Anhedonia

Anhedonia, defined as the inability to experience pleasure, is evaluated in rodents using the sucrose-preference test and the intracranial self-stimulation test. The sucrose-preference test measures the tendency of an animal to consume a sucrose solution over regular water when provided with access to both.[2] Healthy animals will drink a greater volume of sucrose, while those exhibiting anhedonia will show a reduced preference for the sugar. The intracranial self-stimulation test evaluates the motivation of rodents to engage in an activity (pressing a lever or running on a wheel) that is paired with a rewarding electrical stimulus delivered through electrodes implanted in the brain.[3]

Appetite and Sleep Dysregulation

Appetite and sleep disturbances are another common component of major depressive disorder. People with depression tend to sleep and eat less than usual, although individuals with atypical depression display an increase in sleep and in food consumption. Changes in appetite can be easily assessed in experimental animals by quantifying food intake and body weight, while sleep abnormalities can be measured using electroencephalographic recordings. Like depressed patients, some animal models of depression display altered sleep patterns.[4]

Behavioral Despair

Behavioral despair refers to the tendency of an individual to view their circumstances as immutable and to cease trying to control the outcome of the situation. Behavioral despair can be screened for in