Wikipedia

Rat Park

Forschungsprojekt
Dies ist eine alte Version dieser Seite, zuletzt bearbeitet am 14. Dezember 2004 um 12:58 Uhr durch SlimVirgin (Diskussion | Beiträge). Sie kann sich erheblich von der aktuellen Version unterscheiden.

Rat Park was a 200-square-foot housing colony built for a group of white Wister laboratory rats in 1981 by American psychologist Dr. Bruce Alexander at Simon Fraser University in British Columbia, Canada. The colony was built to examine Alexander's hypothesis that drug addiction is a myth. Drug abuse, particularly the abuse of heroin, is not a neurophysiological phenomenon, he believes, but is largely, and perhaps entirely, the product of unhappiness. Heroin is not, in itself, addictive.

Datei:Opium-poppy.jpg
An opium poppy

Most animal studies do not support Alexander's hypothesis. Once introduced to morphine (heroin converts to morphine), rats will usually self-administer it whenever they can. The problem with these studies, Alexander told the Canadian Senate in January 2001, is that laboratory rats, descended from wild Norway rats, are "gregarious, curious and active creatures" but are isolated in cramped metal cages, "subjected to surgical implantations in the hands of an eager (but seldom skilful) graduate student, followed by being tethered in a self-injection apparatus." In other words, they are miserable. These experiments do not show that rats become addicted, Alexander argued, but simply that "severely distressed animals, like severely distressed people, will relieve their distress pharmacologically if they can," (Alexander, 2001). [1]

Do happy rats also self-administer morphine? To find out, Alexander built Rat Park. It was airy and spacious, 200 times the square footage of a standard laboratory cage, with a peaceful British Columbian forest scene painted on its plywood walls. Kept comfortably warm with an abundance of food, there were empty tins for burrowing, bright balls and wheels for play, and lots of companionship: 16-20 rats of both sexes in residence, a special space for mating, aromatic cedar shavings for nesting, and a private place for giving birth. It was rat heaven.

The physicalist model of drug addiction

In the 19th century, drug addiction was regarded as a sign of akrasia, or weakness of the will, indicating low intelligence and a weak moral character. Late 20th century brain research seemed to invalidate the moral or psychosocial model and replaced it with a morally blameless, physicalist disease model, according to which addiction to a drug is a by-product of the chemical structure of the drug itself. As social psychologist Dr. Stanton Peele puts it, "Tolerance, withdrawal, and craving are thought to be properties of particular drugs, and sufficient use of these substances is believed to give the organism no choice but to behave in these stereotypical ways, "Peele, 1985). [2]

 
Ursula, a heroin addict in her thirties living in the streets of Colombo, Sri Lanka, was photographed in 1991 by photojournalist Robin Loznack. Used with permission.

The physicalist model is reflected in the familiar claims Western governments make about drugs, such as "Heroin is so good; don't even try it once," or "Crack cocaine is instantly addictive," (Alexander, 2001) [3].

The physicalist/disease model makes two claims, according to Alexander (Ibid.)

  • Claim A: All or most people who use heroin or cocaine beyond a certain minimum amount become addicted.
  • Claim B: No matter what proportion of the users of heroin and cocaine become addicted, their addiction is caused by exposure to the drug.

Time and again, animal studies back up these claims. Professor Avram Goldstein of Stanford University wrote in 1979 that: "If a monkey is provided with a lever, which he can press to self-inject heroin, he establishes a regular pattern of heroin use — a true addiction — that takes priority over the normal activities of his life . . . Since this behavior is seen in several other animal species (primarily rats), I have to infer that if heroin were easily available to everyone, and if there were no social pressure of any kind to discourage heroin use, a very large number of people would become heroin addicts. (Goldstein, 1979).

Twenty years later, Goldstein maintains the same position. In a paper delivered to a 1997 U.S. methadone conference [4], he wrote: "Every addictive drug used by people is also self-administered by rats and monkeys. If we arrange matters so that when an animal presses a lever, it gets a shot of heroin into a vein, that animal will press the lever repeatedly, to the exclusion of other activities (food, sex, etc.); it will become a heroin addict. A rat addicted to heroin is not rebelling against society, is not a victim of socioeconomic circumstances, is not a product of a dysfunctional family, and is not a criminal. The rat's behavior is simply controlled by the action of heroin (actually morphine, to which heroin is converted in the body) on its brain."

