Temporal reorganization of maternal care during early life stress in mice.

Maternal separation is a widely used early-life stress (ELS) paradigm in rodents. Disrupted maternal care by separation of pups from the dam for several hours per day across neonatal and juvenile development has been found to alter hypothalamic-pituitary-adrenal axis function, molecular and circuit-level brain development and function, and behaviors associated with anxiety, depression, and cognition. However, dams have been found to temporarily increase their care towards pups upon reunion - typically associated with positive outcome measures - calling into question whether this increase in care compensates for care lost during separation. Using a mouse model of ELS, we quantified maternal home cage behaviors from postnatal day P2-16 across three observation periods per day (prior to maternal separation, immediately following reunion, and several hours following reunion), with maternal separation beginning on P10. Four composite variables of home cage behavior frequency were created: total dam-pup contact, rough contact, no contact, and dam self-care. Consistent with previous reports, we found a transient increase in care upon reunion, along with an increase in rough contact and a decrease in dam self-care. We then calculated geometric area-under-curve across the day and found that the increase in total contact among ELS litters does not result in overall more care, as indicated in previous publications, but rather a temporal reorganization of care. These findings provide important nuance to understand how maternal separation disrupts offspring care.