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Scientists at Gladstone Institutes uncovered a stunning purpose why dopamine-producing neurons, essential for easy physique actions, die in Parkinson’s illness.
In mice, when these neurons have been saved overactive for weeks, they started to falter, first shedding their connections after which dying altogether. This mirrors the selective neuron loss seen in sufferers, the place overworked cells within the substantia nigra finally collapse.
Parkinson’s Thriller: Why Key Mind Cells Die
Sure teams of mind cells management the physique’s capacity to maneuver with precision and coordination. When these cells stay in an overactive state for prolonged intervals, they start to deteriorate and finally die. Researchers on the Gladstone Institutes lately noticed this course of, providing recent perception into what would possibly go unsuitable within the brains of individuals with Parkinson’s illness.
Scientists have lengthy acknowledged {that a} particular sort of neuron is misplaced as Parkinson’s progresses, although the explanations behind this decline have remained unsure. A brand new examine, printed within the journal eLife, exhibits that in mice, extended overstimulation of those neurons can immediately result in their dying. The researchers counsel that in Parkinson’s, this overactivity could also be fueled by a mixture of genetic dangers, environmental exposures, and the additional pressure on surviving neurons as they attempt to make up for these already misplaced.
“An overarching query within the Parkinson’s analysis subject has been why the cells which are most weak to the illness die,” says Gladstone Investigator Ken Nakamura, MD, PhD, who led the examine. “Answering that query may assist us perceive why the illness happens and level towards new methods to deal with it.”
Parkinson’s Signs and Rising Neuron Exercise
Greater than 8 million individuals world wide are at the moment affected by Parkinson’s illness, a progressive dysfunction of the mind that results in tremors, slowed actions, muscle stiffness, and issue with strolling and steadiness.
Researchers know that the neurons liable for producing dopamine, which is essential for voluntary movement, are among those that die in Parkinson’s patients. Evidence also shows that these neurons often become more active as the disease advances, both before and after degeneration begins. What has remained unclear is whether this surge in activity is simply a response to the disease or if it plays a direct role in driving cell death.
Continuous vs. Short-Term Activation
In the new study, Nakamura and his colleagues tackled this question by introducing a receptor specifically into dopamine neurons in mice that allowed them to increase the cells’ activity by treating the animals with a drug, clozapin-N-oxide (CNO). Uniquely, the scientists added CNO to the animals’ drinking water, driving chronic activation of the neurons.
“In previous work, we and others have transiently activated these cells with injections of CNO or by other means, but that only led to short bursts of activation,” says Katerina Rademacher, a graduate student in Nakamura’s lab and first author of the study. “By delivering CNO through drinking water, we get a relatively continuous activation of the cells, and we think that’s important in modeling what happens in people with Parkinson’s disease.”
Within a few days of overactivating dopamine neurons, the animals’ typical cycle of daytime and nighttime activities became disrupted. After one week, the researchers could detect degeneration of the long projections (called axons) extending from some dopamine neurons. By one month, the neurons were beginning to die.
Importantly, the changes mostly affected one subset of dopamine neurons—those found in the region of the brain known as the substantia nigra, which is responsible for movement control—while sparing dopamine neurons in brain regions responsible for motivation and emotions. This is the same pattern of cellular degeneration seen in people with Parkinson’s disease.
Connecting Mouse Findings to Human Parkinson’s
To gain insight into why overactivation leads to neuronal degeneration, the researchers studied the molecular changes that occurred in the dopamine neurons before and after the overactivation. They showed that overactivation of the neurons led to changes in calcium levels and in the expression of genes related to dopamine metabolism.
“In response to chronic activation, we think the neurons may try to avoid excessive dopamine—which can be toxic—by decreasing the amount of dopamine they produce,” Rademacher explains. “Over time, the neurons die, eventually leading to insufficient dopamine levels in the brain areas that support movement.”
Shared Gene Patterns in Patients and Mice
When the researchers measured the levels of genes in brain samples from patients with early-stage Parkinson’s, they found similar changes; genes related to dopamine metabolism, calcium regulation, and healthy stress responses were turned down.
The research did not reveal why activity of the dopamine neurons might increase with Parkinson’s disease, but Nakamura hypothesizes that there could be multiple causes, including genetic and environmental factors. The overactivity could also be part of a vicious cycle initiated early in disease. As dopamine neurons become overactive, they gradually shut down dopamine production, which worsens movement problems. Remaining neurons work even harder to compensate, ultimately leading to cell exhaustion and death.
“If that’s the case, it raises the exciting possibility that adjusting the activity patterns of vulnerable neurons with drugs or deep brain stimulation could help protect them and slow disease progression,” Nakamura says.
Reference: “Chronic hyperactivation of midbrain dopamine neurons causes preferential dopamine neuron degeneration” by Katerina Rademacher, Zak Doric, Dominik Haddad, Aphroditi Mamaligas, Szu-Chi Liao, Rose Creed, Kohei Kano, Zac Chatterton, Yuhong Fu, Joseph H Garcia, Victoria M Vance, Yoshitaka J Sei, Anatol Kreitzer, Glenda Halliday, Alexandra B Nelson, Elyssa Margolis and Ken Nakamura, 26 August 2025, eLife.
DOI: 10.7554/eLife.98775
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