Tuesday, July 12, 2005

For Some Parkinson's Drugs, the Side Effect May Be Gambling

First, note that the latest Grand Rounds is up at Shrinkette (don't you just love that name?).  

On to today's story: This story appeared in today's LA Times.  They mean it literally.  Dopamine agonists such as ropinirole (ReQuip ®) and pramipexole (Mirapex ®) have been linked to about forty cases of compulsive gambling.  Researchers reported those cases as having a definite link to the drug.  They estimate that perhaps one percent of the patients given these drugs actually develop compulsive gambling.

Dopamine agonists are used in the treatment of Parkinson disease and Restless Leg syndrome.  Dopamine is a chemical messenger in the brain that is involved in the brain's reward system.  The effect, however, does not appear to be caused by other drugs that increase dopaminergic effect, such as carbidopa/levodopa (Sinemet ®).  This is interesting, because it illustrates the subtlety of the brain.  Sinemet causes all dopamine receptors to see increased activation.  Mirapex and ReQuip are selective in which types of dopamine receptor they activate.  Plus, they act differently.  Sinemet increases release of dopamine from dopamine neurons.  ReQuip and Mirapex act directly on receptors.  

The exact mechanism of this is not known.  The article mentions, however, that some other patients reported "increased appetites for food, alcohol and sex."  That sounds like hypomania.  I know there is at least one article that indicates that Mirapex can be used to potentiate the effect of antidepressants.  Antidepressants are well known to cause hypomania or mania in a small number of people.  Therefore, it is tempting to speculate that what the researchers are seeing may actually be a form of hypomania, rather than a specific effect of causing gambling.  I'll be curious to see what emerges from this line of research.

Categories: science, neuroscience, armchair musings
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