Question

Leptin is a hormone that signals an organism to suppress appetite. Leptin is released from fat cells in white adipose tissue and binds to receptors on cells in the hypothalamus, a region of the brain that controls appetite.

  a) Identify the way that leptin produced by fat cells of adipose tissue in the abdomen can send a signal to the neuroendocrine cells in the hypothalamus.

Answer 1

Leptin is a hormone that is produced by your body's fat cells

It is often referred to as the "satiety hormone" or the "starvation hormone."

Leptin's primary target is in the brain — particularly an area called the hypothalamus.

Leptin is supposed to tell your brain that — when you have enough fat stored — you don't need to eat and can burn calories at a normal rate

TRANSPORT OF LEPTIN FROM THE ADIPOSE TISSU TO THE BRAIN

Leptin is produced by your body's fat cells. The more body fat they carry, the more leptin they produce

Leptin is carried by the bloodstream into your brain, where it sends a signal to the hypothalamus — the part that controls when and how much you eat

The fat cells use leptin to tell your brain how much body fat they carry. High levels of leptin tell your brain that you have plenty of fat stored, while low levels tell your brain that fat stores are low and that you need to eat

Leptin acts on receptors in the lateral hypothalamus to inhibit hunger and the medial hypothalamus to stimulate satiety.

• In the lateral hypothalamus, leptin inhibits hunger by
  • counteracting the effects of neuropeptide Y, a potent hunger promoter secreted by cells in the gut and in the hypothalamus
  • counteracting the effects of anandamide, another potent hunger promoter that binds to the same receptors as THC
• In the medial hypothalamus, leptin stimulates satiety by
  • promoting the synthesis of α-MSH, a hunger suppressant

Leptin binds to neuropeptide Y (NPY) neurons in the arcuate nucleus in such a way as to decrease the activity of these neurons. Leptin signals to the hypothalamus which produces a feeling of satiety. Moreover, leptin signals may make it easier for people to resist the temptation of foods high in calories.

Leptin receptor activation inhibits neuropeptide Y and agouti-related peptide (AgRP), and activates α-melanocyte-stimulating hormone (α-MSH). The NPY neurons are a key element in the regulation of hunger; small doses of NPY injected into the brains of experimental animals stimulates feeding, while selective destruction of the NPY neurons in mice causes them to become anorexic. Conversely, α-MSH is an important mediator of satiety, and differences in the gene for the α-MSH receptor are linked to obesity in humans.

Leptin interacts with six types of receptors (Ob-Ra–Ob-Rf, or LepRa-LepRf), which in turn are encoded by a single gene, LEPR. Ob-Rb is the only receptor isoform that can signal intracellularly via the Jak-Stat and MAPK signal transduction pathways, and is present in hypothalamic nuclei.

Once leptin has bound to the Ob-Rb receptor, it activates the stat3, which is phosphorylated and travels to the nucleus to effect changes in gene expression, one of the main effects being the down-regulation of the expression of endocannabinoids, responsible for increasing hunger.In response to leptin, receptor neurons have been shown to remodel themselves, changing the number and types of synapses that fire onto them.