Animals that are descendants of ancestors who were exposed to an environmental compound generations earlier have been found to develop an amplified reaction to stress, states new study.
The findings put a new twist on the notions of nature and nurture, with broad implications for how certain behavioural tendencies might be inherited.
The researchers at The University of Texas at Austin and Washington State University exposed gestating female rats to vinclozolin, a popular fruit and vegetable fungicide known to disrupt hormones and have effects across generations of animals.
The researchers then put the rats' third generation of offspring through a variety of behavioural tests and found they were more anxious, more sensitive to stress, and had greater activity in stress-related regions of the brain than descendants of unexposed rats.
"We are now in the third human generation since the start of the chemical revolution, since humans have been exposed to these kinds of toxins. This is the animal model of that," said David Crews at Texas at Washington State.
Michael Skinner of the same University said, "The ancestral exposure of your great grandmother alters your brain development to then respond to stress differently. We did not know a stress response could be programmed by your ancestors' environmental exposures."
The researchers had already shown exposure to vinclozolin could effect subsequent generations by affecting how genes are turned on and off, a process called epigenetics. In that case, the epigenetic transgenerational inheritance altered how rats choose mates.
The new research deepens their study of the epigenetics of the brain and behaviour, dealing for the first time with real-life challenges like stress. It also takes a rare systems biology approach, looking at the brain from the molecular level to the physiological level to behaviour.
"We did not know a stress response could be reprogrammed by your ancestors' environmental exposures," said Skinner, who focused on the epigenetic transgenerational inheritance and genomics aspects of the paper.
"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," he stated.
This could explain why some individuals have issues with post traumatic stress syndrome while others do not, he noted.
Crews said that increases in other mental disorders might 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," said Crews, who focused on the neuroscience, behaviour and stress aspects of the paper.
"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," he added.
The researchers also saw intriguing differences in weight gain, opening the door to further research on obesity.
The research was published in the latest Proceedings of the National Academy of Sciences.