Neurobiology of Eating and Eating Disorders Midterm 2

CR

Conditioned Response

CS

Conditioned Stimulus

Disconcordant

Different, something changing how they eat, metabolize, etc. --gut microbiota is different

Incentive motivation

Drive behavior but not immediate reward

Episodic Memory

Remembering features of a memory but not learning it

Primary function of the MC4-Receptor

-To inhibit feeding -Eliminating these receptors results in obesity

Learning and Motivation

Through conditioning, learned (conditioned) cues (CSs) not only acquire behavioral conditioned responses (CRs, food-cup approach) but also acquire the ability to change attentional and motivational processing: CS can stimulate the motivation to eat--cue-induced feeding; CS can stimulate instrumental responding for the food reward--PIT

Incongruous eating

not consistent; see 300ml or 500ml and eat either the same or opposite

Transplanting human microbiota to mice

-To see which microbiota will be more invasive when co-housing -Part 1: Ob microbiota-->mouse gained weight: Ob twin has some kind of bacteria that leads to weight gain -Part 2: which is more evasive-->put mice together Ob microbiota mouse-->becomes leaner; somehow lean influences ob

Calorie Intake during Chronic Stress (question 1)

-Total daily calories: (+)>R(+)>(-) & R(-) -negative effect of stress and positive effect of comfort food -Both stress groups were gaining less weight than controls (without stress) and eating less -Both comfort food access groups were gaining more weight than chow-only groups and eating more calories -Caloric efficiency calculated as a ratio of body weight change divided by calorie intake -(+)>(-)>R(+)>R(-) -Ratio of BW change divided calorie intake -R(-) not gaining weight efficiently-having rewarding food is rescuing them (R(+)) -Glucocorticoids-role in glucose metabolism; stimulate gluconeogenesis; fasting increases release of glucocorticoids, which helps maintenance of normal concentrations of glucose in blood

Food and Cues associated with food stimulate eating: priming

-Using cues (or food itself) in brief exposure prior to a meal

How is Cephalic Insulin Secretion in Anticipation of a Meal by Cues Associated with Meals/Feeding accomplished/via which pathways/nerves?

-Via the Vagus nerve (DMX) -This could reduce the post-prandial increase in glucose (and prevent hyperglycemia) but could cause low glucose and hypoglycemia--habit switches the normal pattern

Time of day, distraction/boredom effect on intake

-We are driven by circadian rhythm -We are very aware of time of day--regulates when we ear food -Boredom may or may not be physiological; time spent watching television correlates significantly to body fat content, snacking, and caloric intake

In the LHA is NPY-neuron input directly connected with neurons that make orexigenic peptides?

-Yes: NPY axons innervate MCH and ORX cell bodies and dendrites-- not colocalized (coexpressed) in the same neurons -Also co-express AGRP (Agouti-related peptide)--because of Dale's principle we can consider them to be the same -NPY and AGRP are colocalized (coexpressed) in the same neurons

Example for Modulation of Satiety by factors not (directly) related to calories

-(hot) soup -sensory-specific satiety -time of day -used different foods as preloads to test hypothesis that some foods are more satiating than others: highly satiating foods when eaten prior to/at start of a meal should decrease overall calories consumed in the meal -Soup vs. equicaloric crackers, cheese and apple juice vs. no preload, followed by a meal -meal was decreased by eating soup first -did not significantly eat less with crackers and cheese; temperature and volume may matter

Pairing arbitrary cues with food to determine if after repeated pairings they can stimulate insulin release

-2x2 design to test whether an olfactory cue (smell/odor) and time of day could become cues that predict a meal and stimulate insulin release Group 1: odor given prior to the daily meal and the meal was at the same time each day Group 2: odor given prior to the daily meal but the meal given at random time Group 3: the meal was given at the same time each day, but odor presented at random time of the day Group 4: odor and meal presented at random in respect to the meal -Measured insulin after odor presentation at specific meal time, no food given: odor only highest -Groups 1, 2, 3 but not 4 showed conditioned insulin release in anticipation of a meal: rats secreted insulin the the presence of stimuli that reliable predict feeding -Insulin secretion can be stimulated by arbitrary cues that have been previously paired with food: initially neutral environmental cues through learning (Pavlovian Conditioning) acquire ability to signal food and stimulate insulin release

How does CS get to the feeding circuitry? What brain structure/s and circuitry are critical?

