Scientists have discovered a "secret passage" in mice that connects the brain to the body's lymphatic system.
The network of vessels appears to constitute a neglected brain drainage system that plays a crucial role in maintaining the health and function of the central nervous system.
If the findings extend to humans, they could radically change how scientists understand the circulation of the fluid that bathes the brain and spinal cord: the colorless cerebrospinal fluid (CSF) that carries nutrients to the central nervous system, maintains fluid balance, and removes waste from brain tissue.
In humans, CSF is constantly being drained and replaced, fluctuating three to five times daily. This process can slow down with age, especially as it is linked to sleep quality and cognitive function.
For decades, experts believed that CSF drained through special veins surrounding the brain and spinal cord. However, recent data suggests this idea is wrong.
A new study, conducted by researchers at the South Korean Institute of Basic Sciences and the University of Missouri in the United States, identified a previously unknown pathway that transports CSF from the brain to the lymph nodes in the neck.
There is a distinctive network of lymphatic vessels near the top of the throat in mice, just behind their nose, that had not been clearly identified before.
By inserting fluorescent markers into rodent brain tissue and the brains of living mice, the researchers mapped a network called the nasopharyngeal lymphatic plexus, indicating that it is a major center for cerebrospinal fluid drainage.
In a review for the journal Nature, University of Bern physiologists Irene Spira and Steffen Proulx praised the latest discovery. As authors of studies suggesting the possibility of such a “secret passage,” they say the findings provide “indisputable evidence that the nasopharyngeal lymphatic plexus, at least in mice, has a critical role in filtering the central nervous system.”
The lead researchers also examined the brains of crab-eating macaques, and found a similar structure in the exact same place.
However, it is still unclear how cerebrospinal fluid drains from the nasal cavity to the lymph nodes in the neck.
The research team provided the most convincing explanation yet: two groups of lymphatic vessels drain cerebrospinal fluid to the deep cervical lymph nodes in mice.
Why is Earth the only planet where there is fire?
Ancient humans used fire to cook food, to see in the dark, and to ward off dangers (such as predators).
Historical evidence reveals that humans first began using fire about 1.5 million years ago, and this is likely one of the few ancient discoveries that remains equally important today. Earth is the only planet that has a suitable environment for fires to occur.
What makes Earth the only planet where there is fire?
There is no other planet in the universe that has fire, not even the Sun, as many people believe.
The sun looks like a glowing ball of fire. However, what we see is not actual fire, but rather an atomic reaction that produces massive amounts of light and heat, giving the Sun its fiery appearance.
There are active volcanoes on Venus and Io (one of Jupiter's moons), but the lava that erupts from those volcanoes is not accompanied by fire.
Experts explained that the fire is caused by three factors: molecular oxygen (O2), heat, and fuel.
There are planets (Venus) within our solar system that contain small amounts of oxygen in their atmospheres, and some of them have heat (Mercury) in addition to oxygen.
But the oxygen in their atmosphere is not readily available for combustion. In addition, all of these planets lack the fuel needed to start fire, which on Earth comes from decaying organic matter.
Earth contains all three components in the right proportions with the right temperature and pressure, making it the only planet capable of producing fire.
The effect of fire on humanity
Some experts believe that human interaction with fire is the first indicator of human intelligence.
Fires may have contributed significantly to the early human population by reducing the number of deaths caused by cold weather, predators, and food poisoning (from uncooked foods containing pathogens).
The scientist Charles Darwin believed that fire and language were the most important discoveries of humanity.
“Fire has long been seen as one of the fundamental human technological innovations underlying human evolutionary success, including our widespread distribution and guiding subsequent adaptations,” says Catherine MacDonald, an archaeologist from Leiden University, in her study focusing on fire.
Fire and the future
Even if you ignore the role of fire in the evolution of plants and animals, many other factors associated with the existence and continuation of life on Earth are affected by fire, such as oxygen, which makes up about 21% of the Earth's atmosphere and is necessary for the survival of most life forms.
However, if the oxygen concentration jumps to 30 or 40%, the forests may cease to exist, as well as all life forms that depend on them. Too much of it leads to oxygen toxicity in humans and animals (causing respiratory dysfunction), physiological stress in plants, and increased frequency of forest fires.
Studies indicate that atmospheric oxygen is regulated by fire.
“The higher frequency and intensity of fires regulates oxygen in the atmosphere by inhibiting plant growth and biomass production on land, which means there is less organic matter available to bury carbon on land and via transport to the ocean,” the researchers explained.
However, we must realize that fire, which regulates many aspects of the Earth's environment, can also turn everything into ash and cause massive disruption if the climate change crisis is not controlled.