Born Smart

PCB’s (polychlorinated biphenyls) were used in a wide variety of products like transformers and capacitors, electronic components, pesticides and flame retardants.  The production of PCB’s were banned in the 1970’s yet exposure to this toxin still occur when the dumped products release PCB’s into the air or are leached into the groundwater to contaminate our food chain and drinking water.  30 years later, in three different studies, scientists are finally able to provide compelling evidence how PCB’s alter the developing brain.

“There is a large body of scientific literature in humans that points the finger at PCB’s, linking them to neurodevelopmental problems we see in kids,” said Pamela Lein, lead author.

The first showed that low level exposure in utero and neonatal exposure alter the development of brain cells.  In fact low level exposure had more pronounced effects than a higher dosage.

“We think that one of the major reasons we have not seen effects in previous studies is that at higher doses PCB’s become toxic to cells and the brain has defense mechanisms to deal with disposing of these damaged cells,” said Pessah.  “Future studies of PCB’s and related compounds should be examined at lower doses more relevant to human exposures” he continued.

The second study showed that PCB’s affected brain-cell circuits in the hippocampus, an area in the brain known to be impaired in many neurodevelopmental disorders and behavioral disorders like autism, ADHD, learning disabilities, sensory deficits, developmental delays and mental retardation.

The third study describes the effect of PCB’s in detail on a molecular level.  They found that PCB’s lock the calcium channels in the brain in the open position, resulting in over-excitations on neural circuits.

Calcium channels are responsible for generating the signals needed for the extension and branching of dendrites.

PCB exposure, in utero and neonatal, alters dendritic plasticity.  Dendrites receive signals from other cells in the body, and changes shape in response to the signals they receive.  The study showed how this alteration in plasticity negatively affected learning.

Pamela Lein said, “Dendritic plasticity is important to how we process information and, when you perturb that, you interfere with complex behaviors like learning and memory.”

Examining the hippocampus, Pessah said he believes PCB’s lead to overgrowth of dendrites and inhibition of neonatal pruning that takes place during gestational development.  Brain cells exposed to PCB’s cannot respond to proper learning.

Explaining why some children go on to develop autism while others don’t, Pessah said, “We think that in autism, for example, at-risk children have deficient inhibitory circuits.  So, if you have a PCB that promotes the excitatory side of the circuit, they would be much more at risk of developing the disorder.”

The question for me now is why “at risk children” have deficient inhibitory circuits? Are there some other chemicals out there that can cause deficient inhibitory circuits, like for example cigarette smoke, and is it possible that certain nutrients, a hormone like vitamin D or overall a good nutrient rich diet can protect against this predisposition?

You can find more information on PCB’s here

http://www.sciencedaily.com/releases/2009/04/090413204546.htm