Autumn 2005
O'Shaughnessy's
Journal of the California Cannabis Research Medical
Group
|
Addiction and Learning
Gregory Gerdeman’s poster described how behavior
in rats associated with drug dependence — “amped-up running
around the cage” after an injection of cocaine— diminished
dramatically after five days on Rimonabant.
“
I’m funded to look at mechanisms of drug reward and addiction,” says
Gerdeman. “I’m interested in how the cannabinoids interact
with that. The pathways of drug reward interact with the pathways of
motor function and are key to understanding psychomotor disorders like
Parkinsons and, I believe, obsessive-compulsive disorder and Tourette’s
syndrome.”
Gerdeman studies an area of the brain called the nucleus accumbens. His experiments
question: By what mechanisms do neurons change their synaptic connection as habits
are learned and unlearned? How, exactly is the endocannabinoid system involved?
By what mechanism does the antagonist compound (Rimonabant) disrupt learning
and memory at the cellular level?
Gerdeman, 31, is a naturalist, as interested in ocean life as he is
in neurotransmission. He has a knack for clear exposition. With his
long hair,
soft spoken manner
and democratic commitment to keeping the public (your correspondent)
informed about
advances in his field, I imagined that he might feel constrained, if
not compromised, by reliance on funding from NIDA. I asked directly, “Did
you do this work because of your interest in addiction or because you
knew NIDA was interested
in addiction? Did the fact that the money is there for this kind of research
influence your study design?”
Gerdeman replied, “My interest is synaptic plasticity, which refers to
brain mechanisms of cellular learning. These processes are involved in drug addiction,
which I see as a strongly learned state of thinking and behavior. The cellular
pathways we relate to ‘learning’ addiction are sensitized by addictive
drugs and are clearly modulated by cannabinoids. I joined a lab as a postdoc
and our funding structure is from NIDA and it is a grant based on studying the
connection between cannabinoids and drug-abuse paradigms. That’s what the
experiments were proposed to do. So yes, focusing on addiction is where the funding
is, and it’s a major part of keeping my agreements about where
I spend the money.
I think the therapeutic role of Rimonabant is interesting but what
compels me is using the drug as a tool to investigate the function
of endocan-nabinoids.
It’s interesting that Rimonabant may be effective to help curb a psychostimulant
addiction, especially given the credible reports that some people use cannabis
as a substitution therapy for addiction. That’s something that I’ve
had in mind as I’ve been doing the NIDA-funded work.
“
If this neurocircuitry choreographed by endocannabinoids is playing a role in
sustaining our habitual behavior, it is likely not a simple matter of the cannabinoid
receptor being some kind of on-switch and when you turn it off you’re blocking
addiction. It’s not anything so elementary like that. There are discrete
neural circuits involved in our behaviors and how we define them to ourselves.
When you start to influence that circuitry through manipulation of the cannabinoid
system, it may open windows for rewiring the pathways related to your habitual
behavior. Intention also feeds into this, and is very, very important. It’s
been long known that people have to have a motivation to quit drugs.”