Appetite (Hypothalamus)

Role of Leptin

- Fat cells produce leptin and secrete it into the bloodstream. - Leptin works to suppress hunger by acting on receptors in the hypothalamus (e.g., arcuate nucleus). - Endocrine Adipocyte

What does the hypothalamus regulate?

- Metabolic rate - Food intake -Body weight

The arcuate appetite system relies on two sets of neurons with opposite effects. What are they?

- NPY/AgRP neurons - POMC/ CART neurons

Hypothalamus monitor a number of hormones that are related to hunger:

- Orexin - Ghrelin - Insulin - Leptin - PYY

Role of PYY

- Pancreatic Peptide Tyrosine Tyrosine - Small peptide produced by the small intestine: from cells in the ileum and colon - Has low baseline levels that increase quickly when eating -Increased PYY levels - Decrease appetite - High doses of PYY have been reported to cause conditioned taste aversion in animals and nausea in humans. -Receptors located in the arcuate nucleus and vagus nerve input to the brainstem

HYPOTHALAMUS & APPETITE: THE VENTROMEDIAL HYPOTHALAMUS (VMH)

- Stimulating this depresses hunger. - Destroying this leads an animal to eat excessively (thereby developing extreme obesity).

HYPOTHALAMUS & APPETITE: THE LATERAL HYPOTHALAMUS (LH)

- brings on hunger. - Low blood glucose levels stimulates the LH to produce / release the hormone orexin, which triggers eating. - Destroying this leads an animal to have no interest in eating.

Ghrelin AKA the "hunger" hormone

-Peptide hormone released from cells in the stomach -Increases during fasting and decreases after a meal -Increased ghrelin levels produce increased appetite -Receptors located in multiple brain areas: arcuate nucleus, lateral hypothalamic area, nucleus accumbens, ventral tegmental area -Treating rats with ghrelin acutely stimulates food intake and growth hormone release; chronic ghrelin administration causes weight gain. -Intravenous infusion or subcutaneous injection of ghrelin to humans increases feelings of hunger as well as food intake. -Obese individuals have low baseline levels levels do not drop after a meal so no signal for "just ate a meal"

What are the major hypothalamic nuclei involved in appetite/ feeding?

1. Lateral Hypothalamus (LH) 2. Ventromedial Hypothalamus (VMH) 3. Arcuate nucleus 4. Paraventricular nucleus (PVN)

What are the two main functions of POMC/CART and NPY/AgRP neurons?

1. Some projections stay in the arcuate and influence each other's activity. 2. Other projections leave the arcuate and make connections in other nuclei of the hypothalamus particularly PVN and LH.

Increases in adipose tissue occurs in two ways

1.Fat cell hypertrophy 2.Fat cell hyperplasia

THERAPEUTIC USE FOR GHRELIN?

Because of observations of altered ghrelin levels (and ghrelin function) in obese individuals, the idea of blocking ghrelin signaling with GHS-R antagonists is of interest as a means of preventing obesity.

What happens to fat cell size and fat cell number when adults lose weight?

Fat cells shrink to a smaller size than adipocytes of non-obese people, but number remains same.

Leptin increase

Fat cells, decreases hunger

EMOTIONAL INFLUENCES ON EATING

Food sensory input can activate the brains 'Reward' system as well as 'Disgust' system Negative emotions Fear, sadness, anger can disrupt eating Sometimes increases and sometimes decreases eating

Orexin increase

Hypothalamus, increases hunger

Hunger

Internal state of an animal seeking food

PYY

Intestines; decreases hunger; exert ongoing minute-to-minute control on appetite

Total number of fat cells increases during 3 general periods of life:

Last trimester pregnancy, 1st year life, adolescence

Orexin

Produced in the Lateral Hypothalamus (LH); increases appetite and food intake by suppressing inhibitory post-ingestive feedback

COGNITIVE INFLUENCES ON EATING

Sensory (Taste & Odor, Visual aspects) Memory - Early childhood eating habits - Food preferences generally - Cultural influences

Ghrelin increase

Stomach, increases hunger

What are blood glucose levels monitored by?

They are monitored by receptors in the stomach, liver, and intestines.

THE ARCUATE NUCLEUS & LEPTIN

activates POMC/CART neurons and inhibits NPY/AgRP neurons, so leptin works to suppress hunger.•Leptin's effects on the arcuate are long-lasting.

THE ARCUATE NUCLEUS & PYY

acts mainly by inhibiting NPY/AgRP neurons (reducing appetite, which is in opposition to effects of ghrelin).

Anorexia Nervosa

condition in which a normal-weight person (often an woman in teens to mid-20s) continuously loses weight but still feels overweight.

Leptin

fat cells, decreases hunger information about current energy stores, inhibits NPY/AgRP neurons and stimulating POMC/CART neurons

Satiety

feeling of fulfillment or satisfaction.

Insulin increase

pancreas, increases hunger

NPY/ AgRP neurons

produce neuropeptide Y (NPY) and agouti-related peptide (AgRP). stimulate appetite and lower metabolism, promoting weight gain.

POMC/CART neurons

produce pro-opiomelanocortin (POMC) and cocaine and amphetamine related transcript (CART) to inhibit appetite and raise metabolism, promoting weight loss.

THE ARCUATE NUCLEUS & GHRELIN

stimulates NPY/AgRP neurons, which increases appetite

Ghrelin

stomach, increases hunger exert ongoing minute-to-minute control on appetite