|The Brain: The Origins of Dependence|
Posted by FoM on February 05, 2001 at 17:53:52 PT|
By Sharon Begley
New research on how cocaine, heroin, alcohol and amphetamines target neuronal circuits is revealing the biological basis of addiction, tolerance, withdrawal and relapse
One by one, each crack addict took his turn in the fMRI tube, its magnets pounding away with a throbbing bass. A mirror inside was angled just so, allowing the addict to see a screen just outside the tube. Then the 10-minute video rolled.
For two minutes, images of monarch butterflies flitted by; the fMRI, which detects active regions in the brain, saw nothing untoward. Then the scene shifted. Men ritualistically cooked crack... an addict handed cash to a pusher... users smoked. It was as if a neurological switch had been thrown: seeing the drug scenes not only unleashed in the addicts a surge of craving for crack, but also triggered visible changes in their brains as their anterior cingulate and part of the prefrontal cortex—regions involved in mood and learning—lit up like Times Square. Nonaddicts show no such response.
The fMRI had pinpointed physical changes in the brain that apparently underlie cue-induced craving, showing why walking past a bar, passing a corner crack house or even partying with the people you used to shoot up with can send a recovering addict racing for a hit. “The brain regions that became active are where memories are stored,” says Dr. Scott Lukas of McLean Hospital in Massachusetts, who led the 1998 study. “These cues turn on crack-related memories, and addicts respond like Pavlov’s dogs.”
“Drugs of abuse change the brain, hijack its motivational systems and even change how its genes function.”
— Dr. Alan Leshner, Director, National Institute on Drug Abuse
“This is your brain on drugs”: it’s not just an advertising line. Through fMRI as well as PET scans, neuroscientists are pinpointing what happens in the brain during highs and lows, why withdrawal can be unbearable and—in one of the most sobering findings—how changes caused by addictive drugs persist long after you stop using. “Imaging and other techniques are driving home what we learned from decades of animal experiments,” says Dr. Alan Leshner, director of the National Institute on Drug Abuse. “Drugs of abuse change the brain, hijack its motivational systems and even change how its genes function.”
An addicted brain is different—physically different, chemically different—from a normal brain. A cascade of neurobiological changes accompanies the transition from voluntary to compulsive drug use, but one of the most important is this: cocaine, heroin, nicotine, amphetamines and other addictive drugs alter the brain’s pleasure circuits. Activating this circuit, also called the reward circuit, produces a feel-good sensation. Eating cheesecake or tacos or any other food you love activates it. So does sex, winning a competition, acing a test, receiving praise and other pleasurable experiences. The pleasure circuit communicates in the chemical language of dopamine: this neurotransmitter zips from neuron to neuron in the circuit like a molecular happy face, affecting the firing of other neurons and producing feelings from mild happiness to euphoria.
How? “Drugs of abuse increase the concentration of dopamine in the brain’s reward circuits,” says Nora Volkow of Brookhaven National Lab. The drugs do that more intensely than any mere behavior, be it eating a four-star meal or winning the lottery. But each drug turns up this feel-good neurochemical in a different way:
Cocaine blocks the molecule that ordinarily mops up dopamine sloshing around neurons. When all the seats on this so-called transporter molecule are occupied by cocaine, there is no room for dopamine, which therefore hangs around and keeps the pleasure circuit firing. The intensity of a cocaine high, Volkow found in 1997, is directly related to how much cocaine ties up the seats on the transporter bus.
Amphetamines block the transporter, too. They also push dopamine out of the little sacs, called vesicles, where neurons store it. More dopamine means more firing of neurons in the pleasure circuit.
Heroin stimulates dopamine-containing neurons to fire, releasing the neurochemical into the nucleus accumbens, a key region in the pleasure circuit. Nicotine does the same. Heroin also excites the same neurons that our brain’s natural opioids do, but much more powerfully.
After igniting these acute effects, an addictive drug isn’t nearly through with the brain. Chronic use produces enduring changes. The most important: it reduces the number of dopamine receptors. Receptors are simply little molecular baseball gloves that sit on neurons, grab passing neurotransmitters like fly balls and reel them in. Animal evidence suggests that the more you take an addictive drug, the more dopamine receptors you wipe out, as the brain attempts to quiet down an overly noisy pleasure circuit. Having fewer dopamine receptors means fewer of those passing dopamines get caught, and the pleasure circuit calms down. But now the law of unintended consequences kicks in. With fewer dopamine receptors, a hit that used to produce pleasure doesn’t. This is the molecular basis for tolerance. Drugs don’t have the effect they originally did. To get the original high, the addict has to up his dose.
