The fruit fly Drosophila melanogaster – wild type

Animal models

Is it really possible to use experimental animals to study human behaviour and decision making?

In many areas of biomedical research, animals such as mice and rats are used to find out about underlying physiological mechanisms. Such experiments cannot be done on people, but the results of experiments on rodents are of relevance to human biology. But can the same be true of complex behaviours, given that the human brain is so different from those of other animals?

While extrapolation from animals to humans should always be made with caution, it is turning out to be possible to study behaviour in animals and to make connections between behaviour, brains, cell biology and genetics.

Different strains of mice, for example, vary in certain behavioural traits. Some are particularly neurotic, for example, and possible genetic contributions to this trait have been identified. This does not reveal a ‘gene for neuroticism’, but does suggest a possible biological mechanism influencing neuroticism in mice and, by extension, humans.

A similar approach is to use genetic techniques to ‘knock out’ particular mice genes and to see what effect that has on behaviour. A good example is the 2005 knockout of the stathmin gene, which turned mice into daredevils, transforming their normally timid nature. Stathmin is active in the amygdala, and seems to be crucial in the animal’s fear responses. Without stathmin, the mice show much less fear. For humans, the end result could be a better understanding of anxiety and (eventually) new treatments for anxiety disorder or post-traumatic stress disorder.

Studies can also provide clues to the physiological changes associated with behaviour. Mice that are repeatedly bullied, for example, become very reclusive and are reluctant to mix with other mice – a response known as ‘social defeat’. This response can be overcome by long-term treatment with antidepressants. It has been found to depend on a molecule known as brain-derived neurotrophic factor; without this protein, the mice do not become reclusive when bullied. The distinctive social defeat response resembles human anxiety and depression, and studies in mice should help us understand the biochemical nature of these psychological conditions.

Fly sexuality

Even simple animals can provide clues to the mechanisms underlying behaviour. Much research is carried out on the fruit fly, and some studies have identified the factors underpinning their sexual orientation.

Fruit fly mating is very stereotyped. Males court other females by walking behind them doing a kind of dance. This behaviour is dependent on a gene known as fruitless, which comes in male and female forms. If a female fly is genetically engineered to make the male version, it adopts the male courting behaviour, though in other respects it is a typical female. The difference in behaviour has also been linked to very specific changes to neural pathways in the fly brain.

This does not, of course, mean that there is a single human gene that controls human sexual orientation. Human sexuality is far more complex than fruit fly courting. But it does illustrate how gene changes can affect the brain and hence behaviour in an animal with complex behaviours, and suggests new ways to study such behaviours in other animals.

Lead image:

The fruit fly Drosophila melanogaster – wild type.

Audio-visual, London School of Hygiene & Tropical Medicine/Wellcome Images CC BY NC ND

References

Further reading

About this resource

This resource was first published in ‘Thinking’ in September 2006 and reviewed and updated in August 2014.

Topics:
Genetics and genomics, Neuroscience, Psychology
Issue:
Thinking
Education levels:
16–19, Continuing professional development