Behavioural Brain Research 111 (2000) 153 – 163 Research report Unconditioned anxiety and social behaviour in two rat lines selectively bred for high and low anxiety-related behaviour Markus S.H. Henniger * , Frauke Ohl, Sabine M. Ho ¨ lter, Petra Weißenbacher, Nicola Toschi, Patrick Lo ¨ rscher, Alexandra Wigger, Rainer Spanagel, Rainer Landgraf Max Planck Institute of Psychiatry, Kraepelinstr. 2 -10, 80804 Munich, Germany Received 25 October 1999; received in revised form 13 January 2000; accepted 13 January 2000 Abstract Individuals of high anxiety-related behaviour (HAB) and low anxiety-related behaviour (LAB) rat lines were selectively bred for differences in anxiety-related behaviour on the elevated plus-maze. The goal of this study was to investigate whether this behavioural difference is restricted to the test used as the selection criterion or whether it is a stable and robust trait also in other conflict or non-conflict situations. Therefore, behaviour of male and female HAB and LAB rats was examined in two further tests of unconditioned anxiety: the black – white box and the social interaction test. Furthermore, behaviour of group-housed male HAB and LAB rats was studied in their home cages. In addition to standard statistics, discriminant analyses were performed. The difference in anxiety-related behaviour between the two lines was highly consistent in all tests of unconditioned anxiety. There were also differences in home cage behaviour, LAB rats being more active than HAB rats; this is likely to be a consequence of the LAB rats displaying a higher aggressiveness in social behaviour, compared to HAB rats. In all tests used HAB and LAB rats were clearly distinguished by discriminant analysis. However, while in the elevated plus-maze and the black – white box test the most important parameters for discrimination between the two lines were mainly those generally seen as closely related to anxiety, the discrimination in the social interaction paradigm was primarily due to differences in locomotor activity. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Emotionality; Elevated plus-maze; Black – white box; Social interaction test; Home cage behaviour www.elsevier.com/locate/bbr 1. Introduction We recently reported on two Wistar rat lines which were selectively bred over several years for extremes in anxiety-related behaviour on the elevated plus-maze [12 – 14]: the high anxiety-related behaviour (HAB) and the low anxiety-related behaviour (LAB) lines. These lines represent a useful animal model for studying the neurobiology of inborn anxiety and the mechanism(s) of actions of anxiolytic compounds [13]. Anxiety has been shown to be a highly complex construct and it has been suggested that different tests of anxiety-related behaviour measure various aspects of anxiety [2,24]. When using animal models of inborn anxiety it is, therefore, of great interest to evaluate whether differences in anxiety-related behaviour occur globally or are restricted to variables measured by the test used as selection criterion. Therefore, we tested HAB/LAB rats in different paradigms, which have been shown to measure distinct dimensions of emotionality. First, the elevated plus-maze was used to confirm the selected line differences. Then we tested HAB and LAB rats in two other tests of unconditioned anxiety, the black – white box and the social interaction test. The elevated plus-maze test is a widely used test paradigm to investigate anxiety-related behaviour (for reviews see Refs. [6,10,25]) and has extensively been validated for use in both rats [19] and mice [15]. It is based on the test-induced conflict in rodents between * Corresponding author. Tel.: +49-89-30622641; fax: +49-89- 30622569. E-mail address: henniger@mpipsykl.mpg.de (M.S.H. Henniger) 0166-4328/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII:S0166-4328(00)00151-0