NPY and obesity due to melanocortin 4 receptor deficiency: Low-concentration nicotine (100–1,000 nM) has a regulatory effect on anorexic POMC neurons, NPY neurons, and secretin/orexin neurons in the hypothalamus, and can mediate neuropeptide Y, leptin, orexin and its receptors and uncoupling proteins, as well as the level and activity of neurotransmitters such as dopamine and monoamine, with the effect of controlling food intake and reducing obesity (Li et al., 2000; Huang et al., 2011).