28 Mar Why Only Some Smokers Need a Pack a Day
Nicotine is known for its ability to alter brain function and produce chemical changes that support a particularly tenacious form of addiction. However, not all smokers develop a high level of attachment to the drug’s effects. While some people become heavily addicted and smoke multiple packs of cigarettes every day, others develop only minor attachments to nicotine and smoke only lightly or occasionally. Current evidence indicates that much of an individual’s susceptibility to nicotine stems from the specific characteristics of sites in the brain called nicotine receptors that give the drug access to the brain’s primary nerve cells, called neurons.
Nicotine Receptor Basics
Technically, the nicotine receptors in the brain are known as nicotinic acetylcholine receptors, or nAChRs. They belong to a larger group of receptors referred to simply as acetylcholine receptors. The natural function of acetylcholine receptors is to react to the presence of a neurotransmitting chemical called acetylcholine. Inside the brain, this chemical forms the core of a larger neurotransmitter complex that helps keep the organ from activating too many neurons at a time and becoming overly excited. In the body, acetylcholine and its receptors play an essential role in facilitating basic muscle movement.
Nicotinic acetylcholine receptors, which sit on the surfaces of neurons in certain parts of the brain, get their name because they respond to the presence of nicotine as well as to the presence of acetylcholine. When nicotine accesses these receptors, it forces the associated neurons to produce dopamine, a neurotransmitter that activates the brain’s pleasure/reward circuitry and sharply increases the level of pleasure generated by that circuitry. As is true with most forms of substance addiction, nicotine addiction typically begins when the brain starts to view its increased dopamine supply as a normal condition instead of unique, unusual situation.
Nicotine Receptor Variations
While every nicotinic receptor serves the same basic function inside the brain (i.e., the acceptance of acetylcholine), not all of these receptors are constructed from identical types of chemical subunits. According to findings reported in 2012 by researchers from the Scripps Research Institute, some nicotinic receptors contain a specific type of subunit that changes the response to nicotine and produces unpleasant effects. The presence of these altered receptors does not rid the brain of nicotine’s pleasurable effects; however, these receptors do create a more complex reaction to nicotine that mixes pleasure with displeasure. Some people have more of these altered nicotine receptors in their brains than others.
The Bigger Picture
The circuitry in the brain that produces pleasure in response to nicotine is known as the limbic system. When this system is activated by nicotine, smokers find their behavior rewarding. People who experience particularly strong pleasurable reactions to the drug’s effects have an added incentive to keep smoking and may develop strong nicotine addictions that rely on a steady influx of cigarette smoke throughout the day.
Another circuit in the brain, known rather tongue-twistingly as the medial habenula-interpeduncular pathway (MHb-IPN), counters the effects of nicotine-generated pleasure in the limbic system. When this pathway is active, smokers tend to focus on the negative feelings associated with nicotine use, such as nausea, headaches and mouth, nose, throat or eye irritation. In broad terms, people with relatively high levels of activity in the limbic system and relatively low levels of activity in the medial habenula-interpeduncular pathway tend to experience smoking as a rewarding activity. Conversely, people with relatively low levels of activity in the limbic system and relatively high levels of activity in the MHb-IPN tend to experience smoking as an unrewarding activity.
As noted previously, some people’s brains contain relatively large numbers of the altered nicotine receptors responsible for diminishing the pleasure generated by the limbic system during smoking. Practically speaking, this means that their limbic systems experience less activation than the limbic systems of people who don’t have large numbers of altered receptors. In turn, reduced activation in the limbic system grants greater influence to the medial habenula-interpeduncular pathway, which as we’ve seen, emphasizes the negative aspects of smoking. In all likelihood, those who smoke lightly or occasionally have large populations of altered nicotine receptors and higher levels of MHb-IPN activity; therefore, on a subconscious chemical level, they view smoking more ambivalently than their heavy-smoking peers.
Find relief in recovery. Life gets better with addiction treatment.
Call our experts today.(855) 837-1334