Lecture 30 - Behavioural and Developmental Aspects of Dependence Flashcards

1
Q

Describe dopaminergic projections in the reward pathways in the brain

What is the normal role of this system?

A
  1. VTA (ventral tegmental area)
  2. Nucleus accumbens
  3. PFC (prefrontal cortex)

Normal role:

  • Dopamine is released in response to the normal reward stimuli
    • Eating, drinking, sleeping, sex etc.
  • This reward reinforces these behaviours, ensuring the survival of the species.
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2
Q

Describe the release and interaction with receptors of dopamine

A
  1. Dopamine released by dopaminergic neurons
  2. Dopamine acts on dopamine receptors on the post-synaptic neuron in the nucleus accumbens
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3
Q

What is the pharmacological action of cocaine?

What is the general action of cocaine?

A
  • General action:
    • Hijacks the natural reward system in the brain
    • The brain thinks that the drug taking is a very important behaviour for survival, and so this behaviour is heavily reinforced
  • Pharmacological action:
    • Cocaine binds and blocks dopamine transporter protein
    • Dopamine not recycled back into pre-synaptic neurons
    • Increased action of dopamine on its receptors, as it is in the synaptic cleft for longer
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4
Q

Compare the action of the following drugs on the reward pathways in the brain:

  • Heroin
  • Alcohol
  • Cannabis
  • Cocaine
A

Heroin:

  • Converts to morphine in the body
  • Acts on endogenous opioid receptors on GABA interneurons, inhibiting them
  • VTA neurons become disinhibited by GABA interneurons
  • Activates descending pathways of analgesia

Cannabis:

  • CB binds CB R on GABA interneurons
    • ​GABA interneurons usually inhibit the dopaminergic neurons in the VTA
  • Disinhibition of the dopaminergic neurons in the VTA
  • Projection of the neurons to the nucleus accumbens

Alcohol:

Cocaine:

  • Blocks re-uptake of dopamine in the nucleus accumbens
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5
Q

Give the DSM IV definitino of substance dependence

A

“Maladaptive pattern of use, leading to clinically significant impairment or distress, manifested by at least 3 of the following in a 12 month period:

  • Tolerance
  • Withdrawal
  • Substance taken in greater doses / longer than intended
  • *Persistent desire *
  • Unsuccessful efforts to decrease or control substance use
  • etc.”
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6
Q

Characterise patterns of heroin relapse

A

Physiological dependence is much easier to deal with than psychological dependence.

Relapse rates are significant, even after successful detoxification

  • 42% use within days of leaving detox
  • 66% readdicted 6 mths later
  • After 7 years:
    • 48% still using
    • 12% dead
    • 5% in prison
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7
Q

What factors need to be taken into account in understanding addiction?

A
  • Intense cravings
  • Loss over control of use
  • Compulsive patterns of behaviour
  • High rates of relapse
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8
Q

Compare the effect of various drugs on the dopaminergic systems in brains of drug users, and non-drug users

A

Drug users:

  • Decreased effect of reward stimuli
  • Measured with MRI imaging of dopaminergic system
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9
Q

What features are similar across all drugs of abuse?

What differs?

A
  • All drugs of abuse increase dopamine in the reward systems
  • However, they perform this action in different ways
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10
Q

Why do people take drugs?

Why do people continue to take drugs?

A
  • To feel good
    • ​Drugs release neurotransmitters in the pleasure centres
    • This does not explain why people continue to take drugs:
      • ​In the long term, the drugs do not have the same effect
      • In addition, there are many adverse outcomes associated with taking the drug
  • Continuing use:
    • ​*
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11
Q

Compare physiological and psychological dependence

A
  • Physiological:
    • Experience
      • ​Tolerance
      • Withdrawal
    • This can happen to anyone that takes the drug for long enough
    • The individual does not feel a drive to continue taking the drug
  • Psychological:
    • ​Individual actively seeks out the drug
    • Drug taken in larger doses
    • Continue the behaviour, despite the knowledge of the negative effects
    • etc.
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12
Q

Define tolerance

A
  • Increasing doses required to elicit the same response
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13
Q

Define withdrawal

A
  • When drug is taken away, strong unpleasant feelings
  • The symptoms of withdrawal are the opposite of the effect of the drug
    • Depressants → stimulation in withdrawal
    • Stimulants → fatigue and lethargy in withdrawal
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14
Q

Describe the role of environment in addiction

A
  • Environmental cues can play a role in conditioning of reward
  • The cue can act as a secondary reinforcer
    • ​In the absence of the primary reward, the individual will perform the behaviour in order to get the secondary cue
  • Once detoxed, exposure to the cue will predict relapse, as well as withdrawal symptoms
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15
Q

Describe hedonic allostasis

A
  • A system can not be continually activated by stimuli
  • eg Night out
    • ​An individual spends the night out, having a really good time; mood is elevated
    • The next day, the person feels flat, as the neurotransmitters are depleted
  • The reward set point of the system changes
    • ​It becomes harder and harder to elicit the release of dopamine by the system, and thus to get the same high
  • With drug use:
    • ​Once a person is taking drugs, natural highs don’t come close to activating the system, as the set point is now so elevated
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16
Q

Describe Anhedonia in drug users

How was this researched experimentally?