-Amygdala -Major divisions: Central Nucleus of the Amygdala (CEA) and Basolateral Amygdalar Area (BLA)

Acute Stress and Eating

-Associate cortisol and food intake -Hypothesis: those who secreted more cortisol in response to stress would: 1. eat more calories, 2. choose sweet or high fat foods -Three stress sessions, one rest session (not a great set up--rest session not a true baseline) -After stressors, participants given a basket of snacks (with sweet and salty and high and low fat foods) and left for 30 min while leisurely reading -Salivary cortisol samples collected before, during and after test; significant levels of anxiety spike right at the end of the test -Separated by high and low reactors so they don't cancel out: high reactors consumed far more calories on stress days; almost equal on rest days--but low reactors show large increase between stress and control day -Total calories consumed on the stress day significantly related to change in cortisol after stress -High ate more sweet and high fat food on stress day -Low on control day ate more savory foods -Increases in average negative mood during the stress session were related to food intake after stressor; dieting was not related to consumption after stress, but was significantly lower on the control day

Time of Day of Food Intake influences on overall intake

-Biggest meal is dinner -Satiety ratio defined as the duration of the inter-meal interval divided by the meal size-->dinner had the lowest because they could not satiate -Overall goes down if we consume more at breakfast -Overall goes up if we consume the most at dinner -However, whether or not you eat dessert is not necessarily due to dinner satiation levels

Similarities between Rat Chronic stress study and Women

-Both show sweet and high fat food preference -Total consumption is different and more complicated -Total calories decrease in stress and increase in comfort food groups

Anorexigenic Peptides in HY

-CART: Cocaine and Amphetamine Regulated Transcript; gene changes with cocaine or amphetamine administration, has broad effects, one of which is anorexigenic -CART expressing neurons are located in the Arcuate Nucleus of the HY--very strongly expressed

Stress reduction and comfort food (question 2)

-CRH mRNA, ACTH, Corticosterone -Used different stresses -Corticosterone R(+) has less response than R(-); simple physiology learning--blunting of new stress response -Chronic stress increased consumption (appetitive drive) of palatable food -Consumption of palatable food blunted next stress response

Corticotropin-releasing hormone/factor

-CRH/CRF -HPA axis: paraventricular nucleus of hypothalamus (PVH) acts as a hormone-->ACTH (pituitary gland)-->glucocorticoids (adrenal gland) -Non HPA axis: also expressed in other forebrain areas, which are not part of the HPA axis or endocrine system--does not act as a hormone-->lateral hypothalamus, amygdala, nucleus accumbens -action within HPA axis, CRH/CRF acts as a hormone and goes to the endocrine system -central action, CRH/CRF acts as a neurotransmitter and goes to the brain -CRH/CRF forebrain systems activated in response to aversive (stressful) and appetitive (positive) events/stimuli

How could stress increase appetitive drive?

-Chronic stress increased consumption of palatable food -Consumption of palatable food blunted next stress response

How is Ghrelin integrated within the hypothalamus? What neurons/substrates in the HY does Ghrelin act on?

-Co-expression of G receptor and specific mRNA for peptides (which identifies specific neurons)-->Neuropeptide Y (NPY) mRNAs in the hypothalamic neurons

Pre-meal Glucose decline

-Could be due to lack of nutrients/energy (metabolic hunger signal) -Could be because cues predicting meals stimulate (small bursts) of insulin, which in turns produces a decline of glucose in the blood

Ventromedial Prefrontal Cortex (vmPFC)

-Critical for emotional decision-making -Not proximally necessary for survival: Phineas Gage

Levels of CART (mRNA) under food deprivation?

