Mice Inherit the Fears of Their Fathers
There’s no question that the trauma gets handed down from one generation to the next.
In one highly publicized example, researchers in New York studied several dozen women who were pregnant on September 11, 2001, and had been in the vicinity of the terrorist attacks. Some of these women developed post-traumatic stress disorder (PTSD), and this group shows lower levels of the stress hormone cortisol in their saliva than do those who did not develop PTSD. But here’s the rub: At 9 months old, the babies of the women with PTSD have significantly lower cortisol levels than babies of healthy mothers.
In earlier work, the same researchers had reported low cortisol levels in adult children of Holocaust survivors with PTSD. And in yet another study, Kerry Ressler’s group at Emory University showed that the so-called “startle response” to a sudden stimulus — a marker of anxiety — is more pronounced in kids whose mothers were physically abused as children then in those whose mothers were not abused. I could go on.
But how, exactly, does a parent’s stress leave such a deep impression on its progeny?
Part of it is nurture. A parent’s sadness and stress naturally affects how they interact with other people, including their children. The Holocaust study, in fact, found that the survivors with PTSD tended to emotionally abuse or neglect their children. And we know from some remarkable experiments in rats that parental care affects the offspring’s genes: Rat pups that get a lot of licking and grooming from their mothers show distinct changes in their epigenome, the chemical markers that attach to DNA and can turn genes on and off. Neglected pups, in contrast, don’t show these epigenetic tweaks.
Now a fascinating new study reveals how traumatic experiences can work themselves into the germ line. When a male mouse becomes afraid of a specific smell, this fear is somehow transmitted into his sperm, the study found. His pups will also be afraid of the odor, and will pass that fear down to their pups.
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