Convergent activity but divergent anxiety dimensions in male and female C57BL/6 mice across the open field and elevated plus maze
Anxiety disorders are among the most common psychiatric illnesses, with a significantly higher prevalence in females than in males. The open field (OF) and the elevated plus maze (EPM) are the two assays used most often to model anxiety-like behavior in mice. It is usually assumed that they index a common underlying trait, yet few studies have investigated this in a large group of male and female mice using an advanced analytical approach. The goal of these studies was to determine sex differences in locomotor activity and anxiety-like behavior in the OF and the EPM, and to establish which behavioral parameters correlate between the tests. Adult male and female C57BL/6 mice (n = 61; 29 male, 32 female) were given a single 15 min session in the OF, analyzed as a whole and in three consecutive 5 min blocks, and a single 5 min EPM trial. Males and females did not differ on any OF measure over the cumulative 15-minute session. Locomotion and stereotypy declined over time with females habituating faster than males while center exploration did increase. In the EPM, females made more closed-arm entries than males while open-arm exploration was identical. Every significant correlation between the two tests involved an activity measure. All four pairs formed between OF and EPM activity parameters were significant whereas none of the six pairs formed between OF center parameters and EPM open-arm parameters were significant. Hierarchical clustering revealed the same structure, placing the activity measures of both tests in one cluster, the EPM open-arm measures in a second, and the two OF center measures in a third. The cross-test activity correlation was strongest during the initial five minutes of the OF and weakened as the session progressed. These studies indicate that the OF and EPM yield convergent measures of activity, but divergent measures of anxiety-like behavior.