7. Appetite Flashcards
Central regulation of appetite
Integration of tonic and episodic signals
NUCLEUS TRACTUS SOLITARUS
a nerve pathway in the brainstem/ hindbrain that carries signals to the ARC in the lateral hypothalamus area
Coordinates reflex to food, is it food, is it good??
Long term regulators
Tonic signals
Insulin from pancreas
Lepton from fat cells
Both of these secrete in proportion to fat cells (in the fatter you are, the more you produce)
Act directly on neurones in ARC
have an inhibitory effect on NPY and AgRP Neurones which normally promote food intake
Excite POMC and CART neurones which normally inhibit food intake
Both usually inhibit food intake, balance affects drive to eat. Therefore both are satiety signals
There are increased levels of these in obese people due to more fat cells. So why don’t they stop eating. Resistance, desensitisation
NPY and AgRP neurones
In the ARC
inhibited by insulin and lepton
They normally promote food intake
Therefore effect of hormones is to indicate satiety and reduce intake
POMC and CART neurones
ARC neurones
Excited by insulin and lepton
They normally inhibit food intake
Therefore net result is to indicate satiety and reduce intake
Blundell
2007
When tonic signals are weak, episodic signals also become ineffective
Resulting in no satiety signals!
(In diabetes tonic signals are weak due to desensitisation and resistance, therefore episodic signals also absent. No satiety signals so keep eating)
Secondary neurones in the hypothalamus
Homeostatic regulation
Paraventricular nucleus: coordinated neuroendocrine functions and autonomic function such as gastric motility
Ventromedial hypothalamus: satiety and motivation
Lateral hypothalamic area: behavioural and cognitive response- hunger
Top down control
Hypothalamus (corticolimbic) functions are mediated by the PFC
Right PFC is associated with inhibition and restraint
DelParigi et al
2007
Successful dieters show increases right PFC activation when presented with palatable food
Berridge
2009
Components of food reward
Learning,
Liking
Wanting
McClure et al
Emotion memory is an important factor in deciding food preference
This is exploited by advertising agencies
Grill and Norgen
1978
Facial expressions to nice and nasty tastes
Similar reactions amongst mice and humans
Nice- tongue protrusion
Nasty- gapeing
Feature of implicit liking- shown by even decerebrate animals, in hindbrain
? Innate, feature to enable us to indicate food preferences to ensure we get the right nutrients and also to indicate if food may be bad for us ie poison
Yeomans
2002
Implicit liking is controlled by opioids neurotransmitters
Found that naltrexone decreased consumption of palatable food
Kringelbach
2004
Explicit liking is a conscious experience in the PFC
Option pathways found in the PFC
Implicit liking
Controlled by hindbrain
Option transmitters
Explicit liking
Controlled by the PFC along opioid pathways
Implicit wanting
Dopamine pathways from VTA to NaCC are most crucial for wanting
Volkow et al
1999
The amount of dopamine for optimal reward varied between people
People may overeat because they do not get enough stimulation ‘self medication’
Wang et al
2001
Obese people have reduced amount of dopamine receptors due to resistance.
Therefore they eat more to get the same stimulation
Obese people also have increased activation of reward areas to high calorie food. This may act as a motivator to consume it
Brain studies show less grey matter in PFC for obese people- therefore less top down modulation. Less inhibition
Short term signals
Episodic signals/ regulators
Sensory input triggers: CEPHALIC PHASE RESPONSE
Central and peripheral responses BEFORE ingestion: salivation, increased gastric motility and insulin secretion etc
Post ingestive hormones: generated by presence of nutrients in the gut. Many different ones- system redundancy. Indicate satiety
Some work directly on the Arcuate nucleus
Some hormones stimulate the vagus nerve- to the brainstem
Most signals are inhibitory
Blundell 2006
Quote this paper if saying Anything about tonic or episodic signals
Tonic signals reflect the metabolic state of adipose tissue. If you’re fat, you don’t need to eat because you have enough energy therefore more insulin to give satiety signals
Episodic signals generated by the act of eating. Rise and fall with eating
Most,y arise from GI tract
Integration of these reflects the brains recognition of the dynamic state of energy stores- by the NTS
Rate of gastric emptying is an important action of these
