Brain neurochemistry

• Brain neurochemistry 


  -When we inhale cigarette smoke the nicotine enters our bloodstream and is delivered to the brain.

  -Nicotine has a profound influence in the mesolimbic pathway 9rewad centre) which is through the nucleus accumbens, ventral tegmental area and the prefrontal cortex.
• The desensitisation hypothesis - 1 


  -when someone smokes nicotine travels to the brain and binds to nAchR in the VTA.

  -Activation of the nAchR triggers release of dopamine along the mesolimbic pathway and the mesocortical pathway to the frontal cortex to provide feelings of reward.

  -Nicotine molecules bind with nicotine receptors and cause the receptors to shut down and become de-sensitised leading to the downregulation of neurons.
• The desensitisation hypothesis - 2


  -Chronic activation of nAchR results in long term desensitisation and decrease in receptors which means more nicotine is needed to create the same effect it had on the initial amount.

  -Increase amount of nicotine explains effect of tolerance.
• The nicotine regulation model - 1

  -Nicotine is metabolised and removed from the synapse.

  -Desensitised nAchR become active (resensitised) again which leads to upregulation of neurons. High levels of acetylcholine stimulates receptors and results in anxiety and restlessness.

  -Decreased dopamine levels which results in low mood.
• The nicotine regulation model - 2


  -Individual increases nicotine levels to reduce and desensitise the nAchR to acetylcholine and stimulate the release of dopamine.

  -Individual can therefore regulate levels of nicotine to avoid and reduce symptoms of withdrawal.
• Evaluation:

  + Real life application: NRT administers nicotine in controlled doses to the addicts to prevent withdrawal symptoms. They can prevent effects of withdrawal by gradual weaning themselves off cigarettes.

  +Individual differences: Schiffman et al studied chippers (people who regularly smoke but are not addicted/dependency. Those who smoked on average 5 cigarettes a day and showed no signs of withdrawal syndrome when abstained. Therefore, may be other factors that protect some smokers from addiction.
• Evaluation:

  +Nicotine and Parkinson's disease: Research found that smokers are less likely to get PD than those who have never smoked, suggesting nicotine may have a neuroprotective function against development of PD and can be beneficial in this treatment. Fagerstrom et al treated 2 elderly PD patients with nicotine gum and patches. Increased dopamine levels caused by nicotine administration.
• Evaluation


  -Reductionism: neurochemical explanation are reductionist accounts of why people became addicted to nicotine. They explain addiction at the simplest level of activity of neurotransmitters. Roughly only half of those who experiment with nicotine become addicted suggests non-biological factors are involved.