Genes dictates everything in you: from height, eye and hair color to the way you smile or grin.

And not only.

A recent research made on rats by a team at Cambridge University points that physical differences in the brain dictated by genes may rise the chances of an individual to fall to drugs consume.

Variations in the rats' brain structure were found to make them more likely to opt for cocaine.

Only in the UK up to 500,000 people are currently addicted to Class A drugs (like cocaine, heroin and amphetamines).

Scientists are still puzzled by the origin of differences noticed in the brains of human drug users, believed to be involved in how humans respond to drugs. By now, it is not known if they are the result if genetic variations amongst individuals or the result of the drugs intake.

By scanning the rats' brains, the research team discovered similar variations - just like in the case of humans - in neurotransmitter receptors in certain brain areas.

Some rats had far fewer dopamine receptors, brain proteins to which drugs like cocaine and heroin attach inducing their effect. The rats were put to play a game: they had to wait to press a button and receive a reward, coupled with detailed brain scans, to assess impulsiveness in individuals with lower dopamine receptors.

Impulsiveness is linked in the human behavior with drug use.

Indeed, lower amounts of dopamine receptors was linked to higher level of impulsiveness and when all the rats were exposed to drugs, the "impulsive" ones were much more likely to do so than the rats with normal quantities of dopamine receptors. "This showed clearly that the brain differences, and the impulsivity linked to them, pre-dated any exposure to drugs, with the possibility that the situation in human drug users could be the same. What we are talking about here is a possible physical trait producing vulnerability to drug use. The next step is identifying the gene or genes that cause this diminished supply of brain receptors. This may provide important new leads in the search for improved therapies for attention deficit/hyperactivity disorder (ADHD) and compulsive brain disorders such as drug addiction and pathological gambling", said Dr Jeff Dalley, who led the study.

Even so, the researchers warn that the reasons for humans to become addicted to any drug are more complex, including also other factors besides the genetic ones. "There are lots of reasons unconnected to genes why people use drugs, and I can't see that any test would be useful", added Dalley.

"It is well known that some personality traits are associated with a vulnerability to cocaine and other addiction problems. This study is extremely interesting because it has identified a biological basis in rats for some of the behaviors that we know are associated and shows how they can lead to drug addiction", said Lesley King-Lewis, Chief Executive of Action on Addiction.

"The differences found in the rats were very likely to have their equivalent in the human brain. This is a very exciting study which has successfully identified the biological basis of some of the behaviors that we know are associated with higher risk of cocaine and other addictions in humans. It also pinpoints a potential cause of relapse in abstinent drug users - what makes them start taking a drug again despite all the problems they know it will cause them. This means that we can start to investigate treatments that, at least partially, correct this deficit in the hope that these will prove successful in preventing relapse", said Dr Gerome Breen, from the Institute of Psychiatry in London