Loud noise exposure worsens motor deficits in Parkinson’s disease model

In the development of Parkinson's disease, it may not be a good idea to turn the amp to 11. High-volume noise exposure produced motor deficits in a mouse model of early-stage Parkinson's disease, and established a link between the auditory processing and movement areas of the brain, according to a study published November 4^th in the open-access journal PLOS Biology by Pei Zhang from the Huazhong University of Science and Technology in Wuhan, China, and colleagues.

The environment can play an important role in the development of Parkinson's disease, but how sound volume in particular might impact the severity of symptoms was unknown. To understand how noise might play a role in Parkinson's symptoms, the researchers used a mouse model of early-stage Parkinson's disease, where mice do not yet show symptoms. They exposed the animals to either acute or chronic loud noise between 85 and 100 decibels - about as loud as a power mower or a blender. 

After just one hour of noise, mice with early-stage Parkinson's disease moved more slowly and showed reduced balance compared to control mice. The animals recovered one day later, but after receiving noise exposure for one hour per day for a week, the early-stage Parkinson's mice showed chronic movement problems. The scientists also stimulated an area of the brain called the inferior colliculus, which processes sound. They showed the inferior colliculus connects to the substantia nigra pars compacta-a dopamine-producing area severely damaged in Parkinson's. Chronically activating the inferior colliculus, they showed, mimicked the behavioral effects of noise damage in the Parkinson's mouse model. Noise exposure and activating the inferior colliculus both reduced a protein called VMAT 2, which transports dopamine, and killed dopamine producing cells in the substantia nigra. Inhibiting the inferior colliculus, or expressing extra VMAT2, on the other hand, could reverse the harms of acute and chronic noise in the early-stage Parkinson's mice.

While the results are in a mouse model, and other brain areas might also be involved, these results suggest there is an important connection between sound processing areas of the brain and those damaged in Parkinson's disease, and that environmental factors like noise can affect the symptoms and progression of the illness.

The authors add, "Our study reveals that environmental noise exposure changes the IC-SNc circuit, leading to motor deficits and increased neuronal vulnerability in a Parkinson's disease mouse model. This highlights the potential role of environmental factors in exacerbating Parkinson's Disease pathogenesis."

The authors note, "It was particularly fascinating to observe how the environmental noise-induced dopaminergic neurodegeneration and motor deficit, offering new insights into non-genetic risk factors for Parkinson's disease."