Social experiences during adolescence affect anxiety-like behavior but not aggressiveness in male mice.

Adolescence has lately been recognized as a key developmental phase during which an individual's behavior can be shaped. In a recent study with male mice varying in the expression of the serotonin transporter, escapable adverse social experiences during adolescence led to decreased anxiety-like behavior and increased exploratory and aggressive behavior compared to throughout beneficial experiences. Since in this study some behavioral tests took place with a delay of one week after the last social experiences have been made, it was not clear whether the observed effects really reflected the consequences of the experienced different social environments. To test this, the present study focused on the direct effects of beneficial and adverse social experiences on aggressiveness and anxiety-like behavior in C57BL/6J mice. In contrast to the previous study, behavioral testing took place immediately after the last social experiences had been made. Interestingly, whereas individuals from an escapable adverse environment showed significantly lower levels of anxiety-like and higher levels of exploratory behavior than animals from a beneficial environment, aggressive behavior was not affected. From this, we conclude that different social experiences during adolescence exert immediate effects on anxiety-like but not aggressive behavior in male mice.