Exploring how pollution can affect the brain

Over the years, researchers have looked at the link between pollution and neurological diseases such as Parkinson’s and Alzheimer’s.

Although the evidence is growing, scientists have not yet explained how airborne particles can affect the brain. Recently, researchers at Penn State University, PA, investigated possible links between pollution, sense of smell and neurological disease. Their findings were published in the journal eLife. The researchers showed particular interest in the flow of cerebrospinal fluid (CSF).

CSF is a fluid that surrounds the central nervous system (CNS), which includes the brain and spinal cord. It was initially thought to act as a regulator that protects the CNS but, over time, scientists have discovered more of its roles.

Professor Patrick Drew, one of the study’s authors, explains: “It is becoming increasingly clear that it not only protects the brain, but can also carry information from the brain and spinal area.”

The role of CSF in the disease

Researchers are increasingly interested in the role of CSF in the removal of metabolic wastes and the way it flows around the CNS. To date, researchers have not clarified what controls the production and outflow of CSF.

Neurological conditions, such as Parkinson’s and Alzheimer’s, are characterized by an accumulation of defective proteins. Probably the CSF could play a role in this.

The scientists wanted to understand how the pollution in the air we breathe affects the CSF and how the airborne elements reach the CSF.

Another study author, Jordan N. Norwood, a graduate student, explains his first clue: “I was trying to label the cerebrospinal fluid with a staining for an experiment. “We began to see this stained cerebrospinal fluid flowing through the nose.”

Although this finding was astonishing, Norwood was not the first person to speculate that the CNS could come out of the brain through the nose. When looking at old research papers, there were some reports about this possibility.

The scientists also noted that researchers have already shown that reduced sense of smell is sometimes an early sign of neurological conditions. For example, a study published in the journal Neurology concluded that poor performance on an odor recognition test may, one day, be a useful way to predict Alzheimer’s before the classic symptoms of the disease appear.

Destroying the sensory nerves

To further investigate the issue, the researchers destroyed the olfactory sensory nerves in mice with zinc sulfate. Interestingly, these nerves are the only part of the mammalian CNS that comes in direct contact with the external environment. As expected, the destruction of the sensory nerves deprived the mice of the ability to smell. It also “reduced” the flow of the CSF through the nose. The researchers then investigated whether this affected the mice.

According to Professor Drew, “Animals and humans are constantly producing CSF, so if it does not come out, the pressure will increase, but we found that the pressure did not increase after the flow from the nose stopped.”

The authors believe that the system should be offset in other ways. For example, the glyphosate system, which is the “brain” of the lymphatic system, may play a role.

Alternatively, the body may produce less CSF to avoid increasing pressure within the CNS.

Taking all these findings into account, the researchers hypothesize that over time, the pollution damages the olfactory sensory neurons. This causes a change in the flow or production of the CSF. Because CSF is vital for the removal of metabolic waste from the CNS, it plays a role in the development of neurological diseases.

The authors write: “The reduction of CSF may be a factor that contributes to the accumulation of toxic metabolites and proteins that cause neurodegenerative disorders.”

The authors did not prove that this is the exact process by which pollution affects the brain, but the theory is interesting.

“Next, we’d like to work with a lab at the Materials Research Institute that manages soot or jet fuel particles to see if we have the same effect,” explains Norwood.

Although it is still early, it will be surprising to see the evolution of this theory.