Scientists adhering to the physicalist model are reductionists. Behavior, writes Goldstein, is "the business of the brain," (Ibid.). A bundle of neurons deep in the brain called the mesolimbic dopaminergic pathway — the so-called "reward pathway" — is the site of action of heroin and all other addictive drugs, according to Goldstein. The reward pathway mediates feelings of pleasure. Within this pathway, heroin causes dopamine neurons to release dopamine, the "pleasure hormone." Dopamine neurons are normally held in check by so-called inhibitory neurons, but heroin shuts these down, allowing the dopamine neurons to "run wild," writes Goldstein. The brain responds with feelings of euphoria, but the stimulation is excessive. The brain adapts. It becomes less sensitive to the heroin. This has two consequences. First, more heroin is required to produce the "high." Second, the reward pathway becomes less sensitive to the effects of endorphins, which regulate the release of dopamine, so that without heroin, there is a persistent feeling of sickness. After repeated use of heroin, the user becomes tolerant and dependent, and undergoes withdrawal symptoms if the heroin supply is terminated (Ibid.). The user loses control; that is, becomes an addict.

Against this view, Alexander argues that "the only actual evidence for the belief in drug-induced addiction comes 1) from the testimonials of some addicted people who believe that exposure to a drug caused them to "lose control" and (2) from some highly technical research on laboratory animals." The physicalist model has been "embellished in the news media", to the point, writes Alexander, "where the belief in drug-induced addiction has acquired the status of an obvious truth that requires no further testing." The widespread acceptance of this belief "is a better demonstration of the power of repetition than of the influence of empirical research . . . " (Alexander, op cit.)

Relinquishing the physicalist model would be contentious for a number of reasons. People who feel they are addicted to a drug may want to believe themselves caught in the grip of uncontrollable physical urges, their free will destroyed by altered brain chemistry. According to the "attribution theory," whereby people are said to attribute causes to their behavior that will maximize their self esteem, drug users may be resistant to claims that their perceived addiction is an illusion (Davies, 1992), and that, in fact, they could stop using the substance whenever they wanted to with little difficulty. In addition, there would be serious socio-economic implications for governments willing to acknowledge that poor social conditions might alone be responsible for drug abuse, rather than the addictive qualities of the drugs themselves. Instead of spending money on law enforcement and the "War on Drugs," governments of all political persuasions might have to consider diverting those funds, or increasing taxation, to improve living conditions for all citizens by, for instance, cleaning up the inner cities and spending more on education. Instead of prescribing methadone for a heroin user, a doctor might have to consider prescribing a decent home, paid for by government.

Furthermore, the idea that some drugs, like heroin, create an almost instant neurophysiological addiction strengthens the hand of politicians who may want the trade of these drugs to remain illegal, and of law enforcement authorities who require special powers and funds to disrupt the black markets that evolve as a consequence. For all these reasons, argues Alexander, an inadvertent marriage of convenience has formed between drug users, law enforcement authorities and governments, each group with its own reason to promote the view that certain substances are addictive, and that anyone coming into contact with them is at their mercy.

The Rat Park experiments

To avoid disrupting the rats' idyllic lifestyles with the usual daily weighing of the morphine containers, Alexander built a short tunnel large enough to accommodate one rat at a time. At the far end of the tunnel, the rats could drink a fluid from one of two drop dispensers, which automatically recorded how much each rat drank. One dispenser contained a morphine solution and the other plain tap water.

 
Diagram from the U.S. National Institute on Drug Addiction of a rat self-administering a drug

WIthout exception, the experiments indicated that "rats living in Rat Park had little appetite for morphine," (Alexander, op. cit). In some experiments, Alexander forced the rats to consume morphine for 57 days on end, giving them no liquid to drink except the morphine-laced solution before allowing them to choose the tap water instead. In other experiments, he made the morphine solution so sweet that no rat could resist trying it. Whatever he did to induce the rats to use the morphine, Alexander found significantly less morphine consumption in Rat Park than in the normal rat cages. In some experiments, the caged rats were consuming 20 times more morphine than the rats in Rat Park.

In an experiment called "The Seduction", the researchers put 16 lab rats into Rat Park and kept 16 others in standard cages. Because plain morphine is bitter, and rats have a sweet tooth, the researchers gave both sets of rats morphine-laced water with sugar added, just a little at first, with the sweetness increasing each day. Both rats also had plain tap water to choose from.

Alexander found the results startling. The caged rats took to the morphine instantly, even with virtually no sweetener. But no matter how sweet the morphine became, the rats in Rat Park resisted it. They would try it occasionally — with the females trying it more often than the males — but invariably they showed a preference for the plain water. By the end of the experiment, the caged rats had consumed 16 times more morphine than the Rat Park rats. It was, writes Alexander, "a statistically significant finding."

