Brain neurochemistry - including the role of dopamine

Question 1

Nicotine

Answer 1

Nicotine is the main active ingredient of tobacco.
Nicotine is absorbed through the lining of the mouth and nose and by inhalation in the lungs.
After inhalation, nicotine reaches peak levels in the bloodstream and the brain in less than 10 seconds.
Nicotine crosses the blood-brain barrier and affects the function of the neurons in the brain.

Question 2

Nicotine imitates the action of

Answer 2

a natural neurotransmitter called acetylcholine.
It binds to a particular type of acetylcholine receptor - known as the nicotinic acetylcholine receptor - in the brain.

Question 3

how dopamine is released

Answer 3

1)Nicotine binds to nicotinic acetylcholine receptor sites on the neurons of the ventral tegmental area (VTA).

2. These neurons then trigger the release of the neurotransmitter dopamine in the nucleus accumbens – leading to feelings of pleasure
   (repeated nicotine stimulation increases the amount of dopamine released in the
   nucleus accumbens)

3.This subsequently boosts activity in the prefrontal cortex (decision making centre

Question 4

The nucleus accumbens (NAc) is referred to as

Answer 4

he pleasure centre of the brain, and is associated with reward - the release of dopamine in this part of the brain produces feelings of pleasure. This pleasure encourages the individual to repeat the smoking behaviour.

Question 5

Between cigarettes chronic smokers maintain a high enough concentration of nicotine

Answer 5

to deactivate the receptors and slow down their recovery (they cannot be triggered by acetylcholine -> downregulation).

Question 6

Smokers develop a tolerance to nicotine

Answer 6

and experience reduced pleasure from it over time, because the nicotinic receptors become desensitised to the effects of nicotine. Therefore, they need to smoke more to achieve the same desired effect

Question 7

The Nicotine Regulation Model:

Answer 7

Individuals continue to smoke to avoid withdrawal symptoms e.g. impairment of mood and concentration.
These withdrawal symptoms are brought about due to nicotine levels in the blood dropping, which causes a decrease in dopamine levels, as well as nicotinic acetylcholine receptors becoming upregulated and sensitive to the effects of acetylcholine again, resulting in feelings of anxiety, agitation and restlessness.

Question 8

E: Dani and De Biasi’s (2001) found that

Answer 8

part of the reason nicotine is so addictive is because it acts on the dopaminergic systems, which helps reinforce rewarding behaviour.
C: This highlights a direct link between the neural mechanisms in the brain and the rewarding effects felt whilst smoking.

Question 9

E: Watkins et al. (2000) reviewed the research into the

Answer 9

neurobiology of nicotine addiction. They found that dopamine release was reduced following chronic exposure to nicotine.
C: This could explain how a tolerance to nicotine develops over time as the level of reward felt decreases with prolonged exposure.

Question 10

P: Dopamine is only part of the neural action: the reason that nicotine is so addictive is due to several complex explanations.

Answer 10

E: Research increasingly shows that there are many other neurochemical mechanisms involved and that there is a vastly complex interaction of neurochemical systems. For example, neurotransmitter pathways such as GABA and serotonin, plus other systems such as endogenous opioids (endorphins) have been implicated.

C: However, the dopamine system is arguably central to the neurochemistry of nicotine addiction and these other systems interact with it to have their effects.

Question 11

P: The role of dopamine could further support the idea that there is a genetic link to smoking addiction.

Answer 11

E: Comings et al. found that nicotine addicts show a greater prevalence of the A1 variant of the DRD2 gene (48% in smokers, compared to 25% amongst non-smokers), which is related to fewer dopamine receptor sites and lower levels of dopamine in the brain.

C: The dopaminergic mechanism in some individuals could therefore lead them to feel the rewarding effects of nicotine to a greater extent, thus increasing the likelihood of them becoming addicted to smoking.

Question 12

P: However, there is evidence to suggest that there are gender differences in the effects of nicotine on the brains of men and women.

Answer 12

E: Cosgrove et al. (2014) found that nicotine led to different effects on dopamine pathways in males and females. They 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 (8 men and 8 women) while smoking a cigarette.
For women, there was a rapid and strong dopamine effect in an area of the brain called the dorsal putamen, whereas men only had moderate to low activation in this area. Men had a rapid and strong activation effect in the ventral striatum, whereas women were only mildly affected.

C: Cosgrove concluded that the reasons for nicotine use differ in women and men….
Men may smoke for the rewarding effects of nicotine
Women may smoke to manage stress and mood

Question 13

P: The neurochemical explanation of nicotine addiction is considered to be reductionist.

Answer 13

E: This is because it only explains nicotine addiction on a biological level in terms of the role of dopamine. There is evidence to suggest that psychological and social factors also play an important role in nicotine addiction e.g. stress relief, influence of peers and family.

C: It is likely that dopamine, although implicated, cannot offer a complete explanation for nicotine addiction and many levels of explanation should be considered besides a purely biological one.