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. 

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

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.
           

University of Vermont

Cellular: 
-Simultaneous inhibition and excitation
-Complicated cell responses
Behavioral: 
-Anxiety
-Depression 
-Mood

Serotonin Roles and Functions

Serotonin Reference Library

The activity of serotonin systems have been to mood.  Tryptophan depletion leads to symptom relapse in people in remission from depression.

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