Dopamine has always been known as the neurotransmitter responsible for the feeling of happiness and pleasure. But apparently that’s not the only thing the ‘happiness hormone’ does.
Dopamine is a neurotransmitter (a substance that transfers ‘messages’ from one nerve cell to another) that is part of our reward system. Yet that is not the whole story. When dopamine neurons die, people have trouble moving. This is what happens in Parkinson’s disease. Researchers have been puzzling over this for years. Because how can a molecule that is responsible for the feeling of happiness and pleasure also have to do with movement? Researchers now think they can explain it.
Parkinson’s disease
For decades, scientists have wondered how it is possible that patients with Parkinson’s disease lose dopamine neurons and then have difficulty moving. “It’s not that people with this disease just lose their sense of happiness because their dopamine response is damaged,” said researcher Daniel Dombeck. “There’s something else going on that’s affecting their motor skills.”
More about Parkinson’s disease
The fastest growing neurological disorder in the world is Parkinson’s disease. This is a slow, progressive condition that affects the central nervous system, where nerve cells slowly die. This leads to disturbances in movement, muscle control and balance. Symptoms come on slowly and become more severe as the disease progresses. The exact cause of the disease is usually unknown.
To study this issue, the researchers conducted experiments with mice. The team labeled neurons in the brains of several genetically modified mice using fluorescent sensors. This allowed the researchers to see which neurons lit up during certain behaviors. This may ultimately reveal which neurons drive specific functions.
Movement
The researchers discovered three genetic subtypes of dopamine neurons. And although it was thought that these neurons only respond to rewards, the experiments show that some dopamine neurons also secretly regulate completely different things. In fact, one subtype, which accounts for about 30 percent of the dopamine neurons in a particular part of the brain, lit up when the mice moved. And, even more surprisingly, these neurons curiously do not respond to reward at all.
Microscope image of the newly discovered subtype that is associated with movement and does not respond to rewards. Image: Maite Azcorra and Zachary Gaertner
“This genetic subtype is correlated with acceleration,” said researcher Rajeshwar Awatramani. “Whenever the mouse accelerated, we saw activity. Remarkably, we saw no activity in response to a rewarding stimulus. This goes against what most people think these neurons do. It shows that not all dopamine neurons respond to rewards.”
Brain
In addition, the team found that the dopamine neurons correlated with acceleration are located in the same place in the brain as the ones that die in people with Parkinson’s disease. “So we’ve found a subtype related to motor function, and these neurons are also located right where dopamine neurons die in people with Parkinson’s disease,” Dombeck summarizes. “This is an important clue. It suggests that there is a genetic subtype that becomes more susceptible to degradation over time as people age.”
In short…
While dopamine is often associated with the brain’s reward system, it apparently also plays a critical role in movement. Its dysfunction can lead to movement disorders such as Parkinson’s disease. The findings from the study therefore help explain why the loss of dopamine neurons leads to this nasty disease.
Delay
The findings not only shed new light on the mysterious nature of our brain, it also opens up new avenues of research for a better understanding and possibly even better treatment of Parkinson’s disease. Namely, the researchers found that not only do dopamine neurons correlated with acceleration die, the dopamine neurons that survive are correlated with deceleration. And that may also cause people with the disease to have difficulty moving. “This could well explain some of the symptoms,” said Dombeck.
The researchers plan to further study this hypothesis in follow-up research. “We are still trying to figure out exactly what our findings mean,” Awatramani says. “This is a starting point. Our results provide a new perspective on the brain in Parkinson’s.”
2023-08-04 13:05:06
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