A
  • Drug users do not derive pleasure from natural reward stimuli
  • Experimental design
    • ​Non-/Drug users were exposed to a range of images
      • ​Positive reinforcers
      • Negative
        • ​Snakes, drug use
    • Responses were recorded in a number of ways:
      • ​Reporting of how they felt
      • Facial expression
      • Cortical activity
  • Results:
    • ​For every parameter, heroin users were overreactive to the opiate images and under-reactive to the natural reinforcers
17
Q

Which brain regions are altered in drug users?

What is the function of these regions?

A
  • Regions
    • Orbitofrontal cortex
      • ​Making long term goals
      • Weighing up short vs. long term goals
    • Anterior cingulate cortex
      • ​Keeping one on track with goals and plans

Experimental studies:

  • Two groups:
    • ​Drug naïve
    • Drug users
  • Perform various tests
    • Wisconsin card sorting test
      • ​Test of executive function
      • No difference between the groups
    • Gambling test
      • ​Two decks
        • ​Advantageous
        • Disadvantageous
      • Drug users and those with OFC lesions consistently select from the disadvantageous deck, and ultimately lose all their money
18
Q

Which comes first: the brain deficits, or the addiction?

A
  • NB brain deficits:
    • Decreased activity of OFC and ACC
  • It is unclear which comes first
    • ​Chicken and the egg scenario
  • Experimental studies have indicated that the deficits can be pre-morbid
    • ​Smaller OFC in kids age 12 that go on to use cannabis at age 16, compared to those who don’t
    • Poorer response on brain function tests measuring function of these areas in kids with a strong family history of alcohol, than those with no family history
      • ​These kids have never had alcohol
19
Q

Describe Anhedonia in adolescents

What is thought to be the evolutionary basis for this?

What are the implications?

A
  • Increased anhedonia in adolscents
    • Compared to younger or older individuals
    • Increased ‘boredom’
    • Experience positive experiences as less pleasurable than others
  • Evolutionary basis
    • During adolescence, one must learn to look after oneself, gain new experiences, risk take etc.
    • Anhedonia could perhaps lead adolescents to seek these new experiences
  • Implications:
    • Adolescents are more at risk of addictive behaviours?
20
Q
A
21
Q

Describe the developmental changes that occur in the brain over time

A

Childhood:

  • Massive proliferation of connections

Adolescence:

  • ‘Pruning’ : removing the connections that aren’t needed
  • Myelination: insulation of the important connections
  • This doesn’t happen in an ordered way
    • Certain areas develop faster than others
      • ​Limbic system develops first
        • ​Region that tells individual to go out and try new things
      • PFC develops later
        • ​By age 25
        • Region that is important for judgements and control of behaviour
22
Q

Outline the studies into alcohol intake in adolescent and adult rats

A
  • ‘Rat bar’ experiment
  • Rats able to consume alcohol at will / intermittently
  • Adult rats consume less alcohol than adolescent rats
  • When alocohol consumption is restricted, adolescent rats drink more alcohol per day
    • ​⇒ more likely to binge drink
23
Q

Compare the effect of alcohol on adult and adolescent rats

A
  • Adults
    • ​Motor control more affected than adolescent rats
  • Adolescents:
    • ​Suffer less from the immediate physical effects (such as motor impairment)
    • However, brains are more vulnerable to damage
      • ​Memory and learning functional impairment
    • Suffer more frequently from black outs
24
Q

Describe studies into hippocampal size in the brain of adolescents who consume large amounts of alcohol

A
  • Hippocampus size is reduced in alcohol dependent adolescents
  • Size of hippocampus is inversely proportional to the amount of alcohol consumed
25
Q

Describe the addictive features of nicotine

A
  • Adult rats will not hit a lever in order to receive nicotine
  • Unless they are previously injected and thus dependent
  • In contrast, adolescents love nicotine
    • ​esp. females
  • This is linked to depression
26
Q

Which age group is most at risk of the harms of alcohol?

A

Adolescents