Open Field

Open Field Test: The automated open field assay has been customized to address changes related to affective state and exploratory patterns. The field (40 x 40 cm) is relatively large for a mouse, which is designed to pick up changes in locomotor activity associated with exploration. In addition, there are four holes in the floor to allow for nose-poking, an activity specifically related to exploration. Several additional factors have been designed to heighten the affective state associated with this test. The open field test is the first experimental procedure in which the mice are tested, and the measurements taken are the subject's first experience with the chamber. In addition, the open field is brightly lit. All these factors heighten the natural anxiety associated with novel and open spaces.

The pattern and extent of exploratory activity, especially the center-to-total distance traveled ratio and sum time in center, may be able to discern changes related to susceptibility to anxiety or depression. Knockouts of genes known to be involved in these processes, such as the serotonin transporter (unpublished data), the dopamine transporter (Giros et al., 1996), and the GABA receptor (Homanics et al., 1997) exhibit phenotypes in the open field test. Decreased anxiety-related behavior has been observed in the open field test after administration of diazepam (benzodiazepine receptor agonist) (Mathis et al., 1994). The test is initiated when the animal is placed in the center of the brightly lit 40 x 40 cm chamber. The mouse's activity is measured for 20 minutes and data from this test are analyzed in five 4-minute intervals. The total distance traveled (cm), vertical movement number (rearing), number of hole pokes, sum time in center, and the center-to-total distance ratio are recorded.

Displayed below is a sample graph of how open field total distance traveled and center-to-total distance ratios are presented. In comprehensive phenotypic data packages graphs are interactive. Raw or calculated data and statistics can be seen by clicking on points in the graph.

Figure illustrates total distance traveled (left panel) and center-to-total distance (right panel) for male and female mutant mice. Activity of wild type littermates (green square), homozygous mice (red circle), and recent historical wild type mice (purple line) are plotted against long-term means (+/- 2 standard deviations) for wild type animals (green shading). Recent wild type values are calculated from data collected within 60 days of current measures and long-term historical means are derived from data collected on more than 10,000 wild type mice.

Rearing and Nose Poke Activity
A large arena (40 cm x 40 cm) with infrared beams at three different levels is used to record rearing and hole poke activity. The number of vertical movements (rearing) and hole pokes are recorded automatically. Median values are calculated and presented in table format.