Neurochemical explanations for nicotine addiction Flashcards
(17 cards)
What is neurochemistry
The study of chemical and neural processes associated with the nervous system
What is dopamine
The main neurotransmitter of the reward system in the brain. It plays a role in many different
emotions and behaviours, including giving feelings of pleasure, euphoria and alertness when we engage in certain behaviours that activate this reward system.
What is nicotine?
The main active ingredient of tobacco.
When inhaled through cigarette smoke, nicotine can have a range of different effects including
tranquilisation, decreased irritability, increased alertness and improved cognitive functioning.
What is nicotine paradox
The finding that nicotine has both stimulant and relaxation effects.
Smoking can feel invigorating at sometimes and calming at others.
This can be explained by the fact that smoking only appears relaxing because smokers are often in a state of mild nicotine withdrawal, so smoking a cigarette allows the nicotine level in the body to return to normal.
How does nicotine activate the reward system
Nicotine attaches to neurons which trigger the release of dopamine in the nucleus accumbens
Nicotine also stimulates the release of the
neurotransmitter glutamate, which triggers additional release of dopamine.
This release of dopamine produces pleasure and a disposition to repeat the behaviours that led to it.
It is this pleasure and the drive to repeat the process that leads to addiction.
How does nicotine affect GABA, Glutamate
Nicotine’s effects on glutamate and GABA are responsible for the longer lasting pleasurable effects of nicotine.
Nicotine causes glutamate to speed up the dopamine release, but nicotine also prevents GABA from slowing it down after dopamine levels have been raised
Dopamine release and the inhibition of GABA results in an increase in dopamine and an amplification of the rewarding properties of nicotine. This strengthens the smoking habit by maintaining the feelings of pleasure.
What is MAO
Cigarette smoke also contains an unknown substance that blocks the action of an enzyme called monoamineoxidase
(MAO) MAO is responsible in breaking down dopamine after it has had its effects.
The blocking of MAO results in an increase in dopamine and an amplification of the rewarding properties of nicotine. This strengthens the smoking habit by maintaining the feelings of pleasure.
What is the function of the nicotine receptor nAChR
Can bind with both ACh and nicotine. When nicotine molecules bind with nicotinic receptors the neuron becomes stimulated. Immediately after this the nicotinic receptors shut down and temporarily cannot respond to neurotransmitters. The number of active receptors is said to be downregulated because fewer of them are available. This leads to desensitisation of the neuron.
What causes withdrawal symptoms
When smokers go without nicotine for a prolonged period, the drug is metabolised and disappears from the body.
This allows more ACh receptors to become functional (upregulation) and neurons to become sensitised again.
This creates an acute withdrawal syndrome with symptoms including anxiety and agitation.
The increase in ACh transmission is associated with decreased dopamine functioning.
Smoker is motivated to avoid unpleasant physiological and psychological withdrawal states by having another cigarette.
Describe tolerance
The smoker avoids withdrawal states by having another
cigarette. This is why smokers often describe the first cigarette of the day as the most enjoyable because it follows a period of abstinence.
The whole daily cycle of morning upregulation and night-time downregulation begins again.
Repetition of this process over time creates chronic desensitisation of nicotinic receptors (nAChRs) which can only be overcome by increasing nicotine intake
- tolerance has developed. Over time, continuous exposure of nicotinic ACh receptors to nicotine creates permanent changes to brain neurochemistry.
Outline the genetic explanation of nicotine addiction
A variant of the D2 dopamine receptor gene called A1 may be associated with addiction to nicotine.
Comings et.al found that 48.7% of smokers and ex-smokers carried the A1 variant compared to 25.9% of the general
population.
People with this variant have significantly fewer dopamine receptors in the brain’s reward centre.
This suggests that they are more likely to become addicted because the nicotine causes more stimulation of these few receptors to compensate.
What are strengths of the neurochemical explanation for nicotine addiction
Practical applications
Supported by research
What are limitations of the neurochemical explanation for nicotine addiction
Reductionist
Treat men and women differently
Evaluate practical applications as a strength of the neurochemical explanation for nicotine addiction
P: Offers practical applications.
E: For example, it allows researchers to focus solely on the neurochemistry and create drug treatment which mimics the role of nicotine in cigarette smoking. For example, nicotine replacement therapy (NRT) in the form of patches and
inhalers. The release of nicotine binds to nAChRs stimulating the release of dopamine and experiencing the same
pleasurable effects which occur with cigarette smoking and managing the withdrawal symptoms.
E: This can help the individual quit smoking as it reduces the unpleasant withdrawal symptoms of nicotine addiction; a common cause of relapse. The potential practical benefits go beyond nicotine addiction.
L: As NRT is successful in helping a large number of smokers abstain from cigarette smoking it strengthens the claims of
the neurochemical explanation.
Evaluate research support as a strength of the neurochemical explanation for nicotine addiction
P: Research support from the treatment of patients with Parkinson’s disease.
E: Parkinsons disease is a neurodegenerative disorder, characterised by a gradual loss of dopamine- producing nerve cells.
Fagerstrom et al (1994) treated two elderly PD patients with nicotine gum and patches. They found significant changes
in symptoms that were attributed to the increased levels of dopamine caused by the nicotine administration.
E: This suggests that nicotine may have a neuroprotective function against the development of PD and may also be beneficial in its treatment.
L: This evidence offers support for the link between nicotine and dopamine.
Evaluate reductionism as a limitation of the neurochemical explanation of nicotine addiction
P: Reductionist.
E: It reduces a complex behaviour such as addiction down to a simple explanation of activity of neurotransmitters.
E: It doesn’t consider alternative explanations of nicotine addiction. For example, learning theory suggests that nicotine
addiction is maintained due to operant conditioning. The behaviour is positively reinforced through the social and physiological rewards a smoker experiences, for example peer approval and feeling relaxed.
L:Therefore the neurochemical explanation is limited and social factors need to be considered.
Evaluate the nicotine acts differently in women and men as a part of the neurochemical explanation of nicotine addiction
P: Nicotine may affect men and women differently.
E: Cosgrove et al (2014) studied the brains of men and women using PET scans in order to measure the changing levels
of dopamine when smoking. They observed the dopamine levels of 16 long-term cigarette smokers while smoking a
cigarette. (8 men and 8 women).
For women, there was a rapid and strong dopamine effect in an area of the brain called the dorsal putamen.
Men only had moderate to low activation in this area. Men had a rapid and strong activation effect in the ventral stratium, whereas women were only mildly affected.
E: These findings support the claim that men and women smoke for different reasons. Men for the nicotine effect itself,
and women to relieve stress and manage mood.
L: Current neurochemical explanations may suffer from beta bias by not acknowledging these gender differences.
