Dynamic rebalancing of approach and withdrawal motivations underpins the decline of rat maternal behavior: A behavioral analysis of dam-pup interactions

Abstract

The decline of rat maternal behavior during the postpartum period is a critical transition, yet its underlying mechanisms, particularly the interactive effects of the mother's internal state and offspring characteristics, remain incompletely understood. Using a 3 × 3 factorial design, we examined maternal behavior in Sprague-Dawley rats across three postpartum stages [postpartum day (PPD) 5/6, PPD 11/12, PPD 17/18] when presented with pups of three postnatal ages [postnatal day (PND) 5/6, PND 11/12, PND 17/18]. Behavioral assessments included a home-cage maternal behavior test, a pup retrieval test on an Elevated Plus Maze (EPM), and a pup versus male preference test. Our results demonstrate a dynamic rebalancing of maternal motivations: as pups aged and dams progressed through later postpartum stages, classic approach-related behaviors (e.g., pup retrieval, licking, crouching/hovering over pups) significantly decreased, while withdrawal-related behaviors (e.g., pup avoidance, self-grooming, and dam's distance from the nest) correspondingly increased. This shift was distinctly modulated: pup characteristics primarily influenced the decline in approach motivation, whereas maternal condition predominantly governed the increase in withdrawal motivation. In the EPM, pup age specifically affected pup retrieval and general activity but not anxiety-like behavior. Late-postpartum dams lost their preferential interest in younger pups in the pup versus male preference test. Furthermore, we validated a set of behavioral indicators (e.g., resting away from pups, dam's distance from the nest) as reliable measures of withdrawal motivation. Collectively, these findings underscore that the decline of maternal behavior arises from a dynamic rebalancing between approach and withdrawal motivational systems, jointly driven by the dam's evolving internal state and the changing stimulus characteristics of the developing pups. Additionally, our work extends the Approach-Withdrawal biphasic motivational framework to the natural decline phase of maternal behavior and provides validated tools for assessing withdrawal motivation.

Keywords: Maternal anxiety; Maternal behavior; Maternal motivation; The Approach-Withdrawal biphasic motivational theory.