MotivationandtheRegulationofInternalStatesChapter6

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MotivationandhomeostasisHunger:acomplexdriveObesityAnorexia,Bulimia,andBingeEatingDisorder

MotivationandHomeostasis• Motivation

•  “Tosetinmotion”•  Factorsthatinitiate,sustain,anddirectbehaviors.

•  TheoreticalApproachestoMotivation•  Instinct:

•  Automaticandunlearnedbehavior

•  Occursinallmembersofaspecies

•  Drivetheory:Thebodymaintainshomeostasis—equilibrium—initssystems.

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Low High Arousal

Per

form

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Optimal Level

MotivationandHomeostasis

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•  TheoreticalApproachestoMotivation•  Drivetheory:Isconcernedprimarilywithexplainingphysicalsystemslikehungerorthirst.

•  Incentivetheory:Peoplemotivatedbyexternalstimuli•  Arousaltheory:Peoplebehavetosatisfyacertainlevelofsensation

•  Challengestodrivetheoryhavedrivenemphasisondrivesasstatesofthebrainratherthanconditionsoftissues•  HomeostaticDrive:A“controlsystem”maintainsconditionsaroundasetpoint.

•  Whenconditionsdonotequalthesetpoint,theorganismwillbehavetoreturnthedrivetothesetpoint.

MotivationandHomeostasisFigure6.2:SelectedNucleioftheHypothalamus•  TemperatureRegulation

•  Ectothermscannotregulatebodytemperatureinternallyusingenergyreserves...(Lizard/Snake)

•  Endothermsmaintainaconstantinternaltempbychangingmetabolism,constricting/expandingbloodvessels,ormovingtowarmer/coolerlocation[Mammal]

•  Preopticareaofthehypothalamusreceivestemperaturesignalsfromtheblood/skin.

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SOURCE: Adapted from Nieuwenhuys, Voogd, & Van Huijzen, 1988

MotivationandHomeostasisFigure6.3:ThirstControlSignals&BrainCenters

•  Thirst•  Osmoticthirst:whenfluidincellsdrop,cellstakewaterfrombloodstream

•  OVLTofhypothalamussignalsmedianpreopticnucleustotriggerdrinking

•  Hypovolemicthirst:whenbloodvolumedrops

•  Kidneysreleaserenin,increasingangiotensinII.

•  Subfornicalorganthensignalsmedianpreopticnucleus

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Hunger:AComplexDriveTheRoleofTaste.•  Hunger

•  Tastebudsontonguepapillaedetectfiveprimarycategoriesofchemicals.

•  Sweet:carbohydrates•  Salty:ionsforneuraltransmission•  Sour:spoiledorrottenfood•  Bitter:toxicchemicals•  Umami:proteincontent.

•  Someevidencethattastepreferenceandsensitivityaredevelopedearlyinlife

•  Signalstraveltotheinsula(theprimarygustatorycortex),andtothenucleusofthesolitarytract(NST).

•  Ratswithlesionsinventromedialhypothalamuseatuncontrollablyandbecomeveryobese

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Hunger:AComplexDriveSensory-SpecificSatiety:VaryingtheChoices

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•  Sensory-specificsatiety•  Foodislessappealingthemoreyoueat,encouragingvariationinchoices

•  AreaNSTofthemedulla.•  Learnedtasteaversion

•  Avoidingfoodsassociatedwithillnessorpoornutrition.

•  Learnedtastepreference•  Preferencefortheflavorofafoodthatcontainsaneedednutrient.

• Wisdomofthebodywillhaveusnaturallychoosingabalanceddiet,however...

•  Oftencounteractedbytasty,high-caloriefoods

Hunger:AComplexDriveDigestion&TwoPhasesofMetabolism.Figure6.6:TheDigestiveSystem

•  Mouth•  Salivastartsbreakdownofstarchesintoglucose

•  Stomach•  Hydrochloricacidandpepsinmixeswithfoodtodigestproteinsintoaminoacids.

•  SmallIntestine•  Duodenumiswheretherestofdigestiontakesplace.