-Decreases mRNA in Arcuate Nucleus -ob/ob mice: use expression of DMH as a control, shows that they either do not have it or are not expressing it-->leptin regulates CART

Episodic Memory and Expected Satiation Study

-Experiment 1 -Covertly manipulating what they see vs what they eat -Incongruous eating -Hunger/satiety assessed via button and ratings -At 0 min: Hunger goes down when they eat what they see--less hungry when they eat more, but both report less hunger post-eating-->CCK driving this effect -At 1hr no significant effect -At 2 and 3 hrs: hunger goes up, 300mL seen is more hungry regardless of what was consumed -Visual more salient--episodic memory of what we saw -Experiment 2: 24 hr after experiment 1, participants shown a bowl containing 400ml of soup and asked to evaluate/predict how satiating they expect it would be--must decide based on memory (seen not satiety) -Overall expected satiation level by size but also satiety because high-->high -Implicates the hippocampus

Neuropeptide Y (NPY)

-Extremely potent stimulant of food intake -Can induce a dose-dependent 10-fold increase

Lateral Hypothalamic Area (LHA)

-Feeding/hunger center -Contains orexigenic peptides (appetite-inducing): MCH and ORX

Biphasic Insulin Response During Meals

-First peak: early elevation before the nutrients, so due to anticipation of nutrients; driven by sensory cues, so due to food cues -Second peak: late elevation due to nutrients (glucose rise) -Someone who does not consistently eat after smelling the food (ie chef): Just 2nd peak especially after 1 year on the job -Sham feeding: only would have the first peak because there was the food cues but no actual nutrients absorbed -Stomach-tube feeding: would only have the second peak because that was no anticipation of nutrients before the body got them

NPY mRNA levels under food deprivation and leptin regulation

-Food dep: Increases; overexpressed in ob/ob; increases by lack of adiposity signal -Leptin down regulates NPY (/AGRP), Ghrelin stimulates NPY (/AGRP): in ob/ob there is no leptin, and because it stimulates food intake and decreases energy expenditure, chronic stimulation causes weight gain

Diet matters in microbiota effeciency

-Highly processed foods have been linked to a less diverse gut macrobiota -Only effective if low fat/high fiber (fruits/vegetables) diet--we can only survive with this specific diet even with bacterias-->need both to be interactive

Examples for Modulation of Satiety by Factors not (directly) related to calories

-Hot soup (temperature, volume, fat molecules) -Sensory-Specific Satiety (eating or just chewing or smelling food reduces subsequent pleasantness rating of that food) -Time of day (early in the day easier to reach satiety)

Orexin

-Hypothalamic neuropeptide -Fasting up-regulates mRNA -Intracerebroventricular injection simulated food consumption (more=more) -Degeneration of neurons leads to narcolepsy: critical for arousal/wakefulness, eating/motivation to eat -When mice are food deprived they are more active and show bursts of activity in looking for food--w/o this peptide there is no activity in looking for food

Stress Response

-Hypothalamo-pituitary-adrenal (HPA) axis -Hypothalamus (corticotropin-releasing Hormone (CRH))-->Pituitary Gland (Adrenocorticotropin hormone)--> Adrenal Gland (Glucocorticoids: cortisol (Humans) Corticosterone (rat)) -Could stress via the release of stress hormones (glucocorticoids) modulate eating: how much and what we eat?

Olfactory Sensory-Specific Satiety in Humans

-If we smell a particular food we will feel more satiated -first ate either banana or chicken to satiety, then smelled specific foods and rated the pleasantness of smell, then rated taste -Pleasantness of smell and taste of both banana and chicken goes down -Same effects shown when just chewing food for a few minutes without eating and smelling food without caloric intake -Smelling food without caloric intake is sufficient to modulate subsequent perception of taste (and smell) similar to the effects when the food had been eaten

Can NPY release be conditioned?

