Neurobiology of Feeding Behaviour

Question 1

Lactase

Answer 1

-Is an intestinal enzyme that is necessary for metabolizing lactose, the sugar in milk

Question 2

Sham-feeding

Answer 2

-A procedure in which everything that an animal swallows leaks out a tube connected to the esophagus or stomach

Question 3

What is the main signal to end a meal?

Answer 3

• Distension in the stomach (ie. an enlargement or ballooning effect)
• Later research found that meals end after distension of either the stomach OR the duodenum

Question 4

What part of the body conveys information to the brain about the stretching of the stomach walls?

Answer 4

-The vagus nerve

Question 5

Duodenum

Answer 5

• The part of the small intestine adjoining that stomach
• Is a major site for absorbing nutrients
• Nerves from the duodenum inform the brain not only about distension, but also about the type and amount of nutrition

Question 6

How do your intestines know what you ate?

Answer 6

• You have taste receptors in your digestive tract, similar to the ones on your tongue
• They do not provide you with a conscious experience, but they do alter brain activity to influence your sense of satiety

Question 7

What does distension of the duodenum release?

Answer 7

-Releases the hormone cholecystokinin (CCK)

Question 8

Cholecystokinin (CCK)

Answer 8

• Is released by distension of the duodenum
• Limits meal size in two ways:
  1. First, CCK constricts the sphincter muscle between the stomach and the duodenum, causing the stomach to hold its contents and fill more quickly than usual
  2. Second, CCK stimulates the vagus nerve to send signals to the hypothalamus, causing cells there to release a neaurotransmitter that is a shorter version of the CCK molecule itself

-CCK produces short-term effects only, therefore, it can’t really be manipulated to help people lose weight. It limits the size of the meal, but an animal that has eaten a smaller than usual meal compensates by overeating at the next meal

Question 9

What are 2 ways that CCK increases satiety?

Answer 9

1. When the duodenum is distended, it releases CCK, which closes the sphincter muscle between the stomach and the duodenum. CCK therefore increases the rate at which the stomach distends
2. Also, neural signals from the intestines cause certain cells in the hypothalamus to release CCK as a neurotransmitter, and at its receptors, it triggers decreased feeding

Question 10

What two pancreatic hormones regulate the flow of glucose into cells?

Answer 10

-Insulin and Glucagon

Question 11

What is the process going on before, during, and even after meals? (in relation to insulin and glucose)

Answer 11

-Immediately before a meal, as well as during and after a meal, the pancreas increases release of insulin, which enables glucose to enter the cells

• Some of the excess glucose produced by a meal enters the liver, which converts it to glycogen and stores it
• Some also enters fat cells, which convert it to fat and store it
• The net effect prevents blood glucose levels from rising too sharply
• As time passes after a meal, the blood glucose level falls, insulin levels drop, glucose enters the cells more slowly, and hunger increases
• The pancreas increases release of GLUCAGON, stimulating the liver to convert some of its stored glycogen back to glucose

Question 12

Simple process of hunger and insulin levels?

Answer 12

• Hunger
• ->Eating
• ->Blood glucose increase, insulin release decreases
• ->Insulin helps glucose enter cells for use or storage, hunger decreases
• ->Blood glucose levels decline, insulin level decrease
• ->Feel hungry and cycle repeats

Question 13

Leptin

Answer 13

• Tells your body you’re FULL!! (ie. it decreases your appetite)
• Is limited to vertebrates
• The body’s fat cells produce leptin: The more fat cells, the more leptin
• Leptin signals your brain about your fat reserves
• When your fat reserves decrease, leptin levels decline, and you react by eating more and becoming less active, to save energy
• When leptin levels return to normal, you eat less and become more active
• A mutation in the leptin gene does not make leptin, and therefore your brain reacts as if its body has no fat stores and must be starving
• Mice with this mutation will eat as much as possible, conserve their energy by not moving much, and fail to enter puberty

Question 14

What area of the brain is considered the master area for controlling appetite?

Answer 14

-The arcuate nucleus of the hypothalamus

Question 15

Arcuate nucleus

Answer 15

-The arcuate nucleus has one set of neurons sensitive to hunger signals and a second set sensitive to satiety (full) signals

Question 16

Ghrelin

Answer 16

• Part of the input to the hunger-sensitive cells comes from axons releasing the neurotransmitter ghrelin
• The stomach releases ghrelin during a period of food deprivation, where it triggers stomach contractions
• Ghrelin also acts on the hypothalamus to increase appetite

Question 17

What are the several types of input that the satiety-cells of the arcuate nucleus receive?

Answer 17

• Distension of the intestines triggers neurons to relase the neurotransmitter CCK, a short-term signal
• Blood glucose (short-term signal) directly stimulates satiety cells in the arcuate nucleus and prompts the pancreas to release insulin, which also stimulates the satiety cells
• Body fat releases leptin, a long-term satiety signal
• Nicotine also stimulates the satiety neurons, therefore smoking decreases appetite

Question 18

Where does much of the output of the arcuate nucleus go?

