Living in a dangerous world decreases maternal care: a study in serotonin transporter knockout mice.

Adverse early experiences can profoundly influence the adult behavioral profile. When pregnant and lactating mice are confronted with soiled bedding of unfamiliar males (UMB), these stimuli signal the danger of infanticide and thus simulate a "dangerous world". In a previous study, offspring of UMB treated mothers were shown to display increased anxiety-like behavior and reduced exploratory locomotion as adults, compared to mice treated with neutral bedding (NB, "safe environment"). The aim of this study was to elucidate the mechanisms conveying these effects of living in a "dangerous world" to offspring behavior. We hypothesized the mother to be the major link and focused on the influence of UMB on maternal stress hormones and behavior. Thus, we investigated fecal corticosterone metabolites (CM) and maternal care of pregnant and lactating mice either treated with NB or UMB. The offspring were subsequently tested for their anxiety-like and exploratory behavior. Mothers treated with UMB showed a significantly higher increase of fecal CM following the initial treatment, than NB treated mothers, indicating that the odor cues of potentially infanticidal males represented an ethologically relevant stimulus. Whereas the hormonal stress response habituated, living in a "dangerous world" led to a distinct and consistent reduction of maternal care behavior, particularly concerning the duration of licking and grooming the pups. Surprisingly, we could not confirm our former findings of altered phenotypes in the offspring of UMB treated mothers. In summary, we hypothesize that the frequently described effects of early life adversity on the offspring's behavioral profile are mediated primarily by maternal care in altricial rodents.