Mothers who carry large amounts of stress, either from personal life experience or inherited through inter-generational stress – children of Holocaust survivors among the most famously studied – may indeed pass this stress onto their own children, but now scientists argue the mechanisms by which this transference happens could be biological in nature.

Previous studies have combed through the various psychological pathways for transferring stress across generations, largely finding that mothers who experienced mentally taxing events were more likely to produce certain hormones that affect the developing fetus – most often through the placenta. A new study suggests this stress inheritance may also take place through the germline, as indicated by a heightened expression of a stress biomarker in the mothers’ and childrens' brains.

"The notion that biological traits that are not coded by the sequence of DNA can be transmitted across generations is the focus of a field of research called epigenetics,” Dr. John Krystal, editor of Biological Psychiatry, said in a statement. “This new paper implicates epigenetic regulation of a well-studied contributor to stress response, CRF1, in the intergenerational transmission of patterns of stress response.”

CRF1 (corticotropin releasing hormone receptor 1) is a protein in the brain responsible for telling cells to release hormones related to stress and anxiety. An increased expression in CRF1 typically signals to researchers that a person is experiencing some form of stress. Science has long observed this response, and now researchers are hoping to unveil the mechanism behind it.

In the current study, female rats carrying a lot of stress demonstrated an increased expression of CRF1 in their frontal cortex, an area of the brain devoted to decision-making and emotional regulation. Females also displayed increased expression of CRF1 in their egg cells – a checkpoint on the germline that partners with sperm cells. The germline is term used to refer to the line of cells replicated originally from the zygote. After the female rats mated, their offspring showed greater CRF1 expression

"It seems that CRF1 is a marker molecule that tracks the stress experience across generations,” said study leader Dr. Inna Gaisler-Salomon, at University of Haifa in Israel, “perhaps via the germline, and maternal care is minimally involved in this particular effect.”

Gaisler-Salomon and her colleagues also observed the offspring of stressed rats displaying behavioral differences, particularly in tests of emotional and exploratory behavior. In adult offspring, however, the patterns persisted only when the offspring experienced a stressful event personally. Inheritance had little effect by that point, suggesting that CRF1 expression concerned individual experience combined with maternal experience.

"So why is this important?" Gaisler-Salomon said. "Traditionally, it was believed that only genetic information is transferred from generation to generation via eggs and sperm cells. This study contributes to the notion that soft-wired information that is not written into the genetic code can also be transferred from one generation to the next via the germline."

Many mental disorders, from schizophrenia to anxiety, are implicated as having relationships with stress. Being able to actively control for certain genes’ expression may lead scientists to develop treatments for such disorders.