Transcript Ch 16 - Motivation - Biology Courses Server

Neuroscience: Exploring the
Brain, 3e
Chapter 16: Motivation (Hypothalamic control of
eating, drinking and temperature)
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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
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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
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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
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The Long-term Regulation of Feeding
Behavior
• Energy Balance
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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
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Hormonal and Hypothalamic Regulation
of Body Fat and Feeding
• The Hypothalamus and
Feeding
– Anorexia: lateral
hypothalamic syndrome
– Obesity: ventromedial
hypothalamic syndrome
– Both related to leptin
signaling
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Hormonal and Hypothalamic Regulation
of Body Fat and Feeding
• The Hypothalamus and Feeding
– Hypothalamic nuclei important for the control of
feeding
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Hormonal and Hypothalamic Regulation
of 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
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Hormonal and Hypothalamic Regulation
of Body Fat and Feeding
• Response to Elevated Leptin Levels
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Hormonal and Hypothalamic Regulation
of 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
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Hormonal and Hypothalamic Regulation
of Body Fat and Feeding
• Response to Decreased Leptin Levels
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Hormonal and Hypothalamic Regulation
of Body Fat and Feeding
• The Control of Feeding by Lateral Hypothalamic Peptides
– LH neurons stimulating feeding behavior contain:
• Melanin-concentrating hormone (MCH)
• Orexin
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Hormonal and Hypothalamic Regulation
of Body Fat and Feeding
• Summary: Anorectic and Orexigenic Peptides of the
Hypothalamus
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The Short-Term Regulation of Feeding
Behavior
• Model for short-term regulation of feeding
– 3 phases: Cephalic; Gastric; Substrate
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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
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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
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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
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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 selfstimulation
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Why Do We Eat?
• Mesocorticolimbic dopamine system
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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
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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
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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”)
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Other Motivated Behaviors
• Drinking: Pathways triggering volumetric thirst
– Hypovolemia: Decrease in blood volume
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Other Motivated Behaviors
• Drinking: Pathway triggering osmotic thirst
– Hypertonicity: Increased concentration of dissolved
substances in blood (salt)
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Other Motivated Behaviors
• Drinking: Vasopressin - Antidiuretic hormone or ADH
• Acts on kidneys to increase water retention
• Inhibit urine production
• Diabetes insipidus - loss of vasopressin
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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
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Other Motivated Behaviors
• Temperature Regulation (Cont’d)
– Process during a fall in temperature:
TSH released by
anterior pituitary
TSH stimulates
release of thyroxin
from thyroid gland
Increase in cellular
metabolism
– Visceromotor response: Goosebumps
– Involuntary somatic motor response
• Shivering, seeking warmth
– Rise in temperature: Metabolism slowed by reducing
TSH release
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Other Motivated Behaviors
• Temperature Regulation (Cont’d)
– Hypothalmic responses to stimuli that motivate
behavior
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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
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End of Presentation
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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
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