Arcuate nucleus: POMC neurones versus NPY and AgRP neurones
In the arcuate nucleus (a cluster of neurones within the hypothalamus), neurones making POMC (a precursor protein) suppress appetite, while neuropeptide Y (NPY) and agouti-related peptide (AgRP) neurones stimulate it.
Remember
POMC neurones reduce appetite through α-MSH (a peptide cut from POMC), while neuropeptide Y and agouti-related peptide neurones stimulate it.
Memory aid
POMC is the brake on eating and the neuropeptide-Y group is the accelerator
Use the picture to keep the two arcuate groups apart: POMC neurones are the brake on eating, and the neuropeptide-Y group is the accelerator.
The arcuate nucleus senses hormones and nutrients in the blood. Within it, two opposing sets of neurones push appetite in opposite directions: the excitatory neurones stimulate appetite, while the inhibitory neurones suppress it. The names describe each group's effect on appetite.
POMC neurones are the inhibitory group. They release several smaller peptides cut from POMC (pro-opiomelanocortin), a large precursor protein. One of these, α-MSH (α-melanocyte-stimulating hormone), acts on melanocortin-4 receptors to reduce the drive to eat.
The excitatory group releases neuropeptide Y and agouti-related peptide, and both stimulate appetite. Agouti-related peptide acts at the same melanocortin-4 receptor as α-MSH, but it blocks the receptor, so it works against α-MSH.
Ghrelin (a peptide hormone) is released from the stomach wall when the stomach is empty and activates the excitatory neurones, so hunger rises during fasting. Once eating starts, stretch of the stomach wall inhibits ghrelin release. Leptin (a hormone from fat cells) activates the POMC neurones and inhibits the excitatory ones, so a fall in leptin increases hunger.
Key facts
- Site
- the arcuate nucleus, a cluster of neurones in the hypothalamus, senses hormones and nutrients in the blood.
- Appetite-suppressing neurones
- POMC neurones, whose product α-MSH acts on melanocortin-4 receptors to suppress appetite.
- Appetite-stimulating neurones of the arcuate nucleus
- they release neuropeptide Y and agouti-related peptide, and both stimulate appetite.
- Receptor
- the melanocortin-4 receptor is activated by α-MSH to suppress feeding, and blocked by agouti-related peptide.
- Ghrelin
- released by an empty stomach, it activates the excitatory neurones, and stretch of the stomach wall after eating inhibits its release.
- Leptin
- a hormone from fat cells, it activates POMC neurones and inhibits the neuropeptide Y neurones, so a fall in leptin increases hunger.
Exam traps
- Agouti-related peptide acts at the same melanocortin-4 receptor as α-MSH, but it blocks the receptor, so it opposes α-MSH and does not suppress appetite.
- Orexin, a signal that induces feeding, does not suppress appetite after eating: orexin neurones in the lateral hypothalamus are inhibited by food ingestion, and orexin itself induces feeding.
- Ghrelin does not suppress appetite: it is released from the stomach wall when the stomach is empty and activates the excitatory neurones of the arcuate nucleus, so it promotes hunger.
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