Stress in young rats can be passed on two generations, say U of Haifa researchers

Although it is a common – but incorrect view – that people can hand down their traits with their DNA sequences unaffected by what happens to them during their lifetime, epigenetic changes caused by external or environmental factors can affect offspring.Now, University of Haifa research has found that the effects of exposure of females to stress during adolescence are transmitted not only to children, but also to grandchildren. “Our studies suggest that there are processes, unrelated to maternal care, that can explain how information is transmitted from generation to generation,” said Dr. Inna Gaisler-Salomon. Carried out with her doctoral student Hiba Zaidan, in collaboration with Prof. Micah Leshem, the study has just appeared in the journal Psychoneuroendocrinology.In previous studies, they found that exposing rats to stress during adolescence, before they ever become pregnant, causes behavioral changes among their direct offspring when the latter reach adulthood. The team also found a gene (CRF1) related to stress that expresses itself differently in the brain of individual offspring from the moment they are born. According to the researchers, this finding suggests that it is not maternal care that affects variations involving stress in offspring.In previous studies, they found that exposing rats to stress during adolescence, before they ever become pregnant, causes behavioral changes among their direct offspring when the latter reach adulthood. The team also found a gene (CRF1) related to stress that expresses itself differently in the brain of individual offspring from the moment they are born. According to the researchers, this finding suggests that it is not maternal care that affects variations involving stress in offspring.To determine the effects of stress on offspring, they tested the CRF1 gene for the presence of the hormone corticosterone, a stress hormone that corresponds to cortisol in humans and is released in response to stress. As in previous studies, they again exposed female adolescent rats to minor stress involving changes in temperature and routine for a week. Their direct offspring grew up without any stress-inducing intervention, as did their grandchildren.The third generation of rats (the grandchildren) underwent different tests that measure anxiety-like behavior and the acquisition of fear. In addition, for the second and third generation offspring, the levels of the CRF1 expression in the brain as well as the levels of corticosterone were also measured.The findings indicate that the effects of stress on the first-generation mother rat continue to influence her grandchildren on all three levels – behavioral, hormonal and the manifestation of the CFR1 gene. On the behavioral level, the third-generation descendants (mainly females) were, perhaps surprisingly, more “daring,” spent more time in the “frightening” parts of the maze and exhibited less-anxious behavior in various tests when compared with the offspring of rats that were not exposed to stress. In addition, both male and female offspring of rats exposed to stress showed a more rapid acquisition of fear relative to the descendants of the control group.“It’s possible to try to explain the results as showing that the rats whose grandmother was exposed to stress displayed more adaptive behavior to their surroundings. Wherever greater curiosity was needed to improve their chances of survival, they displayed curiosity, but the moment they were exposed to a frightening event, they learned quickly and reacted more extremely to this event,” the researchers said. “This is a complex effect that depends on the context of the situation.”They also found that behavioral differences among the first generation of rats exposed to trauma were different from those found among the second generation.In other words, the effect of the trauma is transmitted between generations, but it affects each generation differently.“Adolescence is a very sensitive period, and our studies show that exposure to stress at this stage of life affects not only the affected female, but also the behavior and stress hormone levels of her first- and second-generation offspring. Similar studies have been done, but most of them explore the consequences of stress to males, not females. Our studies further suggest that there are processes unrelated to maternal care that can explain how information is transmitted from generation to generation,” concluded Gaisler-Salomon.