But there’s worse. The dearth of dopamine receptors means that experiences that used to bring pleasure become impotent. A good meal, a good chat, a good massage—none ignite that frisson of happiness they once did. The only escape from chronic dysphoria, irritability, anxiety and even depression, the user believes, is to take more drug. Initial use, in other words, may be about feeling good. But addiction is about avoiding abject, unremitting distress and despair.
The agony of withdrawal is also a direct result of drugs’ resetting the brain’s dopamine system. Withdrawal and abstinence deprive the brain of the only source of dopamine that produces any sense of joy. Without it, life seems not worth living. When a junkie stops supplying his brain with heroin, for instance, he becomes hypersensitive to pain, chronically nauseated and subject to uncontrollable tremors. “This is why addiction is a brain disease,” says NIDA’s Leshner. “It may start with the voluntary act of taking drugs, but once you’ve got it, you can’t just tell the addict ‘Stop,’ any more than you can tell the smoker ‘Don’t have emphysema.’ Starting may be volitional. Stopping isn’t.”
Although the biological basis of tolerance, addiction and withdrawal is yielding some of its secrets, relapse is harder to explain. Why does an addict who has abstained for weeks, months or longer suddenly reach for the needle or the bottle? According to lab-animal studies, abstinence allows dopamine receptors to eventually return to normal, so after some period of withdrawal agony the brain should stop craving the drug. Yet addiction is practically the dictionary definition of a relapsing disease. One clue might lie in Scott Lukas’s fMRI findings about cue-induced craving. The memories of drug abuse are so enduring and so powerful that even seeing a bare arm beneath a rolled-up sleeve reawakens them. And just as Pavlov’s dog learned to salivate when he heard a bell that meant “chow time,” so an addict begins to crave his drug when he sees, hears or smells a reminder of past use. Relapse might also reflect enduring genetic changes. Drugs can act as DNA switches, turning genes on or off. In lab animals, for instance, bingeing on cocaine turns down the activity of a gene that makes a dopamine receptor, finds Dr. Mary Jeanne Kreek of Rockefeller University. If that gene remains chronically inactive, it could lay the basis for relapse as an addict tries to compensate for a crippled pleasure circuit.
The Complete Series:
Newsweek's Special Report on Addiction
• The War on Addiction: http://msnbc.com/news/526153.asp
• The Origins of Dependence: How It All Starts Inside Your Brain: http://msnbc.com/news/526132.asp
• Treatment: New Ways to Stay Clean: http://msnbc.com/news/526141.asp
• Waging a Public Battle: Robert Downey Jr. Takes One Day at a Time: http://msnbc.com/news/526156.asp
• 'Traffic's' Screenwriter on Addiction: The Enemy is Every One of Us: http://msnbc.com/news/526161.asp
• Addiction and Genius: From Kubla Khan to Kurt Cobain: http://msnbc.com/news/526014.asp
• International: The Hell of Addiction: http://msnbc.com/news/526134.asp
Comment #8 posted by dankhank on February 06, 2001 at 07:13:59 PT:|
|I agree, John.|
Even if this article breaks no new ground it would seem to offer an interesting peek into how the brain does all of that "stonin'" business ...
I would have liked to have seen the marijuana mechanism discussed as a counterpoint to the ones described here, but I realize that NIDA won't mention it since it markedly differs with the processes described here.
Receptors "built-in" to the brain for the THC molecule would be too hard to explain as justification for the most egregious of legal harassments, the stealing of your body to be locked away.
so it would seem that this article is interesting for what it said AND for what it didn't say ...
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|Comment #7 posted by John on February 06, 2001 at 06:39:32 PT|
|Personaly, even though marijuna is not mentioned here, or is a control, I think this is a great artical on how the brain and drugs work.|
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Comment #6 posted by Dan B on February 06, 2001 at 02:02:32 PT:|
|I was just about to post on exactly the same phenomenon--that they deliberately compared reactions of mundane scenes of butterflies to activities these people have grown to regard as pleasurable because they have engaged in those activities. The same brian centers would be active if they showed, say, cheesecake to people who like cheesecake, of sexy pictures to . . . well, just about anyone!|
The most telling thing about this article is that it states quite clearly, "For two minutes, images of monarch butterflies flitted by; the fMRI, which detects active regions in the brain, saw nothing untoward." Proof positive that the person addicted to hard drugs, like crack cocaine, has no impairment--no differences from those not addicted--when it comes to normal stimulation from normal, everyday pretty pictures.
