Effects of recreational drugs Flashcards
Recreational drugs
These include stimulants, sedatives, hallucinogens and opioids. Each ‘operates’ in a particular way, increasing or decreasing specific neurotransmitters at the synapse.
Cocaine -
Stimulant effect on the central nervous system (CNS), especially on the brains main reward system.
Cocaine alters synaptic transmission involving several neurotransmitters ( e.g noradrenaline, serotonin, acetylcholine)
GREATEST IMPACT ON THE ACTIVITY OF DOPAMINE
- all recreational drugs increase the release of dopamine in the reward centres of the brain. This ‘reward centre’ creates a sense of pleasure when activated.
-cocaine blocks the reuptake of dopamine by binding with dopamine transporter molecules on the terminal buttons of the presynaptic neuron (responsible for recycling dopamine back to the neuron that produced it).
-As cocaine prevents this process, the synapse is flooded with surplus quantities of dopamine, all available for binding with postsynaptic receptors (probably the main cause of the euphoric ‘high’ associated with cocaine use).
Long-term effects of cocaine
After repeated cocaine use, dopamine receptors become downregulated (fewer receptors are active, some are damaged and shut down and the quantity of dopamine produced declines).
This explains withdrawal, craving for the drug and the higher doses needed to get the same effects (tolerance)
Heroin
depressant effects on the CNS, slowing down activity (including activity of neurons involved in pain)
Heroin is usually injected intravenously and most of it is processed in the brain into the closely-related opioid, morphine.
Morphine binds with a specific opioid receptor at the synapse found in the cerebral cortex, limbic system and hypothalamus .
Heroin/morphine receptors exist because the CNS has its own opioid system- endorphins and enkephalins are produced by the body as natural pain killers. Heroin taps into this natural opioid system, binding with receptors of the system to massively enhance the natural response
Agonist and Antagonist :
Heroin is an agonist drug because it mimics the action of another natural biochemical
Naxalone (used to manage withdraws) is an antagonist that blocks opiate receptors.
Long-term effects for heroin
Repeated heroin use results in down regulation
Opioid receptors on post-synaptic neurons constantly bind with morphine molecules, desensitising them to the effects of the drug, which is the basis of tolerance
A strength is support for dopamine from research using non-animals
A commonly used procedure involves deliberately damaging the mesocorticolimbic pathway in the brains of mice
Neurons cannot produce levels of dopamine normally associated with reward, so mice then fail to self-administer cocaine intravenously (does not occur when the lesions are performed in other parts of the mice brain)
This finding supports the view that cocaine effects are due to the activity of dopamine in the brains reward system
A weakness is problems with the validity of non-human animal studies
Transmission processes in mammals are similar, but there are differences because the human brain is more complex than the mouse brain
Complex effects of drugs on transmission are not explained by just one mode of action. The interactions of dopamine with other transmitter systems are not well understood
This means that extrapolation from non-human animals to humans is risky and should be undertaken only very cautiously
Competing argument
Evidence of drug effect on CNS transmission also comes from studies oh humans. Volkow et al used PET scans to track activity od dopamine transporters correlated positively with the course of the subjective experience
This support the view that evidence from animal models is valid, as human studies produce similar results
Application : Knowledge leads to more and better addiction treatments
For example, once heroin was identified as an agonist that binds to opioid receptors, other drugs were developed with a reverse mode of action
Naloxone is an antagonist (blocks opiate receptors, prevents heroin occupying them). So no rewarding euphoria is associated with heroin. Can manage the withdrawal process because user stops taking heroins (which has no effect)
This is a treatment that developed from greater knowledge of the transmission effects of drugs
Issues and debates
Shows how psychological knowledge can be used within society
A clearer understanding of how recreational drugs affect CNS functioning may lead to them being used in a wider range of legitimate ways
For example, Morgan et al give a controversial view - that recreational drugs may have potential benefits (eg the pain reducing effects of cannabis)
This highlights the valuable contribution that psychological research can make to addressing social issues, with benefits for individuals and wider society