-Important for anticipation--setting up physiology so we can eat more -7 consecutive days of brain (ICV) injection of saline or NPY at the same time of day--no food given at time of injections -They were fed at a particular time and then received injections later to dissociate NPY from feeding -Training/Testing: Saline/Saline, Saline/NPY, NPY/Saline*, NPY/NPY -Intake 1hr-post injections: NPY/Saline group eats more than saline/saline because cascade of events triggered by NPY injections occur even without NPY--learned -No significant changes in peripheral parameters: insulin, glucose, or ghrelin levels because brain can stimulate these events without recruiting peripheral because it is going down the vagus nerve pathway, not up--conditioned NPY targets in the brain

Blocking endogenous CART with antibody against CART (anti-CART)

-Increased nighttime feeding indicates the endogenous signal -Indicates close association with actions of leptin and NPY

Emotional Eating Theory

-Individuals eat to cope with stress and that could lead to Stress-Eating-Obesity Nexus -Testing 2 hypothesis: 1. Eating chocolate will have an immediate effect on negative, but not on positive or neutral mood 2. The effect will be due to palatability -Showed sad, happy and neutral clips from movies -Compared baseline with no eating and engaged with movie -Chocolate vs water -Biggest effect is with sad film: tweaking us back to 0 faster--effects not huge--some people were reported as emotional eaters and those had the biggest effects

Testing Leptin regulation of CART

-Inject ob/ob mice with leptin -Control 1: received saline -Control 2: was pair-fed (like dieting)--is it leptin or a change in body weight -Looking for independent change with leptin: injected by IP (systemically) -CART only at measurable amounts with Leptin treated mice--can induce CART with leptin before a change in body weight occurs -CART peptide was administered centrally (ICV): amount eaten decreases--seemingly dose-dependently -NPY and CART: driver and inhibitor competing: still a decrease in intake: CART is very strong, even with high levels of driver -CART peptide ICV injections inhibited feeding in non-food deprived and food-deprived animals and completely blocked NPY-induced feeding

; Can food consumption be conditioned?

-Learning can influence what children prefer to eat -Learning can influence how much they eat: latency to approach food--once song played you measure how long it takes them to go get food: CS+ (song and light always played before snack)-they also eat more -Only kids who actually identified what the cue meant showed learning -Based on earlier work in rats

a-MSH

-Melanocortins are a family of peptides that are cleaved from pro-opiomelanocortin (POMC) precursor molecule) -Bind to melanocortin receptors (MC-R) -An agonist for MC4-R (AGRP is an antagonist to MC4-R, and binds and stimulates eating) -Can induce weight loss by increasing energy expenditure (metabolic rate) and inhibitory effects on food intake -Same neuron as CART -Food deprivation decreases CART/a-MSH -Leptin promotes CART/a-MSH

Antibiotics and Microbiota

-Mice given low doses of antibiotics developed ~15% more body fat compared to control mice

NPY administration ICV

-Mimics the normal reaction -"how hard they are willing to work": If given, mice are willing to increase work for the same reward -"how much are they willing to endure": if shocked while drinking milk, higher dose=more willing to receive shock to keep drinking -Milk+Quinine (bitter): when satiated first w/ and w/o it, those with more of it will eat almost as much as when it tasted good -Decreased energy expenditure

Is CRH a motivator for rewarding foods during stress?

-Must detect stress and promote motivation -This is the 1st step--stress and behavioral response --in the nucleus accumbens

What is the role of central CRF (non HPA) in (motivation for) reward? Where does it act within the forebrain?

-Nucleus Accumbens within the Ventral Striatum -The ACB has: CRF-fibers, CRF-receptors, local neurons expressing CRF--are neurons that may only express it under stress

What type of neurons within the Lateral Hypothalamus are critical for Cue-Induced Feeding?

