New study shows how nicotine stimulates drug-associated memories.

Researchers at the laboratory of Professor John Dani, at Baylor College of Medicine in Texas have published new research that helps explain how nicotine creates memories of drug-related cues. In a series of studies of laboratory mice they found that mice would learn to go to a place where they received nicotine (a paradigm called “conditioned place preference”). In addition to reinforcing preference for places where nicotine is received it seems that the neurotransmitter, dopamine, which is released by nicotine, signals that the environment at that place is particularly salient and should be remembered. It is as if nicotine takes over the brain’s natural mechanism for helping us learn that elements in an environment are particularly relevant for survival (e.g. have food, water, shelter etc), and instead leads the brain to expect something rewarding to happen in that situation. The result is that when either a mouse or a human returns to an environment with stimuli that were thereon previous occasions they had nicotine, they will have a cued desire for the drug, that likely leads to cravings and increased drug-seeking behavior.

This animal research may explain why ex-smokers sometimes experience a sudden strong urge to smoke when they go to a place, or are in a situaution in which they formerly smoked. Professor Dani’s research shows that dopamine is not simply a “reward” neurotransmitter but also plays a role in stimulating the connections between neurons that underlie learning and memory. In the research, Dani’s team found that when the dopamine release was prevented, the animals did not learn half as well as when nicotine was allowed to stimulate dopamine release in a normal manner.
It has been obvious for a long time that cravings to smoke are triggered in places or situations in which the person usually smokes. What this new research adds is a more detailed explanation of the mechanism, and the role of the neurotransmitter, dopamine.

This finding may help explain why taking some smoking cessation medicines for a few weeks prior to quitting may be helpful. Wearing the nicotine patch for a couple of weeks before quitting may prevent cues being attached to specific situations (because the smoker also receives nicotine between cigarettes). Taking varenicline (which partially blocks nicotine-induced dopamine release) may similarly similarly reduce the extent to which nicotine-related situations cause later cravings.

Reference:
Tang J, Dani JA. Dopamine enables in vivo synaptic plasticity associated with the addictive drug nicotine. Neuron. 2009 Sep 10;63(5):673-82.

Labels: dopamine, J Teng, John Dani, jonathan foulds, laboratory, nicotine, smoking cessation

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