Exam 3 (Final) Flashcards
Describe a study that investigates the role of NPY in conditioning rats.
Training:
- 7 consecutive days of brains (ICV) injections of Saline or NPY at the same time of the day
- No food was given at time of injections
- During the training rats were fed at a particular time (at 10-2) and at a later time received injections of saline or NPY (at 4)
Test:
- Food intake (1-hour) measured after ICV injections of Saline or NPY
What are the test groups in the NPY conditioning study?
- Saline/saline – control, can be stressful to receive injections
- Saline/NPY – eating a certain amount, didn’t learn about NPY, then eat more when administered NPY (acute effect)
- NPY/saline – supposed to have learned that NPY was coming at a certain time of the day, expect that if they eat more it shows that they learned to expect to eat more at that time of the day – time of the day alone is enough to induce this change in intake (learning, not actual physiological change)
• This is the group of interest - NPY/NPY – positive control
What were the results of the NPY conditioning study?
Results: Tested intake during 1-hour post saline or NPY injections
- Sal/NPY, NPY/Sal, and NPY/NPY increased in a clear bar graph cascade
- Sal/sal had the lowest food intake
- The NPY/Saline group did not receive NPY prior to test but ate similar amounts to those that received NPY prior to test
What did the NPY conditioning study indicate?
- This is revealing a principle that we already know in reference to salivation and insulin – they learned to eat more even when not administered the drug
- The effect in NPY/Saline group was accomplished by conditioning NPY targets in the brain
How was Pavlovs work expanded upon in reference to feeding substrates?
Early work of Pavlov showed that salivation can be conditioned. Later work showed that peripheral (insulin) and central (brain;NPY) feeding substrates can be conditioned
Describe a study involving conditioning food consumption in children.
STUDY: Conditioned Meal Initiation in Young Children
- Learning can influence how much children eat.
- Children played a song
- Latency is how long it took for the children to go to the table
- Learning caused the children to eat a larger amount
- Both latency and amount eaten affected by CS
- CS+ is a conditioned stimuli
- Children who learned (were able to identify cues correctly) ate more
How does conditioned stimuli get to the feeding circuitry?
Human amygdala
What are the two domains of the amygdala?
o Central Nucleus of the Amygdala (CEA;CN)
o Basolateral Amygdalar Area (BLA; ABL)
What are the four cues in a Pavlovian conditioning study?
o US: unconditioned stimulus
o UR: unconditioned response
o CS: conditioned stimulus
o CR: conditioned response
What do CS+ and CS- mean?
o CS+ the cue paired with food
o CS- the control cue, not paired with food
What were two studies with the CEA and BLA?
Study 1: Tested if CEA and/or BLA are critical for cue (CS) induced feeding
Study 2: Tested if the BLA gets to the feeding circuitry via the Lateral Hypothalamus (LHA)
Describe: Study 1: Tested if CEA and/or BLA are critical for cue (CS) induced feeding
What enzyme used?
- Selective neurotoxic, bilateral lesions of the Basolateral Amygdala (BLA) or Central Nucleus of the Amygdala (CEA)
- NMDA – is an agonist for glutamine and over-excites neurons until they die
- Bilateral neurotoxic lesions of the BLA lesions abolished CS-driven feeding
- Therefore need BLA to have CS-driven feeding
- Bilateral neurotoxic lesion of the Central Nucleus of the Amygdala (CEA) performed similar to sham-lesioned controls
How are cue induced feeding studies performed?
