BPA exposure can alter memory in adults, rodent study suggests.

Nov 17, 2011

Eilam-Stock, T, P Serrano, M Frankfurt and V Luine, 2011. Bisphenol-A impairs memory and reduces dendritic spine density in adult male rats. Behavioral Neuroscience http://dx.doi.org/10.1037/a0025959.

Synopsis by Steven Neese

Bisphenol-A at a level below the U.S. safe daily dose impairs memory and alters brain structure in adult male rats exposed to the chemical just once.

Adult male rats exposed to a single dose of the contaminant bisphenol A (BPA) had trouble remembering an object's look or location after only a couple of hours, according to a study published in Behavioral Neuroscience.

Researchers also found changes in brain proteins and cells involved in learning and memory. The part of the brain cell – called dendritic spines – that allow cells to talk to each other were less dense in the memory regions of the brain after exposure to BPA.

The study specifically measured memory consolidation – the first process of remembering where an experience is converted into a memory.

This is one of the first studies to measure the effects of a one-time, low dose BPA exposure on memory processes and brain cell formation in adult males. The results echo prior studies that also find BPA impairs memory. Although it was an animal and not human study, these results suggest that exposures to the chemical have the potential to disrupt memory processes and interfere with brain processes associated with learning.

BPA is a high production chemical used in the manufacture of a variety of plastic products, in epoxy resin linings of food cans and in some thermal receipt paper. The chemical can escape from these products. Common routes of exposure include eating contaminated food and drink, absorption through the skin and breathing it in.

BPA has hormonal properties. The chemical can mimic estrogens – the female sex hormones. On the opposite end, it can also disrupt the actions of estrogens and androgens – the male sex hormone. Both estrogens and androgens can play a role in memory.

Most research has studied the effects of developmental BPA exposures, while few have addressed potential health effects in adults.

Researchers test sight and spatial memory in rats by measuring their ability to recognize objects and their locations. In this study, adult male rats explored two identical objects for three minutes. Immediately after, the rats were injected with 40 micrograms per kilograms (μg/kg) body weight of BPA. The current U.S. Environmental Protection Agency reference dose the exposure dose that is considered safeis 50 μg/kg body weight per day.

Two hours later, one of the objects was either moved to a new location or replaced with a different object. Researchers measured the time the rats explored the original objects as well as the moved and new objects. More time with an original object that was already known indicates the rat did not remember. They also analyzed dendritic spine density and certain brain proteins associated with processing memories.

The BPA-exposed rats explored the new and original objects and their placement for the same amount of time before and after treatment. Unexposed rats, on the other hand, spent less time with the original objects, indicating they "remembered" them.

Exposure to BPA also reduced the density of dendritic spines in the hippocampus and prefrontal cortex – two brain regions important for memory. A dendritic spine is part of a cell that is important for communication between cells.

BPA also altered two brain proteins important to learning PSD-95 and pCREB. The changes in expression of these brain markers in the brain may be related to the memory impairment seen after chemical exposure.

Since human exposure to BPA is ubiquitous, future studies will need to confirm if these findings apply to people, too.

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