Social aversive stimuli presented to the mother produce the precocious expression of fear in rat pups.

During the stress hypo-responsive period, rat pups do not display fear responses toward adult males, yet they exhibit distress behavior in isolation. Since the mother modulates her offspring's affective development, we hypothesized that by altering the mother's behavior, a prolonged stressful situation would modify the ontogeny of the fear responses and distress behaviors in pups. Therefore, we repeatedly exposed the mother-litter dyad to different socially stressful stimuli and subsequently evaluated in 8-day-old pups their fear responses toward an anesthetized male, as well as their distress behavior in isolation. Our results show that repeated exposure to unfamiliar males and females, which altered maternal behavior by eliciting aggression in the mother, was associated with the precocious fear responses in pups, though without altering their distress behavior in isolation. We propose that the mother, as the principal mediator of environmental influences, provokes the precocious expression of fear in pups through alterations in her maternal behavior.