Rats taking cannabis get taste for heroin

news@nature.com ^ | 5 July 2006 | Michael Hopkin

[neverdem]

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Published online: 5 July 2006; | doi:10.1038/news060703-9

Rats taking cannabis get taste for heroin

Study suggests cannabis-users may be vulnerable to harder drugs.

Michael Hopkin

Neuroscientists have found that rats are more likely to get hooked on heroin if they have previously been given cannabis. The studies suggest a biological mechanism — at least in rats — for the much-publicized effect of cannabis as a 'gateway' to harder drugs.

The discovery hints that the brain system that produces pleasurable sensations when exposed to heroin may be 'primed' by earlier exposure to cannabis, say researchers at the Karolinska Institute in Stockholm, Sweden, who carried out the study.

There has long been a debate about whether exposure to drugs such as nicotine or marijuana might lead to harder habits. Many argue that the most important factors in the equation are social ones: people who get one drug from a dealer are probably more inclined to try another. But researchers are still interested to know whether there is any physiological effect that might additionally predispose users of so-called soft drugs to harder-drug addiction.

To rule out social factors, the researchers turned to an animal model. They dosed some rats with the active ingredient of cannabis and others with a neutral compound during their adolescence (when they were about four to six weeks old). After that, they gave the rats intermittent access to heroin for several weeks, obtained by pressing a lever.

Although all rats helped themselves to heroin, the ones given cannabis's key compound, called -9-tetrahydrocannabinol (THC), during their formative years showed a greater escalation in their self-dosing during the experiment. By the end, rats that'd had cannabis in their 'teens' were pressing the lever that delivered heroin about 1.5 times more than the rats that had previously been drug-free.

We now know that these drugs have an impact on behaviour later in life.  Yasmin Hurd, Mount Sinai School of Medicine, New York

The researchers report the findings in the journal Neuropsychopharmacology¹.

Hard to kick

"It's a nice study, although somewhat preliminary," comments Ian Stolerman, a psychopharmacologist at Kings College London. "It's too early to say there's a consensus, but a small number of studies like this suggest that there is a physiological basis for this effect."

The rat results may be due to the fact that both THC and heroin act on a pleasure pathway in the brain called the opioid system, explains study leader Yasmin Hurd, now at Mount Sinai School of Medicine in New York. Exposure to opiates such as heroin triggers the release of chemical messengers in the brain called opioids that stimulate pleasant sensations.

The receptor molecule to which THC binds is also found on brain cells in the opioid system, Hurd adds. Over-stimulation of these receptors through exposure to cannabis may alter these cells so that the brain either feels intensely rewarded by subsequent heroin exposure, or needs an ever-increasing dose to feel the same pleasure — both of which could lead to addiction.

If so, a similar effect may be seen with drugs such as cocaine and amphetamines, which involve another brain pathway called the dopaminergic system, Stolerman adds. Cells involved in this pathway also have THC receptors, possibly indicating that they could also be modified by cannabis exposure.

A slippery slope

But even if the gateway effect is one day found to also have a biological basis in humans, the effect is undoubtedly complicated by social factors. Some social commentators have ascribed the perceived gateway effect to the simple fact that cannabis is cheaper than many other illegal drugs, meaning that adolescents are more likely to use it before graduating to other substances.

Hurd, however, feels that softening the law against marijuana at this point would be "ridiculous", given the number of unknowns about its effects. She adds that two other drugs that also stimulate opioid cells, and could therefore also feasibly cause a gateway effect, are nicotine and alcohol. "If we turned back the clock with the knowledge we have now, these two drugs would never have been legalized," Hurd says.

The discovery also warns against complacency that cannabis does not have any lasting effect in young people who use the drug. "Lots of mothers say 'oh well, at least it's not cocaine'," Hurd says. "But this is not about the short-term effects. For adults to do it is one thing, but we have to consider the effects on children."

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References

1. Ellgren M.,

   Spano S. M.&

   Hurd Y. L. . Neuropsychopharmacology, . - doi:10.1038/sj.npp.1301127

[Moonman62]

and that groups like the Libertarian Party that espouse such nonsense are losers.

Empty namecalling.

It's a fact. The LP is a loser, and that's because of its policies and reputation. It can no longer pull more than half a per cent in a national election. The same goes for the other groups I mentioned.

[Moonman62]

Alcohol was never banned. During Prohibition possession was legal,

A distinction without a difference, as manufacture, sale, or transportation was prohibited.

Then why is it the pot activists want to chip away at marijuana prohibition by making possession legal ?

[Moonman62]

Mighty thin reeds on which to hang your distinction. Cocaine is prescribable ... does that mean it's not banned?

How often is it prescribed? Whiskey was prescribed millions of times during alcohol "prohibition."

If these are such thin reeds, why are the pot activists pushing so hard to put the same weaknesses in marijuana prohibition that doomed alcohol prohibition?

[Moonman62]

Incorrect as usual; the U.S. Constitution, the "supreme law of the land, states as one of its purposes to "secure the Blessings of Liberty".

I don't don't think the Founding Fathers would consider drug addiction and all the social ills that go along with it a blessing of liberty.

[Moonman62]

So you think Roe v Wade and Lawrence v Texas were properly decided? Conservatives don't.

And it's improper to equate the right to be a drug addict to something as important as the right to life. Abortion is an active political topic among responsible elected national leaders. Every session of Congress takes steps to chip away at it, and it's always the most important issue when a new Supreme Court justice is selected.

In contrast the advocates for the liberty to be a drug addict are Libertarians, Anarchists, criminals and drug addicts. In other words, the government's right to keep law and order is going to usurp the right of an individual to be a drug addict for a long time to come.

[Know your rights]

Then why is it the pot activists want to chip away at marijuana prohibition by making possession legal ?

I don't know anyone who wants possession legal but manufacture, sale, and transportation legal ... and if that ever became the case I'd mock the notion that marijuana was no longer banned.

[Know your rights]

How often is it [cocaine] prescribed? Whiskey was prescribed millions of times during alcohol "prohibition."

How infrequently must a legally-prescribable drug be prescribed before it's "really" banned in your book?

If these are such thin reeds, why are the pot activists pushing so hard to put the same weaknesses in marijuana prohibition that doomed alcohol prohibition?

You think Prohibition fell because of alcohol prescriptions?! LOL! Speakeasies, rumrunners ... they all meant nothing. Your FR name is appropriate.

[Know your rights]

I don't don't think the Founding Fathers would consider drug addiction and all the social ills that go along with it a blessing of liberty.

What makes you think the Founding Fathers believed that liberty produced only blessings ... or that one could 'fine-tune' liberty so as to produce only blessings yet remain liberty?

[Know your rights]

the Supreme Court still decides where the "powers" of the government end, and the rights of the people begin.

So you think Roe v Wade and Lawrence v Texas were properly decided? Conservatives don't.

And it's improper to equate the right to be a drug addict to something as important as the right to life.

Nobody "equated" anything, Dodgy McSquirm; I just pointed out that your complete deference to the Supreme Court disqualified you as a conservative.