New research has linked changes in the expression of genes that regulate stress responses, to the way mothers care for their children. These epigenetic studies also reveal how environmental stress can have a damaging effect on maternal care causing a vicious cycle that transcends generations.

Professor Michael Meaney and his team from the McGill University Canada, have discovered how mothers’ affection towards their young cause epigenetic, functional changes in the activity of a gene that protects against stress. He presented the findings to the conference of the Association for Child and Adolescent Mental Health in London on 11 March 2011.

Rat pups, he said, that are licked and groomed more were calmer than ones that were licked less. Licking in rats would fulfill a similar function as hugging and cuddling in humans.

Meaney’s team tracked the effects of maternal care in the young rats and found functional changes in their brains. The licking had modified the chemistry of DNA through a process called DNA methylation. The DNA methylation process blocks transcription factors (proteins that control flow of information from DNA) from binding into the DNA, which in turn alters the activity of the glucocorticoid receptor gene, the NRC31 gene. When turned on, this gene produces a protein that helps reduce the concentration of stress hormones in the body.

The gene is activated through an epigenetic switch, which was working inefficiently in rats that had not been licked enough by their mothers. As a result, rats that had not been licked sufficiently were living in a constant state of anxiety even in the absence of stressors.

While the amount a rat mother licks its pups is a very fixed trait, Meaney’s team found that chronic stress reduced the amount the rats licked their pups. Hence, rats that were stressed reared pups that were stressed.

Since the amount of licking a mother rat does is related to the amount of licking it received when it was a pup, being exposed to stress can cause epigenetic changes which are passed on for generations.

While this might all hold true for rats, what makes the study relevant for humans is the fact that stress reactions in rats and humans are highly similar. Looking at human brains of suicide victims’, Meaney and his colleague Gustavo Turecki found same epigenetic changes in the same NR3C1 gene, only in those suicide victims that had experienced abuse. Meaney infers that just as the rats, the mistreated humans would have experienced a state of heightened anxiety, making them susceptible to mental health problems and perhaps even contributing to their suicide.

Whereas a little anxiety might be useful in a dangerous environment where a carefree rat can easily become eaten, living in a constant state of anxiety can cause poor physical and mental health, poor quality of life and an untimely death.

Hence it is promising that being fostered by more affectionate rat mothers or simply being stroked by lab assistants to give them added affection reversed the effects of a pup being born to a non-affectionate low-licking mother.

However, for humans preventive programs that start very early, such as the Family Nurse Partnership, which contributes to better maternal support during pregnancy and promotes more sensitive early mothering, may be the key to breaking the cycle that a poor environment can have. Meaney stresses that unlike genetic mutations, epigenetic changes that affect the way our genes function can be reversed and neither rats nor humans need have their destinies (literally) set in DNA.