Motivation (neuro)

Question 1

What is motivation?

Answer 1

• driving force
• physical need
• wanting, liking

Question 2

Hypothalamus

Answer 2

• Maintain homeostasis by regulating three interrelated functions:
  • endocrine secretion
  • autonomic nervous system
  • emotions and drive/behaviour (motivated behaviour, e.g. drinking, eating)

Question 3

Long term regulation of feeding

behaviour and body fat

Answer 3

energy balance and body fat:

• normal energy balance leads to normal adiposity
• prolonged positive energy balance leads to obesity
• prolonged negative energy balance leads to starvation

Question 4

Long term regulation of body weight

Answer 4

• maintenance of body weight around a set value
• body weight is normally stable
• if an animal is force fed, it will gain weight
• the weight is lost, however, as soon as the animal can regulate its own food intake
• weight lost during a period of starvation is rapidly gained when food is freely available

Question 5

Effects of Parabiosis on body weight in ob/ob mice

Answer 5

• Parabiosis: sharing of blood circulation between animals.
• Blood borne signals are shared and can affect the hypothalamus.
• Example 1:
  • A genetically obese mouse ob/ob: its fat cells do not produce leptin. (Leptin inhibits food intake)
  • Connected to a normal mouse (which produces leptin) will lead to a reduction of obesity in the ob/ob mouse

Question 6

Venteromedial hypothalamus (VH) and Lateral hyopthalamus (LH)

Answer 6

• Lateral hypothalamic syndrome: diminished
  appetite for food; anorexia
• Venteromedial hypothalamic syndrome: overeating
  and obesity
• Both related to leptin signalling

Question 7

Feedback

Answer 7

• arcuate nucleus
• leptin travels to the brain to tell you to stop eating
• fatty tissues produce leptin when ‘satisfied’

Question 8

Arcuate nucleus

Answer 8

• important for control of feeding (effect of leptin on arcuate nucleus)
• three important nuclei that control feeding:
  • arcuate nucleus
  • paraventricular nucleus
  • lateral hypothalamic area

Question 9

Anorexic response

Answer 9

• the response to elevated leptin levels
• a rise in leptin levels in the blood is detected by neurons in the arcuate nucleus that contains the peptides alphaMSH and CART
• these neurons project axons to the lower brain stem and spinal cord, the paraventricular nuclei of the hypothalamus, and the lateral hypothalamic area
• each of these connections contributes to the coordinated humoral, visceromotor and somatic motor responses to increased leptin levels
• injection of CART/alphaMSH mimics high concentration of leptin

Question 10

Response to elevated leptin levels

Answer 10

• Activation of arcuate neurons that
  release αMSH and CART peptides
  • Anorectic peptides—diminish appetite
• Project to regions that orchestrate coordinated response of humoral, visceromotor, and somatic responses
  • Paraventricular nucleus (humoral response)
  • Intermediolateral gray matter of spinal cord
  (visceromotor response)
  • Lateral hypothalamus (somatic response)

Question 11

Orexigenic

Answer 11

• the response to decreased leptin levels
• a reduction in blood levels of leptin is detected by neurons in the paraventricular nuclei that control the release of TSH and ACTH from the pituitary
• they also activate the neurons in the lateral hypothalamic that stimulate feeding behaviour
• some of the activated lateral hypothalamic neurons contain the peptide MCH (melanin-concentrating hormone)
• injection of NPY/AgRP mimics low concentration of leptin

Question 12

Competition for activation of the MC4 receptor

Answer 12

• competition for activation of the MC4 receptor
• one way that alphaMSH, an anorectic peptide, and AgRP, an orexigenic peptide, exert opposite effects on metabolism and feeding behaviour is via an interaction with the MC4 receptor on some hypothalamic neurons
• while alphaMSH stimulates the MC4 receptor, AgRP inhibits it

Question 13

Control of feeding by lateral hypothalamic peptides

Answer 13

• LH neurons stimulating feeding behavior
  contain:
  – Melanin-concentrating hormone (MCH)
  • Widespread connections in the brain
  • Prolongs consumption
  – Orexin
  • Also with widespread cortical connections
  • Promotes meal initiation

Question 14

Hypothalamus and the control of

bodyweight and food intake

Answer 14

• Motivated behaviour
• Accurately regulated by leptin produced by adipose tissue and hypothalamic peptides
• Hypothalamus plays an important role in regulating feeding behaviour (long term)
• Disruption of this regulation leads to
  • Hyperphagia
  • Anorexia
  • Bulimia nervosa

Question 15

Short term regulation of feeding

Answer 15

• Motivation to eat also depends on:
  • How long it has been since last meal
  • How much one has already eaten
  • What type of food has already been eaten

Question 16

Satiety

Answer 16

• Satiety is the feeling of fullness and the suppression of hunger for a period of time after a meal
• Feelings of satiety can influence how soon
  and how much you next eat
• The feeling of satiety occurs due to a number of bodily signals that begin when a food or drink is consumed and continue as it enters the gut and is digested and
  absorbed

Question 17

Model for short-term regulation of feeding

Answer 17

• a hypothetical model for the short term regulation of feeding behaviour
• graph shows a possible means of regulating food consumption by satiety signals
• satiety signals rise in response to feeding
• when satiety signals are high, food consumption is inhibited
• when satiety signals fall to zero, inhibition is eliminated, and food consumption ensues

Question 18

Cephalic phase

Answer 18

• Cephalic: hunger
  • Ghrelin released when stomach is empty
  • Activates NPY/AgRP-containing neurons in arcuate nucleus
  • Removal of ghrelin-secreting cells of stomach thought to cause loss of appetite

Question 19

Satiety signals which ends meal

Answer 19

• Gastric distension signals brain via vagus nerve.
• Works synergistically with CCK released in intestines in response to certain foods
• Insulin also released by β cells of the pancreas -
  induces satiety by acting on arcuate nucleus of the
  hypothalamus

Question 20

Why do we eat?

Answer 20

• we like food - hedonic aspect
• we want food - drive reduction
• Liking and wanting mediated in part by separate brain circuits
• Dopaminergic system involved in wanting/ craving (or liking?)

Question 21

Reinforcement and reward

Answer 21

• Positive reinforcement (anything added that follows a behavior that makes it more likely that the behavior will occur again in the future)
• Negative reinforcement (a response or behavior is strengthened by stopping, removing or avoiding a negative outcome or aversive stimulus)

Question 22

Microdialysis

Answer 22

• Measuring neurotransmitter release in vivo

- Association with behaviour parameter

Question 23

Dopamine and reinforcement

Answer 23

• Dopamine release in the nucleus accumbens is correlated with motivation but not liking (hedonic)
• Its also release in anticipation of reward
• Note that dopamine also involved in movement

Question 24

Seratonin, food and mood

Answer 24

• Mood and food are connected
• 5HT in hypothalamus
  • Rises in anticipation of food
  • Spike during a meal (carbohydrates in particular)
  • Association anorexia nervosa, bulimia with
  depression (low serotonin)