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Lecture 13

Lecture 13 - Mar 8.doc

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PSYC 342
Jens C Pruessner

PSYC 342 Lecture 13 - Mar. 8 Eating & Eating Disorders: • Hedonic foods, such as chicken wings and cupcakes, that are high in fat and sugar, act on the reward pathway of the brain and increase their incentive salience Hedonic Feeding: • The maintenance of a steady state of an organism by physiological or behavioural feedback control mechanisms • Feeding behaviour is fundamentally governed by homeostasis, due to the body’s need to maintain an optimal energy “set point” • Evolutionarily speaking, humans were often in a state of starvation, so it was adaptive to prefer high sugar and fat foods. However, in recent years, this adaptation with the dramatic increase in food supply has led to higher incidences of obesity • Orexigenic peptides: increase motivation to eat • E.g., ghrenlin, NPY, AgRP, MCH, Orexin A, Orexin B, Gallatin • Anorexigenic peptides: decrease motivation to eat • E.g., leptin, insulin, alpha-MSH, CRH, TRH, CART, POMC, GL-PI Ghrelin: • A peptide hormone produced by the stomach cells; it is thought to increase feelings of hunger • Also an Orexigenic hormone (stimulating appetite) • May have evolved as a response to the feast or famine conditions of early humans • In recent years, however, this in direct conflict with the dangerous phenomenon of overeating in the developed world Overview: • Secreted from the stomach into the bloodstream, it travels to receptors in the brain to stimulate food intake • Also produced in the hypothalamic arcuate nucleus, it stimulates the secretion of growth hormone from the anterior pituitary gland • Also activates the mesolimbic cholinergic-dopaminergic reward link, a circuit that communicates the hedonic and reinforcing aspects of natural rewards, such as food • Systematic injections of ghrelin stimulate food intake and increase body mass in rats • Increased hyperphagia, weight gain and adiposity occur after continuous systematic ghrelin administration at much lower doses than previously thought • Findings point to a physiological role for circulation of ghrelin in the regulation of food intake • Blood concentrations of ghrelin levels increase nearly twofold immediately before each meal and fall within one hour after eating • Ghrelin levels showed a diurnal rhythm that is exactly in phase with that of leptin - ris- ing and falling at the same times during the day • This rise and fall supports the hypothesis that ghrenlin plays an important role in mean initiation in humans Prader Willi Syndrome: • Genetic disorder with mild growth retardation • Hyperphagia and obesity common • Fasting plasma ghrelin levels elevated Leptin: • Leptos: “thin” • Adipokine Hormone • Produced in fat (adipose) tissue • Levels are higher in larger people, and after meals, and lower in thinner people and during fasting periods Actions of Leptin: • Active transport mechanism brings leptin across BBB • Binds to receptors in hypothalamus to inhibit eating and send satiety signals • Leptin levels are proportional to body fat • High while fat is being stored • Fall rapidly when fat begins to be metabolized • High levels of lepton cause long-term satiety Rodent Studies: Mutations in mice in genes coding for leptin (“ob”) or leptin receptors “db” • • Leptin treatment of ob/ob mice caused significant weight loss • Mutation of both leptin and leptin receptor genes have been found in humans, though very rare • The ob(lep) gene is found on chromosome 7 • Can be treated with daily leptin injections Farooqi et al, 2005: • As Leptin cannot cross the blood brain barrier by itself, obesity may be a result of a malfunction of an active transfer mecha- nism • Obese people exhibit heightened levels of blood leptin, which does not appear to be absorbed into the CNS Aging may also contribute to leptin resistance • • Study by Dalton et al in 2003 showed that when rats are chronically stressed (and maybe people), they crave high-fat foods in an attempt to reduce anxiety...this may explain some parts of the epidemic of obesity occurring in Western culture • Dalton’s suggests that glucocorticoids work differently in the long term than in the short term → chronic release of glucocorti- coids and CRH drive stressed individuals to seek out pleasurable foods which leads to weight gain Summary: • Both hedonic feeding and homeostasis are important for the regulation of human food intake via anorexigenic and orexigenic factors • Ghrelin is an orexigenic hormone produced by the stomach and arcuate nucleus • Leptin is an anorexigenic hormone produced by fat cells; dysregulation can lead to obesity; obese individuals may have lep- tin resistance • Insulin is an anorexigenic hormone produced by the pancreas that regulates long-term patterns of food intake • Evidently, feeding is a complex process regulated by many hormones. Researchers are still in the process of finding out how we can use them to tackle issues such as obesity Eating Disorders: Anorexia & Bulimia • What is Anorexia Nervosa? • What is Bulimia Nervosa? • Gender ratios • Hormonal factors affecting gender ratios • Environmental factors affecting gender ratios Anorexia Nervosa: DSM IV Criteria • Refusal to maintain body weight at or above a minimally normal weight for age and height • Intense fear of gaining weight or becoming fat, even though underweight • Disturbance in the way in which one’s body weight or shape is experienced, undue influence of body weight or shape on self-evaluation, or denial of the seriousness of the current low body weight • In postmenarcheal females, amenorrhea, i.e., the absence of at least three consecutive menstrual cycles Anorexia Nervosa: The Facts • Symptoms associated with AN seem to have existed as far back as the 1600s • Individuals with AN tend to be highly perfectionist • Only psychiatric disorder in the DSM-IV that requires an endocrine dysfunction as criteria for diagnosis (menstrual abnormal- ities) • 10% diagnosed die Alterations Observed in Anorexia Nervosa: • Hypogonadism • Amenorrhea • Oligomenorrhea (irregular menstrual cycles) • Delayed puberty • Hypercortisolism (elevated cortisol) • Increased CRH in the CNS • Increased Basal/Pulsatile GnRH secretion • Increased Osteoporosis • Lower circulating leptin levels • Decreased Insulin secretion • Increased vasopressin in the CNS • Altered Melatonin levels Bulimia Nervosa: DSM IV Criteria • Recurrent episodes of binge eating characterized by both: • Eating in a discrete period of time (e.g., within any 2-hour period), an
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