Features
Sick of Treatment
Psychology prof hopes studies of marijuana compounds will help cancer patients cope better with chemotherapy
BY DAVID DICENZO
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| Controlling anticipatory nausea in cancer patients is the goal of research by Prof. Linda Parker. Photo by Martin Schwalbe |
Unlike most people, Prof. Linda Parker, Psychology, doesn't mind being around rats. The behavioural scientist first took an interest in the rodents as an undergraduate at California State University at Long Beach back in the early 1970s. She was intrigued with experimental psychologist John Garcia's studies of conditioned taste aversion in rats. He found that the animals quickly developed an aversion to food that was accompanied by a nausea-inducing stimulus, and that the aversion persisted for a long time.
Parker says Garcia's work came at a time when behaviourism was rampant, and the impact on the academic community — and her — was significant.
“It shook up the rules of learning,” says Parker, a Tier 1 Canada Research Chair who arrived at Guelph last summer. “At the time, it was thought that, for an animal to learn a relationship between two stimuli, the stimuli couldn't be separated for more than a second. But Garcia showed that, when those stimuli are biologically meaningful, such as food and sickness, rats will learn even when the stimuli are separated by hours. Rats learn to avoid the food in a single trial, and the memory of that trial remains throughout their lifespan.”
More than 30 years later, Parker has made her own contributions to the field of behavioural neuroscience, taking it to new levels. She comes to U of G after spending 17 years at Wilfrid Laurier University, which followed stints at the University of New Brunswick and Laurentian University. In the late 1990s, she also served as dean of graduate studies and research at Humboldt State University in California for a year.
Her first exposure to Canada came when she went to Memorial University in Newfoundland to do her PhD with Sam Revusky, Canada's best-known taste-aversion researcher at the time. She quickly fell in love with the country.
Parker says she's most comfortable doing research, which is why she left her position at Humboldt to return to Laurier. “The most fun part of this job is the data,” she says. “Good data are the high of the job. That's what drives us all.”
A large part of her work has been devoted to examining anticipatory nausea in chemotherapy patients, a situation where patients become sick when they return to the hospital environment where they previously received their cancer treatment. Current anti-nausea treatments are ineffective in counteracting this type of nausea, she says.
Parker has researched the effect that two compounds found in marijuana — THC and cannabidiol — have in mitigating the nausea. To aid in the studies, she began using house musk shrews, which have the ability to vomit, unlike rats, which experience only gaping when they feel ill. The shrews are found naturally in the Philippines, Japan and Australia, and her colony is now housed at Guelph's Central Animal Facility.
What Parker found in her research is that both THC and cannabidiol suppress vomiting in the shrews and gaping in the rats. The difference is that THC has an intoxicating effect and cannabidiol does not. Those results are consistent with evidence from humans who claim that smoking marijuana prior to a treatment helps prevent nausea.
Her work in this area caught the attention of Raphael Mechoulam of the Hebrew University in Jerusalem, who is credited with identifying THC back in 1964 and whose lab also discovered anandamide, the “brain's own THC,” in the early 1990s.
“Out of the blue, through snail mail of all things, a letter appeared in my mailbox from the Hebrew University,” she says. “I opened it up and it said: ‘Dr. Parker, I read with interest your paper. I, too, am a cannabinoid researcher.' That was an understatement because he's the person who discovered the whole thing.”
Parker ended up collaborating with the 76-year-old Mechoulam, publishing a series of papers via e-mail before the two finally met at a conference of the International Cannabinoid Research Society in California a few years back. Their collaboration also got her interested in the role that anandamide, a natural cannabinoid, plays in controlling nausea.
“The discovery of anandamide in the '90s was like the discovery of endorphins in the '70s,” she says. “First, the cannabinoid receptors were discovered in the late 1980s. Since the brain has receptors for a compound like the psychoactive ingredient in marijuana, THC, it must produce something like THC that acts on those receptors — anandamide. It is currently a hot topic in science circles.”
Parker notes that anandamide is not normally freely available in the brain. Instead, it's produced on demand when needed and is active for only a few minutes, being deactivated by the enzyme fatty acid amide hydrolase (FAAH). “It does its thing, then it's gone, returning to an inactive pre-storage state.”
One of Parker's projects since joining Guelph has involved collaboration with pharmacologist Daniele Piomelli of the University of California, Irvine, who developed the compound URB 597. The drug prolongs the action of an anandamide by inhibiting FAAH, the enzyme that deactivates it, so when the anandamide is released, it remains active for longer.
“So what we're doing is manipulating the natural chemical rather than delivering plant-derived THC, which acts on all cannabinoid receptors and floods the system,” she says. “Here, we're just prolonging the action of what normally occurs in the brain.”
She'll be working with a team of researchers at U of G to test the potential of the compound to reduce nausea and vomiting induced by toxins by prolonging the anandamide, among other studies.
Because of U of G's plan to expand the critical mass of neuroscientists on campus and invest in a new state-of-the-art facility, Parker exhibits the same enthusiasm for her future work that she did as a green student. She notes that one of her mandates was to facilitate the development of cross-disciplinary research in neuroscience. To this end, she has organized “Neuroscience Day at the University of Guelph,” to be held March 23 at the Arboretum. It's an opportunity for faculty and students across campus with an interest in neuroscience research to learn about each other's work. She also hopes to work towards developing a cross-disciplinary research centre in the neurobiology of learning and memory.
“I was just amazed by the support of the entire university, from the faculty all the way up to the senior administration, for my research program and for providing the space and equipment needed to do really world-class research,” she says.
In some respects, Parker's career has come full circle. She was recently honoured by her Long Beach alma mater as the inaugural recipient of the John Garcia Recognition of Excellence Award.
“It was such an honour,” she says of receiving the plaque, which hangs on the wall of her office. “John Garcia's work is what got me interested in all of this in the first place.”
Ken Green, Parker's master's supervisor and a post-doc of Garcia's, says she was an obvious choice for the award.
“Linda's career has been marked by concern for others, well-conceived research and shy good humour,” says Green. “She has become a key figure in the field of psychology and has done so against considerable odds. Some, including myself, would say she has accomplished the impossible.”
With so much on her professional plate, Parker admits she has little time for anything else. Entertainment typically consists of a walk along the Grand River near her home in Waterloo with her musician husband, Ernie Shockley, and their schnauzer/poodle-cross dog, Molly.