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5 - Obesity and satiety


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What effect does electrical stimulation of the ventromedial hypothalamus have on feeding? What effect do lesions in this area have?
Stimulation supresses food intake, whereas lesions cause uncontrolled eating.
What effect does electrical stimulation of the lateral hypothalamus have on feeding? What effect do lesions in this area have?
Stimulation causes uncontrolled eating, whereas lesions result in anorexia.
How does injection of CCK affect eating behavior? How does this affect long-term weight?
It provides inhibitory signals which cause cessation of eating. This is a transient effect and does not change weight over time. Caloric intake remains constant because although meals are smaller, they are more frequent and more numerous.
Describe the effect of injection of exogenous ghrelin.
It provides a transient appetite stimulation and increased intake of food.
Do serum levels of endogenous ghrelin remain constant in the blood? How do the levels of ghrelin in obese persons compare to those of normal persons?
Ghrelin levels rise and fall in a cyclic manner related to timing of meals. In obese persons, ghrelin levels are actually lower than normal.
What are 3 pieces of evidence for the existence of a set point of body weight?
1.Body weight does not change more than 1-2 lbs/year.
2.Identical twins maintain similar weight, even if they are separated.
3.There are numerous hereditary obesity diseases.
Increase in mass of adipose tissue is thought to provide a signal to the CNS which then effects a decrease in tissue mass. What is the effector mechanism here?
The CNS stimulates diet-induced thermogenesis which speeds metabolic rate through sympathetic innervation to reduce the mass of adipose tissue.
What gene codes for leptin? In what tissue is this gene expressed? What evidence exists that leptin is a secreted compound?
*the obese gene
*expressed in adipose tissue
*has a signal peptide
What happens when obese mice are injected with exogenous leptin?
They lose adipose tissue (not lean mass) due to decreased intake and increased metabolic rate.
How is leptin connected to amenorrhea in female athletes?
Female athletes have less adipose tissue, thus secrete less leptin. Leptin is thought to have a stimulatory role in the secretion of estrogen. Low leptin means low estrogen and thus amenorrhea.
What is the blood level of leptin in obese persons? What does this mean?
Most obese persons show an excess of functional leptin. In only a few isolated cases has obesity been associated with leptin deficiency. This has led to the idea that obesity is associated leptin resistance.
What is the protein product of the "diabetes" gene? Where is this gene expressed?
This gene codes for the leptin receptor. It is expressed in the ventromedial area of the hypothalamus.
What happens when a db/db mouse is parabiotically attached to an ob/ob mouse?
The ob/ob mouse loses weight because it receives leptin from the db/db mouse. The db/db mouse remains obese.

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