It has long been known that the hormone leptin acts in the central nervous system to reduce food intake and body weight, but experiments with rats have now shown that it operates through a particular molecular key, or receptor, in the brain. Receptors are distinct sites on the surface of cells which have the right molecular shape for specific chemicals to bind on to and exert their effects. The principle is similar to a key fitting a lock. In the case of leptin, the hormone binds to the melanocortin-4 (MC4) receptor, causing a "reduce weight" signal to be released.
Research carried out at the University of Washington, in the United States, found that rats which had their MC4 receptors chemically blocked were unaffected when treated with leptin. Those in which the receptors were left unaltered consumed less food and lost weight when given the same amount of the hormone. Dr Randy Seeley, who led the research, said: "Identifying a role for the MC4 receptor in mediating the effects of leptin in the brain may be an important step in advancing our understanding of how the brain controls food intake and body weight, and, subsequently, will help us treat health problems such as obesity."