copyright © 2007 wolters kluwer health | lippincott williams & wilkins neuroscience: exploring...

Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Neuroscience: Exploring the Brain, 3e

Chapter 16: Motivation (Hypothalamic control of eating, drinking and temperature)


The Hypothalamus, Homeostasis, And Motivated Behavior 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


The Hypothalamus, Homeostasis, And Motivated Behavior (Cont’d)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


The Long-term Regulation of Feeding BehaviorThe Long-term Regulation of Feeding Behavior• Energy Balance

– Prandial state - Anabolism: Energy storage as glycogen and triglycerides

– Postabsorptive state - Catabolism: Breaking down complex macromolecules


The Long-term Regulation of Feeding BehaviorThe Long-term Regulation of Feeding Behavior

• Energy Balance


Hormonal and Hypothalamic Regulation of Body Fat and FeedingHormonal 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


Hormonal and Hypothalamic Regulationof Body Fat and FeedingHormonal and Hypothalamic Regulationof Body Fat and Feeding• The Hypothalamus and

Feeding

– Anorexia: lateral hypothalamic syndrome

– Obesity: ventromedial hypothalamic syndrome

– Both related to leptin signaling


Hormonal and Hypothalamic Regulationof Body Fat and FeedingHormonal and Hypothalamic Regulationof Body Fat and Feeding• The Hypothalamus and Feeding

– Hypothalamic nuclei important for the control of feeding


Hormonal and Hypothalamic Regulationof Body Fat and FeedingHormonal 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


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


Hormonal and Hypothalamic Regulationof Body Fat and FeedingHormonal 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


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


Hormonal and Hypothalamic Regulationof Body Fat and FeedingHormonal 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


Hormonal and Hypothalamic Regulationof Body Fat and FeedingHormonal and Hypothalamic Regulationof Body Fat and Feeding• Summary: Anorectic and Orexigenic Peptides of the

Hypothalamus


The Short-Term Regulation of Feeding BehaviorThe Short-Term Regulation of Feeding Behavior• Model for short-term regulation of feeding

– 3 phases: Cephalic; Gastric; Substrate


The Short-Term Regulation of Feeding BehaviorThe 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


The Short-Term Regulation of Feeding BehaviorThe 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


The Short-Term Regulation of Feeding BehaviorThe 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


Why Do We Eat?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



• Mesocorticolimbic dopamine system


Why Do We Eat?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



• 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



• 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”)


Other Motivated BehaviorsOther Motivated Behaviors• Drinking: Pathways triggering volumetric thirst

– Hypovolemia: Decrease in blood volume


Other Motivated BehaviorsOther Motivated Behaviors

• Drinking: Pathway triggering osmotic thirst

– Hypertonicity: Increased concentration of dissolved substances in blood (salt)



• Drinking: Vasopressin - Antidiuretic hormone or ADH

• Acts on kidneys to increase water retention

• Inhibit urine production

• Diabetes insipidus - loss of vasopressin



• 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


Other Motivated BehaviorsOther 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

TSH released by anterior pituitary

TSH stimulates release of thyroxin from thyroid gland

Increase in cellular metabolism



• Temperature Regulation (Cont’d)

– Hypothalmic responses to stimuli that motivate behavior


Concluding RemarksConcluding 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


End of Presentation


IntroductionIntroduction

• 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

copyright © 2007 wolters kluwer health | lippincott williams & wilkins neuroscience: exploring...

Documents

control of feeding slide

body fat reserves

body surface

visceromotor response

starvation slide

temperature slide

warmth homeostasis slide

cold body shivers