neuro: drug use, addiction and the brains reward circuits Flashcards
what is the idea behind physical dependence theories of addiction
traps addicts in a viscous cycle of drug taking and withdrawal symptoms
what did early drug addiction programmes involve and why were they unsuccessful?
→ withdrawing drugs from addicts in a hospital environment
didn’t work because:
→ some highly addictive drugs don’t produce severe withdrawal distress
→ patterns of drug taking involves cycles of binges and detoxification
habitual drug users, continue to use drug despite its adverse effects on health and social life, despite repeated efforts to stop using. what type of individual is this?
drug addicted individuals
theory that people take rugs to obtain positive effects not to escape or avoid the unpleasant consequences.
positive incentive theories of addiction
what is the most important factor of positive incentive theories?
the drugs HEDONIC (pleasurable) effects
how does the ICSS paradigm support the positive incentive theory?
ICSS = intracranial self stimulation
→ rats, humans, other species will self administer bursts of electrical stimulation to own brains → pleasure centres → mesotelencephalic dopamine system
what are the different explanations of drug taking?
peer pressure, social and environmental stress, prior life experiences, novelty seeking, useful (alcohol and caffeine)
why do some people become addicted?
→ experience hedonic effects → + incentive theories
→ have a need for drug
→ incentive-sensitisation theory
state of decreased sensitivity to a drug that develops as a result of exposure to it =
tolerance
how can tolerance be shown with drug taking?
→ given dose has less effect than it had before drug exposure
→ takes more of the drug to produce same effect
what is cross tolerance?
when one drug can produce tolerance to other drugs that act by the same mechanism
sensitisation is the ______ of tolerance
opposite (inverse)
increasing sensitivity to a drug =
drug sensitisation
what happens when the pleasurable effects of cocaine become sensitised?
gives the compulsion to take more of the drug with repeated use
withdrawal =
drug dependence
after significant amounts of a drug has been in the body for a period of time its sudden elimination can trigger adverse physiological reaction =
withdrawal
give an example of how the effect of drug withdrawal shows the opposite effects of what the drug does
sleeping pills → withdrawal effect = insomnia
longer exposure to _____ doses = ______ withdrawal effects and dependence
greater, greater
tolerance only develops to drug effects that are experienced. what tolerance is this?
contingent
maximal tolerance effects are seen in the environment in which the drug has been taken. what tolerance is this?
conditioned
describe before and after experiment to show the effect of contingent tolerance
CONTINGENT TOLERANCE TO ANTICONVULSANT EFFECTS OF ALCOHOL
→ 2 groups of rats receive alcohol injections (1 injection every 2 days)
group 1 → injection one hour BEFORE mild convulsive stimulation (allows anti convulsant effects of alcohol to be experienced)
group 2 → injection one hour AFTER mild convulsive stimulation (effect of alcohol can’t be experienced)
→ end of experiment → rats receive injection and then stimulation
results:
rats that had alcohol before became tolerant to anticonvulsant effects so had increased duration seizure, rats who had it after developed no tolerance so had lower duration seizure
describe the rat study that shows the effect of conditioned tolerance
→ 2 groups of rats received 20 alcohol and 20 saline injections
group 1 = 20 alcohol injections in colony room and 20 saline injections in distinctive room
group 2 = other way round
→ after all injections tolerance of hypothermic effects of alcohol were tested in both environments
results:
tolerance to cold only observed in environment where rat was given alcohol injections
shows situation specifity of drug tolerance, idea that drug users may be susceptible to lethal effects of overdose when drug is taken in new context due to lowered tolerance
describe how taking a drug in a different environment increases risk of death
drug users become more tolerant when self administer in same environment → increase dose to counteract tolerance → if drug user takes bigger dose in different environment → no tolerance effects → greater risk of death
describe support evidence about heroin tolerant rats
heroin tolerant rants died following higher dose taken in novel environment than rats in usual injection environment → example of conditioned learning
what are the different drug administration routes?
oral ingestion, injection, inhalation, absorption through mucous membranes
describe how a drug works through oral digestion
swallowed → dissolves in stomach → carried to intestine → absorbed into blood stream
why does alcohol have quick effects?
passes readily through the stomach (doesn’t have to be carried to the intestine)
why do some drugs take longer to work?
aren’t readily absorbed or have to be broken down into inactive metabolites before they can be absorbed
what is the advantage and disadvantage of oral ingestion?
\+ = easy and relatively safe - = unpredictable
injection under the skin =
subcutaneously (SC)
injection into large muscles =
intramuscularly (IM)
injection into veins with direct delivery to the brain =
intravenously (IV)
what are the disadvantages of injections?
→ dangerous → fast effects mean little opportunity to counteract overdose
→ impurities
→ allergic reactions
→ develop scar tissue, infections, collapsed veins
absorbed into the blood stream through capillaries in the lungs, tobacco, weed
inhalation
what are the disadvantages of inhalation?
difficult to regulate dose and damage to lungs
where are the enzymes synthesised that metabolise drugs into their non active form?
liver
how does drug metabolism cause drug elimination?
eliminates a drugs ability to pass through lipid membranes of cells so they can no longer penetrate the blood brain barrier
what affects a drugs addictive properties?
how available it is to the body and how quickly it gets to the brain
what drugs elicit an effect quickly?
cannabis, LSD, ecstasy
what pathway of dopamine plays an important role in mediating intra-cranial self stimulation?
mesocorticocolimbic pathway
includes many of the brain sites where self stimulation occurs
ICSS is associated with an ______ in dopamine release
increase
dopamine agonists → ______ ICSS
dopamine antagonists → _______ ICSS
increase,
decrease
what tends to disrupt ICSS?
lesions in the mesocorticocolimbic pathway
there has been lots of research into the role of dopamine on ICSS. what are the 2 types of methods for measuring the rewarding effects of drugs?
→ drug self administration paradigm (skinner box)
→ conditioned place preference paradigm
(both methods show dopamine plays an important role in the rewarding effects of ADDICTIVE DRUGS and NATURAL REINFORCERS)
rats press a lever to inject drugs into themselves using operant conditioning. what method is this?
skinner box (drug self administration paradigm)
rats receive drug in 1 compartment of a 2 part box and when the drug free rat is placed in box is found to spend more time in the compartment where the drug was given. what method is this?
conditioned place preference paradigm
what 3 drugs act directly on dopamine?
cocaine, amphetamine, MDMA
what 4 drugs don’t act directly on dopamine?
heroin, caffeine, alcohol and cannabis
how do drugs directly act on dopamine?
blocking reuptake and reversing reuptake transporters → more dopamine in synapse
how does an indirect effect of a drug work on dopamine?
causes dopamine neuron to fire
where are nicotine receptors found?
on dopamine receptors themselves
what is an important brain site linked to dopamine?
nucleus accumbens
what receptors does caffeine have?
adenosine receptors
features of cannabis:
→ THC = primary psychoactive constituent
→ binds to cannabinoid receptors
how does alcohol work on the brain?
potentiates the action of GABA (inhibitory)
morphine, codeine and heroin =
opiates (obtained from opium poppy)
bind to opioid receptors
have medical uses
