Hypothalamus and Feeding Flashcards
What are the three hypothalamic responses to maintain body homeostasis (with general descriptions)?
The humoral response (hormonal modulation)
The viscero-motor response (ANS sympathetic and parasympathetic systems)
Somatic motor response (Move appropriate somatic motor behaviour)
What cells secrete vasopressin? What behaviour does this motivate?
Magnocellular cells of the peri-ventricular posterior hypothalamus control drinking signals
What hormones are secreted by the anterior pituitary gland and what behaviours do they motivate?
TSH and ACTH control eating signals and Thermal signals
How does the brain signal feeding? What is the visceromotor response?
Leptin and Insulin lower, which lowers ACTH and TSH, which increase parasympathetic activity and hunger
What hormone is associated with thermal change?
TSH
What is the relationship between temperature and TSH release? What are the visceromotor responses?
They are inverse, low temp increases TSH (sympathetic activity) and high temp decreases TSH (increase in parasympathetic activity)
What are the two brain signals to promote drinking?
Higher angiotensin 2 and higher blood tonicity
What kind of ANS activity does the expression of vasopressin lead to?
Sympathetic nervous activity
What is the feeding behaviour cycle as a wholistic brain approach?
- Attention is given to the stimulus
- The prefrontal cortex demonstrates cognitive control to process the information
- The amygdala/hippocampus evokes emotion/memory about the information
- The hypothalamus maintains homeostasis and takes into account the state of the body
- The reward system is linked to motivating feeding
What is the difference between the anabolic and catabolic metabolism states?
Anabolic - prandial state - nutrients in the blood go to cells and storage
Catabolic - postabsorptive state - nutrients go from storage to cells
Where are nutrients stored in the body and what is the most efficient nutrient storage pathway?
It is stored in the liver, skeletal muscle, and adipose tissue is the most efficient storage.
What is the role of glycogen in the metabolism system?
It is the storage form of glucose, which is important for cell activity and is the most important neuronal fuel
What nutrients are present in the blood from food?
Glucose, fatty acid, and ketones
What is stored glucose called in adipose tissue?
triglycerides
When is stored fat in the body bad?
When there is an excess that is not stored where it is supposed to be, and is stored around organs like the liver or heart
What is the lipostatic hypothesis?
The brain monitors adipose tissue and acts to maintain an adequate amount
How is adipose regulated in the long run and short run?
Short run - meal size/frequency
Long run - lipostatic hypothesis (fat reserve maintenance)
What is the estimated heritability rate of body weight/obesity?
0.7-0.8
Are twins or people that grew up together more likely to share the same level of obeisity?
Twins
How did Coleman determine the effect of molecules on feeding?
Parabiosis of mice (WT, db, ob)
What was Friedman’s role on leptin research?
He cloned the leptin gene
What was the finding/conclusions of the parabiosis of a WT mouse and a ob mouse?
Ob mouse reached a normal weight indicating there was something in the blood of the WT mouse that reduced feeding
What was the finding/conclusions of the parabiosis of a WT mouse and a db mouse?
WT mouse died of starvation, indicating elevated blood presence of leptin (high satiety)
What is the physiological difference that Coleman found between the db and ob mice?
Db mice: missing leptin receptor leading to high level of leptin in the blood
Ob mice: missing leptin - always hungry
How do we treat ob/ob patients in the scope of this lecture, when does this not work?
Leptin treatment can reduce the feeling of hunger, but this does not work in the case where leptin receptors are non-functional.
Where is leptin produced?
In the adipose tissue
What two bodily responses are observed in the presence of leptin in the brain?
It suppresses food intake and increases energy expenditure
What maintains the homeostasis of fat levels in the body?
Leptin levels are detected by neurons in the brain to maintain optimal levels
What happens to leptin and the body after weight loss?
Leptin levels fall, stimulating appetite and reducing metabolism and increasing ANS parasympathetic activity
What happens to leptin and the body during weight gain?
Leptin levels are high, reducing appetite, increasing ANS sympathetic activity and metabolism
What are the 3 important hypothalamic nuclei?
Paraventricular nucleus
Lateral Hypothalamic nucleus
Arcuate nucleus
What would happen to a mouse with a damaged paraventricular nucleus?
