Mice that were conditioned to fear a specific smell passed down this fear to their offspring, suggesting that traumatic events can affect gene expression.
Adult male mice were trained to 'fear' the smell of acetophenone, a chemical commonly used in perfumes for its sweet, floral fragrance, by being given electric shocks. They then produced offspring that had the same 'startle' response and were seen to shudder when exposed to the smell.
The second-generation offspring – the 'grandchildren' of the fear-conditioned mice – were also 'extremely sensitive' to the smell.
'Our results allow us to appreciate how the experiences of a parent, before even conceiving offspring, markedly influence both structure and function in the nervous system of subsequent generations', the researchers from the Emory University School of Medicine, USA, wrote in journal Nature Neuroscience.
The researchers ruled out the possibility that the offspring were taught to fear the smell, as pups raised by 'foster parents' that had not been conditioned still showed a fear response.
The mice also showed differences in the parts of the brain associated with smell. Their offspring had more neurons that produced an odour receptor protein, Olfr151, which is specifically linked to the smell of acetophenone.
Even pups born as a result of IVF responded to the smell, suggesting that the sperm of the fear-conditioned mice was to blame. When the researchers looked at the sperm DNA, they saw that the Olfr151 area showed epigenetic changes, meaning that while the DNA itself had not been altered, the way that the genes would be expressed had changed.
'These types of results are encouraging as they suggest that transgenerational inheritance exists and is mediated by epigenetics, but more careful mechanistic study of animal models is needed before extrapolating such findings to humans', Professor Wolf Reik from the Babraham Institute commented.
Professor Marcus Pembrey, chair of the Progress Educational Trust, commented on the study. He said: 'It provides compelling evidence of biological transmission of such a "memory", together with associated brain changes, from shocked adult male mice to their sons and then grandsons'.
'It is high time public health researchers took human transgenerational responses seriously. I suspect we will not understand the rise in neuropsychiatric disorders or obesity, diabetes and metabolic disruptions generally without taking a multigenerational approach', added Professor Pembrey.