Arcuate nucleus: A collection of neurons (nerve cells) in the hypothalamus of the brain. Some arcuate neurons contain dopamine and act to inhibit the release of the hormone prolactin by the pituitary gland. Other arcuate neurons contain a substance called neuropeptide Y (NPY) and influence hunger. When activated, these neurons can produce remarkable increases in eating that result in obesity. These neurons may be regulated by glucose, insulin, and the hormone leptin. By monitoring the blood levels of these substances, arcuate neurons are kept informed of whether or not the body has sufficient calories and nutrients so that it can adjust feeding accordingly.