Factor analysis of behaviour in the porcine and murine elevated plus-maze models of anxiety

The elevated plus-maze, a widely used and well-validated test for studying anxiety-related behaviour in rodents, has recently been suggested for studying anxiety- or fear-related behaviour in swine. There are, however, clear evolutionary, and thus behavioural differences, between these two species. The aim of the present experiment was therefore to compare the behaviour of mice and swine in the murine and porcine elevated plus-maze (PEPM), respectively. To analyse the behaviour of swine, a database including 84 naive weaned pigs was used, while the analysis of mouse behaviour was based on a database of 79 naive individuals. Plus-maze behaviour of the two species was compared on the basis of factor analysis. Based on the hypothesis that the elevated plus-maze induces behaviour related to anxiety in pigs, as well as in mice, it was predicted that factor analysis of pig behaviour should produce factor loadings similar to those found for mice. More specifically, elements predicted to be anxiety-related for pigs (percent open entries, open arm time, percent open arm time) should load highly and independently on a single factor. Furthermore, elements predicted to be activity-related (closed entries and total entries) should also load highly and independently on a separate factor. The orthogonal factor pattern confirmed these predictions. On the other hand, pigs did not express the unconditioned avoidance of open arms observed for mice. It is therefore concluded that the present data provide only equivocal support for the validity of the PEPM. (C) 2002 Elsevier Science B.V. All rights reserved.