By Hannah Stainbank, Second Year, English
The Student Union recently passed a motion to 'End All Forced Swimming Experiments at the University of Bristol', following a string of protests against this experiment.
Though the University of Bristol used the Forced Swim Test (FST), to understand the neurobiology of stress, this test is used elsewhere as an increasingly criticised model of depression.
It involves keeping the rats in an inescapable beaker of water and observing their behaviour. Stopping swimming or attempting an escape is categorised as an indication of despair. This has been used to test the effectiveness of anti-depressants. If the rat keeps swimming longer the anti-depressant is seen as more effective.
This method has been widely criticised as the lack of movement could also be an adaptive behaviour and not an indication of depressed mood. In the UK, the Animals in Science Commission (ASC) recommended that use of this test as a model of depression should be rejected. Lord Sharpe, when working for the Home Office, went a step further and wrote that he aims to 'completely eliminate' it's use, including how it is used at our university.
There are other ways in which animals are used to model depression – with varying success. As a disorder that is largely characterised by psychological symptoms, it is interesting to consider how rodents (who seem to have a less complex inner life than humans) are tools of research.
A study conducted in 2019, titled 'Animal models of major depression: drawbacks and challenges', looked at the uses and limitations of rodents in studies of major depressive disorder (MDD). They defined the core symptoms of MDD to be anhedonia (decreased ability to feel pleasure) and a depressed mood linked with feelings of despair. Other symptoms such as feelings of worthlessness or thoughts of death are impossible to see in rodents, so are left out from animal studies. As you can imagine, it's a bit tricky to just ask the rats about their thoughts and feelings.
Anhedonia is fairly easy to study, most often tested by offering the animal a choice of a sweet sucrose solution or normal water. If they are experiencing anhedonia they will not show a significant preference for the sweet drink.
'Depressed mood', on the other hand, poses some more challenges, as seen with the controversial FST. Other tests, such as suspending the rat from their tail and observing when they stop struggling, similarly face the problem that adaptive behaviour could be misconstrued as despair.
The 2019 study concluded that so far, animal models have 'failed to lead to the development of new treatments and the biological mechanisms of depression are still poorly understood'. This includes a wide range of animal studies that meet validity criteria, not just the FST. This indicates that perhaps the use of animal models should be refined further to lead to improvements. Or, that rat models of depression are not that similar to human depression. Though it can be useful in identifying things like genetic predisposition to MDD, it seems clear that animal models have their limitations.
The obvious alternative to animal studies of depression are human studies. Recruitment for this can be time consuming and expensive, though researchers collaborating with King's College London are seeking to change this by recruiting 40,000 people with depression or anxiety. This will provide a pool of participants for future studies.
MDD is also categorised by a wide range of symptoms, not all of which are present in each patient. The symptoms themselves are often subjective, so the effectiveness of treatments is often difficult to define. Though this issue is also applicable to animal models, especially as the subjective symptoms are often difficult or even impossible to identify in animals.
Studies of depression using animal models have a long way to go. By continuing to criticise and refine these techniques, researchers can phase out ineffective tests and limit the waste of animal life. And, hopefully, get closer to effective research that leads to development in treatment.
Featured image: PETAHere is the University of Bristol's full statement:
