Lecture 30 - Behavioural and Developmental Aspects of Dependence Flashcards
Describe dopaminergic projections in the reward pathways in the brain
What is the normal role of this system?
- VTA (ventral tegmental area)
- Nucleus accumbens
- 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.
Describe the release and interaction with receptors of dopamine
- Dopamine released by dopaminergic neurons
- Dopamine acts on dopamine receptors on the post-synaptic neuron in the nucleus accumbens
What is the pharmacological action of cocaine?
What is the general action of cocaine?
-
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
Compare the action of the following drugs on the reward pathways in the brain:
- Heroin
- Alcohol
- Cannabis
- Cocaine
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
Give the DSM IV definitino of substance dependence
“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.”
Characterise patterns of heroin relapse
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
What factors need to be taken into account in understanding addiction?
- Intense cravings
- Loss over control of use
- Compulsive patterns of behaviour
- High rates of relapse
Compare the effect of various drugs on the dopaminergic systems in brains of drug users, and non-drug users
Drug users:
- Decreased effect of reward stimuli
- Measured with MRI imaging of dopaminergic system
What features are similar across all drugs of abuse?
What differs?
- All drugs of abuse increase dopamine in the reward systems
- However, they perform this action in different ways
Why do people take drugs?
Why do people continue to take drugs?
- 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:
- *
Compare physiological and psychological dependence
- 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
- Experience
- Psychological:
- Individual actively seeks out the drug
- Drug taken in larger doses
- Continue the behaviour, despite the knowledge of the negative effects
- etc.
Define tolerance
- Increasing doses required to elicit the same response
Define withdrawal
- 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
Describe the role of environment in addiction
- 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
Describe hedonic allostasis
- 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