How Garbage Disposal Works in the Brain

Cerebrospinal fluid removes harmful metabolic products

US researchers led by Maiken Nedergaard from the University of Rochester discovered the biological mechanism behind this twelve years ago: More precisely, they discovered an entire drainage system in the head. The team discovered that the fluid does not just trickle around aimlessly between the brain structures but is channelled through in a targeted manner.

In doing so, it also flushes through the tiny gaps between the cells.

The researchers named the underlying mechanisms the “glymphatic system,” a new word created from glia (the name given to the non-neuronal cells of the brain) and lymph (the corresponding fluid in the body). The discovery of the previously completely unknown processes was a sensation at the time.

Blood vessels pump the cerebrospinal fluid flow

The pulsating blood vessels that run through the entire brain and supply it with oxygen act as pumps for the cerebrospinal fluid. The cerebrospinal fluid flows into the gaps that open around the blood vessels.

This also explains why the system was only discovered so late: unlike the lymph fluid, which performs similar functions in the body, the brain’s drainage system does not have its own vessels.

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Cerebrospinal fluid stream passes through the brain

According to the as yet unproven hypothesis, the cerebrospinal fluid also absorbs harmful metabolic products and transports them through the brain until they are finally channelled into the lymphatic system and transported away. The lymph itself cannot do this because it is separated from the brain by the blood-brain barrier.

However, Nedergaard’s team had only demonstrated this observation in rodents. In order to track the flow of the cerebrospinal fluid, they had marked it with radioactive particles. This procedure is not suitable for testing on humans due to the possible side effects.

First evidence in the human brain

A group of researchers led by Juan Piantino from the Oregon Health and Science University Portland has now been able to prove for the first time that the human brain is also equipped with a glymphatic system.

Five test subjects suffering from brain tumors volunteered for the experiment. After brain surgery to remove the tumors, the three men and two women had access to the cerebrospinal fluid space of the brain. The team injected a harmless gadolinium contrast agent into this space and then tracked its journey using a magnetic resonance imaging (MRI) scanner.

The subjects underwent an MRI 12, 24 and 48 hours after the treatment. This allowed the researchers to track how the contrast agent migrated through the brain, just like in the mouse experiments.

Do problems with “garbage disposal” contribute to Alzheimer’s

This evidence is even more important as the glymphatic system could play a central role in the development of neurodegenerative diseases such as Alzheimer’s. The cerebrospinal fluid flow could also normally dispose of harmful proteins such as beta-amyloid, which make up the typical Alzheimer’s plaques.

This would also explain why people with chronic sleep disorders have an increased risk of Alzheimer’s. In fact, it has been observed that the glymphatic system is normally particularly active during sleep.

Poor sleep could hinder the removal of beta-amyloid and other problematic molecules and thus promote plaque formation in Alzheimer’s disease, for example.

Effects for residents here in the UAE

The stress and fast-paced lifestyle in the UAE contribute to reduced sleep, which can impair the brain’s ability to clear toxins through cerebrospinal fluid (CSF), increasing the risk of neurological problems over time.