Migraine - Role of animals

Scientists have made and continue to make great advances in understanding human migraine by studying animal models that mimic specific aspects of the condition.

Many of the brain structures and brain chemicals involved in migraine are very similar in people, cats, dogs, rats and mice.

Animals may or may not have migraines themselves, it is virtually impossible for us to know. However, many of the brain structures and brain chemicals involved in migraine are very similar in people, cats, dogs, rats and mice. And it would be extremely risky to do many of the experiments in people that are possible in animals.

Over the years, many of the key advances in our understanding of migraine have come from studies in dogs and cats. These are familiar research animals but unlike rats and mice they are big enough to provide tissue samples that can be easily worked with and big enough to examine brain function easily in the living but anaesthetised animal. As well as using these large animals to test out their theories of what causes migraine, researchers use them to check in a living animal that potential medicines hit their targets and achieve the desired result. It is essential to know, for example, that previously unknown chemicals actually do narrow the target blood vessels without having the same effect elsewhere in the body. It is not possible to make the same measurements in people or acceptable to try out strange chemicals on humans that might seriously affect their whole circulation.

When it comes to mimicking human migraine in an animal, the most widely used model involves electrical, mechanical or chemical stimulation of parts of the trigeminovascular system, which researchers believe is central to how migraine develops. The test animals are anaesthetised so that they feel no pain and do not become stressed.

Drugs known to have an anti-migraine effect in people reduce the activity of the trigeminal nerve in the animal model. This activity is measured in a number of ways. One is to look at how fast proteins move out of the blood vessels that the nerve touches – this leakage of proteins may be partly responsible for the inflammation seen in human migraine. Another option is to measure electrical activity elsewhere in the brain because stimulation of the trigeminal nerve is thought to result in messages being sent out into the brain to produce aura and other characteristics of migraine. Thus scientists have a model for at least one way of treating migraine and can test out possible medicines without putting patients at risk.

However, although reduction in trigeminal activity is a good indicator of anti-migraine potential, it does not guarantee a drug’s success in all people. After safety tests have been done in animals, potential medicines are tested in several stages on people i.e. in human clinical trials. If they are proven to work and to have few side-effects they will be licensed. Only then will doctors be able to prescribe them.