Novel Explanation for “Runner's High” Running is a pleasant thing. And the happiness, freedom and the feeling of energetic is never just owing to the function of endorphin. A recent study published on Cell Metabolism suggested that dopamine, an important neurotransmitter, has influence on this so-called “runner’s high” too. The researchers pointed out that this “reward effect” in exercise is under the regulation of leptin, which can inhibit the body’s physical activity through dopamine neurons in the brain. Leptin, secreted by the adipose tissue, can help the body to produce satiety. So, the more the fat, the more the leptin. And we will have less appetite. All along, scientists believe that the hormonal signals that regulating eating and the ones that regulating exercise may have a close association. With the endurance capacity highly evolved, the opportunity to find food are maximized for mammals. However, this study shows that leptin played an important role both in the regulation of energy balance and the regulation of exercise. In this study, researchers investigated mice running on a treadmill and these mice can run up to seven kilometers a day. Firstly, they built a genetically modified mouse, in which the STAT3 that was activated by leptin was inhibited. Compared to normal mice, the tested mice that lack STAT3 run faster and in contrast, the normal mice is not as active as genetically modified mice when running. This might be explained this way, the researchers commented: “The leptin molecule is capable of activating STAT3 in the dopaminergic neurons, providing a sufficient signal in the body and then no activities are needed to find food.” Then, whether the impact of leptin on human activity is equally important? The researchers noted that previous studies have found that the leptin level is related to time length of the running-the lower the leptin level, the longer the running time. And this current study, by adopting genetically modified mice, revealed that leptin is also involved in the “rewarding effects” in movement process. The scientists speculated that for humans, lower levels of leptin will increase the motivation to exercise and people are more easily to get pleasant from movement.