Researchers writing in PNAS state they have seen an increased reaction to stress in animals whose ancestors were exposed to an environmental compound, vinclozolin, a popular fruit and vegetable fungicide, even generations earlier.

The findings put a new twist on the notions of nature and nurture and may have implications for how certain behavioral tendencies might be inherited.  They exposed gestating female rats to vinclozolin and then put the rats' third generation of offspring through a variety of behavioral tests and found the descendant rats were more anxious, more sensitive to stress, and had greater activity in stress-related regions of the brain than descendants of unexposed rats.

The researchers had previously shown exposure to vinclozolin can have epigenetic  consequences, effecting subsequent generations by affecting how genes are turned on and off. In that instance, the epigenetic transgenerational inheritance altered how rats choose mates.

The new research deepens their study of the epigenetics of the brain and behavior, dealing for the first time with real-life challenges like stress.  It also takes a systems biology approach, looking at the brain from the molecular level to the physiological level to behavior.

"The ancestral exposure of your great grandmother alters your brain development to then respond to stress differently," said co-author Michael Skinner from the Center for Reproductive Biology at Washington State University, who focused on the epigenetic transgenerational inheritance and genomics aspects of the paper. "We did not know a stress response could be programmed by your ancestors' environmental exposures. So how well you socialize or how your anxiety levels respond to stress may be as much your ancestral epigenetic inheritance as your individual early-life events."

This could explain why some individuals have issues with post traumatic stress syndrome while others do not, he says.

Co-author David Crews from  Section of Integrative Biology, University of Texas at Austin, who focused on the neuroscience, behavior and stress aspects of the paper, says that increases in other mental disorders may be attributable to the kind of "two-hit" exposure that the experiment is modeling. "There is no doubt that we have been seeing real increases in mental disorders like autism and bipolar disorder. It's more than just a change in diagnostics. The question is why? Is it because we are living in a more frantic world, or because we are living in a more frantic world and are responding to that in a different way because we have been exposed? I favor the latter."

The researchers also saw differences in weight gain, opening the door to further research on obesity.

Citation: David Crews, Ross Gillette, Samuel V. Scarpino, Mohan Manikkam, Marina I. Savenkova, and Michael K. Skinner, 'Epigenetic transgenerational inheritance of altered stress responses', PNAS 2012 ; published ahead of print May 21, 2012, doi:10.1073/pnas.1118514109