Reduced Dopamine Shown to Impact Activity in Brain Motor Cortex

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by Marisa Wexler |

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Reduced dopamine signaling leads to abnormal activity in the motor cortex— the part of the brain chiefly responsible for controlling movement — a new study in mice illustrates.

This result helps to shed light on the biological underpinnings of Parkinson’s disease, which is characterized by abnormally low dopamine levels and by motor symptoms.

The study, “Reduced Dopamine Signaling Impacts Pyramidal Neuron Excitability in Mouse Motor Cortex,” was published in eNeuro.

Dopamine is a neurotransmitter, or a chemical messenger that allows nerve cells to communicate with each other. Among its many functions, this particular neurotransmitter is known to be important for controlling voluntary movements. However, the exact biological mechanisms by which dopamine signaling in the brain controls movement are incompletely understood.

Better understanding these mechanisms, according to researchers, may aid in advancing knowledge of Parkinson’s, which is caused by the death and dysfunction of dopamine-producing neurons in the brain.

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Now, a trio of scientists at Stony Brook University, in New York, conducted a series of experiments in mice to understand how dopamine signaling regulates the activity of the primary motor cortex, called M1. As its name suggests, this part of the brain is critical for controlling movement.

The team measured the electrical activity of M1 neurons under different conditions, including when D1R or D2R — two protein receptors for dopamine — were blocked.

The results showed that, when dopamine signaling was blocked, M1 neurons became more excitable, meaning that they were more likely to “fire” and send an electrical signal. The exact effect varied somewhat depending on the specific type of M1 neuron, and which specific receptor was blocked.

“Our results show that acute impairment of D1R and D2R signaling increases the excitability of [neurons in M1] along with the excitability of one of their primary … partners,” the researchers wrote.

“Together, these changes may lead to hyperactivity in M1, an effect associated with motor impairment and movement disorders like PD [Parkinson’s disease],” they wrote.

The scientists said in a press release that their finding “supports a new line of research regarding the origins of changes in the motor cortex and its role during PD.”

Moreover, this research identified the primary motor cortex as a potential “site of intervention” for treating motor symptoms, and possibly improving outcomes for people with Parkinson’s.

“The results we showed support the idea that changes in motor cortex activity due to loss of dopamine are very important for the pathophysiology of PD,” said Arianna Maffei, a professor at Stony Brook and co-author of the study.

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