Examining stress and inflammation in the heart may be key to predicting risk of Parkinson's disease, say researchers, as it may help physicians test new therapies and delay the progression of the disorder.

According to researchers, by the time Parkinson's patients are diagnosed -- typically based on the tremors and motor-control symptoms -- about 60 per cent of them also have serious damage to the heart's connections to the sympathetic nervous system. When healthy, those nerves spur the heart to accelerate its pumping to match quick changes in activity and blood pressure.

"This neural degeneration in the heart means patients' bodies are less prepared to respond to stress and to simple changes like standing up. They have increased risk for fatigue, fainting and falling that can cause injury and complicate other symptoms of the disease," said Marina Emborg, from the University of Wisconsin-Madison, US.

For the study, published in the journal npj Parkinson's Disease, the teams used rhesus macaque monkeys as models for Parkinson's symptoms, who received neurotoxin doses that caused damage to the nerves in their hearts in the same way as Parkinson's affects human patients.

The team found that tracing the progression of nerve damage and the progression of potential causes of that damage, the radioligands can also be used to test the efficacy of new treatments to protect the neurons that regulate the activity of the patients' hearts. "We know there is damage in the heart in Parkinson's, but we haven't been able to look at exactly what's causing it. Now we can visualize in detail where inflammation and oxidative stress are happening in the heart, and how that relates to how Parkinson's patients lose those neuronal connections in the heart," said lead author Jeanette Metzger, from the varsity.