Reciprocal embryo transfer and newborns cross-fostering between mouse lines selected for high or low swim stress-induced analgesia

Pain tolerance varies significantly among humans, with disparities attributable to genetic factors and environmental influences. The developmental origins of health and disease approach postulate that pre- and early postnatal maternal environment affects individuals' health and well-being. In the present study, we aimed to determine the influence of prenatal and early postnatal maternal environment and care on the offspring's physiology and pain response. To this end, we analysed the influence of bidirectional embryo transfer (ET) and cross-fostering (CF) between two mouse lines divergently selected for high (HA) and low (LA) swim stress-induced analgesia (SSIA) on offspring phenotype, SSIA-related traits and opioid component of SSIA. Our findings reveal that both the fetal development and early maternal care significantly influence the level of SSIA in mice. HA mice born after ET to LA surrogate mothers showed reduced SSIA levels alongside a diminished effect of the opioid antagonist naloxone, suggesting a decreased opioid component in SSIA regulation. This effect was preserved in the F2 generation of individuals originating from ET, but not CF. Additionally, both ET and CF resulted in changes in body weight and body temperature towards an average value of the surrogate or foster maternal line; however, these changes were not preserved in the F2 generation. Together, our findings indicate that maternal influence during fetal development and the early postnatal period may influence physiological parameters, as well as traits associated with stress response. Maternal influence is more pronounced in progeny subject to ET, indicating a stronger influence of the prenatal period.