its level decreases during starvation As mentioned in the previous question, NPY is an Orexigenic i.e. appetite stimulant. Thus its level increases during starvation to increase food intake and reduce energy expenditure (decrease thermogenesis). NPY is a neurohormone released by hypothalamus. The hypothalamus can sense the body's state of starvation or welfed through a peptide hormone released by adipocytes -Leptin. When the amount of adipose tissue increases (signalling excess energy storage), the adipocytes produce increased amounts of leptin. Leptin acts on hypothalamic nuclei initiating multiple actions that decrease body's fat storage. These actions are: (1) inactivation of NPY-AGRP neurons decreasing production of appetite stimulators, such as NPY and AGRP; (2) activation of POMC neurons, causing release of cc-MSH (melanocoicotropin) and activation of inelanocoin receptors; (3) increased production in the hypothalamus of substances, such as coicotropin-releasing hormone, that decrease food intake; (4) increased sympathetic nerve activity (through neural projections from the hypothalamus to the vasomotor centers), which increases metabolic rate and energy expenditure; and (5) decreased insulin secretion by the pancreatic beta cells, which decreases energy storage. Thus during starvation, leptin production is decreased causing increased levels of NPY. As mentioned in the previous question, there are 2 types of neurons in the hypothalamic nuclei regulating appetite i.e. 1) NPY-AGRP neurons - which release orixogenic substances NPY and AGRP. 2) POMC (proopiomelanocoin) neurons - which release a-MSH (a-Melanocyte stimulating hormone or melanocoicotropin) and CA (Cocaine and amphetamine regulated transcript). These are anorexigenic i.e. decrease food intake and increase energy expenditure. Note that some students were of the opinion that one of the option was - `NPY and melanocoicotropin have same effect'. In that case this is a false statement as NPY is orexigenic, increases food intake. Melanocoicotropin or MSH is anorexigenic, decreases food intake. "NPY is a polypeptide containing 36 amino acid residues"- Ganong 23/e p145