Complex brain function: reward Flashcards
LO and Lecture outline
LO
- Describe the different components of reward: hedonic vs motivation
- Describe which structures of the brain are involved in the rewarding effects of food
- Describe the neural substrates that have been identified in the different components of reward
Lecture outline
- Introduction to pleasure, food reward and feeding behavior
- Eating disorders
- Key structures of the brain that co-ordinate feeding homeostatic circuits vs reward circuits
- Neural substrates of hedonic and motivational aspects of food reward
- Insight to eating disorders
Pleasure and behaviour
‘‘We recognize pleasure as the first good innate in us, and from pleasure we begin every act of choice and avoidance, and to pleasure we return again, using the feeling as the standard by which we judge every good.” – Epicurus
What does eating serve as an essential role in?
Survival and homeostasis
What can food intake be influenced by?
Food intake can be influenced by the pleasurable effects of food
What is the pleasure of eating food generate by?
The pleasure of eating food is generated by a ‘liking’ reaction in the brain
‘Liking’ circuits are also called what?
‘Hedonic’ circuits
Tell me about Hedonic feeding
Hedonic feeding is not driven by a metabolic need
Hedonic or ‘liking’ systems are a component of reward
What sort of things are included under the term eating disorders?
Eating disorders can include obesity, bulimia and anorexia
How has the number of severely obese and obese children changed over the last 10 years?
The number of severely obese and obese children has increased and almost doubled in the last ~10 years
What underpins the potential for therapeutics with feeding?
Neural mechanisms and circuitry that underpin the reward of feeding behaviour has potential for novel therapeutics
Brain systems controlling food intake and feeding
Homeostatic system
Tell me about the Orexigenic and Anorexigenic neurons
Orexigenic= appetite increase
Anorexigenic= appetite suppressing
Who identified reward centers existed in the brain of rodents and what did this approach become known as?
Olds and Milner (1954) identified reward centers existed in the brain of rodents
This approach became known as brain stimulation reward
Tell me how what was done during the development of the brain stimulation reward?
- Different positioning of the electrode allowed further mapping of the brain circuitry of reward
- The reward system is the neural network that receives and evaluates the rewarding properties of stimuli
- The network consists of multiple interacting neural circuits.
- Robust self-stimulation behaviour is obtained with electrodes along the medial forebrain bundle (MFB)
Self-stimulation is observed from electrodes located in several brain areas, including what?
- Nucleus Accumbens (NAcc)
- Lateral hypothalamus (LH)
- Ventral Tegmental Area (VTA)
- Cortical structures
Tell me some of the key structures of the reward circuit
What did Berridge et al 2020 identify?
Berridge et al 2020: Affective orofacial liking reactions can be quantified to provide a readout for how much the subject likes a substance; food
Information from animal studies gives us the opportunity to learn more about reward in humans via facial expressions for example
What are endogenous opioids and give some examples
Endogenous opioids are neuropeptides and include: enkephalins, dynorphins and endorphins
Tell me 3 opioid receptor subtypes
3 opioid receptor subtypes: mu, kappa and delta
What types of receptors are opioid receptors?
G-protein coupled receptors
What can opioid receptors be activated by?
Provide examples
Can be activated by Agonists which include morphine and heroin, Antagonist: Naloxone
What molecules are endogenous endocannabinoids and provide some examples?
Endogenous endocannabinoids are lipid molecules: anandamide and 2-arachidonoylglycerol (2-AG)
Name 2 cannabinoid receptor subtypes?
CB1 and CB2
What type of receptors are cannabinoid receptors?
GPCR
What is the CB1 subtype predominantly express in?
CB1 subtype is predominantly expressed in the central nervous system
Name an cannabinoid agonist?
Agonists include the drug THC (this is a component of marijuana)
Tell me the effect of Morphine and Naloxone?
Morphine enhances ‘liking’ responses of rats for palatable foods
Naloxone decreases food intake in rats, especially when sucrose is used
Injection of opioid receptor agonist (DAMGO) and measuring of facial ‘liking’ reaction identified what?
- Role for mu opioid receptors
- Precise map of the nucleus accumbens
- Hedonic hotspot (10% of Nacc)
- A larger region for food intake (‘wanting’)
Hedonic hotspots of the brain
Hedonic hotspots are functionally connected
What is the active ingredient of cannabis?
What effect does it have?
Anecdotal evidence: the active ingredient of cannabis, 9-tetrahydrocannabinol increases food intake, particularly sugary foods.
What does targeted injection of anandamide into the NAcc increase?
Targeted injection of anandamide into the NAcc increases facial liking expressions to sucrose
There is an endocannabinoid hotspot in the NAcc that overlaps with what?
The opioid hotspot
What has CB1 been co-localising with and what do they function to do?
CB1 receptors and mu receptors have been identified as co-localizing in neurones of the nucleus accumbens
Function together to co-ordinate the release of neurotransmitters
What are the neural substrates of the ‘wanting’ aspects of reward?
Dopamine established as a key neurotransmitter in reward: Olds and Milner
Hypothesis: dopamine signals reward ‘pleasure’
Hypothesis: dopamine signals reward ‘pleasure’
This hypothesis was tested 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 feeding did make rats aphagic
New hypothesis: Dopamine is required for ‘wanting’ motivational aspects of food reward
Summary
- Dopaminergic pathways generate ‘wanting’ (incentive salience)
- The ‘wanting’ circuit is larger than the hedonic hotspot network
- ‘This network can generate intense incentive motivation without enhancing hedonic ‘liking’
- The ‘Liking’ circuits are composed of interconnected ‘hotspots’ (white in diagram)
- Signalling in one ‘hotspot’ can recruit other ‘hotspots’ to enhance ‘liking’ reactions.
- Disruption to one ‘hotspot’ can disrupt the recruitment of other ‘hotspots’