-Orexin/Hypocretin Neurons

Could chronic stress increase consumption of palatable foods and reduce HPA responses to stress?

-Paraventricular nucleus (PVH/PVN) has CRH neurons-->Pituitary gland w/ adrenocorticotropin hormone-->Adrenal gland w/ glucocorticoids

Cue-Induced Eating in Rats

-Phase I: Pavlovian Conditioning: US induces UR wihtout learning: Food (US)-->Feeding behavior (UR); Tone (CS)-->Neutral in respect to feeding -Rats are food-restricted during training to motivate learning: CS-US -Before conditioning: US-->UR, CS-->no feeding response -During Conditioning: CS presented repeatedly before US, CS-US pairings -After conditioning: CS-->CR, rats approach the location where food given: food-cup behavior -Phase II: Food Consumption Tests: satiated rats tested in 2 tests: Satiated rats+food+CS+-->eat ~20% of daily intake; Satiated rats+food+no cues-->not eat/eat very little; Satiated rats+food+CS- -->not eat/eat very little

Environment (ambience/context) on Food intake and food choice

-Physical surroundings: food presentation and location, colors, light, sound, temperature, smell -Social Variables

Learning and Homeostatic Mechanisms: Cephalic Insulin and NPY

-Post-Prandial insulin: secretion that occurs after ingestion of food; in response to high blood glucose (physiological stimulus)-->however we would always be hyperglycemic after each meal -Cephalic insulin: occurs prior to ingestion of food, released in response to cues that predict eating, including taste; anticipatory/preparatory response, driven by the brain and cues for food -Viewed food for 5 mins and told they would eat it in 15min: resulted in biphasic response -Ob had higher insulin responses to sight/smell of food (error was high) -Large individual differences: majority of subjects had a biphasic response, some had one smaller peak, and some no response or a decrease

PIT experiment

-Prior to testing (phase 3) rats received microinjections of Vehicle, CRF, or Amphetamine -Rats press more on sucrose (active) than on control (inactive) lever: evidence of PIT--pressing on active lever is enhanced during CS+ -After AMPH is given rats enhance pressing on sucrose level selectively during CS+, no change on control lever, or pressing during prs-CS or CS- -After CRF given rats enhanced pressing on sucrose lever selectively during CS+ no change on control elver, or pressing during pre-CS or CS- -Enhancement of appetitive motivation by CRF; CRF injections in the Nucleus Accumbens enhanced cue-triggered lever pressing (similar to AMPH injections) -CRF system in the medial shell of the nucleus accumbens enhances appetitive motivation (positive incentive motivation) triggered by a reward cue (a cue previously associated with reward: CS+)

What would happen to feeding if we eliminated LHA on both sides of the brain (bilaterally)

-Rats would not eat -Want to eliminate a particular function

Anticipator Mechanisms/Anticipatory Motivation

-Role in starting eating: meals initiated without physiological deficits, eating in anticipation of future deficits, cues that predict food, feeding could initiate eating -Role in ending eating: satiety mechanisms stop eating before body weight is gained in anticipation of imminent replenishment -learned anticipation is actually adaptive and helps use food best--a purpose to decrease homeostatic disturbance

Ventromedial Nucleus of the Hypothalamus (VMH)

-Satiety center

Cue induced feeding, the CEA, and the BLA

-Selective neurotoxic bilateral lesions of the BLA or CEA: Study 1 -Phase 1: all groups had similar CRs--all learned equally well to approach the food-cup during CS-->neither lesions of the BLA or CEA had an effect on learning the CS-US association based on food-cup approach -Phase 2: After conditioning food consumption tests with CS presentations or no cue presentations, the difference in the amount eaten between the two tests show: CEA lesions did not change CS-induced feeding; BLA lesions abolished CS-induced feeding -BLA lesions did not impair learning but they impaired motivation to eat driven by learned food cue -BLA is not the sole mediatory--ultimately, it has to act via the feeding circuitry-->hypothalamus

