25.5 Drug Addiction and Recreational Drugs Flashcards
What is addiction?
When drug-seeking and use becomes compulsive, despite negative consequences
What is the role of the mesolimbic reward pathway in addiction?
Mesolimbic reward pathway → key biological circuit implicated in addiction.
*Dopaminergic projections from VTA in midbrain that project to NAc in ventral striatum (+amygdala/ hippocampus)
*Constitutes key reward processing pathway imp for reward + salience processing.
Dopamine release → ↑ activation of spiny stellate neurons in NAc → feeling of reward + motivation → drives goal-oriented behaviour.
What is the common effect of addictive drugs?
Increased dopamine transmission
What does dopamine normally do relating to reward?
- Conveys unexpected receipt of reward; ‘This is worth remembering’
- Conveys cues predicting upcoming reward; ‘This is worth attending to and responding to’
- Initiates movement and habit formation; ‘I can take action’
What brain mechanism underlies the addiction of many recreational drugs?
- Many recreational drugs activate the mesolimbic dopamine pathway, which is a reward pathway
- This means that drug use leads to aberrant positive reinforcement, leading to addiction
What is the role of dopamine signal in the mesolimbic reward pathway?
Dopaminergic neurons do not signal reward itself, but reward predicting errors.
What is dependence liability?
The tendency of a drug to cause dependence/addiction
What is a key determinant of dependence liability?
The rate at which drugs reach the brain
What are four things that drug seeking behaviour and addiction are sustained by?
- Positive reinforcement (euphoria)
- Negative reinforcement (avoidance of withdrawal)
- Environment (behavioural conditioning)
- Genes
Which recreational drugs have the highest dependence liability?
Opiate analgesics
Which recreational drugs have the second highest dependence liability?
Psychostimulants
Which recreational drugs have the lowest dependence liability? Why?
Psychomimetics - as they have little effect on the mesolimbic reward system.
What are some different recreational drugs?
Opiates, nicotine, cannabinoids, psychostimulants, ethanol, benzodiazepines, psychotomimetics (LSD, mescaline), amphetamines, cocaine.
Give a mechanism of action for cocaine
Inhibits DAT → dopamine accumulates in synapse + potentiates transmission.
What are the actions of amphetamines?
promotes dopamine release.
*Binds to TAAR1 stimulating ↑ cAMP + PKA production.
*PKA –phosphorylates→ monoamine transporters → ↑ synaptic [dopamine].
*Inhibits VMAT1 + VMAT2
*Usually transport dopamine into vesicles in pre-s cleft.
*Inhibition → dopamine accumulation in cytosol –via DAT→ synapse.
