Regulation of Energy Intake and Body Weight Regulation

Question 1

What part of the brain is intimately involved in both the control of short- and long-term regulation of body weight?

Answer 1

Hypothalamus

The paraventricular nucleus (PVN), ventromedial nucleus (VMN), arcuate nucleus (Arc), and lateral hypothalamus (LH) (Figure 2) regulate food intake and disposition by processing information concerning peripheral energy stores and then stimulating or inhibiting feeding or altering gastric motility and food metabolism/utilization.

Question 2

What is the “hunger center” involved in short-term regulation of eating?

Answer 2

Lateral Hypothalamus

Stimulation of the lateral hypothalamus (LH) produces voracious eating, even in a food replete animal, and lesions in this region produced aphagia (no eating).

Two peptides have been identified that are expressed in the brain only by neurons in the LH: melanin concentrating hormone (MCH) and orexins (also known as hypocretins).

Question 3

What peptides are in the lateral hypothalamus and promote hunger?

Answer 3

melanin concentrating hormone and orexines

Question 4

What is the “satiety center” involved in the short-term regulation of food?

Answer 4

ventromedial nucleus (VMN)

Stimulation of this region results in cessation of eating even in hungry animals. Animals with lesions in this region eat excessively and become obese.

VMN lesions have the effect of “resetting” the regulated weight to a higher level.

Question 5

Arcuate nucleus

Answer 5

Contains “first order” neurons that promote either food intake or satiety.

Activation of arcuate neurons that produce both neuropeptide Y (NPY) and agouti-related peptide (AgRP) promote feeding while activation of the arcuate neurons that produce both α-melanocyte stimulating hormone (α-MSH) and cocaine and amphetamine-related transcript (CART) promote satiety.

Question 6

Melanocortin receptors (MCRS)

Answer 6

Activation of MCRs induces satiety.

α-MSH activates MCRs

Question 7

neuropeptide Y (NPY)

Answer 7

Neuron that stimulates hunger and food intake

increases hunger when injected into the hypothalamus and decreases energy expenditure

Question 8

Where do long-term signals of weight regulation come from compared to short-term?

Answer 8

Short-Term Signals – meal-related

Long-Term Signals – adiposity-related

Question 9

What are non-homeostatic mechanisms that affect our energy balance?

Answer 9

Internal inputs: 
Reward and Motivation
Cravings
"Thinking about food"
Restraint
Learned behaviors
Attention
Cognitive/Executive Decisions

External inputs:
Environmental Cues
Availability/portions
Social Context
Time cues

Question 10

Leptin

Answer 10

‘satiety hormone’ from adipose tissue was identified when the gene that is defective in an obese strain of mice, the ob/ob strain, was cloned

Question 11

AgRP

Answer 11

Agouti-related peptide

Inhibit the MCRs (inhibiting satiety) so basically increasing hunger

Question 12

Ghrelin

Answer 12

Secreted from the stomach that induces feeding
Meal-to-meal basis
Gut hormone
“The hunger hormone”

Question 13

PYY, GLP1

Answer 13

Secreted from distal ileum
Gut hormone
SATIETY signaling meal-to-meal

Question 14

CCK

Answer 14

Hormone that goes up after a meal

The duodenum signals the presence of nutrients to the brain via the release of cholecystokinin (CCK).

Short-term meal-to-meal signaling

Question 15

Do overweight or weight-gaining prone individuals have more leptin?

Answer 15

Yes, but still report more hunger

Resistant to leptin?

Question 16

Do signals not work properly in overweight people? What are the theories behind this?

Answer 16

Very possible

Our biologic signals are primarily designed to protect us during times of undernutrition.
Perhaps it’s all about “resistance” to these signals, ie leptin resistance?
Perhaps it’s just much more complicated

Question 17

MRI scan studies when show lean and overweight people picture of food

Answer 17

When lean people are hungry, increased brain activity when you look at pictures of food in brian regions that are important for: Attention, Reward, Motivation, Memory. When fed, that activity decreases.

When obese people: are fasted, they have less activity than lean people, but when they’re fed their activity goes up.

Activity of lean people and overweight people on MRI studies are opposite.

Question 18

Glucose and hunger-signaling

Answer 18

Hypoglycemia stimulates eating and hyperglycemia inhibits eating.

Question 19

Insulin and weight balance

Answer 19

Functions as a long-term regulator of food intake, energy balance, and adiposity in a similar manner as leptin.

Circulates at levels that parallel body fat mass, and both fasting and meal- or glucose-stimulated insulin concentrations are well correlated with body fat content.

Insulin receptors are located in the glucose sensitive regions of the hypothalamus and brainstem, and it is transported into the brain by specific transporters.

Question 20

What part of the brain is likely involved in the food-reward pathway?

Answer 20

Nucleus accumbens

Like opioid and drug reward