Like a rat in a cage
How are animal studies used to study addiction?
Among the many addiction experiments using laboratory animals are studies of treatment and relapse (returning to use of the substance), as well as initial addiction. Rats and mice lack some features of human behaviour and intelligence, but most parts of their brains are small versions of the human equivalents.
Sometimes, the animals ignore food and water in favour of another tiny hit of cocaine, for example. Building on this, researchers have learned a great deal about the brain circuits involved in addiction.
The results show that drugs are usually blunt instruments that affect the delicate complexity of the brain in lots of different ways. For example, the brain sites at which drugs produce physical dependence – and withdrawal symptoms – are distinct from those involved in the drugs’ habit-forming effects. That second set are tied up with the circuits that regulate rewards.
Different substances produce similar effects in different ways. Drugs that are addictive to humans, and that animals also seek out, nearly all exploit the natural reward mechanisms in the brain. They can do this either by increasing the rate at which neurons fire in particular brain regions, or by boosting production of the key neurotransmitter chemical, dopamine.