Leptin is a satiety hormone produced by fat cells and released into the bloodstream. It signals fullness to the brain, helping to regulate eating behavior by shutting it off. Leptin receptors are found in various brain regions, including the choroid plexus, cortex, and several hypothalamic nuclei. Genetic defects in the gene responsible for leptin production can cause a false underreporting of body fat, leading to overeating and obesity.