•  Fatstransformedintofattyacidsandglycerolbybile.

•  Hepaticportalveintransportsproductstotheliver

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Hunger:AComplexDriveFigure6.7:SummaryoftheAbsorptiveandFastingPhases

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Requires capacity to store reserves, allocate them during fasting period, and monitor when reserves get low.

Hunger:AComplexDriveFigure6.8:HungerControlSignalsandBrainCenters

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•  Hungerfromlow•  Glucose(Glucoprivic)•  FattyAcids(Lipoprivic)•  Ghrelinisreleased(excessmayleadtostubbornobesity)

•  Nucleusofsolitarytract(NST)ofmedulla

•  ArcuateNucleus•  Monitorsnutrientlevels•  ReleasesNPYandAgRPwhichexcite…

•  Paraventricularnucleus(PVN)andLateralhypothalamus(LH)triggereating

Green pathways

Hunger:AComplexDriveFigure6.8:HungerControlSignalsandBrainCenters

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•  Stomachstretchreceptorsstimulated

• Whenfoodentersduodenum,intestinesrelease•  Cholecystokin(CCK)inhibitsNSTandLateralhypothalamus(LH)

•  PeptideYY3-36(PYY)inhibitsarcuatenucleus&helpsusconserveenergy

•  Eatingslows•  Leptin(releasedbyfatcells)inhibitshungeronalong-termbasis

Red pathways

Hunger:AComplexDriveTable6.1:SummaryofFeedingSignals

Stimuli SignalSource PathwayStartmeals

1.Glucose,fattyacids Liver,asnutrientsinbloodaredepleted

Vagusnerve>NST>Arcuatenucleus

2.Glucose(brain) Receptorsnear4thventricle MedullatoArcuatenucleus

3.Ghrelin Stomach,duringfasting Bloodstream>Arcuatenucleus

Endmeals

4.Stomachvolume Stomach:stretchreceptors Vagusnerve>NST>Arcuatenucleus

5.CCK Stomach,Intestines Vagus>NST;Blood>brain

Longterm6.PYY Intestines

Blood>Arcuatenucleus;InhibitsNPYNeurons7.Leptin Fatcells

8.Insulin Pancreas

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ObesityFigure6.14:BodyMassCalculationChart(foradults)

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SOURCE: Adapted with permission from “Obesity: How Big a Problem?” by I. Wickelgren, Science, 280, pp. `364-1367. Copyright 1998 American Association for the Advancement of Science. Reprinted with permission from AAAS.

ObesityHealthEffects.Figure6.13:UnderweightandObesityAccordingtoCountry

•  Correlatedwithhigherriskof•  Diabetes(type2),Heartdisease,HighBloodPressure,Stroke,ColonCancer,Reducedlifespan

•  Brainchanges:reducedtemporallobe,cognitivedecline,Alzheimer’srisk

•  Doubledsince1980inU.S.,globalepidemic

•  MythsaboutObesity•  Lackofimpulsecontrol,pooreatingstyles,temptationtoeat.

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SOURCE: From “Controlling the Global Obesity Epidemic,” by World Health Organization, 2003.

ObesityContributionsofHeredityandEnvironment.Figure6.15:CorrelationsofBodyMassIndexAmongTwinsFigure6.16:ob/obmouse

•  Heritability•  Obesity:50-90%•  BMR:40%

•  Genes•  Obesity(ob)•  Diabetes(db)•  FTOgene(Aallele)

•  Environment•  Epigeneticcharacteristics:geneexpressionchangesduetoenvironment(AgRP).

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SOURCES: Top right: Based on data from Grilo and Pogue-Geile (1991). Bottom right: From “Positional Cloning of the Mouse Obese Gene and Its Human Homologue,” by Y. Zhang et al., Nature, 335, pp. 11-16. Reprinted by permission of Nature © 1994.

