Exploring the science behind the loss of smell in Parkinson’s patients

Impact of α-Synuclein Pathology on Olfaction in Parkinson's Disease Mouse Model.

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Parkinson’s disease is a neurodegenerative disorder commonly associated with motor symptoms such as tremors, stiffness, and slowness of movement. However, another common symptom of Parkinson’s disease is the loss of smell, also known as hyposmia or anosmia.

Studies have shown that about 75-90% of Parkinson’s patients report a diminishing sense of smell, even before the onset of motor symptoms.

Researchers at Yale School of Medicine have discovered the biological mechanism behind the loss of smell in Parkinson’s disease, a common but less studied symptom. 

Using an alpha-synuclein A30P mouse model, they found that mice with later-stage symptoms of Parkinson’s disease exhibited olfactory impairment due to severe pathology in projection neurons of the olfactory pathway and reduced neurogenesis in the olfactory bulb. This is in contrast to healthy aging brains that continue to form new neurons in the olfactory bulb throughout life.

Parkinson’s patients had been reporting diminishing sense of smell for years, says the corresponding author, Charles Greer, Ph.D., vice chair of research at the Neurosurgery department and professor of neuroscience at the Yale School of Medicine. However, since the disease’s motor symptoms were more debilitating, very little research had been done to understand the underlying biological mechanism of the olfactory dimension.

Sreeganga Chandra, Ph.D., associate professor of neurology and neuroscience from yale university, said, “We are excited to begin to understand the basis of anosmia in Parkinson’s disease patients.”

Dr. Greer. said, “We set out to understand the nature of a symptom associated with Parkinson’s disease that’s been largely anecdotal. People diagnosed with Parkinson’s disease would report loss of smell up to 10 years before their diagnosis. These findings could help develop a very early diagnostic tool for the disease.” 

“α-Synuclein Pathology and Reduced Neurogenesis in the Olfactory System Affect Olfaction in a Mouse Model of Parkinson’s Disease” provides an overview of the research question and the context for the study.

The experiment is focused on Parkinson’s disease, which is a neurodegenerative disorder characterized by motor symptoms such as tremors, stiffness, and slowness of movement. The introductory part highlights that Parkinson’s disease is also associated with non-motor symptoms, such as the loss of smell or olfactory impairment. The researchers explain that about 75-90% of Parkinson’s patients report a diminishing sense of smell, even before the onset of motor symptoms, and that this symptom is now recognized as a non-motor symptom of Parkinson’s disease.

This study examined how Parkinson’s disease affects the sense of smell in mice. The researchers found that mice with advanced symptoms of Parkinson’s disease had trouble with their sense of smell, which was linked to changes in their brains. Specifically, the mice had damage to specific cells in the olfactory pathway. They reduced the growth of new cells in the olfactory bulb, which could contribute to smell problems. 

The researchers also found problems with how cells in the olfactory bulb communicate with each other. These findings suggest that Parkinson’s disease can affect the sense of smell by causing damage to specific brain parts.

This study used mice with the condition that mimics Parkinson’s disease to understand how the disease affects their sense of smell. The researchers found that mice with advanced symptoms of Parkinson’s disease had trouble smelling, linked to changes in specific brain cells. 

They also found that the mice had fewer new cells growing in their olfactory bulb and problems with how cells communicate with each other. These changes likely contribute to the smell problems seen in Parkinson’s disease.

Overall, the study provides important insights into the biological mechanisms underlying olfactory impairment in Parkinson’s disease and suggests potential therapeutic strategies for improving olfactory function in these patients. The conclusion highlights the significance of these findings and their potential implications for Parkinson’s disease research and treatment.

Journal Reference:

  1. Eduardo Martin-Lopez, D. J. Vidyadhara, etal.α-Synuclein Pathology and Reduced Neurogenesis in the Olfactory System Affect Olfaction in a Mouse Model of Parkinson’s Disease. Journal of Neuroscience DOI: 10.1523/JNEUROSCI.1526-22.2022
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