Maternal traits during lactation period reduce the anxiety-related behavior in male offspring: Results from a fostering study in Hatano rats

The Hatano strains of the Sprague Hawley rats have been selectively bred to create high- (HAA) and low- (LAA) active avoidance variants. We previously reported that HAA rats display more anxiety-related behavior than LAA rats, but whether this strain difference is affected by postnatal environmental factors remains unclear. In this study, we performed in- and cross-fostering between the HAA and LAA strains and investigated the effect of postnatal maternal traits on the emotional responses in each strain of the male offspring. We evaluated the effect of the fostering treatment on the emotional responses of the male offspring using the elevated plus maze test. The male LAA offspring reared by HAA dam showed higher anxiety-related behavior than those reared by LAA dam. Next, we quantified and typed various maternal behavior under the in- and cross-fostering conditions during the lactation period using a snapshot sampling method. This method allowed us to evaluate potential maternal traits that may influence the emotional responses of the offspring observed in our first experiment. We found that HAA dams showed long-term resting without offspring and offspring arrangement compared with LAA dams. These findings suggest that postnatal environmental factors may alter anxiety-related behavior in the male LAA offspring and that less direct contact with their offspring during the lactation period may induce anxiety-related behavior in male offspring.