Dr Emma Robinson from the Department of Pharmacology, and her colleagues at the Cambridge Behavioural and Clinical Neuroscience Institute, may have resolved this debate. Using positron emission tomography (a PET scan), the team discovered that rats that were behaviourally impulsive, but which had not been exposed to drugs, had significantly less brain dopamine receptors than their more restrained counterparts. Dopamine is a neurotransmitter in the brain that has been implicated in the rewarding effects of drugs of abuse. These changes in dopamine receptors suggest that the animals may have altered sensitivity to reward.

Additionally, these same impulsive rats were found to be considerably more likely to self-administer cocaine intravenously, thus linking impulsive behaviour with drug addiction vulnerability. This demonstrates that both impulsivity and the reduced numbers of dopamine receptors pre-date drug use, and are therefore not the result of prolonged drug addiction.

The new findings, published in Science, one of the world’s most prestigious journals, may lead to more targeted treatments for drug addiction and other compulsive behaviour disorders, with less side effects than current alternatives. Government reports estimate there are up to half a million individuals addicted to Class A drugs in England and Wales. This new research should help understand why and how people become addicted. Dr Robinson said “The findings may have important ramifications for a range of addictive substances and could help us understand why some individuals are more susceptible to drug addiction.”

The next step is to identify the gene or genes that cause this diminished supply of brain receptors.

Dr Emma Robinson / Department of Pharmacology