Exposure to a specific toxin known as PCBs (technically called polychlorinated biphenyls), appears to effect the development of brain cells according to the results of three new studies.
Toxic substances all around us have long been connected with problems in youngsters, but research couldn’t explain exactly how PCB toxins impact the brain.
Once PCBs were used in everything from pesticides, caulking, flame retardants and electronic components, though the U.S. banned their use in the 1970s. And though that seems like long ago, these chemicals hang around in the environment because they aren’t easily broken down.
They’re still in the air, seep into our water, are in the ground and contaminate the food we eat, like fish. PCBs are still detectable in all of us, even today.
The latest group of studies has found that these environmental toxins negatively affect the development of brain cells and overexcite brain circuits. This has been linked by earlier work to developmental problems.
“We think we have identified the way in which a broad class of environmental contaminants influences the developing nervous system and may contribute to neuro-developmental impairments such as hyperactivity, seizure disorders, and autism,” stated researcher Isaac N. Pessah, PhD. The last of the studies appears in the April 2009 online issue of PLoS-Biology.
One surprise that came from the research is that lower levels of PCB exposures sometimes were more harmful than higher level exposures.
The first of the three studies found that exposures to low doses of PCBs impaired animal subjects’ ability to learn to navigate a maze, a common way to test learning in the lab.
It looks like even low doses of PCBs affected the plasticity of the dendrites adversely, which are critical to learning and memory. Issues in this area have been linked to conditions like autism, schizophrenia and even mental retardation.
The first study was published in the March 2009 issue of Environmental and Health Perspectives.
For the second of the studies, tissue from an animal’s hippocampus (part of the brain that manages memory and emotion) was researched in order to analyze the excitability of neurons prior to and during exposures to two different PCBs.
The normal brain should have a balance between excitation and inhibition of the neurons, as too much excitability isn’t useful. Conditions like autism and attention deficit hyperactivity disorder (ADHD) may involve an imbalance between the two states.
The second study appears in the March 2009 issue of Toxicology and Applied Pharmacology.
The third study looked at a cellular level, looking specifically at how PCBs might affect cell development (as they saw from the first study) and the level of excitement (what they found from that second study).
The researchers exposed receptors in the brain cells that control the release of calcium (key to keeping signalling normal from cell to cell) to PCBs. They found that PCBs bind to the receptors and hinders the release of calcium.
It’s this that may account for the findings in the other two studies.
“I think that these studies represent a kind of a turning point for our recognition of how these chemicals, PCBs, can interfere with brain development,” says R. Thomas Zoeller, PhD, professor of biology at the University of Massachusetts, Amherst.
Now that there’s a lab-backed explanation of how PCBs do their damage, this adds even more weight to the work researchers have done to link exposures to these environmental toxins and developmental problems.
It may also allow us come up with new ways to evaluate the safety of chemicals that have taken the place of PCBs, and maybe remove the dangerous ones before they become widely used.
The work shows us that even low dose exposures to PCB toxins aren’t always safe.