Phase I – Pavlovian conditioning
- Rats are food restricted during training to motivate learning
- Food (US) – feeding behavior (UR)
- Tone (CS) – neutral in respect to feeding
- Rats move to the chamber where they can be fed when they hear a tone
Phase II – Food Consumption Tests
- Rats are satiated before tests to show that the food-cue motivates eating without hunger
- Tested in 2 tests, counterbalanced order: One test with a cue that signals food (CS; food-cue) and the other test with no cue
Describe the following study: Study 2: Tested if the BLA gets to the feeding circuitry via the Lateral Hypothalamus (LHA)
- Rats with Sham, Ipsilateral or Contralateral BLA-LHA lesions tested for Food Consumption with CS+ or CS- presentations
- Disconnection of BLA-LHA system (Contralaterally) produced a similar effect as bilateral BHA lesions: abolished CS-Induced Feeding
- Sham group and ipsilateral group still experienced CS induced feeding
How is the BLA connected with the LHA?
The BLA is connected with the LHA via direct (monosynaptic) and indirect (polysynaptic) pathways. These connections are ipsilateral.
What are the different types of brain connections?
o Unilateral – one side
o Bilateral- two sides
o Ispilateral – stays on the same size
o Contralateral – crossing over between sides
Describe contralateral lesion design.
o Unilateral lesions of the BLA and unilateral lesions of the LHA
o But on the opposite sizes of the brain
o The procedure disconnects functional BLA-LHA circuitries on both sides of the brain (in both hemispheres) because connections between these structures are ipsilateral (within the same hemisphere).
- What would happen to feeding if LHA was eliminated on both sides of the brain?
What type of neurons within the lateral hypothalamus are critical for cue induced eating?
Orexin/Hypocretin Neurons
Describe how episodic memory and appetite regulation were studied in humans.
o Covertly manipulating the amount participants believed they ate
o Self-refilling soup bowl apparatus
o They can refill/remove the soup without the people knowing
o “Incongruous eating” – pit against their visual cues and their bodily cues
o How much they ate vs how much they saw
Describe what was discovered in the episodic memory experiments?
Experiment 1:
- Given bowl of soup and asked to eat when it gets to a certain line
- At time zero the amount eaten has a more dramatic impact on hunger than the amount seen
- At 1 hour no significant effects
- After more time what matters is more what they saw than what they ate when they are rating their hunger, more significant effect of the amount of soup seen
- We are most accurate right after eat, after 2 or 3 hours episodic memory plays more of a role
Experiment 2:
- 24h after experiment 1 participants were shown a bowl containing 400ml of soup and asked to evaluate/predict how satiating they would expect it would be
- Expected satiation from a fixed portion: 400ml bowl
- If they saw a bigger bowl they expect more satiation, if they saw a smaller bowl it’s the opposite, memory/the size of the bowl they saw has a bigger impact on expected satiation than how much they ate.
What are the two types of memory that affect feeding?
Associative (learning and memory) and episodic memory
Describe how associative learning and memory is regulated in the brain.
- Amygdala – LHA circuit allows learned cues to override satiety and promote eating
- Tone food pairings
Describe how episodic memory affects feeding.
- Hippocampus suspected
- Episodic memory and appetite regulation – really was satiety not appetite
- When things are looking visually differently it really confuses the body
What are DZ and MZ twins?
DZ – dizygotic (siblings)
MZ – monozygotic (actual identical genetic code)
What was observed in the gut microbiota twin study?
Gut microbiota from twins discordant (different) for obesity modulate metabolism in mice
Describe how the twin mice study was performed.
Transplanted human microbiota to mice from obese twin and lean twin separately to obese and lean mice
- Reliable replication of human donor phenotype in (*gnotobiotic) mice
- = all the microbiota known or not present at all
- Were able to induce adiposity in mice by changing the microbiota
How does the co-housing of obese and lean mice affect the mice?
- Co-housing Ob and Ln mice transforms the adiposity phenotype of cage mates (harboring the obese co-twins microbiota) to a lean state
- When the mice are put together – the obese mice’s gut microbiota changes to the lean microbiota
- Bacteria populations (bacteriodales) from Ln invaded the Ob
How does diet affect changes produced by cohousing obese and lean mice?
