Understanding nicotine dependence

In ten seconds, a cigarette puff sends nicotine racing to the brain, activating pleasure, arousal, cognitive enhancement, memory improvement, a suppressed appetite, reduction of anxiety and overall reinforcement of the smoking experience.

On 25th September 2013, Scott Leischow, from the Mayo Clinic (1) in Arizona, in the U.S., spoke at the 2013 PHASA tobacco workshop in Cape Town, hosted by Global Bridges Healthcare Alliance for Tobacco Dependence Treatment. Megan Harker attended the workshop and later spoke to Scott Leischow about his presentation centred on understanding pharmacodynamics and nicotine dependence.

Leischow has 20 years of research experience in conducting smoking cessation studies on pharmacological approaches and behavioural interventions.  Additionally, he created the Arizona quit line  (2).

In his youth he smoked and stopped . “I’m familiar with the addiction process and understand the challenges people go through," Leischow said, “It’s like playing Russian Roulette –  whether you’ll be able to quit or not, you have no idea if you’re going to get dependent or not.(2)”

According to Leischow, some smokers are slow and others fast metabolisers of nicotine. Slow metabolisers are less likely to become dependent. The limits to this research is it provides no indicator showing who’s dependent and who not (3).

Dose-to- effect is a term he used to explain how a smoker varies his/her puffing technique, to get the required feeling. Puffing can be deep, shallow or varied in between to activate the amount of smoke and nicotine drawn into the lungs. Absorption of smoke is influenced by inhalation depth, amount and duration. As well as the acidity and alkalinity of the smoke and air dilution (3).

Leischow used information from a U.S. surgeon general report to show that  1-2mg of nicotine becomes available to the smoker’s bloodstream in about five minutes when smoking a cigarette. Whereas with slow release, nicotine Replacement Therapies (NRT’s) such as gum, with a nicotine content of 2mg and 4mg, about 1-2mg of nicotine becomes available in 30 minutes. “NRT’s are not as addictive as cigarettes due to the dose and the speed of delivery to the brain,” he said (3).

In addition, nicotine’s half-life is approximately two hours – the amount of nicotine in the body reduces by half – but is variable from one person to another. Nicotine can remain in the body for 6-8 hours after a day of smoking (3).

According to Leischow, the addiction receptors are found in the pleasure-reward pathway also known as the mesolimbic dopaminergic pathway in the brain. And also in the locus ceruleus, ‘a noradrenergic centre in the brain which plays a vital part in cognitive processes and memory’ (3).

Nicotine dependence

Mechanism of action of nicotine in the central nervous system: Nicotine predominantly binds to the nicotinic acetylcholine receptors located in the mesolimbic-dopamine system of the brain. Nicotine specifically activates nicotinic receptors in the tegmental area causing an immediate dopamine release.- Picture and caption information provided by Scott Leischow.

Studies show that nicotine in tobacco smoke increases the number of nicotine receptor sites in the brain by two to three-fold and this multiplication may not be reversible (3). Therefore without nicotine as an activator of the nicotinic acetylcholine receptors, when a smoker tries to quit smoking they starve the receptors resulting in nicotine withdrawal symptoms.

Smokers have known from the outset  by experience (4) that nicotine increases motivation, energy,  alertness, feelings of vigour and cognitive arousal (3). Scientists confirmed this; nicotine stimulates the receptors, produces dopamine and induces perceptions of happiness and pleasure (3).

Moreover, stimulation of brain chemicals like norepinephrine leads to ‘generalized brain activation, increased concentration, intellectual skill, enhanced memory, and improved problem-solving behaviour.’ To add, it reduces appetite, contributing to low weight (3).

Furthermore, Leischow says that we know about environmental factors but we need more information on genetic factors. Tobacco dependence is linked to gene and environmental factors. Genetic factors include-biological pathways including metabolic dopaminergic, opiodergic and serotonergic and nicotinic receptor functioning. “When someone smokes a pack a day it’s most likely attributed to biological factors,” said Leischow (3).

Lastly, Leischow’s advice to smoking cessation counsellors is: “You need to look at the constellation of factors causing a person to smoke. (3)”. For  information on treatment and cessation aids Leischow recommends http://treattobacco.net/ (2).

References and footnotes

  1. The Mayo Clinic created Global Bridges and is sponsored by an unrestricted grant from Pfizer. Also, Global Bridges helps train health care workers globally and in South Africa.
  2. Skype Interview with Scott Leischow, 8 January 2014.
  3. Information derived from Scott Leischow’s referenced Power Point slides, and presentation, delivered on 25th September 2013 at the PHASA conference, tobacco workshop in Cape Town.
  4. Snowdon, C. Velvet Glove, Iron Fist. North Yorkshire, United Kingdom: Little Dice Publishers; 2009.

 

 

 

 

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