Strain-dependent variation in maternal care and early behavioral development in laboratory rats

Understanding how maternal behavior varies among different laboratory rat strains is essential for improving the translational relevance of preclinical neurodevelopmental models. In this study, we compared maternal care patterns and the early development of offspring in three commonly used rat strains: Wistar, Sprague-Dawley (SD), and Spontaneously Hypertensive Heart Failure (SHHF). Maternal behaviors were recorded from postpartum day (PPD) 1 to 5 during both light and dark phases and analyzed using both conventional frequency-based methods and behavioral transition network analysis. Pup development was assessed from postnatal (PND) 6 to 22, including measures of somatic growth, eye-opening, reflex maturation, and ultrasonic vocalizations (USVs). We found significant strain differences in both the frequency and organization of maternal behaviors. SD dams exhibited reduced high-crouch nursing and fewer behavioral transitions across postpartum days. In contrast, SHHF dams spent more time in the nest without nursing and engaged in more frequent self-grooming, particularly during the dark phase. Network analysis revealed distinct transition patterns among strains, capturing qualitative differences in maternal dynamics not evident in conventional analysis. Strain differences also emerged in pup development. SHHF pups showed delayed eye opening, reduced body weight gain, and slower performance in several reflexes compared to Wistar and SD pups. Additionally, USV analyses revealed that SD and SHHF pups emitted fewer and shorter calls in both isolation-induced and maternal-potentiated contexts, especially in the low-frequency range. These findings underscore the importance of considering strain-specific profiles of maternal behavior and infant development when modeling early neurodevelopmental trajectories. SHHF rats may be particularly useful for studying early-life vulnerabilities relevant to human conditions associated with perinatal adversity. Moreover, behavioral transition networks offer a sensitive approach to reveal subtle differences in maternal caregiving strategies across strains.