In the fields of psychology and psychiatry, depression refers to a state of low mood and aversion to activity. Most often depression is described as a disease or dysfunction. The Diagnostic and Statistical Manual of Mental Disorders defines a depressed person as experiencing feelings of sadness, helplessness and hopelessness. Biological causes of depression vary but may relate to malnutrition, heredity, hormones, seasons, stress, illness, drug or alcohol use, neurotransmitter malfunction, long-term exposure to dampness and mold, back injury, and to aerosol exposure. In principle, depression is developed as organism' response to the presence of unavoidable danger. There are also strong arguments for seeing depression as an adaptive defense mechanism. For instance, a low or depressed mood can increase an individual's ability to cope with situations in which the effort to pursue a major goal could result in danger, loss, or wasted effort. In such situations low motivation may give an advantage by inhibiting certain actions. This theory helps to explain why depression is so prevalent, and why it so often strikes people during their peak reproductive years. These characteristics would be difficult to understand if depression were a dysfunction, as many psychiatrists assume (Nesse 2000*).

In laboratory animals, depression-relevant state is mainly measured by means of the forced swim test and tail suspensiosn test, reflecting organism's hoplesneess, which is sensitive to antidepressant' treatments. Monitoring of sucrose prefernce is also a useful indicator of decreased rewarding accompanying depressive-like condition.

*Nesse R (2000). "Is Depression an Adaptation?". Arch. Gen. Psychiatry 57: 1420.


Sucrose Preference



Mice are housed individually for this test. No food or water deprivation is needed before the test. To reduce the possible stressful response to novelty, 24 hours prior to actual testing mice are given 3 hours to choose freely between two bottles (one with 5% sucrose solution and another one with regular water).

During next four days, two bottles (one with water and another with 10% sucrose) are presented. To prevent possible effects of side preference in drinking behaviour, positions of the bottles are switched at 12 hr intervals.

The consumption of water and sucrose solution is estimated by weighing the bottles. Preference for sucrose solution is calculated as the percentage of sucrose solution ingested relative to the total amount of liquid consumed.



Figure 1.Sucrose Preference


Forced Swim Test



The mouse is released into a transparent cylinder (2 L beaker) for 6 minute (water at 25°C; depth of 18 cm).

Following parameters are recorded during the last 4 minutes of testing using OBSERVER 5.0 (Noldus Information Technology): (1) climbing (upward movements), (2) active swimming, and (3) floating.

Each mouse is allowed to dry after the test in the separated cage under the heat lamp. The water is regularly changed between subjects.


Figure 1.Forced Swim Test