Neurochemical Explanation

• Nicotine dependence


  Psychical and psychological factors that make it difficult to stop using tobacco
• Why does nicotine become addictive?


  Actives the areas of the brain that regulate feeling of pleasure - 'the rewards pathway'.
• What chemical does nicotine release?


  Dopamine, causes mood altering changes that make he person feel temporarily good
• How long does inhaled smoke take to reach the brain?


  20 seconds
• Dopamine


  Neurotransmitter which elicits feelings of pleasure,calmness and in high volumes, euphoria
• Common Reward Pathway (Mesolimbic Pathway)


  Interlinked system in the brain which is strongly associated with addiction.
• What does nicotine do in the ventral tegmental area (VTA)?


  Binds to receptors on neurons
• What do the neurons do after nicotine binds onto them?


  Triggers the release of dopamine in the nucleus accumbens (NAc)
• What does the Common Reward Pathway end with?


  Boosting of activity in the Prefrontal Cortex,which stimulates a strong positive emotional response to dopamine
• Glutamate (excitatory)


  Nicotine stimulates the release of which triggers the release of additional dopamine
• GABA (inhibitory)


  Nicotine prevents, which ordinarily slows down neuron activity
• Nicotine Regulation Model


  Abstinence (e.g. overnight) leads to increased sensitivity of nicotinic receptors, causing motivation to smoke
• Opioids


  Substances that act on opioid receptors to produce morphine-like effects
• Nicotine in the brain


  Activates natural opioids (enkephalins and endorphins) creating feelings of pleasure
• endorphins and enkephalins


  Released from pituitary gland, induces euphoria
• Neuroadaptation


  Brain's neurons are affected by external influences.
• Why do persistent smokers have to increase their nicotine consumption?


  Neural networks adapt to produce less dopamine overtime
• Why is there an increase in repetitive behaviour in smokers?


  Areas of the brain responsible for decision making and control are negatively affected by
• Supporting Evidence - Watkins et al (2000)


  Conducted a meta-analysis and found that dopamine release is reduced with chronic exposure to nicotine.
• Provides explanation for role of candidate genes as a risk factor -


  Dopaminergic mechanisms will cause feeling rewards and highs to a greater or lesser extent than others - meaning that they are more or less likely to develop an addiction based on their genetic vulnerability
• Oversimplified biological explanation -

  Neural explanation is likely to be a combination of various chemical responses
• Presynaptic acetylcholine receptors


  Release acetylcholine, neurotransmitter involved in memory and involuntary muscle movement which is also likely to link directly to behavioural symptoms
• Nicotine affects men and women differently -


  Cosgrove et al (2014) studied the brains of men and women using PET scans -

  
  

  Women - dopamine effect in dorsal putamen

  Men - dopamine effect in the ventral striatum
• Addiction is likely to be an interactionist disorder


  Psychosocial risk factors (such as family or peer influences) may be more important.

  50% of regular smokers develop a nicotine addiction, as

  they may be surrounded by 'protective' psychosocial factors (family and peers with anti-smoking views)