Neuroscience: Exploring the Brain, 3e

1. Neuroscience: Exploring the Brain, 3e Chapter 16: Motivation (Hypothalamic control of eating, drinking and temperature)

2. The Hypothalamus, Homeostasis, And Motivated Behavior • Homeostasis • Maintains the internal environment within a narrow physiological range • Role of Hypothalamus • Regulates homeostasis • Three components of neuronal response • Humoral response: Stim hormone release • Visceromotor response: Control autonomic N.S • Somatic motor response: Elicit regulatory behaviors

3. The Hypothalamus, Homeostasis, And Motivated Behavior (Cont’d) • Example of motivated behaviors • Response when body is cold • Body shivers, blood shunted away from the body surface, urine production inhibited, body fat reserves - mobilized • Lateral hypothalamus • Initiates motivation to actively seek or generate warmth - Homeostasis

4. The Long-term Regulation of Feeding Behavior • Energy Balance • Prandial state - Anabolism: Energy storage as glycogen and triglycerides • Postabsorptive state - Catabolism: Breaking down complex macromolecules

5. The Long-term Regulation of Feeding Behavior • Energy Balance

6. Hormonal and Hypothalamic Regulation of Body Fat and Feeding • Body Fat and Food Consumption • Lipostatic hypothesis • Parabiosis: e.g., Siamese twins • Leptin • Regulates body mass • Decreases appetite • Increases energy expenditure • Leptin depletion • Incites adaptive responses to fight starvation

7. Hormonal and Hypothalamic Regulationof Body Fat and Feeding • The Hypothalamus and Feeding • Anorexia: lateral hypothalamic syndrome • Obesity: ventromedial hypothalamic syndrome • Both related to leptin signaling

8. Hormonal and Hypothalamic Regulationof Body Fat and Feeding • The Hypothalamus and Feeding • Hypothalamic nuclei important for the control of feeding

9. Hormonal and Hypothalamic Regulationof Body Fat and Feeding • Response to Elevated Leptin Levels • Activation of arcuate neurons that release αMSH and CART peptides • Anorectic peptides- diminish appetite • Activation of arcuate neurons that release αMSH and CART peptides (Cont’d) • Project to regions that orchestrate coordinated response of humoral, visceromotor, and somatic responses • Paraventricular nucleus (humoral response) • Intermediolateral gray matter of spinal cord • Lateral hypothalamus

10. Hormonal and Hypothalamic Regulationof Body Fat and Feeding • Response to Elevated Leptin Levels

11. Hormonal and Hypothalamic Regulationof Body Fat and Feeding • Response to Decreased Leptin Levels • Activation of arcuate neurons that release NPY and AgRP (Leptin inhibits these cells) • Effects on energy balance: Opposite to the effects of αMSH and CART • Orexigenic peptides– increase appetite • NPY and AgRP inhibit secretion of TSH and ACTH • Activate parasympathetic division of ANS • Stimulate feeding behavior

12. Hormonal and Hypothalamic Regulationof Body Fat and Feeding • Response to Decreased Leptin Levels

13. Hormonal and Hypothalamic Regulationof Body Fat and Feeding • The Control of Feeding by Lateral Hypothalamic Peptides • LH neurons stimulating feeding behavior contain: • Melanin-concentrating hormone (MCH) • Orexin

14. Hormonal and Hypothalamic Regulationof Body Fat and Feeding • Summary: Anorectic and Orexigenic Peptides of the Hypothalamus

15. The Short-Term Regulation of Feeding Behavior • Model for short-term regulation of feeding • 3 phases: Cephalic; Gastric; Substrate

16. The Short-Term Regulation of Feeding Behavior • Model for short-term regulation of feeding • Cephalic: Hunger • Ghrelin released when stomach is empty • Activates NPY- and AgRP-containing neurons in arcuate nucleus

17. The Short-Term Regulation of Feeding Behavior • Model for short-term regulation of feeding • Gastric: Feeling full • Gastric distension signals brain via vagus • Works synergistically with CCK released in intestines in response to certain foods • Insulin also released by B cells of the pancreas - important in anabolism

18. The Short-Term Regulation of Feeding Behavior • Model for short-term regulation of feeding • Changes in blood insulin levels before, during, and after a meal • Highest during “substrate” phase

19. Why Do We Eat? • Reinforcement and Reward • Liking: Hedonic • Wanting: Drive reduction • Electrical self-stimulation: Experiments to identify sites of reinforcement • Effective sites for self-stimulation: • Trajectory of dopaminergic axons in the ventral tegmental area projecting to the forebrain • Drugs that block dopamine receptors: Reduce self-stimulation

20. Why Do We Eat? • Mesocorticolimbic dopamine system

21. Why Do We Eat? • The Role of Dopamine in Motivation • Old belief: Dopamine projection served hedonic reward • New understanding • Dopamine-depleted animals “like” food but “do not want” food • Lack motivation to seek food, but enjoy it when available • Stimulation of the dopamine axons • Craving for food without increasing the hedonic impact

22. Why Do We Eat? • Changes in hypothalamic serotonin levels • Low:Postabsorptive period • Rise: In anticipation of food • Spike: During meals • Mood elevation - Rise in blood tryptophan and brain serotonin

23. Why Do We Eat? • The Role of Dopamine in Motivation • Serotonin, Food, and Mood (Cont’d) • Drugs that elevate serotonin levels • Example: Dexfenfluramine (Redux)- reduce appetite • Disorders: Anorexia nervosa; Bulimia nervosa both often accompanied by depression • Treatment • Antidepressant drugs—elevate brain serotonin levels • Example: Fluoxetine (“Prozac”)

24. Other Motivated Behaviors • Drinking: Pathways triggering volumetric thirst • Hypovolemia: Decrease in blood volume

25. Other Motivated Behaviors • Drinking: Pathway triggering osmotic thirst • Hypertonicity: Increased concentration of dissolved substances in blood (salt)

26. Other Motivated Behaviors • Drinking: Vasopressin - Antidiuretic hormone or ADH • Acts on kidneys to increase water retention • Inhibit urine production • Diabetes insipidus - loss of vasopressin

27. Other Motivated Behaviors • Temperature Regulation • Cells fine-tuned for constant temperature—37°C (98.6ºF) • Neurons for temperature homeostasis • Clustered in anterior hypothalamus • Humoral and visceromotor responses • Neurons in the medial preoptic area of the hypothalamus • Somatic motor (behavioral) responses • Neurons of lateral hypothalamic area

28. TSH stimulates release of thyroxin from thyroid gland TSH released by anterior pituitary Increase in cellular metabolism Other Motivated Behaviors • Temperature Regulation (Cont’d) • Process during a fall in temperature: • Visceromotor response: Goosebumps • Involuntary somatic motor response • Shivering, seeking warmth • Rise in temperature: Metabolism slowed by reducing TSH release

29. Other Motivated Behaviors • Temperature Regulation (Cont’d) • Hypothalmic responses to stimuli that motivate behavior

30. Concluding Remarks • Overview of motor systems • Addressed “how” questions of behavior • e.g., How is movement initiated? • Overview of motivation systems • Addresses “why” questions of behavior • e.g., mechanisms of motivation to drink when dehydrated? • The important discovery of a neural basis for feeding behavior • Allows us to frame new questions that will impact how we view our own behaviors

31. End of Presentation

32. Introduction • Types of behavior • Unconscious reflexes and Voluntary Movements • Motivation • Driving force on behavior • Analogy– ionic driving force dependent upon many factors • Probability and direction of behavior • Vary with the driving force needed to perform the behavior