The forced swim test is a behavioral test that involves placing a rat or mouse in a cylinder with enough water so that it cannot touch the bottom with its hind paws. It is used to test the rats responsiveness to stress. A normal animal will show an immediate burst of activity, try to escape, and then eventually adopt an “immobile” posture, where it will make only those movements necessary to keep its head above water. 

University of Vermont

Studies have shown that low amounts of serotonin in the brain have been implacated in anxiety. One way this phenomena was shown was via a force swim test, as well as through learned helplessness.
           

Serotonin's Role in Anxiety

As rodent models are ubiquitous among neuroscience and biomedical research, researchers have developed standardized assays to test specific behaviors, including but not limited to anxiety, stress, aggression, and cognition.

Behavioral assays with rodents

Serotonin Reference Library

Forced Swim Test

Learned helplessness is a psychological state that occurs when an individual endures repeated, uncontrollable, and stressful events, leading to a belief that they are powerless to change their circumstances. This causes them to cease efforts to exert control, even when opportunities for change become available. The concept was established through Martin Seligman's 1960s experiments where dogs, after being unable to escape electric shocks, later failed to attempt escape even when it was possible. Seligman theorized that this behavior—passivity and a lack of initiative—mirrored symptoms of human depression, suggesting that learned helplessness could be a significant factor in its development.

Learned Helplessness

The elevated plus maze is used to evaluate anxiety-like behaviors in rodents. Subjects are placed in the junction of the maze, and their entries into either the open arms or the closed arms are recorded over a set duration. Unlike traditional methods of measuring anxiety in rodents, such as food deprivation or shocks, the elevated plus maze does not present a noxious stimuli and therefore does not lead to aversive conditioning. Wild-type rodents gravitate toward the dark, enclosed arms of the maze; however, anti-anxiety behaviors can be induced in these rodents (i.e. administration of anxiolytics), which can be strongly correlated to more time spent in the light, exposed arms of the maze.

Elevated Plus Maze

The open field test is used to evaluate fear in rodents. Subjects are placed in the center of a box with a defined “center” region, and are free to explore the box for a set duration. During the open field test, rodents exhibit a behavior known as “thigmotaxis,” in which they initially hug the walls of the area and later venture out into the center. This behavior is attenuated via anxiolytic drugs and is intensified in rodent strains with high anxiety.

Open Field Test

The Morris water maze, created by neuroscientist Richard G. Morris, is used to evaluate learning and memory in rodents. The maze consists of a pool of water with a single circular platform raised slightly above the water’s surface. To establish working memory, the rodents are placed in different quadrants of the pool and are allowed to freely swim and search for the platform. After the first day of training, the platform is submerged, and the next several days are dedicated to finding the submerged platform. Finally, the platform is removed, and the rodents’ memory is tested. More time spent in the platform’s quadrant correlates to stronger memory retention.

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