Social-Affective Context in Pre-School Children

-Snack food given in 4 ways: 1. As a reward 2. Non-contingently paired with adult attention 3. In a nonsocial context 4. at snack time (familiarity control) -Assessed with cartoon faces showing liking or disliking -Test preferences over 4 weeks -#1 makes them like the food most, then #2-->continued over 6 weeks--very potent -Most choices are influenced by learned processes

Effect of Ambience on Food intake and food choice

-Social Variables: -Social facilitation: eating with others increases a meal size, presence of other people during food consumption enhances the actual intake, social facilitation occurs regardless of age, time/meal of day, place (home/restaurant), or species; contributing factors can be: Duration of meal, rewarding component (meals are rated higher in palatability when eaten with others), affective component (more eaten with friends than with strangers), learned component -Social modeling: effect of family and peers: learning: children's intake influenced not only by what is served at home, but also the communication style; social-affective context: the effect of emotion on learning and memory

External Signals that Influence Food Intake and Body Weight

-Sound (higher intake) -Lighting (more light=eat more) -Bigger breakfast -Environment -Social Factors -Learning -Stress, Emotion, Mood -Reward

Ghrelin

-Stimulates GH secretion -Peptide hormone produced by stomach -Stimulates feeding -Stimulates the vagus nerve, which communicates with the NTS -Neurons in the NTS also contain it, and send axons to the hypothalamus, where they release it, which induces feeding (explains why central injections--not just peripheral--increase effects)

CRH/CRF and Appetitive Motivation

-Stress leads to CRF in the ACB which leads to increased motivation to sucrose cues -Hypothesis: elevated CRF neurotransmission in the Nucleus Accumbens would enhance motivation for sucrose reward -To test: effects of CRF in the Nucleus Accumbens on incentive motivation of sucrose reward cues via Pavlovian-Instrumental Transfer (PIT)

Testing if the BLA gets to the feeding circuitry via the LHA

-Study 2: BLA is connected with the LHA via direct (monosynaptic) and indirect (polysynaptic) pathways--connections are ipsilateral -Contralateral-lesion design: unilateral lesions of the BLA and unilateral lesions of LHA but on opposite sides of the brain: disconnects function BLA-LHA circuitries on both sides of the brain (in both hemispheres) because connections between these structures are ipsilateral (within the same hemisphere) -Contralateral, ipsilateral, and sham (not real lesions but had surgery and recovery) lesioned groups -Phase 1: pavlovian conditioning: BLA-LHA disconnection to CS+/CS- learning: all rats learned equally well to approach the food-cup during CS+ but not CS- -Phase 2: Food consumption tests with cues (CS+ or CS-): no motivation to eat in contralaterally lesioned rats--not known why it is stimulatory

Is vmPFC part of the circuitry for cue-induced feeding?

-Study 3 -Part A: Behavioral Preparation -Eating environment: conditioning to context: 1. paired: in new environment with a new food; 2. in a new environment and food given back at home cage -Food consumption test: food in the new environment but in a different place: rats previously fed in that context ate more than the controls; neither eat the chow--are sated; same enviro with same food=specific increase in consumption-->cravings induced by location -Contextual cues associated with the environment in which we eat (eating context) could become food cues (conditioned stimuli) that can stimulate intake in that environment/context and that appetite is specific to the food used during training -Part B: Lesions Effects: Trained food: lesions not impaired in consumption but not in inc/enhanced amount--abolishes effect of same environment with same food leading to a specific increase in consumption; Novel food: decrease; Familiar Food: no eating -Lesions of the vmPFC in rats eliminated conditioned context driven eating

Obesity, Dieting and Anticipatory Salivation to Food

-Subjects primed with food cues (smell and sight of food) before a meal -Study 1: subjects were presented with freshly baked pizza and informed that they would be allowed to eat it shortly--measured salivary response: no difference between obese and normal weight, but significant difference between dieters and non-dieter with dieters having a much higher response -Study 2: compared responses to palatable food and non-palatable food (cookies vs. green dyed cookies): dieters produced a higher drive to eat both

