A small population of nerve cells appears to be responsible for blood flow and neural activity across the entire brain, findings that could have significant implications in the study of sleep, dementia, and overall brain health.
The type of cell is referred to as a type-I nNOS neuron. Found in sparse numbers mostly in deep cortical layers, they are considered to be vulnerable to mental stress. To understand more about the type-I nNOS neuron's role, researchers from Pennsylvania State University selectively removed them from the brains of mice to study the effects.
Without type-I nNOS neurons, the brains exhibited reduced blood flow, weaker pulsation of the blood (known as vasomotion), and decreased neural activity. Slow brain waves called delta waves also became weaker, and the left and right sides of the mice's brains were less in sync.
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"In your brain, arteries, veins, and capillaries help move fluid around by constantly dilating and constricting every few seconds, which we call spontaneous oscillation," says biomedical engineer Patrick Drew.
"Previous work from our lab has shown that nNOS neurons are important for regulating blood flow in the brain. After targeting and eliminating a subset of these neurons, we observed a significant reduction in the amplitude of these oscillations."
The research suggests type-I nNOS neurons may play a role in several key brain processes. For example, delta waves are closely associated with sleep, and the researchers noticed that the reduction in blood flow and neural activity was higher during sleep. That means type-I nNOS neurons could be vital to a healthy sleep cycle.
Vasomotion, meanwhile, is important for clearing waste from the brain, a process that goes awry and leads to damage in several neurodegenerative conditions, including Alzheimer's disease and other forms of dementia.
"This demonstrates that a small population of nNOS-positive neurons is indispensable for regulating both neural and vascular dynamics in the whole brain, raising the possibility that loss of these neurons could contribute to the development of neurodegenerative diseases and sleep disturbances," write the researchers in their published paper.
Future studies could confirm these links, which have only been observed in mouse brains. There's good reason to believe human brains may operate similarly, implying common neurological disorders may involve disruptions to our own type-I nNOS neurons.
A steady blood flow in the brain is essential for delivering oxygen and nutrients, and for regulating mental health. Stress or other factors affecting the cells involved in regulating that flow may present a significant trigger for harm and, therefore, targets for future treatments.
"Reduced blood flow is one of many contributing factors to reduced brain function and neurodegenerative diseases," says Drew.
"While we know aging plays a major role in this, losing these rare neurons to chronic stress could be an unexplored environmental cause for poor brain health."
The research has been published in eLife.