While the title may be a bit misleading--the article is pretty good.
From the Chicago Tribune
Experts say love of nicotine is all in mindBy Ronald Kotulak
Tribune science reporter
March 14, 2002
Working to unravel a long-standing puzzle of cigarette addiction, University of Chicago researchers have discovered why smoking is uniquely pleasurable and why nicotine has such ferociously addictive powers.
Published Thursday in the scientific journal Neuron, the research shows that nicotine not only stimulates pleasure in the brain's reward center but has the unique ability to neutralize the "off-switch" that usually throttles down good feelings quickly.
The finding provides major clues to understanding the complex process by which the brain becomes addicted to nicotine and opens new approaches to developing drugs to block nicotine's power to hijack the brain.
For the 2,000 teenagers a day who become smokers, the new evidence helps to explain how a single cigarette quickly teaches the brain cells of a first-time smoker to crave nicotine.
And for the more than 30 million American smokers who try to quit smoking each year and fail, the finding shows why breaking the habit is so hard.
The U. of C.'s Daniel S. McGehee and his colleagues showed how nicotine from a cigarette produces a high that can last up to an hour.
It does so first by quickly turning on the pleasure chemical dopamine in the brain's reward center, something scientists have known for several years. But the dopamine surge ends quickly, and researchers couldn't figure out what caused nicotine's long-lasting high and its ability to induce addiction.
McGehee's finding shows for the first time that nicotine also acts on a group of regulatory cells whose job is to stop the dopamine high. With this control mechanism temporarily disabled, the reward system continues to operate long after it should have been shut down.
The result is a runaway feel-good sensation that the brain commits to its memory bank as something it wants more of.
"This gives an explanation for why the long high happens," said Dr. Glen Hanson, acting director of the National Institute on Drug Abuse. "It's a combination of tolerance happening to several systems at the same time. When you sum everything up, you get an enhancement of the dopamine pleasure pathway."
McGehee's detailed studies of rat brains revealed the step-by-step process by which nicotine takes over the brain's reward system. Neuronal pathways in that system were examined cell by cell to determine how they responded or failed to respond to individual neurotransmitters.
Drug companies have been hampered in their efforts to develop anti-addiction medicines because they didn't know how the brain became addicted, said John Dani, a Baylor College of Medicine neuroscientist who was one of the first to show nicotine's effect on dopamine.
"Dan's work will allow both academic and pharmaceutical researchers to focus on the mechanisms of addiction with a greater understanding of how they work," Dani said.
The brain's reward system, scientists believe, is basically designed to help a person learn what is good for his survival and what is not.
It provides a wide range of sensations from euphoria to just plain feeling good. Experiences such as falling in love, getting a big promotion, coloring between the lines for the first time, seeing your baby's smile and winning the lottery promote some of the biggest dopamine jolts. Eating a good meal, making a new friend, taking a walk on the first morning of spring, working a crossword puzzle and other less intense learning experiences get less of the pleasure chemical.
"These really important events in our lives have a different quality to them that is imparted by the reward system," McGehee said. "What the drugs of abuse are doing is usurping that reward system."
Dopamine is carefully dispensed. A jolt makes a person feel good and helps lay down a memory of a new experience or reinforce an old one.
But dopamine is soon cut off, reducing the pleasurable effect to baseline levels. If it weren't turned down, dopamine would cause a constant feeling of being high, which would impede new learning and reduce the chance of survival.
"Nicotine acts as if it's reinforcing a behavior that should be rewarded," Dani said. "The brain is fooled into thinking that nicotine is a proper participant in life."
An estimated 57 million Americans smoke, which is linked to more than 400,000 deaths annually from cancer, heart attacks, strokes and emphysema. It is the nation's most preventable cause of death.
A cigarette contains about 10 milligrams of nicotine. About 1 to 2 milligrams get into the blood stream and hit the brain's reward center within 10 seconds after inhalation.
An average smoker takes 10 puffs per cigarette over a five-minute period. For a person who smokes 1 1/2 packs daily, his brain gets 300 hits of nicotine.
That nicotine plugs into receptor ports on brain cells stimulating the production of dopamine. Dopamine then turns the brain's pleasure center on.
At the same time, nicotine molecules plug into another set of inhibitory neurons, jamming their ability to turn off the pleasure center. The subsequent high lasts about an hour, the time it takes for nicotine in the blood to subside to the point where the inhibitory system can be reactivated.
"There's no other outcome than excitation when you've got nicotine in the system," he added. "It would be hard to design a drug that acts on the reward center that would be more effective than nicotine."
Copyright © 2002, Chicago Tribune