Researchers at the Montreal Neurological Institute have gained fresh insight into the brain chemistry behind addiction by studying the least likely of addicts — Parkinson’s disease patients.
Typically, those suffering from the neurodegenerative disorder are the polar opposite of an addictive personality. Most patients with Parkinson’s are found to be introverted,
rigid and slow to anger — not the excitable, impulsive temperament that’s necessary for addiction, said Alain Dagher, lead author of the MNI study.
Yet paradoxically, some patients who are treated for the tremors associated with Parkinson’s disease do develop addictive behaviours. For example, the incidence of pathological gambling in treated Parkinson’s patients is eight per cent compared with one per cent in the general population.
What Dagher and his colleagues discovered is that some of these patients might have been given too much medication to stimulate dopamine, a neurotransmitter in the brain. People with the disease lack dopamine.
“In some instances, Parkinson’s disease patients become addicted to their own medication, or develop addictions such as pathological gambling, compulsive shopping or hypersexuality,” Dagher said.
So what does Parkinson’s have to do with addiction? Dagher, a neurologist, has found that people suffering from addiction have elevated levels of dopamine in their brains.
Thus, the link between some Parkinson’s patients under treatment and addicts is higher-than-normal levels of dopamine in their brains. Previously, some scientists had questioned whether too much dopamine in the brain could trigger addiction.
“People with addiction, we think, have an excess of dopamine,” Dagher explained. “And with Parkinson’s disease, you give a drug to increase dopamine in order to relieve symptoms, and some people get overdosed. One of the effects of this excessive dopamine stimulation from the drug appears to be the development of addictions — especially pathological gambling.”
The practical implications of the research means that doctors will have to be much more careful in prescribing medications to patients with Parkinson’s, Dagher said.
As for addiction, researchers will need to focus more on genes that predispose people to elevated dopamine.
Nearly 100,000 Canadians have Parkinson’s. Addiction prevalence is much higher. One out of every 10 Canadians, aged 15 and over, have symptoms consistent with alcohol or illicit drug dependence, according to the Centre for Addiction and Mental Health.
The MNI study was published Wednesday in the journal Neuron. Researchers from McGill and the University of Cambridge were also involved.
By Aaron Derfel
December 3, 2009
The Vancouver Sun