ADDICTION Smoking: Biochemistry

Initiation  Nicotine nucleus accumbens  Brain reward centre  Increases dopamine in mesolimbic pathway  Ventral Tegmental Area in midbrain which stimulates nucleus accumbens  Registers pleasure  Lasting memory of smoking & nicotine leading to pleasure

Maintenance  Early M - Positively reinforcing effect of nicotine  Nicotinic acetylcholine receptors  Long-term M - Irreversible changes  Reduction in positive reward circuits  Down-regulation  Nicotine receptor sites desensitised so larger doses required  Tolerance  Avoiding withdrawal  Down regulation – nicotine leaves bloodstream quickly  Anxiety  Continue to smoke to maintain high enough level of nicotine to avoid withdrawal symptoms

Relapse  Brain has lasting memories linking smoking to pleasurable reward  Smoking changes brain cells  Pleasure memory strong & long-lasting after dopamine returns to normal  Also, mesolimbic pathway ends in orbitofrontal cortex  Decision-making and controlling behaviour  Becomes less effective at decision-making  So self-control weakened so relapses

AO2  Noble (1991)  The A1 variant of the DRD2 gene is present in 49% of smokers compared to 26% in non-smokers  This therefore suggests that smokers’ genes make them vulnerable to initiating, maintaining and relapsing smoking behaviour.  However, since the gene is not found in ALL smokers, it cannot be a necessary requirement for smoking addiction.

AO2  Shields (1962) looked at 42 pairs of twins who had been reared apart. This controls for the role of the environment. 33 pairs were concordant for smoking.  This therefore supports the biological explanation as it supports the biological idea that genetics determine smoking. Especially since the research is robust as the finding cannot be explained by similar environmental factors.

AO2  Schachter (1977) The nicotine regulation model suggests that smokers continue to maintain the level of nicotine in their body so that it is high enough to avoid withdrawal. He found that pts given low nicotine content cigarettes smoked MORE each week than those given high nicotine content.  This suggests that smokers DO maintain smoking behaviour to avoid negative withdrawal effects.

AO2  Grant et al (1998)  Believed that a lack of dopamine may not necessarily inevitably lead to addiction. Environmental influences may affect our likelihood of becoming addicted to smoking. They found that people who grew up in stimulating, engaging surroundings, may be protected against smoking addiction.  Even if people have naturally low dopamine levels, if they have more chances to get pleasure from the environment, they are less likely to seek pleasure artificially from smoking.  This contradicts the biological explanation as it suggests that although there may be a biological predisposition to smoking, the environment plays a more important role.