Food Presentation and Location effect on intake

-availability, variety, physical proximity, portion size, perception/expectations/cultural

Melanin-Concentrating Hormone (MCH)

-injections into the brain: Increase food intake -Targeted mutation: Decrease food intake but not completely abolished -Overexpression: Immunoreactive neurons in the LHA; leads to obesity and insulin resistance; No leptin, gaining weight and has more insulin in serum -A classic homeostatic signaling molecule in the brain

Where are NPY injections the most potent?

-the Arcuate Nucleus of the Lateral HY

Could repeated consumption of palatable foods in turn modulate the motivation brain systems? (Emotional decision-making)

-vmPFC: this brain area is critical for emotional decision-making -lesions of the vmPFC in rates eliminated food-conditioned context driven eating 1. examined neural activation (fos protein induction) in response to cues associated with drug intake: nicotine 2. Examined whether cues associated with natural reward: palatable food (chocolate) activate similar brain systems -Shows similar fos induction in the vmPFC in response to drugs and chocolate

Color effect on intake

-warm colors make us more attracted to the food, could be driven by innate mechanisms and/or could depend on previous experience and expectation

Mechanisms of how gut microbiota effect weight loss

1. efficacy of energy, satiety controls--something related to inflammation? 2. Short chain fatty acids (SCFAs)--impact on how how hosts absorbs them--lean produce and digest more than ob-->increased weight gain in OB mice does not result from increase energy harvest; SCFAs promote leanness by inhibiting fat accumulation in adipose tissue, raising energy expenditure, and enhancing production of hormones associated with feelings of satiety

Pavlovian-Instrumental Transfer (PIT)

Phase 1: Instrumental learning Phase 2: Pavlovian Conditioning Phase 3: test (of pavlovian-to-instrumental transfer)

Chronic stress and eating (study in rats)

Questions: 1. does chronic stress induce consumption of "comfort food"? 2. does consumption of "comfort food" in turn reduces stress? Hypothesis: Chronically stressed rats would: 1. increase "comfort foods" consumption 2. have reduced HPA responses to stress -Chronic stress will increase consumption of palatable food through increased appetitive drive (motivation) -Palatable food consumption will reduce next stress experience, which will be evident in a blunted stress response -Stress: restraint stress (3hr daily for 5 days) -Experiments design: 2x2, stress or no stress x comfort or no comfort food -Experimental groups: 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 -chronic stress increased the proportion of total intake chosen from comfort foods (lard & sucrose--could be taste or calories) -comfort food-access rats gaining more weight (compared to chow) -stressed rats gaining less weight

Phase 3: Test of Pavlovian-to-instrumental transfer

Rats are placed in operant chambers, with both levers present During this stage, the CS+ and CS- are presented to the rats, and the degree of responding during presentations of the cues is assessed No rewards (sucrose) delivered during tests Evidence of Pavlovian-to-Instrumental transfer is that rats increase responding to the active lever during the CS+ compared to the CS-

Phase 2: Pavlovian Conditioning of PIT

Rats are presented with two cues (30s auditory CSs) in the operant chambers One cue is paired with sucrose reward (CS+) and a second cue is paired with no outcome (CS-) Rats learn to approach the food-cup, where the sucrose is delivered, during the presentation of the CS+, but not during CS-

Phase 1: Instrumental Learning of PIT

Rats are presented with two levers placed in the operant chambers Responding on one (active) lever results in the presentation of the sucrose reward, and responding on a second (inactive) lever has no consequence Rats quickly learn to respond on the active lever

CS-

The control cue, not paired with food

CS+

The cue paired with food

UR

Unconditioned Response

US

Unconditioned Stimulus

CART is co-expressed with another anorexigenic peptide

alpha-Melanocyte-stimulating hormone (a-MSH)