recreational drugs and neurotransmission

Question 1

what effect does cocaine have on the central nervous system ?

Answer 1

• has a stimulant effect on the CNS, especially on the neurons of the brain’s main reward system (the mesocorticolimbic which connects subcortical emotional brain centres with frontal areas)

Question 2

how does cocaine achieve its effect ?

Answer 2

by altering synaptic transmission involving several neurotransmitters, such as serotonin or noradrenaline

Question 3

what effect does cocaine have of dopamine ?

Answer 3

cocaine blocks the reuptake of dopamine by binding with dopamine transporter molecules on the terminal buttons of the presynaptic neuron. these are responsible for recycling dopamine back into the neuron that produced it. as cocaine prevents this, the synapse is flooded with surplus quantities of dopamine

Question 4

what are the long-term effects of cocaine ?

Answer 4

dopamine receptors become downregulated (fewer receptors are active, some are damaged and shut down - quantity of dopamine is reduced) - explains craving and withdrawal and why higher doses are needed to get the same effect.

Question 5

what effect does heroin have on the CNS ?

Answer 5

it has depressant effects on the CNS. it slows down CNS activity, including the activity of the neurons involved in pain - why opiates are valued as analgesics.

Question 6

once heroin reaches the brain, what does it turn into and what does this opioid do ?

Answer 6

it is processed into morphine and binds into specific opioid receptors at the synapse found in the cerebral cortex, limbic system and hypothalamus.

Question 7

what natural painkillers are produced by the CNS, and what does heroin do to them ?

Answer 7

endorphins and enkephalins - heroin taps into the natural painkilling system, it binds with receptors of the natural opioid system to massively enhance the natural response

Question 8

is heroin a agonist or antagonist drug ?

Answer 8

heroin is an agonist drug because it mimics the action of another natural biochemical.

Question 9

what are the long term effects of heroin ?

Answer 9

• causes downregulation
• regular use = opioid receptors on postsynaptic neurons are constantly binding with morphine molecules, which desensitises them to the effects of the drug (basis of tolerance)

Question 10

(evaluation) what is a strength of this theory ?

Answer 10

• the explanations are supported with research using non-human animals
• e.g., a commonly used procedure of damaging mice’s mesocorticolimbic pathway (weinshenker and Schroeder) - neurons are unable to produce levels of dopamine normally associated with reward - mice then fail to self-administer cocaine intravenously (this doesn’t happen when the lesions are performed in the other parts of the mouse brain
• this supports the view that cocaine’s effect are due to the activity of dopamine in the brains’s reward system

Question 11

(evaluation) what is a weakness of this theory ?

Answer 11

• problems by using mainly non-human animals in studies to understand drug effects on human CNS transmission
• basic transmission processes in mammals are similar - but some there are some differences as human brains are more complex than the rat brain
• e.g. isolating effects of just one neurotransmitter greatly oversimplifies the process.
• the interactions of dopamine with other neurotransmitter systems are not well understood
• means that the extrapolation from non-human animals to humans is risky and should be undertaken only very cautiously

Question 12

what is a competing argument of the weakness of the theory ?

Answer 12

• evidence of the drug effects on the CNS transmission comes from studies of humans as well.
• e.g., Nora Volkow et al. (1997) used PETscans to track the activity of dopamine transporters during a cocaine-induced ‘high’.
• found that the extent to which cocaine occupied dopamine transporters correlated positively with the course of the subjective experience
• supports the view that the non-human animal studies are valid

Question 13

what is an application of this theory ?

Answer 13

• as we know more about the effects, the more treatments for addiction become available
• e.g, once heroin was identified as an agonist that binds to opiates receptors, other drugs were developed with a reverse mode of action
• naloxone is an antagonist drug that blocks opiate receptors and prevents heroin (morphine) from occupying them - doesn’t produce the same euphoric feeling that morphine is associated with, so it can help manage the withdrawal and reduce symptoms