open arms, compared to RHA rats. In the black/white box, both the latency to enter the black compartment, the number of shuttles, the time spent in the white compartment, and the general activity in the white compartment were higher in RLA rats, compared to their RHA counterparts. Lastly, socially isolated RHA and RLA behaved similarly when exposed to a social interaction test. It is suggested that under particular experimental conditions male RLA rats display less anxiety than male RHA rats, and that the open-field test may provide indices of activity rather than indices of anxiety.