The elevated plus maze (EPM) is a widely used apparatus in behavioral neuroscience, designed to study anxiety-like behaviors in laboratory rodents like rats and mice. It provides a controlled environment to observe responses to perceived threats, serving as a tool for researchers to investigate anxiety mechanisms and evaluate potential treatments, including the influence of genetics or pharmacological agents [1, 2, 3].
The Maze’s Design and Purpose
The elevated plus maze is a plus-shaped apparatus, elevated 50 to 80 centimeters off the ground [3, 4, 5]. It has four arms extending from a central platform: two opposing open arms and two opposing enclosed arms with walls 16 to 30 centimeters tall [1, 3, 5]. Arm dimensions vary; rat mazes typically have arms 45-50 cm long and 10 cm wide, while mouse mazes have arms 25-30 cm long and 5 cm wide [3, 5].
The EPM’s design creates a natural conflict for rodents, forming the basis for anxiety assessment. Rodents have an innate exploratory drive but also an aversion to open, elevated spaces [1, 2, 3]. This aversion comes from their natural fear of heights and exposed areas, where they are vulnerable to predators [2, 3]. The enclosed arms provide a safe zone, while open arms present an anxiety-provoking challenge, forcing a choice between exploration and safety [1, 5]. This approach-avoidance conflict allows researchers to quantify anxiety-like behavior [5].
Conducting the Test
For the elevated plus maze test, a single rodent is placed on the central platform, often facing an open arm [3, 4, 5]. The animal explores the maze for a predetermined period, typically five minutes, though some protocols extend to 10 minutes [3, 4, 5]. An overhead camera and specialized video tracking software record the animal’s movements and time spent in different maze areas [1, 3, 4].
Maintaining a consistent and controlled testing environment is important for obtaining reliable results. This includes ensuring uniform lighting conditions across the maze and minimizing external disturbances like loud noises [1, 3, 5]. Researchers often habituate animals to the testing room for a period, such as an hour, before the test begins to reduce stress from novelty [1, 5]. Cleaning the maze thoroughly between each animal’s session is also a standard practice to eliminate olfactory cues that could influence subsequent behavior [1, 2].
Interpreting the Results
Data from the elevated plus maze test focuses on the animal’s behavior in the open versus enclosed arms. Key metrics include time spent in and entries into the open arms [1, 2, 3]. Rodents with higher anxiety-like behavior spend less time exploring and make fewer entries into the open, exposed arms, preferring the enclosed arms’ perceived safety [1, 4].
Conversely, increased time and entries into the open arms indicate reduced anxiety-like behavior [1, 2, 3]. This makes the EPM a valuable tool for screening potential anxiolytic (anti-anxiety) medications [1, 2, 4]. For example, if a new compound leads an animal to explore open arms more freely, it suggests the compound may reduce anxiety [2, 4]. The EPM provides a quantifiable measure of anxiety-related responses [1, 3].