The PVN induces satiety, so the removal of it would make an ob mouse
What would happen to a mouse with a damaged lateral hypothalamic nucleus?
The LH induces hunger, so the removal of it would cause starvation
What does the presence of a high amount of leptin do in the arcuate nucleus?
The presence of leptin is agonistic to POMC, which upregulates the PVN (satiety) and downregulates the LH (humger)
What does the presence of a low amount of leptin do in the arcuate nucleus?
The presence of leptin is antagonistic to the function of NPY/AGRP, which means the lack of leptin will activate the neurons to upregulate the LH (hunger) and downregulate the PVN (satiety)
What is the mnemonic for the arcuate nucleus neurons that signal hunger?
Never poop yellow, ass gets really pink
What system neurons in the brain are responsible for satiety and hunger in response to leptin?
The hypothalamic melanocortin system neurons
What types of neurons are activated by high leptin levels?
Alpha - MSH (alpha - melanocyte stimulating hormone)
CART - (cocaine and amphetamine regulated transcripts)
What are the three responses of the body to alpha MSH and CART neuron activation by leptin?
- Humoral response - ACTH/TSH activation from pituitary
- Viscero-Motor response - Activation of brain stem and sympathetic ANS
- Somatic Motor response - Inhibit feeding behaviour
What is the detailed explanation of the humoral response to leptin?
PVN upregulation -> TSH+ACTH release -> cortisol/metabolism increase
What is the detailed explanation of the viscero-motor response to leptin?
Axons from the PVN/arcuate nucleus increase ANS sympathetic and decrease ANS parasympathetic activity
What is the detailed explanation of the somatic motor response to leptin?
Arcuate neuron activation -> LH inhibition -> decreased food intake
When POMC is activated, what compounds are secreted throughout the body?
POMC releases ACTH which converts to alpha MSH, beta endorphins are also released through the lipotropin pathway
What type of receptor is MC4R?
It is metabotropic
What is the open leptin receptor MC4R pathway?
An increase in leptin levels releases alpha MSH, which activates MC4R
What is the role of AGRP?
AgRP is an inhibitor of MC4R
What hormones are the anterior pituitary gland responsible for? (6)
ACTH, GH, TSH, FSH, LH, Prolactin
What hormones are the posterior pituitary gland responsible for? (2)
Oxytocin, ADH
What is the name for a hormone related to the hunger response?
Orexigenic
What are the three levels of response to the activation of the NPY/AgRP and where are the effector neurons located?
- Humoral response is inhibited in the paraventricular neurons, ACTH/TSH are released less
- Viscero-motor response, ANS parasympathetic system is activated by arcuate neurons
- Somatic motor response is an increased feeding stimulated by the lateral hypothalamic nucleus
When leptin decreases, what are the final effects?
Food intake increases, energy expenditure decreases, ANS parasympathetic function increases
When leptin increases, what are the final effects?
Food intake decreases, energy expenditure increases, and ANS sympathetic system increase
What is orexin/hypocretin responsible for? Where is it found?
Hunger response is mediated by it in the hypothalamus and is also plays a role in wakefulness (deficiency = narcolepsy)
What is the role of CCK?
Cholecystokinin is a “full” hormone that stimulates fat and protein digestion in response to certain types of food.
What hormones are released to signal satiety?
CCK and GLP-1
What is the difference between leptin, and CCK/GLP-1?
Leptin comes from adipose tissue and is a long term feeding regulator, and CCK and GLP-1 are short term hormone responses to feeding
Where are short term satiety hormones released from?
The intestines
Describe the short term satiety cycle (GLP-1)
Eating releases GLP-1 from the intestines, which acts on the brain stem to release more GLP-1 which acts on the hypothalamus to inhibit appetite.
Rising blood GLP-1 also directly inhibits appetite
What is the hunger signaling hormone?
Ghrelin
Describe the short term hunger cycle (ghrelin)
Ghrelin is released by the stomach, it acts on the hypothalamus to stimulate appetite. Eating decreases blood ghrelin
What hormone other than CCK and GLP-1 plays a secondary role on appetite supression?
Insulin
