Lecture 7 Motivated decision making Flashcards
What is thirst an example of?
A Homeostatic system
How does the thirst homeostatic system work?
Thirst is detected by the detection system, and the behavioural correction system adjusts accordingly (drink/ stop drinking)
What are the 3 components of homeostatic system?
1- signalling system
2- detection system
3- Behavioural correction system
How much of the body is fluid?
55% (women)
66% (men)
2/3 is within each cell 1/3 is outside the cell either in blood (20%) and the rest is in between tissues
What are the two thirst signalling systems?
- Intracellular fluid concentration detection
2. Extracellular fluid concentration in blood
What is intracellular fluid concentration detection?
‘Osmotic thirst’ - How much fluid there is in the cell
There needs to be a balance of how much in in/outside
What is extracellular fluid concentration in blood?
‘Hypovolemic thirst’- How concentrated blood is)
Hypo- low
volemic - volume
Where is osmotic thirst detected?
In lateral preoptic area in hypothalamus
What is the hypothalamus involved in?
Many homeostatic and regulatory processes and communicates between endocrine, peripheral and central nervous system.
What is angiotensin
A peptide produced by the kidneys sensing blood concentration
what two systems are involved in hypovolemic thirst?
1- subfornical organ
2- OVLT (Organum Vasculosum of the lamina terminalsi)
What does the subfornical organ do?
- Senses angiotensin (a peptide produced in the kidneys)
- Senses blood concentration
What does the OVLT do?
- Senses angiotensin
- Receives info on blood volume
What do both the subfornical organ and the OVLT have?
Ordinary capillary walls, not blood-barrier walls.
How does motivated drinking behaviour work?
The lateral preoptic are of the hypothalamus, the subforical organ and the OVLT communicate with reward centres
What reward centres are communicated with in motivated drinking?
The orbital frontal cortex and the ventral striatum
What is the anticipatory satiety mechanism for thirst?
The act of swallowing or stomach distention that tells hypothalamus to inhibit the drive to drink
How long does it take for intra and extra cellular fluid concentration to be at optimum level?
15-20 minutes
Why do most humans and animals drink?
Out of habit
What did Harris et al 1993 do?
Gave rats a B1 deficient diet
Gave them 2 foods, one enriched with B1
Rats preferred enriched food.
This did not happen when more choice was available
What happened when rats were fed cafeteria food?
They became obese, even in enriched environments with an exercise wheel.
What are the individual differences with rats being fed cafeteria food?
Some rats gained more weight than others, not all cafeteria rats became obese, but some did
What did B.J Rolls (1981) find?
Gave one food type to satiety to human participants, and then obtained pleasantness ratings for other foods
Much smaller satiety effect for different foods
Variety leads to greater calorie intake
- Offer 1 verus 4 types of sandwich for lunch - Greater intake with 4 types than with 1
What are the major differences between hunger and thirat
Is it adaptive to eat more than immediate needs to ‘bank’ calories as fat
Different types of food needed.
What peptide is produced in hunger signalling?
Ghrelin- produced by the stomach
Who discovered Ghrelin?
Kojima et al 1999
What can Ghrelin do?
Cross the blood-brain barrier
What does Ghrelin do?
Stimulates target cells in arcuate and lateral nucleus of hypothalamus
What does the hypothalamus do in hunger signalling?
Communicates with forebrain and brain stem to initiate food seeking
What is Ghrelin inhibited by?
Glucose, protein, fat and leptin
What are the satiety mechanisms for hunger?
- A signal is sent from the stretch receptors in the stomach to the arcuate nucleus in the hypothalamus
- Unlike thirst, oropharyngeal stimulation does not anticipate satiety –> the stomach has to fill
- Sham feeding leads to long feeding bouts (disconnect the esophagus from stomach, rats keep eating as stomach doesn’t fill
How many peptides do the stomach and intestine produce in satiety signalling?
12 (Kalat 2012)
What does CKK stand for?
Cholecystokinin - one of the most understood peptides
What does CKK do?
Stimulates peripheral nerves which stimulates the arcuate nucleus which communicates with reward centres
What is another satiety signalling system for hunger?
Circulating levels of glucose and insulin
Does insulin pass blood-brain barrier (BBB)
NO, it is sensed in areas postrema of medulla
What is Leptin?
A peptide produced by fat cells
What does leptin not correlate with
meals
What happens when leptin is high
It modulates (dampens) Ghrelin signalling
Can Leptin cross the BBB?
Yes, to target cells in arcuate nucleus of hypothalamus, which sends axons to hypothalamus and the hypothalamus communicates with reward centres
What are the reward centres for hunger?
Orbitofrontal cortex and nucleus accumbens
Who discovered leptin?
Zhang et al 1994
How was leptin discovered?
Mice with obob genes could not produce leptin and had obesity syndrome
This wsa because high levels of insulin were converting food to fat too quickly, as there was no leptin to interact with.
How can obesity syndrome be treated?
with leptin
What is an issues with the leptin obesity explanation?
There are still high levels of leptin in people with obesity
They have developed leptin resistance (autoimmune)
BUT can be overcome with physical exercise and some restoration of function is found.
