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. 2017 Jan 26:11:13.
doi: 10.3389/fnbeh.2017.00013. eCollection 2017.

Behavior of Male and Female C57BL/6J Mice Is More Consistent with Repeated Trials in the Elevated Zero Maze than in the Elevated Plus Maze

Laura B Tucker  1 , Joseph T McCabe  1
Affiliations

Behavior of Male and Female C57BL/6J Mice Is More Consistent with Repeated Trials in the Elevated Zero Maze than in the Elevated Plus Maze

Laura B Tucker et al. Front Behav Neurosci. .

Abstract

The elevated plus maze (EPM) and elevated zero maze (EZM) are behavioral tests that are widely employed to assess anxiety-like behaviors in rats and mice following experimental manipulations, or to test the effects of pharmacological agents. Both tests are based on approach/avoidance conflict, with rodents perceived as "less anxious" being more willing to explore the brighter, open and elevated regions of the apparatus as opposed to remaining in the darkened and enclosed regions. The goal of this research was to compare, under identical laboratory conditions, the behavior of male and female C57BL/6J mice in EZM and EPM during repeated trials. Mice were tested either daily or weekly, exclusively in the EPM or EZM, for a total of five exposures. During the first trial, the mazes were explored equally as measured by the total distance traveled during the test session. However, mice tested in the EZM spent nearly twice the amount of time in the anxiogenic regions (open quadrants) as the mice tested in the EPM spent in the open arms of that apparatus. After the first trial in the EPM, amounts of ambulation and percent time in the open arms decreased significantly (independent of inter-trial interval) which has been well-described in previous research as the one-trial tolerance phenomenon. In contrast, behavior in the EZM remained comparatively stable for several trials when the animals were tested weekly or daily. Sex differences were limited to activity levels, with females being more active than males. In conclusion, the design of the EZM encourages greater exploration of the anxiogenic regions of the apparatus, and may also be a more suitable test than the EPM for experimental designs in which assessment of anxiety-related behaviors is needed at more than one time point following experimental manipulations.

Keywords: anxiety; behavior; memory; one-trial tolerance; sex differences.

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Figures

Figure 1
Figure 1
The elevated zero maze (EZM; A) and elevated plus maze (EPM; B). Both mazes are elevated 50 cm above the floor. The EZM (A) consists of four equal quadrants; two opposite quadrants are darkened and enclosed and the remaining two are open and exposed. The EPM (B) has two open, exposed arms; perpendicular to those arms are two darkened and enclosed arms. The four arms meet in a 5-cm square region. Illumination in both mazes is approximately 1600 Lux in the open regions and 200 Lux in the enclosed regions.
Figure 2
Figure 2
Behavior of male and female mice in the EPM and EZM during the first exposure. Amount of exploration (total distance traveled, A) was equal regardless of apparatus or sex. The amount of time spent in anxiogenic (bright and open) regions (B) was significantly dependent on apparatus but not sex. *EPM vs. EZM. EPM, elevated plus maze; EZM, elevated zero maze.
Figure 3
Figure 3
Behavior of male and female mice in the EPM during repeated daily (A,B) or weekly (C,D) testing. All mice habituated rapidly to the apparatus as evidenced by a significant decrease in exploration (distance traveled) after the first trial (B,D). When the mice were tested daily, female mice ambulated greater distances on the second day of testing (B). In addition, the amount of time spent exploring the open, anxiogenic regions of the EPM (A,C) were significantly decreased on all days following the first exposure. These changes did not depend on the testing interval. The asterisk (*) denotes a significant difference on the denoted day compared to Day 1. The pound sign (#) denotes a significant effect of sex on the indicated day. EPM, elevated plus maze; EZM, elevated zero maze.
Figure 4
Figure 4
Behavior of male and female mice in the EZM during repeated daily (A,B) or weekly (C,D) testing. There was a main effect of sex on ambulation in the maze during daily testing, with female mice exploring the apparatus more than male mice (B). With daily testing, the amount of exploration decreased after the first trial (B), but this measure remained consistent until the fourth trial when the interval was increased to 1 week (D). The time spent in the open quadrants also remained consistent with further exposure to the EZM, with the percent of time not decreasing until trial 4 or 5 (A,C). The asterisk (*) denotes a significant difference on the denoted day compared to Day 1. The pound sign (#) denotes a main effect of sex. EPM, elevated plus maze; EZM, elevated zero maze.
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