Final answer:
The neuropeptide that increases appetite, leads to weight gain, and promotes deep sleep is ghrelin. It's released when the body needs energy, in contrast to leptin, which promotes satiety. Leptin resistance can lead to overeating and obesity.
Step-by-step explanation:
The neuropeptide that increases appetite, leads to weight gain, and promotes slow-wave sleep in humans is d) Ghrelin.
Ghrelin is a hormone produced mainly by the stomach's endocrine cells and functions as a neuropeptide in the central nervous system. When blood sugar levels get low or the stomach is empty, ghrelin is released into the bloodstream, stimulating appetite and leading to increased food consumption and potentially weight gain. Ghrelin also promotes the slow-wave stage of the sleep cycle, which is deep, restorative sleep.
Ghrelin's counterpart, leptin, is the protein hormone secreted by adipose tissue in response to food consumption that promotes satiety and inhibits hunger. Leptin levels increase with higher fat reserves, which should suppress appetite. However, in obesity, leptin resistance can occur, making individuals prone to overeating. Understanding the roles of ghrelin and leptin is crucial in the pathophysiology of obesity.