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Forced Mice and Rat Swim Tests Fail to Measure Human Depression

From Marc Bekoff, Psychology Today  / Animal Emotions
September 2023

Pfizer has acknowledged that 'none of the compounds tested by Pfizer since 1989 using the forced swim test are currently approved to treat human depression, which means that the test did not lead to marketing these compounds as new medications.

mice swim tests

Animal models of human disease have extremely mixed results, and all too often they do not work well and accomplish their goals of helping humans.1

One such procedure, the forced swim test, is a prime example of an experimental procedure that has all sorts of problems. I'm pleased researcher Stephen Farghali of Black Hills State University could answer a few questions about why it doesn't help us learn more about human depression.

Marc Bekoff: Can you tell readers why, after 45 years of the forced swim test, one of the most prevalent animal experiments fails to measure up?

Stephen Farghali: Imagine you want to know whether a substance, say zinc, alleviates depression. How should you scientifically test this? One good option would be to give zinc supplements to human participants for a length of time while assessing their depression.1

Another would be to grab a lab mouse by the back of the neck and inject either zinc or a placebo down the esophagus. Then drop the mouse into a beaker of tap water and set a timer, watching as the mouse struggles to escape. Eventually, they give up. Instead of trying to escape, the mouse resorts to floating. If mice who get zinc struggle longer than those who donít, a leap of faith is made to conclude that zinc might alleviate human depression.

The latter option is called the forced swim test, and itís one of the most common animal experiments researchers use to study a substance for antidepressant properties. It rests on interpreting that floating behavior as ďdespair." A mouse who's given up trying to escape, the thinking goes, is analogous to a person suffering from depression. But this interpretation has been heavily criticized in the decades since it was originally published in 1977.





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