LONDON (Reuters) - U.S. researchers have identified an important signalling system in the brain that helps to control food intake and body weight and which could lead to the development of new drugs to fight obesity. They found the melanocorotin-4 (MC4) receptor in rats acts as a conductor for leptin, a hormone known to reduce body weight by acting on the central nervous system. "We have identified one neurosystem, the melanocorotin receptor, as being an important mediator of what happens with leptin. It's a basic biological finding," Dr Randy Seely, who conducted the research at University of Washington School of Medicine, told Reuters. Scientists hope that by learning more about how the brain processes signals to control weight, they will be able to treat obesity. Patients with AIDS or tumours who have stopped eating could be encouraged to eat more. Leptin, which is produced by fat cells, was first discovered in 1994 when it was linked with body weight and appetite. Studies have shown high levels of leptin are found in humans and mice who are obese, indicating their bodies are resistant to the hormone. Seely and his colleagues, in a report in the scientific journal Nature on Wednesday, explained how they treated rats with a drug that blocked activation of the MC4 receptor and compared them with a control group that was not given the drug. So far the study has been limited to rats, but other research has shown that the gene that regulates melanocorotin seems to be related to human obesity. Seely believes that effective drug therapy to control human obesity is still five to 10 years away and it will take more than just one drug to deal with the problem, but scientists are getting closer to understanding how the brain controls weight. In developed countries, obesity has reached epidemic numbers. In US it is recognised as second only to smoking as a preventable cause of death. Obesity has been linked to an increase in heart disease, diabetes, stroke and certain cancers.