Reward Pathways & Dopamine

Question 1

What is the primary neurotransmitter involved in the reward pathway?

Answer 1

Dopamine

Question 2

What brain regions are part of the mesolimbic reward pathway?

Answer 2

Ventral Tegmental Area (VTA) -> Nucleus Accumbens (NAcc) -> Prefrontal Cortex

Question 3

What is reinforcement in the context of reward?

Answer 3

When an animal or human repeats a behaviour to obtain a stimulus.

Question 4

What did Olds & Milner (1954) demonstrate about the reward system?

Answer 4

Rats self-stimulate brain regions like the mesolimbic pathway, even prioritising it over food and water.

Question 5

What effect do dopamine D1/D2 antagonists have on reward?

Answer 5

They reduce reward-seeking behaviours and inhibit drug self-administration.

Question 6

How do psychostimulants like cocaine and amphetamine affect dopamine?

Answer 6

Cocaine: Blocks dopamine reuptake

Amphetamine: Increases dopamine release.

Question 7

How do opiates like heroin and morphine increase dopamine release?

Answer 7

They activate μ-opioid receptors on GABAergic neurons, causing disinhibition of dopamine neurons in the VTA

Question 8

How does alcohol (ethanol) affect dopamine neurons?

Answer 8

It decreases after-hyperpolarisation (AHP), increasing the firing rate of dopamine neurons in the VTA.

Question 9

How does nicotine increase dopamine release

Answer 9

By activating nicotinic acetylcholine receptors on dopamine neurons in the VTA increasing firing rates.

Question 10

How do cannabinoids like THC affect dopamine?

Answer 10

THC activates cannabinoid receptors on GABAergic neurons, causing disinhibition of dopamine neurons.

Question 11

What is the dopamine-reward hypothesis?

Answer 11

Drugs of abuse mimic the dopamine release seen with natural rewards like food and sex.

Question 12

What are the key characteristics of addiction?

Answer 12

1. Psychological dependence: craving and compulsive use.
2. Physical dependence: Withdrawal symptoms upon stopping.
3. Tolerance: Need for higher doses for the same effect.

Question 13

What evidence shows dopamine’s role in reward?

Answer 13

Dopamine release in the NAcc is associated with self-administration of drugs and electrical brain stimulation.

Question 14

Which drugs increase dopamine release in the NAcc?

Answer 14

Cocaine, amphetamine, heroin, morphine, nicotine, alcohol and THC.

Question 15

What happens when the mesolimbic pathway is chemically lesioned?

Answer 15

Drug self-administration and reward-seeking behaviours are inhibited

Question 16

What role does the VTA play in the reward pathway?

Answer 16

IT contains dopamine neurons that project to the NAcc and prefrontal cortex, mediating reward.

Question 17

Why do animals self-administer drugs like cocaine and heroin?

Answer 17

These drugs stimulate dopamine release in the NAcc, mimicking natural rewards.

Question 18

What are the natural rewards, and how do they relate to dopamine?

Answer 18

Activities like eating and sex naturally increase dopamine levels in the NAcc

Question 19

How does chronic drug use alter the reward system?

Answer 19

It causes neuroadaptations, leading to tolerance, dependence, and withdrawal symptoms.

Question 20

What clinical interventions target the reward system for addiction treatment?

Answer 20

Dopamine receptor antagonists and medications targeting opioid or cannabinoid receptors.