This 2015 US/Canadian rodent study investigated the effects of natural variation in maternal care:
“The effects of early life rearing experience via natural variation in maternal licking and grooming during the first week of life on behavior, physiology, gene expression, and epigenetic regulation of Oxtr [oxytocin receptor gene] across blood and brain tissues (mononucleocytes, hippocampus, striatum, and hypothalamus).
Rats reared by high licking-grooming (HL) and low licking-grooming (LL) rat dams exhibited differences across study outcomes:
- LL offspring were more active in behavioral arenas,
- exhibited lower body mass in adulthood, and
- showed reduced corticosterone responsivity to a stressor.
Oxtr DNA methylation was significantly lower at multiple CpGs in the blood of LL versus HL males, but no differences were found in the brain. Across groups, Oxtr transcript levels in the hypothalamus were associated with reduced corticosterone secretion in response to stress, congruent with the role of oxytocin signaling in this region.
Methylation of specific CpGs at a high or low level was consistent across tissues, especially within the brain. However, individual variation in DNA methylation relative to these global patterns was not consistent across tissues.
These results suggest that blood Oxtr DNA methylation may reflect early experience of maternal care, and that Oxtr methylation across tissues is highly concordant for specific CpGs, but that inferences across tissues are not supported for individual variation in Oxtr methylation.”
The study focused on whether or not an individual’s experience-dependent oxytocin receptor gene DNA methylation in one of the four studied tissues could be used to infer a similar effect in the three other tissues. The main finding was NO, it couldn’t!
The researchers’ other findings may have been strengthened had they also examined causes for the observed effects. The “natural variation in maternal licking and grooming” developed from somewhere, didn’t it?
The subjects’ mothers were presumably available for the same tests as the subjects, but nothing was done with them. Investigating at least one earlier generation may have enabled etiologic associations of “the effects of early life rearing experience” and “individual variation in DNA methylation.”
http://www.sciencedirect.com/science/journal/0018506X/77 “Natural variation in maternal care and cross-tissue patterns of oxytocin receptor gene methylation in rats”