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Researchers have known that a pregnant woman's diet, drug use and level of stress could all affect the neurodevelopment of an offspring. Since women carry the fetus for months, everything they do can have a slight or drastic impact on the unborn child, which is why researchers have focused on mothers more so than fathers. In a new study, however, researchers from the University of Pennsylvania looked into the possible effects of a father's history of stress on his offspring's brain development. The researchers, led by Tracy L. Bale, Ph.D, associate professor of neuroscience in the Perelman School of Medicine Department of Psychiatry and the School of Veterinary Medicine Department of Animal Biology, found that in male mice, stress during puberty and/or adulthood affected how the offspring dealt with stress.

The research team used male mice and exposed them to different types of chronic stress, which included sudden cage movement, introduction of a foreign object, predator odor and noise. The stress was induced prior to breeding when the mice were either in puberty or already into adulthood. The researchers found that stress affected sperm, which then changed the offspring's hypothalamic pituitary-adrenal axis (HPA) responsible for stress response.

"It didn't matter if dads were going through puberty or in adulthood when stressed before they mated. We've shown here for the first time that stress can produce long-term changes to sperm that reprogram the offspring HPA stress axis regulation," Bale said in a news release. "These findings suggest one way in which paternal-stress exposure may be linked to such neuropsychiatric diseases."

The researchers concluded three distinctive findings. First, the babies of stressed fathers had blunted levels of the stress hormone, corticosterone. This meant that the offspring did not respond to stress normally, which could have both negative and positive repercussions. Second, after looking for changes in gene expression, the researchers found that two regions of the brain responsible for stress regulation in the offspring had changed. The two affected regions were the paraventricular nucleus and the bed nucleus of stria terminals. Third, the researchers looked a series of microRNAs (miRs) located in the sperm that is responsible for offspring gene expression post-fertilization. They found that there were increased expressions in nine niRs.   

"Whether such diminished stress reactivity would be detrimental or beneficial to offspring likely depends on the environment into which they were born, as well as genetic background factors," the researchers concluded. If the environment is subjected to frequent change, a poor response to stress could be detrimental for these offspring.

The study was published in the Journal of Neuroscience.