6.3 Psychoactive effects of nicotine

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In addition to the physical effects outlined in the previous section, nicotine also has acute effects on a smoker's mental state.

Tobacco provides the average daily smoker with an efficient, convenient and socially acceptable way of self-administering a potent psychoactive drug more than 100 times a day1 (about 140 puffs per day for the 14-a-day smoker).1,2

Nicotine has biphasic brain effects, that is, it can improve alertness by stimulating brain function and also produce a feeling of relaxation by depressing functioning. The mental and physical state of the smoker, and the situation in which smoking occurs, influence the way in which a cigarette affects psychological states and physiological responses.3

In order to provide a strong psychoactive reaction, nicotine must be delivered rapidly to the brain. The inhalation of tobacco smoke into the lungs is a highly optimised method of rapidly delivering nicotine via the bloodstream to the brain, where it acts upon neuronal nicotinic receptors.1 Nicotine, like all addictive drugs, causes a complex range of biochemical changes that create dependence, which is reinforced by the aversive effects of withdrawal.4

6.3.1 The neurobiology of the positive reinforcing properties of nicotine

The pleasant and rewarding effects of nicotine reinforce smoking and other forms of tobacco use.1 The neurobiology of nicotine's rewarding effects is only partially understood. The same is true of the biological basis of the abstinence syndrome that occurs after abrupt cessation of smoking; avoiding the abstinence syndrome encourages smokers to continue smoking.4

Like many other addictive drugs, nicotine activates release of the neurotransmitter dopamine in the brain's 'reward system' (the mesocorticolimbic dopamine system).1 Repeated nicotine exposure stimulates dopamine release in the nucleus accumbens,1 a part of the brain that is believed to play an important role in all forms of addiction.5 This region of the brain is also involved in the regulation of emotions and the processing of rewards such as food and sex. It also has a role in the actions of other drugs of abuse, such as amphetamines and cocaine.5

Nicotine exerts its effects by activating specific sites called receptor proteins. These in turn trigger the release of dopamine in the nucleus accumbens and the secretion of other nerve-stimulating chemicals such as acetylcholine and glutamate in the hippocampus and cerebral cortex.1 Their effects improve vigilance, attention and cognition, benefits that smokers often cite as reasons for continuing to smoke. Low doses of nicotine may improve memory, information processing and attentiveness, although the benefits are small and similar to the effects of drinking coffee or other caffeinated drinks.4

Repeated administration of nicotine greatly increases the release of dopamine in a specific region of the nucleus accumbens called the accumbal core. The enhanced dopamine release is central to Pavlovian or classically conditioned learning, which associates the effects of nicotine with cues present in the environment and in tobacco smoke inhaled by the smoker. The linking of these responses to such cues is strongly linked to the transition to addiction, whereby addicted persons find it difficult to control their cravings for the drug.4, 6

According to smokers, nicotine use helps them when they are depressed, stressed, embarrassed, bored, irritable or in a bad mood.7 Alleviating any of these unpleasant feelings by smoking a cigarette reinforces the psychological aspects of tobacco addiction.7 There is no intrinsic reason why tobacco use should serve this purpose, other than that it helps to avert the physiological and psychological discomfort of withdrawal.4 For more information on tobacco withdrawal, see Section 6.9.

References

1. Benowitz N. Nicotine addiction. New England Journal of Medicine 2010;362(24):2295–303. Available from: http://content.nejm.org/cgi/content/full/362/24/2295

2. Australian Institute of Health and Welfare. 2007 National Drug Strategy Household Survey: detailed findings. Drug statistics series no. 22, AIHW cat. no. PHE 107. Canberra: AIHW, 2008. Available from: http://www.aihw.gov.au/publications/index.cfm/title/10674

3. US Department of Health and Human Services. The health consequences of smoking: nicotine addiction. Rockville, Maryland: US Department of Health and Human Services, Public Health Service, Centers for Disease Control, Center for Chronic Disease Prevention and Health Promotion, Office of Smoking and Health, 1988. Available from: http://www.cdc.gov/tobacco/data_statistics/sgr/previous_sgr.htm

4. Royal College of Physicians of London. Nicotine addiction in Britain. A report of the Tobacco Advisory Group of the Royal College of Physicians. London: Royal College of Physicians of London, 2000. Available from: http://www.rcplondon.ac.uk/pubs/books/nicotine/

5. Koob GF and Volkow ND. Neurocircuitry of addiction. Neuropsychopharmacology 2010;35(1):217–38. Available from: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&dopt=Citation&list_uids=19710631

6. Evans DE and Drobes DJ. Nicotine self-medication of cognitive-attentional processing. Addiction Biology 2008;14(1):32–42. Available from: http://www3.interscience.wiley.com/journal/121449078/abstract

7. Parrott A. Stress modulation over the day in cigarette smokers. Addiction 1995;90(2):233–44. Available from: http://www3.interscience.wiley.com/journal/119254683/abstract

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