Early dopamine elevation modifies the behavioral consequences of maternal separation in female and male juvenile mice

Alterations in dopaminergic signaling and exposure to early-life stress are both implicated in the developmental origins of psychiatric disorders, yet little is known about how these factors interact during sensitive periods of brain maturation. We investigated whether increased dopamine availability during early postnatal development modifies the behavioral consequences of maternal separation in female and male C57BL/6 mice. From postnatal day (PD) 1 to PD14, mice received L-Dopa plus benserazide, maternal separation (3 h/day), their combination, or the corresponding control conditions. We assessed mice behavior between PD28 and PD32 using novel object recognition, open-field, elevated plus-maze, marble-burying, and forced-swim tests, followed by hippocampal volumetric analysis. Early L-Dopa exposure produced sex- and behavior-specific effects. In females, L-Dopa increased rearing without altering horizontal locomotion and modified open-arm exploration and stress-coping behavior, whereas in males it increased open-arm exploration and reduced climbing frequency. Maternal separation produced distinct effects in females and males and reduced repetitive digging/burying behavior in both sexes. Importantly, maternal separation frequently modified rather than potentiated the effects of L-Dopa. In both sexes, combined maternal separation and L-Dopa opposed several L-Dopa-associated alterations in open-field, elevated plus-maze, and forced-swim behaviors. Recognition memory was largely preserved across experimental conditions. L-Dopa also reduced hippocampal volume selectively in females, whereas hippocampal volume was higher in females exposed to maternal separation plus L-Dopa than in those receiving L-Dopa alone. Multivariate analyses revealed overlapping rather than treatment-specific behavioral clusters, indicating substantial individual heterogeneity and sex-dependent shifts in multidimensional behavioral profiles. Together, these findings demonstrate that transient alterations in dopamine availability and maternal separation interact non-additively during early postnatal development. Their consequences depend on sex, behavioral domain, and developmental timing, supporting a model in which neurochemical and environmental perturbations dynamically shape behavioral trajectories rather than simply producing cumulative developmental damage.