The only differences shown by this study have to do with the fact that people who enjoy a certain activity will become excited when faced with the prospect of enjoying that activity. If they had tested me with pictures of the Cannabis News site, particularly this section that allows me to post, I would have had the same positive reaction as did the crack addicts to crack. I admit it! I'm addicted to expressing my support for positive change in drug policies!
No wonder Leshner has such a terrible reputation in the community of legitimate, scientific researchers.
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|Comment #5 posted by observer on February 05, 2001 at 20:27:26 PT|
| A cascade of neurobiological changes accompanies the transition from voluntary to compulsive drug use, but one of the most important is this: cocaine, heroin, nicotine, amphetamines and other addictive drugs alter the brain’s pleasure circuits. Activating this circuit, also called the reward circuit, produces a feel-good sensation. Eating cheesecake or tacos or any other food you love activates it. So does sex, winning a competition, acing a test, receiving praise and other pleasurable experiences.|
Oh, so you mean similar fMRI scans to the fMRI scans of cocaine (etc.) users alarmingly reported here, could be obtained by exposing a hungry person to food, and so on? Why, then, are not these breathless "latest scientific results" controlled against "other pleasurable experiences" like "eating cheesecake" or sex? Wouldn't that make sense to do? (Too shy to talk in mixed company about cheesecake?) A control for this "experiment"? I know these great scientists have heard of controls, as in "the experimental control", or "a controlled experiment."
I mean, that (rigorously controlled, peer-reviewed research) is what the good doctor is implying, when he says things like, "Imaging and other techniques are driving home what we learned from decades of animal experiments,” says Dr. Alan Leshner", isn't he? I wonder why NIDA didn't play up the cheese-cake scans or sex fMRI scans or the "I just got $500" scans?
If other pleasurable experiences can elicit the same response in the brain as "demon rum" (or demon crack, or demon meth or demon MDMA or whatever), yet the "Institute" (NIDA) chooses to put a microscope on the pleasure-reactions of illegal drug users only, reporting only illicit drug users' brain activity in detail, while glossing over the identical reactions of those who have other pleasurable experiences (food, sex, praise, etc.), what does that tell you about the goals of such "research"? Are they political goals, goals that perhaps have more to do with bolstering the current policy of jailing drug users, or to lend credence to a policy of coerced and forced "treatment"?
. . . Dr. Alan Leshner, director of the National Institute on Drug Abuse. “Drugs of abuse change the brain, hijack its motivational systems and even change how its genes function.”
Yeah, sure, Lushner, real scary image there. "Hijacked." The "drugs of abuse" they just "hijack its motivational systems", like "other pleasurable experiences" (cheesecake, sex, etc.) "hijack" the brain's "reward centers".
And who ever said "researchers" -- NIDA career propaganda bureaucrats -- like Le$hner are mere quacks and prostitutes? Not me, man.
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|Comment #4 posted by FoM on February 05, 2001 at 20:24:48 PT|
When addition overtakes a person's life, all willpower can seem to completely disappear. Roughly half of all patients relapse within a year of detoxification, causing many health care professionals to wonder if medical intervention is worth the effort. But the truth is not so grim.
Addiction may never be curable for all people. But with medication, counseling, social support and family support, even the most inveterate abuser has a solid chance at success. Join Geoffrey Cowley for a Live Talk on Wednesday, Feb. 7 at noon, EST to discuss the latest addiction treatment methods.
Submit questions any time. http://discuss.washingtonpost.com/zforum/00/submit_020701_addiction.htm
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|Comment #3 posted by MikeEEEEE on February 05, 2001 at 19:53:44 PT|
|It says: One by one, each crack addict took his turn in the fMRI tube|
hello, are these lab animals?
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|Comment #2 posted by Not To Worry on February 05, 2001 at 19:17:47 PT|
| Am I the only one who noticed that Marijuana was not mentioned once here???? Did someone pull the "J" off their keyboard's?? Or are they now willing to admit that Marijuana is less dangerous than booze?? Wait and see, I guess.|
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|Comment #1 posted by Rainbow on February 05, 2001 at 18:21:40 PT|
|Why are we locking people up? It is so obvious that even a pol or police officer should see the light.|
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