“We knew that BPA could cause anxiety in a variety of species, and wanted to begin to understand why and how that happens,” says Dr. Heather Patisaul, an associate professor of biology at NC State.
BPA is a chemical used in a wide variety of polycarbonate plastics and epoxy resins, and is used in consumer products such as some food containers. The anxiety seems to be caused by significant gene expression changes in a specific region of the brain called the amygdala.
Another interesting part of the study found that a soy-rich diet can mitigate these effects.
In the experiment, rats were exposed to low doses of BPA during gestation, lactation (nursing) and through puberty. Blood tests showed that the animals exposed to BPA had BPA levels well within the range found in humans. Similarly, blood tests of animals fed soy showed levels of genistein, an estrogen-like chemical found in soy, were at levels within the human range for vegetarians and others who regularly consume soy foods.
Among adolescent rats on a soy-free diet, both males and females that had been exposed to BPA exhibited significantly higher levels of anxiety. The researchers also found, for the first time, gene changes within the brain associated with this elevated anxiety.
Specifically, the study reveals that gene expression changes in the amygdala, a brain region known to play a role in mediating responses to fear and stress, are associated with the behavioral changes. Two of the affected genes were estrogen receptor beta and the melanocortin receptor 4. Both are required for oxytocin release, thus changes in oxytocin/vasopressin signaling pathways may underpin the behavioral changes. Oxytocin is a hormone and neurotransmitter that has been linked to social behavior.
However, the researchers also found that adolescent rats on the soy-rich diet did not exhibit anxiety – suggesting that the soy-rich diet may mitigate the effects of BPA. But a soy-rich diet raises questions of its own.
“Soy contains phytoestrogens that can also affect the endocrine system, which regulates hormones,” Patisaul says. “It is not clear whether these phytoestrogens are what mitigate the effect of BPA, or if it is something else entirely. That’s a question we’re hoping to address in future research.”
The paper, “Anxiogenic effects of developmental Bisphenol A exposure 1 are associated with gene expression changes in the juvenile rat amygdala and mitigated by soy,” was published in the journal PLOS ONE.
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Source: Press Release, North Carolina State University
Photo: freedigitalphotos.net
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