A wash cycle for the brain: Neuroscientists have proven for the first time that the small blood vessels inside our brains also pulsate. They pump blood through our brain in bursts – independent of the heartbeat and brain activity. These “traveling waves”, which have only now been proven in the brain arterioles, promote the blood supply to the brain. They could also help to mix the surrounding cerebrospinal fluid and dispose of waste products better, as the team reports in “Neuron”.
The bloodstream transports oxygen and nutrients to every single cell in our body and at the same time removes waste products. This also applies to our brain, which is particularly well supplied with blood due to its high oxygen and nutrient requirements. The fresh blood first flows through the large cerebral arteries into smaller blood vessels, the so-called pial vessels, which span the surface of the brain. From there, even smaller arterioles branch off into the interior of the brain.
Arterioles produce wave-like pumping movements
A research team led by Thomas Broggini from Goethe University in Frankfurt am Main has now discovered that the blood flow in the arterioles of the brain is not only driven by the heartbeat, but also by the independent pumping movements of the blood vessels. This so-called vasomotion is a wave-like movement of the vessel walls that is caused by alternating contraction and relaxation of the smooth muscle cells in the walls.
These oscillations occur periodically once every ten seconds (0.1 Hz) independently of the heartbeat and cause a wave-like blood flow. Such pumping movements have previously been observed in the arteries of various mammalian organs and also in the larger pial vessels of the brain. Now Broggini and his team have demonstrated these oscillations for the first time in the fine arterioles of the brain. They discovered them using functional magnetic resonance imaging (fMRI) of the brains of mice.
What are the “travelling waves” used for?
According to the analyses, the newly discovered vasomotion generates long “traveling waves” along all brain arterioles, which spread through the brain at the rather slow speed of two millimeters per second. These waves improve blood flow in the brain veins by 20 percent, as measurements have shown. The effect was also more pronounced in the resting state than in active brain areas. “This shows that vasomotion has a profound effect on blood flow to the brain, independent of neurological signals,” says Broggini.
The researchers also suspect that the wave-like movements of the brain vessels not only cause turbulence and eddies in the blood. They could also help to mix the cerebrospinal fluid that surrounds all brain cells. However, since the vascular waves spread in all directions and sometimes overlap, they cannot enable the targeted transport of nutrients or waste products in the cerebrospinal fluid or blood.
But as Broggini and his team have discovered, vasomotion temporarily creates small bulges on the brain’s arteries, which also spread in a wave-like manner. “This could improve the removal of misfolded proteins and waste products via the cerebrospinal fluid,” explains Broggini. The exact function of vasomotion in the arterioles, however, remains unclear.
Connections with diseases?
In the future, the findings could help to better understand the blood flow in the brain visible in fMRI scans and thus facilitate the diagnosis of various diseases. In addition, the researchers now want to use the new knowledge to investigate whether and how vasomotion affects diseases in which the blood supply or the removal of waste products in the brain is impaired – such as Alzheimer’s.
“In future work here in Frankfurt, we will investigate how the traveling waves are altered in strokes, cerebral hemorrhages and neurodegenerative diseases and what influence they have on the development of the diseases,” says Broggini. New therapies could then modulate vasomotion in the brain in order to improve the blood supply to the affected brain regions. (Neuron, 2024; doi: 10.1016/j.neuron.2024.04.034)
Source: Goethe University Frankfurt am Main
7 August 2024 – Claudia Krapp