- The rescue of obese mice depended on the diet – lower fat, higher fiber most effectively led to the change in phenotype (bacteria fed on the higher fiber diet)
- Highly processed foods have been linked to a less diverse gut microbiota
- Processing kills the bacteria
- Only effective if low fat/high fiber (fruits/vegetables) diet
How do antibiotics affect body weight in mice?
At least one study found that mice given low doses of antibiotic developed 15% more body fat compared to control mice
What are the mechanisms through which bacteria impact metabolism?
- Intestinal microbiota break down and ferment dietary fibers into short chain fatty acids = these fatty acids may be enough to mediate satiety
- They will produce fatty acids but in the end will keep us lean
- The microbiota in lean mice produce larger amounts of SCFAs (Short chain fatty acids) and digest more of the plant fiber present in the mouse’s diet than the microbiota of Ob mice
- Increased weight gain in Ob mice does not result from increased energy harvest
Describe the role of SCFAs
Although SCFAs are a source of energy and they promote leanness by
- inhibiting fat accumulation in adipose tissue
- raising energy expenditure
- enhancing production of hormones associated with feelings of satiety
What are two theories for ways microbiota impact body mass?
- The microbiota might increase efficiency of energy harvested from ingested food
- It might promote low grade inflammation that can result in impaired signaling by various metabolic receptors that control satiety
What is the emotional eating theory?
Individuals eat to cope with stress and that could lead to Stress- Eating-Obesity Nexus
What is innately preferred across species?
sweet taste
Describe the chocolate study.
o Mood induced by watching a movie clip: A sad sequence from the champ, when harry met sally, processing and usage of copper
o Rated their mood then fed a piece of chocolate, just for the taste (control group drinking water – controls for possibility that they would be distracted)
o When fed chocolate it changed the mood for the sad film
o The palatability effects the amount of mood change
What were the results of the chocolate study?
- The experiments showed that eating a small amount of sweet chocolate improved an experimentally induced negative mood immediately and selectively, and that the effect was due to palatability
- The effect was more pronounced in emotional eaters
Describe the physiology of the stress response.
Hypothalamus (Corticotropin-releasing hormone (CRH)) –> Pituitary Gland (Adrenocorticotropin hormone) (ACTH) –> Adrenal Gland (Glucocorticoids) Cortisol (Human) Corticosterone (Rat)
What are glucocorticoids?
- released by the adrenal gland
- stimulate gluconeogenesis (glucose synthesis from protein and fat)
- fasting increases release of glucocorticoids, which helps maintenance of normal concentrations of glucose in blood
- stress causes energy usage
How was the connection between glucocorticoids and stress tested?
(in women)
- First 3 sessions: Exposure to 45 minutes of stress
- Fourth session: Rest session (sat quietly, reading and listening to music)
- After the stressor (or after rest on the last session) participants given a basket of snacks and left for 30 min while leisurely reading
- Salivary cortisol samples collected before, during, and after test:
o Baseline (15 min; 30 min)
o Before stress (45min)
o During stress (60 min; 70 min)
What was the stress in the cortisol/eating behavior study?
Modified version of Trier social stress test
• Subject asked to perform 3 challenging tasks designed to be stressful by giving unrealistic time constraints to perform the expected goals
• 1) visual spatial puzzle
• 2) serial subtraction of a prime number from a high number
• 3) deliver a videotaped presentation they were told would be evaluated from behind a one way mirror
What were the snacks in the cortisol/eating behavior study?
- To account for individual food preferences for sweet versus salty and high versus low fat snacks four snacks were provided
- High fat: chocolate granola bar, potato chips
- Low fat: sweetened rice cake, salty pretzels
What were the results of the cortisol/eating behavior study?
- Results: High cortisol reactors consumed more calories on stress days and preferred sweet/high fat foods compared to low reactors
- Dieting was not related to consumption after stress, but was significantly lower on the control day
Describe the major players in stress response.
