Theories of Addiction I

Question 1

the disease model

Answer 1

addiction is a behavioural pattern of drug use, characterized by high involvement with use of drug, high tendency to relapse after withdrawal.

susceptibility model says the problem is with the individual and not the drug. the exposure model says the drug changes the brain. the combination model (susceptibility + exposure) says there are individual differences but need the right environmental conditions (exposure). everyone is at risk depending on level of exposure (higher exposure = higher risk).

Question 2

negative reinforcement models (4)

Answer 2

physical dependence model, self medication hypothesis, opponent process, allosteric models

Question 3

physical dependence model

Answer 3

this model explains why individuals continue taking the drug regularly. addiction meant having physical dependence. drug is taken to alleviate and then avoid the unpleasant effects of withdrawal - works as a negative reinforcer.

Question 4

problems with physical dependence model (4)

Answer 4

1. does not address reason for developing drug use leading to dependence.
2. addiction can develop without physical withdrawal
3. its not withdrawal that drives craving and relapse
4. self reported craving for cocaine is higher AFTER taking the drug
   - expect the lowest craving after taking the drug as a means of reducing withdrawal but see the opposite - goes against idea of reducing negative withdrawal symptoms.

Question 5

problem with physical dependence model = not withdrawal driving craving/relapse

Answer 5

experiment showing that they take drug because they like it and not to avoid the negative symptoms. in this experiment, self administered morphine directly into VTA. disinhibited DA neurons (increasing DA release) which is perceived as rewarding. the PVG (periventricular gray) is also associated with rewarding effects of substances due to increased density of mu opiate receptors. animals did not self administer into PVG. wanted to make animals dependent so passively infused morphine into VTA and PVG (since they didnt self administer into PVG). injected mu opiate antagonist naloxone to cause severe withdrawal. when animal was constantly infused morphine into VTA, showed low levels of withdrawal. Constantly infused into PVG showed high levels of withdrawal. see most withdrawal symptoms in PVG so expect to see the animals self-administer more morphine into PVG to alleviate withdrawal symptoms. in the area where they do self administer (VTA), dont see much withdrawal. shows that they engage in this behaviour because they like the drug - self administer into VTA because it feels good and not to avoid withdrawal.

Question 6

self medication hypothesis

Answer 6

model says self medication is the driving force for substance use disorder. drug is used to medicate an existing negative state. experiment used valium to show role of self medication in will to use a drug. gave subjects red or blue pill (control and valium). after several days, asked to choose which pill they want. rationale was if they were treating pre-existing condition, they’d choose valium but there was no difference in choice. even those with high levels of anxiety has no difference in pill choice. same results for depression and amphetamine. the exception is seen with preference developing for opiates if pain is expected. doesnt seem that the major reason for substance use disorder is to treat pre-existing condition. false hypothesis.

Question 7

opponent process model

Answer 7

this model indicates that there are 2 phases. suggests that there are probably systems involved in affective homeostasis. the 2 theoretical processes are the a and b process. the A process is induced, triggered by anything that makes us happy (ex: amphetamine high). it shoots up very quickly and after the stimulus is gone, process dies down and goes back to baseline. the B process is the opposite (brings a back to baseline). its slower to start, stays longer after the stimulus is gone and then goes to baseline. in the beginning, the affective state is high since only a is in progress and affective state is lower than normal at the end since only b is in progress until baseline. over repeated exposure, b becomes more efficient - starts earlier, becomes stronger, since the high is not as high the crash is much stronger. this model explains tolerance.
the experiment had experienced users smoke cocaine. measured the concentration in plasma and their subjective feeling. results were what was expected - high in the beginning that quickly drops due to b process before going back to baseline.

Question 8

the allostatic model

Answer 8

suggests that addiction is the result of decreased function of the reward and anti reward systems. the reward system includes the mesolimbic DA, opiate receptors and peptides, GABA receptors. prolonged exposure to drug causes reward system to be deficient. decreased function seen in reduced DA D2 receptor density in the striatum of cocaine addicts and increased ICSS (intracranial self-stimulation) threshold in rats after chronic use. with repeated prolonged exposure to drug, reward system becomes deficient.
experiment = trained rats to self administer cocaine : 2 groups where 1 had limited time access and the other had long exposure with unlimited cocaine access. the ones in unlimited group show this escalation of intake (lose control). reason why they do this is because the reward system is deficient due to high exposure. measure function of reward system by using electrodes in several areas of the brain (lateral hypothalamus). electric current = best reward. higher frequencies are more rewarding resulting in increased responses. animals consider the electrical brain stimulation as less rewarding in the long exposure.

CRF acts as a NT. amygdala has CRF neurons that seem to be sensitized. when we perceive a situation to be stressful, one of the first responses is CRF release.

another system being sensitized/recruited is the counter adaptation / anti-reward system. the “b” process becomes more efficient but the reward process becomes less efficient so there’s this recruitment of the anti-reward system. overall, mood changes because “b” process becomes stronger (goes to lower baseline every time). the individuals is not trying to get high but back to normal levels. the allostatic point gets lower with repeated exposure since the reward system is not as efficient and the anti-reward system is recruited more. taking the drug strengthens this process.