Which hormone activates Melanocortin-secreting neurons?

Leptin is the correct answer because it plays a crucial role in regulating energy balance and body weight through its influence on appetite and metabolism. It is a hormone produced by adipose (fat) tissue and is primarily known for signaling satiety, thereby reducing food intake.

In the context of melanocortin-secreting neurons, leptin directly stimulates these neurons in the hypothalamus, which are integral to the regulation of energy expenditure and appetite suppression. By activating melanocortin pathways, leptin contributes to the inhibition of feeding and promotes energy expenditure, which is essential for maintaining body weight and metabolic homeostasis.

Other hormones mentioned, such as ghrelin, PYY, and CCK, have different mechanisms and functions related to appetite and digestion. Ghrelin is primarily known for stimulating appetite and is released when the stomach is empty. PYY and CCK are involved in appetite regulation as well, but they do not activate melanocortin-secreting neurons to the same extent or in the same manner as leptin does. This distinct role of leptin in the activation of melanocortin-secreting neurons underlines its significance in the physiological processes of hunger and energy balance.