Breaking with Traditional Views – Scientists Uncover Unexpected Function of Dopamine in Movement

by François Dupont
6 comments
Dopamine Neurons in Movement

Recent studies have unveiled an unexpected role of certain dopamine neurons in movement, a shift from the common understanding that these neurons are primarily associated with reward signaling. This newfound subtype of dopamine neurons, linked to movement rather than reward, could significantly alter our knowledge of Parkinson’s disease, a condition marked by the loss of dopamine neurons and motor issues.

The complexity of dopamine neurons is more extensive than previously understood, according to the latest research.

Dopamine’s function extends beyond just rewards.

A research team led by Northwestern University has discovered and studied three genetic subtypes of dopamine neurons in the midbrain region of a mouse model.

Countering the prevalent notion that dopamine neurons primarily or solely react to rewards or indications of rewards, the team found that one of these genetic subtypes triggers in response to physical movement. Even more surprising was the fact that these neurons did not respond to rewards at all.

This revelation not only shines a fresh light on the enigmatic workings of the brain but also paves the way for further exploration and potential treatment of Parkinson’s disease. This illness is characterized by the loss of dopamine neurons but predominantly affects the motor system.

The study was recently published in the Nature Neuroscience journal.

Daniel Dombeck from Northwestern, a co-leader of the study, stated, “People commonly associate dopamine with reward signals. But when dopamine neurons die, people have issues with movement. That’s what occurs with Parkinson’s disease, and it’s been a puzzling issue for researchers. We discovered a subtype that signals motor activity without any reward response, and these neurons are located exactly where dopamine neurons begin to die in Parkinson’s disease. This seems to suggest a more vulnerable genetic subtype that degrades over time as people age.”

A particular genetic subtype of dopamine neuron, which shows activity related to movement but doesn’t respond to rewards, was revealed in a microscopy image. Credit: Maite Azcorra and Zachary Gaertner/Northwestern University

Rajeshwar Awatramani, another co-leader of the study from Northwestern, added, “This genetic subtype is associated with acceleration. We noticed activity whenever the mouse sped up, but in contrast, we did not see any activity in response to rewarding stimuli. This defies the commonly accepted belief about the function of these neurons. Not all dopamine neurons react to rewards. This represents a major shift in our understanding. We have now identified a unique signature for the dopamine neuron that doesn’t respond to rewards.”

The study’s first authors are Maite Azcorra and Zachary Gaertner, both graduate students in Dombeck’s and Awatramani’s laboratories.

Signals Driving Movement

This fresh insight builds upon earlier research from Dombeck’s lab, which discovered a group of dopamine neurons associated with movement in mice.

Dombeck said, “At that time, we assumed it was just a small portion of neurons. And others continued to believe that all dopamine neurons were reward neurons. Perhaps some of them just had motor signals as well.”

To delve deeper into this question, Dombeck collaborated with Awatramani, who used genetic tools to isolate and label groups of neurons based on their gene expression. Using this data, Dombeck’s team tagged neurons in the brains of a genetically modified mouse model with fluorescent sensors, enabling the researchers to identify which neurons light up during behavior, thereby revealing the specific functions of different neurons.

In the experiments, around 30% of dopamine neurons only lit up when the mice moved. These neurons were one of the genetic subtypes identified by Awatramani’s team. The other groups of dopamine neurons reacted to aversive stimuli (leading to avoidance response) or rewards.

The Connection to Parkinson’s Disease

For years, researchers have been puzzled by the fact that Parkinson’s patients lose dopamine neurons yet experience problems with movement.

Dombeck noted, “It’s not as if people with Parkinson’s disease only lose their desire to be happy because their dopamine response is damaged. There is another factor affecting motor skills.”

The new study by Dombeck and Awatramani may offer a key piece to this puzzle.

