A Natural Brake on Smoking
One question that has puzzled researchers is why nicotine addiction comes at so many different dosage levels. One person may only smoke a few cigarettes a day and another will consume 40 or more. Both abuse tobacco and both may be addicted, but the consequences are much greater based on how many cigarettes are smoked.
This is why physicians don’t just ask, “Do you smoke” but also “How many cigarettes do you smoke a day?”
An article from the National Institute on Drug Abuse explains one reason why.
The difference between the aversive and the desired
It has to do with the balance between the aversive effects of nicotine and the desired effects. The nausea, headache and dizziness that comes with nicotine is familiar to any smoker – they’ll remember the first time they lit up or a time when they over indulged. This is one of the normal responses to nicotine poisoning. But, it turns out there is a difference in the receptors for the nicotine in different people.
An animal study now shows that one subtype of receptor, the nicotinic acetylcholine receptor (nAChR), varies between animals who crave more nicotine and those which can stop at a lesser amount. The subtype is called the alpha-5 subtype. Those that have it as part of the receptor will shy away from nicotine while those animals that lack it will increase consumption.
The battle between the negative and the pleasurable
The picture is one of two competing processes in the brain. The nausea and other negative effects fight with the pleasurable effects. The balance is struck at what researchers referred to as the tipping point. Less than this amount of nicotine in the bloodstream and a smoker will crave more. But once the tipping point is passed, the desire to smoke falls away. This is mirrored in the cyclical nature of smoking for most tobacco addicts – blood levels fall and they crave another cigarette. Once they’ve had a dose of nicotine, the craving dies for a time and then the cycle repeats.
By creating mice either with or without the “braking” receptor subtype, researchers were able to control how much nicotine the animals self-administered. If a medication could be found to alter the body’s response to nicotine in humans, it would be possible to use this neurological switch to lower the total number of cigarettes smoked in a day and thereby reduce the lifetime harm caused.