A novel tool, for the first time, helps determine how two distinct sets of neurons in the brain work together to control movement. The tool was developed by a research team at the National Institutes of Health.
The method, called spectrally resolved fiber photometry (SRFP), can be used to measure the activity of these neuron groups in both healthy mice and those with brain disease.
The scientists plan to use the technique to better understand what goes wrong in neurological disorders, such as Parkinson's disease (PD). The study is published in the journal Neuron.
Cui explained that an animal's ability to move was controlled by two groups of neurons in the brain called the direct pathway (D1) and indirect pathway (D2). Based on clinical studies of patients with PD and primate models, some researchers hypothesized that the loss of the neurotransmitter dopamine in the midbrain resulted in an imbalance of neural activities between D1 and D2. Since previous methods could not effectively distinguish different cell types in the brain, the hypothesis remained under debate. However, using SRFP, Cui's team was able to label D1 and D2 neurons with green and red fluorescent sensors to report their neural activity.
"Our method allowed us to simultaneously measure neural activity of both pathways in a mouse as the animal performed tasks," Cui said. "In the future, we could potentially use SRFP to measure the activity of several cell populations utilizing various colors and sensors."
With SRFP, Cui and colleagues found that when neural activity in D1 neurons is stronger than D2 neurons, the animal does a start and go, which means it starts and moves to another location. But, when the activity of D2 neurons is stronger than D1 neurons, the mouse does a start and stop, meaning it initiates a movement, but stops immediately.
Cui said both movements are normal for mice and analyzing them may help researchers predict what kind of movement the animal will make based on its neural activity. This advance may help explain what happens in the brains of mice with PD.
Two of Cui's team members, NIEHS Visiting Fellows Chengbo Meng, Ph.D., and Jingheng Zhou, Ph.D., share first-authorship of the Neuron article.
"The traditional method of electrophysiological recording is good when you want to measure electrical outputs of neurons, but it cannot tell you what type of neurons are generating those signals," Meng said. "SRFP is more specific, because we can distinguish between groups of neurons and see their activity."
While Cui's group is mainly interested in understanding PD, Zhou said SRFP will help researchers studying other brain conditions, such as Alzheimer's disease, stroke, multiple sclerosis, and addiction.