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Medicine to treat Parkinson’s disease leaves patients more susceptible to gambling addictions

The study of Parkinson’s disease, and how the brain sends signals for movement and mood, also is shedding light on the physiology of gambling. Both are linked to dopamine, a neurotransmitter that, among other things, helps us control our bodies and stimulates desire.

When patients being treated for Parkinson’s developed gambling addictions, it didn’t take long to find the link.

“There are many groups of dopamine receptors in the brain,” explains Jian Feng, a neurologist and professor in the School of Medicine & Biomedical Sciences at the University at Buffalo. “One type controls locomotion, one controls the normal cognitive state – when that is not working right, you might see schizophrenia – and the third group affects reward behavior.”

Parkinson’s disease is a result of the death of dopamine neurons in the areas associated with locomotion. The illness is commonly diagnosed when people are in their 60s, Feng said, though its onset could be much earlier.

Drugs called dopamine agonists – which include pramipexole (brand name Mirapex) and ropinirole (Requip) – help restore connections in those receptors, calming the tremors associated with the illness and giving the patient more movement control.

But they aim at a wide target – the entire brain – and that is why, Feng said, they can have unwanted side effects on personality.

“You can’t target the locomotion area, for instance, with the Parkinson’s medication,” Feng said. The medications go to all of parts of the brain.

Including the reward and pleasure centers.

So why gambling?

Feng said that when a person experiences an unexpected reward, like a $50 slot machine win, dopamine triggers a pleasure response. The brain wants to repeat that experience, so it signals the impulse to keep gambling. The very randomness of the reward is what heightens the pleasure, and medication that enhances a patient’s reception to dopamine heightens that pleasure even more – it can make him crave it.

“It’s addictive behavior,” Feng said. “The other aspect is gambling itself. It is basically an addictive thing.”

Mayo Clinic researchers in 2011 estimated that more than 20 percent of patients on Parkinson’s medications also experienced problems with impulse control – including a sudden, compulsive urge to gamble. (Other problems could be hypersexual behavior, binge shopping or overeating.) Indications are that the higher the dose of medicine, the greater the chance a patient will experience the side effects.