Even more significant, he writes, was this: Nalaxone is a substance that negates the effects of opioids but spares the sweet taste of the water. When Alexander added Nalaxone to the morphine-laced liquid, the Rat Park rats began to drink it. They wanted the sweet water, it seemed, so long as it did not disrupt their normal social behavior. The rats wanted to play, eat and mate, Alexander concluded, not be anesthetized. "Nothing that we tried," he wrote, "instilled a strong appetite for morphine or produced anything that looked like addiction in rats that were housed in a reasonably normal environment" (ibid.).

The rats who were given continuous morphine before being allowed to choose the tap water, did show some signs of physical withdrawal when they stopped taking the morphine, but they were minor. Alexander told psychologist Lauren Slater in an interview: "Rats in Rat Park showed what looked to be some minor withdrawal signs, twitching, what have you, but there were none of the mythic [seizure|seizures]] and sweats you so often hear about," (Slater, 2004). [5] "I think withdrawal, like drugs themselves, is consistently overplayed; it's part of the narrative people have heard about drugs, and so continue to tell; it's the paradigm by which drug users may interpret what may be in fact only discomfort, not agony. Certainly the rats did not appear to be in agony," he said, (Ibid.).

Alexander believes Rat Park shows that animal self-administration studies provide no empirical support for the theory of drug-induced addiction.

"The intense appetite of isolated experimental animals for heroin and cocaine in self-injection experiments," he writes, "tells us nothing about the responsiveness of normal animals and people to these drugs. Normal people can ignore heroin . . . even when it is plentiful in their environment, and they can use these drugs with little likelihood of addiction . . . Rats from "Rat Park" seem to be no less discriminating, (Alexander, op. cit). Rat Park shows, he believes, that the "belief in drug-induced addiction, at least with respect to heroin and cocaine, has no status as empirical science, although it has not been disproven. It is believed for some reason other than its empirical support." Chemicals do not cause addiction "in the way that the measles virus causes a rash of red spots," he told Slater, (Slater, op. cit).

Where is Rat Park now?

Datei:BruceAlexander.gif
Dr. Bruce Alexander

The experiment led nowhere and is largely forgotten. The two major biology journals Science and Nature rejected Alexander's paper. It was eventually published in Pharamacology, Biochemistry and Behavior, a respectable but much smaller publication, not widely read. Because of the paper's lukewarm reception, Simon Fraser University withdrew Rat Park's funding.

According to psychologist Lauren Slater, while Rat Park is "extremely significant in its findings, and poses relevant challenges to ourselves collectively and individually, the fact is no one paid much attention, then or now." Some studies did confirm its findings — for example, Bozarth, Murray and Wise in 1989, also published in Pharamology, Biochemistry and Behavior — but nothing came of these either. Slater asked psychiatrist Dr. Herbert Kleber, director of the substance abuse division at the College of Physicians and Surgeons of Columbia University and former deputy drug czar, what was wrong with Rat Park. He told her that Alexander had distorted information in the hope of provoking a public debate. "When I first heard of that Vancouver experiment, I thought it was ingenious," Herbert said. "Now I think it has all sorts of methodological flaws." Slater asked: "Like what?" "I can't remember," Kleber replied. Slater believes that Rat Park's problem is that it was conducted in Vancouver, the "scholarly equivalent of the tundra," (Ibid.').

Just as Alexander's psychosocial study has all but disappeared, the physicalist/disease model of drug addiction continues to gain strength. Scientists know that not all opiate users become addicts. The search is therefore on for the genes that predispose some users to become dependent faster than others. Finding these genes, writes Goldstein, will "validate the disease concept of heroin addiction," and will legitimize long-term treatment with methadone in the eyes of policy-makers, the public and the addicts themselves, (Goldstein, op. cit.).

Alexander has kept Rat Park's plywood walls with their mountains, lakes and pink clouds, but there are no rats living there now, no funding, little interest. "I've only had one good idea in my life," he told Slater, "and that was it. But one good idea, who can complain about that?" (Slater, op. cit.).

Meanwhile, according to Drug Sense, the U.S. federal, state and local governments jointly spent $40 billion dollars on the War on Drugs in 2003, a rate of $1200 every second. [6]

References

Further reading

Abgerufen von „https://de.wikipedia.org/w/index.php?title=Rat_Park&oldid=60239428“