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Updated: May 17, 2026
Elevated Plus Maze for Mice
Published on: December 22, 2008
Altered anxiety and defensive behaviors in Bax knockout mice
Angela C Luedke1, Pierre O Boucher, Lee Niel
1Department of Psychology, University of Toronto-Mississauga, Mississauga, Ontario, Canada.
Abstract:
Developmental neuronal cell death is critically regulated by the pro-death protein Bax. Bax-/- mice exhibit increased neuron number, the elimination of several neural sex differences, and altered socio-sexual behaviors. Here we examined the effects of Bax gene deletion on anxiety and defensive behaviors by comparing the responses of male and female wildtype and Bax-/- mice to two different tests. On the elevated plus maze, Bax-/- mice of both sexes made more entries into and spent more time in the outer portion of open arms, indicating decreased anxiety compared to wildtype animals. Next, we exposed mice to two odors: trimethylthiazoline (TMT), an olfactory component of fox feces that rodents find aversive, and butyric acid (BA), an aversive odor without ecological significance. Each odor was presented individually and all animals were tested with both odors in a counterbalanced design. TMT was consistently more aversive than BA across a variety of behaviors (e.g., mice spent less time close to the odor source). Overall, Bax -/- mice showed fewer stretch approaches to both TMT and BA than wildtypes, but they avoided the odor source more (e.g., fewer contacts and less time spent in proximity). Finally, no effect of genotype was seen in baseline olfactory behavior; all mice were able to locate a buried food item, demonstrating that Bax-/- mice do not have impaired olfaction per se. Collectively, these data suggest a change in strategy with anxiety and defensive behaviors in Bax-/- mice, indicating that alterations in cell number affect more general mechanisms of fear and anxiety in addition to behaviors directly related to reproduction.
Insights
Deleting the Bax gene in mice reduced anxiety and altered defensive behaviors. Bax-/- mice showed less anxiety on the elevated plus maze and different responses to aversive odors.
Area of Science:
- Neuroscience
- Behavioral Neuroscience
- Genetics
Background:
- Developmental neuronal cell death is regulated by the pro-death protein Bax.
- Bax gene deletion in mice leads to increased neuron number, reduced neural sex differences, and altered socio-sexual behaviors.
Purpose of the Study:
- To investigate the impact of Bax gene deletion on anxiety and defensive behaviors in mice.
- To compare the behavioral responses of wildtype and Bax-/- mice to anxiety-provoking and aversive olfactory stimuli.
Main Methods:
- Utilized the elevated plus maze test to assess anxiety levels in male and female wildtype and Bax-/- mice.
- Exposed mice to trimethylthiazoline (TMT) and butyric acid (BA) odors to evaluate defensive behaviors.
- Assessed baseline olfactory function by testing the mice's ability to locate a buried food item.
Main Results:
- Bax-/- mice exhibited decreased anxiety, demonstrated by increased exploration of open arms on the elevated plus maze.
- Bax-/- mice showed altered defensive behaviors towards TMT and BA, including greater avoidance of odor sources, despite no impairment in general olfaction.
- No significant differences in baseline olfactory abilities were observed between wildtype and Bax-/- mice.
Conclusions:
- Bax gene deletion influences anxiety and defensive behaviors, suggesting a broader role beyond reproductive functions.
- Alterations in neuronal cell number due to Bax deletion impact general fear and anxiety mechanisms.
- These findings highlight the complex relationship between cell number regulation and behavioral responses.