In their research, they found that dopamine neurons associated with acceleration in mice appear to be in the same location in the midbrain as those that typically die in Parkinson’s patients. Interestingly, the surviving dopamine neurons are associated with deceleration. This discovery has led to a new hypothesis that Dombeck and Awatramani plan to explore.

“We’re curious if it’s not just the loss of the motor-driving signal leading to the disease but also the persistence of the anti-movement signal that’s active during deceleration,” Dombeck said. “This could be an imbalance in the signal that intensifies the signal to stop movement. This might account for some of the symptoms. It’s not only that patients with Parkinson’s can’t move. It could also be that they are being driven to stop moving.”

Awatramani added, “We’re still trying to understand what all of this means. I would call this a starting point. It represents a new perspective on the brain in Parkinson’s disease.”

Reference: “Unique functional responses differentially map onto genetic subtypes of dopamine neurons” by Maite Azcorra, Zachary Gaertner, Connor Davidson, Qianzi He, Hailey Kim, Shivathmihai Nagappan, Cooper K. Hayes, Charu Ramakrishnan, Lief Fenno, Yoon Seok Kim, Karl Deisseroth, Richard Longnecker, Rajeshwar Awatramani and Daniel A. Dombeck, 3 August 2023, Nature Neuroscience. DOI: 10.1038/s41593-023-01401-9

The research was funded by the Michael J. Fox Foundation for Parkinson’s Research, the National Institutes of Health, the National Institute of Neurological Disorders and Stroke, and the National Institute of General Medical Sciences.

Frequently Asked Questions (FAQs) about Dopamine Neurons in Movement

What is the new finding about dopamine neurons?

The new finding suggests that not all dopamine neurons are involved in reward signaling. Researchers have identified a subtype of dopamine neurons that is associated with movement rather than reward.

How might this new discovery impact our understanding of Parkinson’s disease?

This discovery could significantly impact our understanding of Parkinson’s disease. It could provide a better understanding of why Parkinson’s disease, characterized by the loss of dopamine neurons, primarily affects the motor system. This research could potentially lead to improved treatments for Parkinson’s disease.

How does this research challenge the current understanding of dopamine neurons?

Traditionally, it was believed that dopamine neurons predominantly, if not exclusively, respond to rewards or reward-predicting cues. This new research challenges that notion by demonstrating that one genetic subtype of dopamine neurons activates in response to bodily movement and doesn’t respond to rewards at all.

Who conducted this research study?

This study was conducted by a team of scientists led by Northwestern University. Daniel Dombeck and Rajeshwar Awatramani co-led the research.

Where was this study published?

This study was published in the journal Nature Neuroscience.

Who funded the research?

The study was funded by the Michael J. Fox Foundation for Parkinson’s Research, the National Institutes of Health, the National Institute of Neurological Disorders and Stroke, and the National Institute of General Medical Sciences.

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6 comments

DocSimon August 5, 2023 - 11:54 pm

This is such an important discovery. We’ve been focusing on dopamine as a reward neurotransmitter for so long, it’s time to dive into its role in motor function too.

Reply
JakeL August 6, 2023 - 1:45 am

Woah, this is big! If dopamine’s tied to movement and not just rewards, it could totally change how we look at Parkinson’s! Amazing what science can do!

Reply
Bella_23 August 6, 2023 - 7:17 am

That’s pretty unexpected! Who’d have thought dopamine had a role in moving and not just rewarding. The brain is more complex than we can ever imagine!

Reply
Mark-TechEnthusiast August 6, 2023 - 9:26 am

Science never fails to surprise. A new subtype of dopamine neurons related to movement? Incredible find, congrats to the researchers!

Reply
Samantha_89 August 6, 2023 - 12:35 pm

Seriously didn’t see this coming. I always thought dopamine was all about feeling good, not movin’. Just shows how much we still have to learn about the brain, huh?

Reply
JennyHealthNut August 6, 2023 - 2:01 pm

Fascinated by how this could help with Parkinsons. My grandpa had it, wish this kind of info was out there when he was still around. Go science!

Reply

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