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November 29, 2005

Source: Wilfrid Laurier University:

Laurier prof studies how medical marijuana could help cancer patients

Tiny critters play big role in research to suppress nausea in cancer patients
Monday November 28, 2005

WATERLOO -- A shrew with sharp teeth and a preference for solitude is a partner in a top psychologist's research with medical marijuana that could help cancer patients.

Linda Parker has been exploring how medical marijuana can suppress nausea and vomiting, the debilitating side effects of chemotherapy treatment.

Parker is a professor at Wilfrid Laurier University and one of the country's leading researchers, holding a Canada Research Chair in behavioural neuroscience.

She has recruited a colony of house musk shrews, the only such colony in Canada, to aid in her research.

The marijuana plant has been used for several centuries for relief of vomiting and nausea, Parker said.

At the same time, marijuana has been the subject of endless legal and moral wrangling.

Even some patients with doctors' prescriptions to use the "wonder weed" for therapeutic reasons dislike the high it also gives them.

"Many people don't like the intoxicating effect, especially older people who are taking chemotherapy," Parker said.

So it's significant that Parker -- an alumna of California State University at Long Beach, who adopted Canada after falling in love with Newfoundland -- is working with a non-intoxicating chemical in marijuana called cannabidiol as a treatment against nausea and vomiting.

Cannabidiol is as prevalent in marijuana as tetrahydrocannabinol, better known as THC, which delivers the marijuana buzz.

Both suppress vomiting.

But the fact that cannabidiol is not intoxicating means it might be an effective treatment against chemotherapy's nausea and vomiting, she said.

Parker feels so strongly about its potential that she has a patent on cannabidiol as an anti-nausea treatment.

She filed the patent with the father of cannabis research, Prof. Raphael Mechoulam of Hebrew University in Jerusalem. There are no clinical trials on humans yet.

But that may not be far off. Canada recently approved a drug called Sativex, a medicinal mouth spray featuring a combination of cannabidiol and THC.

"It means the next step would be to see what happens with cannabidiol alone," Parker said.

Now, Parker is focusing on chemicals found naturally in the human body that mimic chemicals in marijuana.

She's also investigating "anticipatory nausea" and vomiting, a phenomenon experienced by some chemo patients when they're re-exposed to treatment cues. The reaction can be so acute that it makes some people avoid chemotherapy altogether.

If Parker is right, a naturally produced chemical in the brain called anandamide could be the anti-nausea chemical of the brain, the chemical that restores balance when we get sick.

If she's right, her work with a drug that makes anandamide last longer after it's released is good news for chemotherapy patients.

And if she's right, the rats and house musk shrews will have provided valuable help in tests on nausea and vomiting in her laboratory at WLU.

It was Parker's work with rats that first drew the attention of Mechoulam, who identified THC as the component causing the marijuana "high" in the 1960s.

You see, rats don't vomit. They don't need to because -- and this may come as a surprise -- rats are incredibly picky eaters when they encounter a new food. Then, if they don't get sick, they return to the food and eat it ravenously.

John Garcia, then a leading biological psychologist at California State University at Long Beach, discovered that if you give a rat a novel taste, then make it sick hours later, the rat will avoid the taste in the future.

This "taste-aversion learning" is "about the strongest kind of learning anyone has ever found," said Parker, who was chosen recently to give the John Garcia Recognition of Excellence Lecture at her alma mater.

"We think that probably rats vomited at one time in their evolutionary history, but they lost the ability because they don't need to," Parker said. "They're so wary about what they eat."

So researchers had ruled out rats for testing chemicals that cause nausea and vomiting, relying instead on larger animals such as dogs, cats and ferrets.

But those animals are more costly, more difficult to care for and are less palatable experimental subjects among members of the public.

Then Parker and Cheryl Limebeer, a postdoctoral fellow in psychology at University of Western Ontario and Parker's former PhD student, proved that rats experience nausea.

When exposed to a taste previously paired with lithium chloride, a drug that made them sick, rats "gape" or open their mouths wide, signalling nausea. Lithium chloride is relatively non-toxic and its effects last about 90 minutes, Parker said.

Parker and Limebeer showed that marijuana's THC interfered with nausea in the rat.

"Mechoulam said, 'a rat for nausea -- just what we need to test out the cannabinoid,' " Parker said.

It was the beginning of a fruitful collaboration between Parker, 57, and Mechoulam, 80, that has resulted in eight to 10 research papers so far. Mechoulam believes Parker's discoveries may be "of enormous clinical value."

"She is an excellent researcher, original and innovative," Mechoulam wrote in an e-mail from Jerusalem.

The rat studies led to Parker's curiosity about shrews. Would these cannibinoids also interfere with vomiting in a species that is capable of vomiting?

Shrews could verify the researchers' use of rats, which are more common and less costly. And the vomiting reaction relates more to humans.

After discovering the use of shrews in Japan, Parker got her original house musk shrews, or suncus murinus, from the University of Virginia. Her colony was born and raised at WLU.

The mouse-sized musk shrew is 10 times larger than the shrew you might find in your backyard. The insectivores are not social, and they have sharp teeth. Research assistants need heavy gloves.

In a room at WLU, the shrews are housed individually in plastic cages -- about as large as three shoeboxes -- in which there are pine wood shavings, shredded paper towels and a house made from overturned cottage cheese containers. There are 40 breeding males and females and a colony of another 40 for experiments.

"We have very luscious quarters for our shrews," Parker said. "The people in Japan laugh at us when I tell them how the shrews live."

Parker has received several federal grants for her research, including one for the evaluation of medical marijuana using the shrews.

She found that shrews, like rats, will avoid a flavour paired with lithium chloride.

But unlike rats, shrews vomit in response to toxins.

She found that both THC and cannabidiol, the intoxicating and non-intoxicating chemicals in marijuana, suppress vomiting in shrews.

They also suppress anticipatory nausea in both rats and shrews.

Parker hopes her work will help cancer patients. The research, the thrill of the chase, has taken her on a winding path from California to WLU where she is respected for both her work and her mentoring of graduate students.

Along the way, she taught male inmates in a Texas prison, where executions had taken place, as part of her teaching load at Sam Houston State University.

The jailhouse classes helped Parker, who was married with two small children, pay the bills. And they sparked some interesting discussions during lectures on how drugs affect the brain. The prisoners knew something about drugs, since many were serving time because of drug-related crimes.

"They knew a lot about that."

Though she hadn't studied much science up to then, Parker got hooked on biological psychology when she was at California State University.

In her early 20s and single then, she bought a white Plymouth Duster and headed for Memorial University in St. John's, Nfld., to study for her PhD with a leading researcher.

The province's beauty, the music, the night life and people's warmth made it "the best time of my life." She stayed three years.

"Where we were working, you could see the Narrows, the harbour, Signal Hill, icebergs floating," Parker said. "It was just beautiful."

After nine years at the University of New Brunswick, a brief stint at Laurentian University in Sudbury and the move to Texas, Parker and her husband, writer-musician Ernie Shockley, and their two sons came to Waterloo in 1989. She and her husband became Canadian citizens.

"I was Canadianized by that time," Parker said.

Canada's universal health care system was a strong magnet.

And Canada is "very open-minded" about the use of marijuana for medicinal reasons compared to the rest of the world.



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