ObesityObesityandReducedMetabolism

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• Basalmetabolicrate(BMR):•  Energyrequiredtofuelthebrainandbody•  75%ofenergyexpenditureatrest.•  Average:1800calories/day

•  SetPointdefendedbyshiftingmetabolism(increasingordecreasingenergyexpenditures)•  33%ofwomenonrestricteddietwhodidn’tloseweighthadlowerBMRs.

•  Prolongedweightchangecanshiftthesetpoint.

ObesityTreatingObesity.DietaryRestrictionversusMedication

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• Dietaryrestrictioniseffective,especiallywhencoupledwithexercise(whichincreasesBMR).•  Formerlyobesewomen-didtheyexerciseafterwards?

•  YES:90%kepttheweightoff•  NO:33%kepttheweightoff

•  HalfofallcaloriesconsumedinU.S.werefromcarbs,andanother1/3werefromfats(asofyear2000)

• Medicationisnotaseffective.•  Drugsthatworkthroughincreasingserotonin,*leptinandinsulin,orthroughdecreasedfatabsorptionhavebeenpromisingbutdonotworkforallpatients

•  Allhavesignificantsideeffects

ObesityTreatingObesity.Figure6.20:ReducedDopaminereceptorsinObesity

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•  TreatasanAddiction•  Obesepeopleshareseveralcharacteristicswithaddicts.

•  ReducedD2receptorsandprefrontalmetabolism.

•  Peptidesthatinduceeatingtargetdopamineneurons.

•  Anti-addictiondrugsareshowingeffectivenessinweightloss.

SOURCE: From “Brain Dopamine and Obesity,” G. J. Wang et al., Lancet, 357, pp. 354-357. Copyright 2001.

ObesityTreatingObesity.Figure6.21:GastricBypassSurgery

•  Anoptionforthemorbidlyobese.•  Weightlossaverages25%after10years,comparedto5%-10%withdietingand,mostoften,relapsewithinayear.

•  ReducesghrelinandincreasesPYYandGLP-1,reducinghunger.

•  Benefitsincludereducedmortalityandmanyhealthimprovements.

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Anorexia,Bulimia,&BingeEatingDisorderFigure6.24:FrenchModelIsabelleCaroinLateStagesofAnorexia

• Anorexianervosa:The“starvingdisease.”•  Restrictors-reducefoodintakeandexerciseexcessivelytomaintainweight

•  Hungerbattle:NPY,ghrelinhigh;leptinlow.• Bulimianervosa:

•  Bingeandpurgecycles,butusuallynormalweight•  Eatlargemeals,thenvomitingfoodbackup•  Highrelapserates

• Binge-EatingDisorder•  Eatlargemeals•  Usuallyhighweight

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Anorexia,Bulimia,&BingeEatingDisorderEnvironmentalandGeneticContributions

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•  Environmentalcontributions•  Culturalemphasisonthinness,asseenintheFijistudy.•  Theincidenceishigherinfemales,whoexperiencemorepressure.

•  Geneticinfluenceissuggestedby:•  Identicaltwins3xmoreconcordancethaninfraternaltwins•  Heritability:56%foranorexia,54-83%forBulimia,45%forbingeeatingdisorder

•  Adolescentstress,hormones,anddietingmayproduceepigeneticchangesingenes

•  Co-morbiditywithobsessive-compulsivedisorder(anorexia)anddepression(bulimia).

Anorexia,Bulimia,&BingeEatingDisorderRolesofSerotonin,Dopamine,andCannabinoids

•  Reducedserotoninactivity•  Bulimics•  SSRIantidepressantsincreaseserotonin,reducingbingeingandpurgingandlowersrelapserates

•  Imbalancedratioofserotoninreceptors•  Anorexicsandbulimicshaveimpairedexecutivecontroloveremotionalresponses

•  Lowactivityincannabinoid,dopaminerewardsystems•  Lackofenjoymentoffoodaswellasotherlifepleasures.•  Eatingincreasesdopaminelevels,andviewingpicturesoffoodstimulatescannabinoidreceptorsininsularcortexofanorexicsandbulimics

•  Eatingalsoincreasesfood-relatedanxiety.Therefore,foodrestriction,whilenotpleasurable,reducesanxiety.

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