Hypothalamus • Paraventricular nucleus (PVH/PVN) • Nucleus right above the arcuate nucleus • Has CRH neurons Pituitary gland Adrenal Gland
What is the PVH/PVN connected to?
(Plays a role in stress response)
Also the PVH/PVN is connected with the feeding circuitry and it receives inputs from NPY/AgRP and CART/aMSH neurons, like the LHA
How were the effects of chronic stress on energy intake studied?
Experiments Design:
- 2x2 Stress or no stress x comfort or no comfort food
- Stress: Restraint stress (3hr daily for 5 days)
- What they chose to eat and how much they ate was measured
What were the experimental groups in the chronic stress, energy intake study?
Group (-) chow only and no stress
Group (+) chow, lard and sucrose but no stress
Group R (-) received restraint stress but chow only
Group R(+) restraint stress, chow, and lard and sucrose
What were the results of chronic stress?
- If animals are expecting something stressful they don’t eat
- Caloric efficiency calculated as a ratio of body weight change divided by calorie intake
- If you don’t change your diet and you’re under constant stress you start losing weight
- Immediately after stress they would start eating more if the food is available
- The stress group that has access/ate comfort food had a blunted corticosterone response to a new stress
- How content/rewarding your life is right before something stressful happens matters
What were the general conclusions from the chronic stress study?
- Chronic stress increased consumption (appetitive drive) of palatable food
- Consumption of palatable food blunted next stress response
How could stress induce appetite drive for palatable foods? Where does this act?
o Corticotropin- releasing Hormone/Factor (CRH/CRF)
- In the HPA axis CRH/CRH acts as a hormone (endocrine system)
- Central Action (non-HPA axis) CRH/CRF acts as a neurotransmitter (brain)
o CRH/CFH forebrain systems can be activated in response to Aversive (stressful) and appetitive (positive) events/stimuli
Where does central CRF (non-HPA) act within the forebrain?
• Nucleus Accumbens (ACB/NACC)
- Part of the ventral striatum
- The ACB has
- CRF-fibers
- CRF-receptors
- Local neurons expressing CRF
How were the effects of CRF within the nucleus accumbens studied?
- Testing subjects for the motivation to obtain reward: sucrose pellets (by level pressing) while being primed by a sound that reminds them of the pellets
-Rats trained using Pavlovian Instrumental Transfer, prior to testing rats received micro injections of
• Vehicle
• CRF
• Amphetamine (positive control)
What is PIT and what was it used to study?
- Pavlovian-Instrumental Transfer (PIT)
- Testing subjects for the motivation to obtain reward: sucrose pellets (by level pressing) while being primed by a sound that reminds them of the pellets
- Used to study effects of CFR in the nucleus accumbens on incentive motivation of sucrose reward cues
How was Pavlovian instrumental transfer trained?
Phase 1: Instrumental Learning
• Rats place in a chamber with two levers: active and inactive, responding on the active lever delivers sucrose (reward) while responding on the inactive level has no consequence
Phase 2: Pavlovian Conditioning
• Rats are presented with two cues (auditory)
• One cue is immediately followed by sucrose CS+ while the other cue is paired with no outcome (CS-)
• Rats have no control of sucrose delivery, however they learn the association between the cue (CS+) and sucrose delivery. They approach the place (food-cup) where the sucrose is delivered, during presentation of the CS+, but not during CS-
Phase 3: Test (of Pavlovian-to-instrumental transfer)
• Rats in operant chambers with both levers present and the CS+ and CS- (tones) are presented to the rats and lever responding is assessed
• No sucrose rewards given
• Evidence of PIT is that the rats increase responding to the active lever during the CS+ compared to the CS-
What were the results of the CRF study in mice?