Answer 18

• To the paraventricular nucleus (PVN) of the hypothalamus

- Certain types of cells in the paraventricular nucleus inhibit the lateral hypothalamus, an area important for eating

Question 19

Melanocortins

Answer 19

• Melanocortin receptors in the paraventricular nucleus are important for limiting food intake, and anything that damages these receptors leads to overeating
• Axons from the satiety-sensitive cells of the arcuate nucleus deliver an excitatory message to the paraventricular nucleus, releasing melanocortins

Question 20

What is orexin’s two roles in feeding?

Answer 20

1. First, it increases animals’ persistence in seeking food

2. Second, orexin increases activity and motivation in general

Question 21

Name three HORMONES that increase satiety and one that increases hunger

Answer 21

Increase satiety:

• Leptin
• Insulin
• CCK

Increase hunger:
-Ghrelin

Question 22

Which neuropeptide from the arcuate nucleus to the paraventricular nucleus is most important for satiety?

Answer 22

-Melanocortins

Question 23

What are the inhibitory transmitters at play when the paraventricular nucleus limits the lateral hypothalamus?

Answer 23

• This inhibitory transmitters here are a combination of:
• GABA
• neuropeptide Y (NPY)
• agouti-related peptide (AgRP)

Question 24

Lateral Hypothalamus

Answer 24

• Controls insulin secretion, alters taste responsiveness, and facilitates feeding in other ways
• Output from the paraventricular nucleus acts on the lateral hypothalamus, which includes so many neuron clusters and passing axons that it has been compared to a crowded train station
• An animal with damage in this area refuses food and water, reverting its head as if the food were distasteful
• In contrast, stimulation to the lateral hypothalamus increases the drive to eat

Question 25

What are the ways that the lateral hypothalamus promotes eating?

Answer 25

• Axons from the lateral hypothalamus to the NTS (nucleus of the tractus solitarius), part of the TASTE pathway, alter the taste sensation and the salivation response to the tastes. When the lateral hypothalamus detects hunger, it sends messages that make the food taste better
• Axons from the lateral hypothalamus extend into several parts of the CEREBRAL CORTEX, facilitating ingestion and swallowing and causing cortical cells to increase their response to the taste, smell, or sight of food
• The lateral hypothalamus increases the pituitary gland’s secretion of hormones that increase insulin secretion
• The lateral hypothalamus sends axons to the SPINAL CORD, controlling autonomic responses such as DIGESTIVE SECRETIONS. An animal with damage to the LH has trouble digesting foods

In simple form: Activity of the lateral hypothalamus improves taste, enhances cortical responses to food, and increases secretion of insulin and digestive juices

Question 26

Ventromedial hypothalamus (VMH)

Answer 26

• Output from the ventromedial hypothalamus inhibits feeding, and therefore damage to this nucleus leads to overeating and weight gain
• Rats with damage to the VMH eat normal-sized meals, but they eat more frequently. One reason for this being that they have increased stomach motility and secretions, and their stomach empties faster than normal. Another reason is that the damage increases insulin production, and therefore much of each meal is stored as fat

Question 27

Damage to the paraventricular nucleus vs damage to the ventromedial area?

Answer 27

• Rats with damage to the paraventricular nucleus eat larger than average meals
• In contrast, rats with damage to the VMH eat normal sized meals, but they eat more frequently

Question 28

Bulimia nervosa

Answer 28

• Is a condition in which people alternate between binges of overeating and periods of strict dieting
• Many, but not all, induce themselves to vomit
• On average, people with bulimia show a variety of biochemical abnormalities, including increased production of ghrelin, a hormone associated with increased appetite. The biochemistry however is probably a result of the binges and purges, rather than a cause

Question 29

Anorexia nervosa

Answer 29

• Anorexia nervosa is characterized by a refusal to eat enough to maintain a healthy body weight
• People with anorexia do not regard food as tasting bad, rather they express an exaggerated fear of growing fat
• Those with anorexia also engage in extensive physical activity which may be motivated by temperature regulation (ie. cold environment causes people to exercise more to gain heat, but this causes them to lose more weight when they are already eating so little)

Question 30

What are the 3 ways that obesity is partly under genetic control?

Answer 30

1. Syndromal obesity occurs if a gene leads to both obesity and other medical problems
2. Monogenic obesity results from a single gene that does not impair other body functions
3. Common obesity is influenced by many genes, as well as environmental factors

Question 31

What is the effect of a hypothalamic lesion in these areas?

• Lateral hypothalamus
• Ventromedial hypothalamus
• Paraventricular nucleus

Answer 31

Lateral hypothalamus:
-Lesion causes undereating, weight loss, and low insulin levels (because of damage to cell bodies); underarousal, underresponsiveness (because of damage to passing axons)

Ventromedial hypothalamus:
-Lesion causes increased meal FREQUENCY, weight gain, and high insulin levels

Paraventricular nucleus:
-Lesion causes increased meal SIZE, especially increased carbohydrate intake during the first meal of the active period of the day