Addiction and Reward

Question 1

Introduction - Addiction and Reward

Answer 1

Drugs changed human life e.g. mental health, surgery, diabetes, HIV.

Drug use offers in cultural perceptions.

Different types of psychoactive drugs categorised based on their effects e.g. depressants, stimulants, analgesics. Some suppress CNS firing. Categories can overlap as alcohol can be a stimulant, reduce pain and a depressant.

Some experience no harm taking drugs, can cause physical harm. Societal costs e.g. drug misuse, healthcare, anti-social behaviour.

Question 2

Describe the different ways to administer drugs

Answer 2

All aim to affect the CNS

1. Oral Ingestion - Easy and safe method, but unpredictable. Can damage digestive system
2. Injection - Strong, fast and predictable effects. Higher infection risk and hard to reduce the effects of.
3. Inhalation - Absorbed into the bloodstream through capillaries in lungs. Difficult to regulate, can damage lungs.
4. Absorption through mucous membranes - Nose, mouth, rectum.

Question 3

How do drugs penetrate the CNS?

Answer 3

Blood brain barrier makes it difficult for dangerous chemicals to pass from blood vessels of CNS into neurons.

Affect the nervous system differently. Bind to synaptic receptors by influencing neurotransmitters or influence chain of chemical reactions elicited in postsynaptic neurons by activation of their receptors.

Drug metabolism mediated by liver enzymes. Eliminates drugs ability to pass through lipid membranes so can no longer penetrate blood-brain barrier.

Question 4

What is drug tolerance?

Answer 4

State of decreased sensitivity to a drug that develops as a result of exposure to it

Shift in the dose dependent curve to the right.

Two categories

• Metabolic intolerance - Changes reduce amount of drug getting to action site
• Functional tolerance - Reduced reactivity of action sites.

Opposite is drug sensitzation.

Question 5

What is drug withdrawal?

Answer 5

Adverse effects of discontinuing drug use. Opposite effects to drug. Suggests that effects may be produced by same neural changes that produce drug tolerance. Exposure changes the nervous system, when no longer present, neural changes create a symptom.

Question 6

Is there a genetic component to drug addiction?

Answer 6

Has a higher genetic predisposition than some diseases.

Sons of alcohol dependent fathers have increased alcohol tolerance and reduced hangovers.

Enzyme aldehyde dehydrogenase involved in metabolism of alcohol. Those deficient experience skin flushing when alcohol is less effectively metabolised.

Question 7

Pinel, Mana and Kim (1989)

Answer 7

• Looking at contingent tolerance (drug effects actually experienced) to the anticonvulsant effect of alcohol.
• Rats that received alcohol before convulsive stimulation became tolerance to its anticonvulsant effect
• Rats that received the same injections after a convulsive stimulation did not become tolerant.

Question 8

Crowell, Hinson and Siegel (1981)

Answer 8

• 2 groups of rats receiving 20 alcohol and 20 saline injections
• One group received all 20 alcohol injections in a distinctive test room and the 20 saline injections in their colony room, while other group of rats received alcohol in colony room and saline in distinctive.
• Assessed the hypothermic - temperature-reducing effects of alcohol.
• Only found tolerance in rats who were injected in the environment that had been paired with alcohol administration. Tolerance has a phycological component. The body predicts it, so makes adjustments.
• Drug addicts may overdose when receive drug in new context. Tolerance in same environment.

Question 9

Siegel et al. (1982)

Answer 9

More heroin tolerant rats died from a large dose in a novel environment compared in familiar.

Shows that drug administration in novel contexts can be deadly.

Question 10

Describe the physical dependence approach to drug addiction

Answer 10

Stats that addicts are trapped in a circle of drug taking and withdrawal syndromes.

Early treatment programs were based on this. Tried to break the cycle. Failed bc some drugs do not produce withdrawal distress and drug taking patterns differ.

Led to positive incentive theories of addiction - addicts take drugs to obtain the pleasure of the drug.

Question 11

Describe intracranial self-stimulation

Answer 11

Self-administered shock to pleasure centers of the brain

Olds and Milner (1954) discovered this, stating that brain sites that mediate self-stimulation are those that normally mediate the pleasurable effects of natural rewards.

The mesocortical pathway plays an important role for reward processing and drug self-administration.
Evidence is that
- Lesions to path disrupt self-stimulation
- Hernandez et al. (2006) - Self-stimulation led to increased DA in pathway.

Question 12

Mesocortical Pathway

Answer 12

Path through which dopaminergic projections travel to reach the neocortex.

Important for reward processing and drug self-administration

Question 13

Nigrostriatal pathway

Answer 13

The dopaminergic tract from the substantia nigra to the striatum.

Associated with motor control.

Degeneration associated with parkinsons.

Question 14

Dopamine and drug addiction

Answer 14

DA antagonists are drugs which interfere or inhbibt the physiological action of DA. They mainly abloish self-administration and conditioned place preference effects.

Dopamine is important in the rewarding effects of drugs.

Question 15

Nucleus accumbens and drug addiction

Answer 15

Part of the mescocortical DA pathway which receives inputs from the ventral tegmental area. Seems to be related to reward and pleasure.

Findings

• Animals self-administered drugs into area
• Injections produced a conditioned place preference for compartment of administration
• Lesions blocked self-administration and development of place preferences.
• Self-administration shows increased levels of extracellular dopamine in area.

Question 16

Habitual Drug Use

Answer 16

Positive incentive theory says ppl motivated to take drugs by the anticipated pleasure. There is a decreased hedonic value (liking) of drug.

Evidence from the brain

• Dopamine from nucleus accumbens associated with wanting of drug rather than liking.
• Changes in brain function from initial drug taking to habitual.
• Addicts show striatum reacts differently and control is shifted from nucleus accumbens to dorsal striatum.
• Impairments in prefrontal cortex - loss of self-control
• Mesotelencephalic DA system plays a role in drug anticipation as neutral stimuli that predict drug administration predict increased firing of DA activity in rats .

Childress et al. (1999) - Cues associated with drug use led to increased activation in drug-associated brain regions.

Question 17

Explain the reasons for drug relapse

Answer 17

• Stress
• Drug-priming - exposure to formerly abused drug.
• Exposure to cues associated with drug taking e.g. US soldiers addicted to heroin in Vietnam war got rid of addiction once returned home.

Pickens et al. (2011) - After cocaine withdrawal there was a gradual increase in lever pressing for cocaine in response to cue. Explains why people relapse after years of absence. Suggested that improving the surroundings of drug addicts is useful.

Question 18

Describe what a stimulant is and provide an example

Answer 18

Stimulants: Drugs which produce increases in neural and behavioural activity. Block doapmine transporters that normally remove dopamine from synapses and transfer it back to presynaptic neurons.

Cocaine

• Addicts often go on cocaine sprees. Become tolerant to europhia producting effects. Ends when has a toxic effect e.g. sleepiness.
• Repeated cocaine exposure makes person more responsive to motor and convulsive effects.