A new study on mice has raised the intriguing possibility that the fear of pain can be inherited by future generations through chemical changes in DNA.
Trauma and post-traumatic stress disorder (PTSD) experienced by human parents are believed to cause physiological changes in their children – not just through social interaction and living in the same environment, but through inheritance.
To test that theory, researchers at the Yerkes National Primate Research Center at Emory University in Atlanta trained laboratory mice to become afraid of an odor by giving them a mild electric shock when exposed to acetophenone, a chemical that smells like cherry blossom.
The mice began to associate the smell with pain, and quivered even when not given an electric shock.
Researchers found that when a mouse learned to become afraid of the smell of acetophenone, their offspring would also be more sensitive to that odor, even though the pups had never encountered it.
Offspring of the sensitized mice were not only more startled by the smell of acetophenone, they were also able to detect small amounts of it. Young mice did not respond in the same way to other smells.
The sensitivity to acetophenone even appeared in the second generation of mice (grandchildren), indicating that information about the pain connected with the odor was being transmitted via the sperm or eggs.
Researchers say the study, which is published in the journal Nature Neuroscience, could lead to new methods of treating psychiatric disorders in families traumatized by PTSD.
“Knowing how the experiences of parents influence their descendants helps us to understand psychiatric disorders that may have a trans-generational basis, and possibly to design therapeutic strategies,” says senior author Kerry Ressler, MD, a professor of psychiatry and behavioral sciences at Emory School of Medicine.
Researchers believe DNA in the sperm of smell-sensitized mice is somehow altered, not in its sequence or coding, but in its packaging or chemical modifications.
In mice taught to fear acetophenone, an odorant receptor gene in the nose that responds to acetophenone has a changed pattern of methylation: a chemical modification that fine tunes the activity of genes.
“While the sequence of the gene encoding the receptor that responds to the odor is unchanged, the way that gene is regulated may be affected,” Ressler explained. “There is some evidence that some of the generalized effects of diet and hormone changes, as well as trauma, can be transmitted epigenetically. The difference here is that the odor-sensitivity-learning process is affecting the nervous system – and apparently, reproductive cells too — in such a specific way.”
Researchers would like to know if the changes are only associated with odors. Could mice trained to be afraid of a particular sound, for example, pass on a sensitivity to that sound?
“We are really just scratching the surface at this point,” says study co-author, Brian Dias, PhD. “Our next goal must be to buffer descendant generations from these effects, Such interventions could form the core of a treatment to prevent the development of neuropsychiatric disorders with roots in ancestral trauma.”
The research was funded by the Howard Hughes Medical Institute and the Burroughs Wellcome Fund.