- After AMPH given rats enhance pressing on sucrose lever selectively during CS+
• No change on control lever or pressing during pre-CSs or CS- - After CRF given rats enhanced pressing on sucrose lever selectively during CS+
• No change on control lever or pressing during pre-CSs or CS-
o Conclusions: CRF enhanced appetitive motivation for reward, similar to the effects of AMPH
How was self control choice and stress studied?
o Experience stress (ice water) then, while in fMRI, choose food items from pictures to eat after the testing, bold brain activation patterns measured
o Was found that stress increased the influence of immediately rewarding taste attributes on choice and reduced self-control
What is self-control failure?
o Self-control failure is defined as choosing a more tasty less healthy item in the subset of trials where health and taste attributes were in conflict because the healthier item was less tasty
What activity was observed in the brain in the stress, self-control choice study?
o Increased functional activity across brain areas related to:
Associative learning: amygdala
Reward: nucleus accumbens (ACB)
Decision-making: prefrontal cortex (PFC), ventromedial (vmPFC) and dorsolateral (dlPF)
What was found to be critical for emotional decision making in the stress, self-control choice study?
o Ventromedial Prefrontal Cortex (vmPFC) critical for Emotional Decision Making
o Greater connectivity between the vmPFC and AMY and ACB when choosing tastier but less healthy food under stress and reduced connectivity between the vmPFC and a region linked to self-control success (dorsolateral prefrontal cortex)
o vmPFC connectivity with amygdala and vSTr(ACB) increased with stress and during tastier choices was associated with cortisol but not PSL
o The opposite was found for vmPFC-dlPF connectivity: decreased connectivity with stress correlated with PSL but not cortisol
How were orexin and reward studied?
o Conditioned Place Preference (CPP)
What is conditioned place preference?
During training rats are exposed to two chambers (contexts). One chamber becomes associated with drug or food reward through repeated pairings, whereas the other chamber is associated with no reward.
Test: No reward is given during the test. Preference for reward is measured by the amount of time animals spend in the reward associated chamber minus the time it spends in the non-rewarded chamber when given free access to both chambers after conditioning
What are place preference scores?
Expressed as the time spend in the reward-paired chamber minus the time spend in the non-rewarded chamber on the test day
What is extinction?
In conditioned place preference: o Extinction – after repeated exposures to the chambers with no rewards, there is no preference for the reward associated chamber
Extinction does not erase prior memory, but rather it is a new learning
Spontaneous recovery of responding (after extinction)
What is recovery after extinction? And how is it induced?
Renewal (reinstatement) of responding (after extinction) can be induced with:
• Brief exposure to the reward (US)
• Cue for the reward
• Stress
How was the relationship between orexin and reward studied (specific)?
o Behavioral evidence for the role or ORX in processing reward by using conditioned-place preference paradigm
o Place preference scores for: Morphine, cocaine, and food (lucky charms) paired environments
Are Orexin neurons activated during CCP/reward seeking?
Examined whether the environment (contextual cues) previously conditioned with food or drug reward activates Orexin neurons
• Activity of orexin neurons was measured with the immediate early gene c-fos protein (Fos) induction
• Fos-induction of ORX neurons positively correlated with preference score
• Orexin neurons in the LHA are critical for reward processing for food and drugs
• ORX neurons are activated by reward cues
Could stimulation of ORX neurons drive relapse (renewal) of drug seeking behavior? Could NPY Y4 receptor activation in the LHA (where ORX neurons are located) reinstate extinguished CPP?
- Stimulation of LHA area where ORX neurons located via NPY-Y4R by rPP (a pancreatic polypeptide) micro infusion reinstated an extinguished CPP for morphine
- A caveat: NPY-Y4 receptors are not only located on ORX in the LHA, but also on other neurons, which could have been stimulated by rPP via NPY-Y4 receptors
Describe the structure of ORX neurons.
ORX Neurons: cell bodies located in LHA and receive axonal projections (input) from NPY neurons
Is the effect of reinstatement induced by Y4 stimulation blocked by systemic ORX-R antagonism?
Systemic administration of ORX-R1 antagonist blocked rPP-induced reinstatement of CPP
