Tracking addiction
is proving to be an extremely popular scientific sport these days. Credit the interest to new-fangled tools that allow scientists to follow brain activity from outside the body. And to increasing concern over the health costs of addictive substances.

In recent months, scientists have shown that nicotine and many other addictive drugs affect the brain in similar ways. In July, a group of Italian scientists at the University of Cagliari (see "Effects of Nicotine on the Nucleus Accumbens..." in the bibliography) used microdialysis (defined) to examine where in a rat's brain blood-borne nicotine has its effects.

As expected, nicotine accelerated the release of dopamine, a neurotransmitter (defined) associated with pleasure, emotions and addiction.

The curious details on dopamine and love...

The increase took place in the nucleus accumbens, a small part of the brain that's associated with substance addiction in rats. (What does "associated" mean? It means that if you give rats morphine or other addictive drugs, dopamine will be released in this area. And if you cut some nerves in the nucleus accumbens, addicted animals stop pressing a lever that causes the drugs to enter their bloodstreams.)

Using precise measurements, the new Italian study tracked the nicotine-stimulated dopamine release to the shell of the nucleus accumbens. The shell is wired to the forebrain, where emotional and motivational processing occurs. The forebrain includes the amygdala, an ancient structure with a tongue-twisting name that is active in many emotional states and is associated with addictive behavior.

The scientists also measured an increase in metabolism -- brain activity, indicated by the presence of a form of available blood sugar -- in the shell of the nucleus accumbens. Nicotine did not raise the concentration of this sugar elsewhere in the brain.

Why are the results significant? Because they add a neurochemical strand of evidence to existing evidence showing that nicotine is addictive. As lead author Francesco Pontieri and his colleagues wrote in Nature, there are behavioral similarities between nicotine addiction and heroin and cocaine addiction. Now, they say, there's strong evidence "that nicotine shares with addictive drugs a discrete neurochemical and functional property, namely, the ability to selectively increase dopamine transmission and energy metabolism in the shell of the nucleus accumbens."

In an accompanying article (see "Smoking is Harmful to the Brain" in the bibliography), pharmacologist Leslie Iverson of the University of Oxford commented that the research "adds new weight to the conclusion that nicotine is indeed addictive."

Other evidence also implicates the mesolimbic dopamine system, a group of structures that include the nucleus accumbens and amyglada, in drug cravings. Working at the University of Pennsylvania, clinical associate professor of psychology and psychiatry Anna Childress showed recovering cocaine addicts "cues," like videos of people taking cocaine, that caused a craving for cocaine. Using positron emission tomography (PET) (defined) scanning, she measured increased activity in the mesolimbic dopamine system.

The implication of these studies, says John Hughes, editor of the scientific journal Tobacco Control, is that "nicotine affects the brain similarly to the other drugs of dependence" like heroin and amphetamine. Indeed, he adds, many alcoholics "say getting off smoking is more difficult than getting off alcohol."

So while smokers might think they've just got a bad habit, their brains seem to consider smoking an extremely serious matter.

Don't stop now! We've just begun discussing the "question" of nicotine addiction.

There are 1 2 3 4 5 6 7 8 9 10 documents. (Glossary | Bibliography)