If you feel scared of a smell which you have never learnt before and you don't know why, probably you should ask your farther or grandfather. Recently, Dr. Brian G Dias and Kerry J Ressler, researchers from Emory University, have discovered that mice can pass their fear of certain smells to next generations by genetic way. It may be a way for parents to warn their unborn children about the harsh features of environment they would encounter in the future.
In this study, male mice (F0) were first fear conditioned with acetophenone, a chemical smell like cherry blossom, by giving electrical shock to the mice with the presence of acetophenone. After training, the mice associated this particular smell with pain and showed startle response even when only acetophenone was present. Intriguingly, this fear response to acetophenone was also observed from the subsequently conceived F1 and F2 generations. They exhibited extraordinary sensitivity to the smell of acetophenone which they have never encountered in the life.
Fig. 1: In human, the neuropsychiatric illness, drug addiction, anxiety and other problems are often seen in both parents and their children.
(Credit: Jane Feldman)
To address the neuronal basis of this behavior, researchers further found that F1 and F2 mice showed F0-like increased structural representation in the olfactory epithelium and olfactory bulb which are significant for the processing of this smell. The same behavioral sensitivity and neuroanatomical changes were also seen from in vitro fertilization-derived (IVF-derived) mice, together suggesting the inheritance of this effect.
Given that the DNA sequence is most likely consistent, the researchers looked into epigenetics for the nature of this transgenerational trauma. Interestingly, by examining the sperms of acetophenone-conditioned F0 mice and their offspring F1 mice, they found significantly less CpG methylation in the locus of the gene code for receptor of acetophenone. While less CpG methylation very often means more transcription, this finding may offer a possible explanation of the increased sensitivity and altered neural structures observed in the offspring.
However, there are still many open questions from this study. For instance, how sperms could be altered due to the odors sensed normally by nose? How many generations can this effect last? And can it be eliminated? In human, the transgenerational trauma is also a very common phenomenon, e.g. while Holocaust survivors showed concentration camp syndrome, their descendants conceived after war also demonstrated higher rate of neuropsychiatric disorders. The researchers expect, with better understanding of how ancestral experience influences descedants, hopefully in the molecular level, better treatments could be brought to prevent the development of neuropsychiatric disorders which have a transgenerational basis.
Dias, Brian G., and Kerry J. Ressler. "Parental olfactory experience influences behavior and neural structure in subsequent generations." Nature neuroscience(2013).