The Temporal Reorganization of Maternal Care During Early Life Stress

Abstract

It has long been established that the quality of maternal care, rather than genetic variation, shapes the future caregiving behaviors of offspring. In rodents, maternal separation (MS) of pups from the dam is a widely used model of early-life stress (ELS). During the first postnatal week, dams typically engage in high frequencies of active maternal behaviors, including licking, grooming, and nesting (LGN). However, previous studies have reported that MS can paradoxically increase compensation for these behaviors upon reunion. To address this controversy, we examined whether changes in maternal care following MS are transient or sustained throughout the day, and whether increased active behaviors could possibly offset the reduction in care experienced during separation. Our study included 16 cages (7 standard-reared, 9 ELS-assigned). ELS was induced from postnatal days 10–16 (P10–P16), during which pups were separated from their dams for 3–4 hours per day. Each cage was observed for 12 days (5 days prior to ELS and 7 days during ELS), three times daily (one hour in the morning, one hour immediately following reunion, and one hour approximately 2–3 hours post-reunion). Twenty behavioral observations were recorded during each session, including nursing, pup-grooming, eating, drinking, and lack of contact. We found that ELS increased nursing at all observation time points, suggesting potential compensation for the pups’ lack of access during the separation timeframe. Notably, active maternal behaviors and total dam-pup time increased only immediately after reunion, returning to baseline—or even decreasing relative to baseline—by the 2-3 hour post-reunion window. These compensatory increases in active care appear to be short-lived and therefore insufficient to balance the overall decrease in maternal contact caused by MS. Moreover, rough maternal interactions (e.g., dragging and stepping) were significantly elevated under ELS conditions. Together, these findings mediate the ongoing debate in the field and confirm that the MS model disrupts both the quality and quantity of dam-pup maternal care.