Pleasure, feeding & reward

Question 1

what is the liking circuit in the brain?

Answer 1

hedonic circuit - circuits composed of interconnected hedonic hotspots

Question 2

hedonic feeding is driven by what

Answer 2

the pleasure of consuming the food

Question 3

what are the three components of feeding and reward

Answer 3

‘liking’ (hedonic: pleasure)
‘wanting’ (motivation) - via sensory cues
Learning (association and predictions)

Question 4

what is incentive salience

Answer 4

motivation for rewards that is driven by both physiological state and previously learned associations about a reward cue

Question 5

give three examples of eating disorders

Answer 5

obesity, bulimia and anorexia

Question 6

ablation of orexigenic neurons in adult rodents causes what

Answer 6

causes cessation of eating and death

Question 7

where do the inputs to the hypothalamus come from after feeding

Answer 7

brainstem, pancreas, intestine, liver

Question 8

what are the two outputs of the hypothalamus that regulate appetite

Answer 8

orexigenic (increases appetite) & anorexigenic (decrease appetite)

Question 9

how did Olds and Milner identify the rewards center in the rodent brain stimulation reward in 1954

Answer 9

Implanted electrode into brain, to deliver electrical stim. The rodent was able to use a lever to start the stimulation. Putting the electrode on different parts, some places it caused the lever to be pressed over 200 times - the work led to the idea that there is a reward system in the brain

Question 10

robust self stimulation behaviour is obtained with electrodes along the______________

Answer 10

medial forebrain bundle MFB

Question 11

other than the MFB what other brain areas result in self stimulation when electrodes are placed on there

Answer 11

• Nucleus Accumbens (NAcc)
• Lateral hypothalamus (LH)
• Ventral Tegmental Area (VTA)
• Cortical structures (prefrontal cortex, orbitofrontal cortex, insular cortex?)

Question 12

what are the key structures of the reward circuit

Answer 12

• Medial forebrain bundle
• Reward circuit includes axons that project from the VTA (ventral tegmental area) to the nucleus accumbens (Mesolimbic Dopamine Pathway)
• VTA connects to the amygdala, septum and regions of the cortex
• Hypothalamus receives inputs from structures within the reward circuitry

Question 13

how can you measure liking reactions?

Answer 13

behavioral analysis of ‘liking’ reactions - positive facial liking: relaxed facial expression and rhythmic tongue protrusions

Question 14

what aversive reactions indicate dislike

Answer 14

facial disliking expression: gapes, turning away and head shakes

Question 15

what neurochemicals are involved in hedonic circuits

Answer 15

Opiods and endocannabinoids

Question 16

give three endogenous opiods

Answer 16

enkephalins, dynorphins and endorphins

Question 17

what are the three opioid receptor subtypes and what kind of receptor are they

Answer 17

mu, kappa and delta (are GPCRs)

Question 18

give an example of an agonist and antagonist of opioid receptors

Answer 18

Agonists morphine

Antagonist Naloxone

Question 19

endogenous opiods are _____

Answer 19

neuropeptides

Question 20

endogenous endocannabinoids are ______

Answer 20

lipid molecules

Question 21

give two types of endocannabinoid

Answer 21

anandamide and 2-arachidonoylglycerol (2-AG)

Question 22

what are the two cannabinoid receptor subtypes - what kind of receptor are they

Answer 22

CB1 and CB2 - GPCR receptors

Question 23

injection of what discovered the different functional regions of the nucleus accumbous

Answer 23

an opioid receptor agonist DAMGO (specific for mu subtype

Question 24

what opiod wanting and liking zones are in the NAcc

Question 25

what opioid wanting and liking zones are in the NAcc

Answer 25

hedonic hotspot (liking increase), hedonic coldspot (liking decrease), wanting hotspot (eating increase) and disliking decrease

Question 26

where are the hedonic hotspots in the brain

Answer 26

orbitofrontal cortex, insular cortex, nucleus accumbens, ventral pallidum, parabrachial nucleus

Question 27

what is c-Fos

Answer 27

is a protein that is expressed when neurons are activated, and so increased expression of this protein provides a readout for when neurons are being activated by the drug that is being injected

Question 28

how was the functional connectivity between hedonic regions of the brain mapped

Answer 28

• One region of the animal’s brain is injected with the DAMGO and then the brain is removed and immunohistochemical staining was used to quantify the expression of a protein called c-Fos in regions of the brain outside of the injection site.

Question 29

how do you induce suppression of the liking responses

Answer 29

Inject noloxane into tissue blocking opioid signaling in one hotspot while simultaneously stimulating another hotspot causes the suppression of enhanced liking responses

Question 30

what region is essential for the liking of pattern of behavior (if removed you completely lose the liking reaction)

Answer 30

ventral pallidium

Question 31

where does the endocannabinoid hotspot overlap with the opioid hotspot

Answer 31

the CB1 and mu receptors have been identified co-localising in neurones of the Nacc to function in the release of neurotransmitters

Question 32

how did experimentation determine that dopamine is responsible for the wanting motivational aspects of food reward

Answer 32

using the facial expression paradigm combined with neurochemical lesions in the brain to reduce dopamine signaling
•depletion of dopamine did not affect orofacial expression of liking in response to sweetness
•BUT: reducing dopamine caused the rats to no longer seek out or consume food

Question 33

what is the mesolimbic pathway

Answer 33

aka the reward pathway, is a dopaminergic pathway in the brain. The pathway connects the ventral tegmental area in the midbrain to the ventral striatum of the basal ganglia in the forebrain.

Question 34

what is the ventral striatum

Answer 34

a subcortical brain region innervated with dopaminergic neurons and involved in tracking the subjective value of stimuli, signaling the presence of/expectation of reward, and encoding errors and outcomes of such predictions
include the nucleus accumbens and the olfactory tubercle.

Question 35

what key structure facilitates crosstalk between the reward and homeostatic systems of the brain (what does it coordinate)

Answer 35

the lateral hypothalamic area (orexin neurons) - coordinating appetite and motivation