Twenty years after the hormone leptin was found to regulate metabolism, appetite, and weight through brain cells called neurons, researchers have found that the hormone also acts on other types of cells to control appetite. Leptin, a naturally occurring hormone, is known for its hunger-blocking effect on the hypothalamus, a region in the brain. Food intake is influenced by signals that travel from the body to the brain. Leptin is one of the molecules that signal the brain to modulate food intake.