Influences of pre- and postnatal early life environments on the inhibitory properties of familiar urine odors in male mouse aggression.

For group-living animals, discriminating among individuals and chasing unfamiliar strangers away from the home range are important to protect their territory. Previously, we reported that the familiar individual information conveyed by urine results in less aggressive behavior by resident male mice toward intruders. A resident male is aggressive toward an intruding unfamiliar castrated C57BL/6J mouse (unfamiliar castrated male [UFC]), whereas there is less aggression by the resident male when the UFC is swabbed with urine collected from the resident's cage mate. Urine is affected by various factors, including the environment. In this study, we investigated the effect of 2 living environments, the early developmental environment and the adult diet, on individual information conveyed in urine. Aggressive behavior toward UFCs was lower when UFCs were swabbed with cage mate urine or urine from a cage mate's littermate that was not living with the resident male (UFCL). Litters were cross-fostered, and we examined whether the pre- or postnatal period was important for formation of individual urine odor. The resident male displayed attack bites toward UFCs that were his cage mate's littermates but were fostered by another C57BL/6J dam. In addition, a castrated male that was reared with a cage mate (sharing the same postnatal environment) but that was not his littermate was also attacked by the resident male, suggesting that littermates that share the same pre- and postnatal environments provide similar (or identical) information, which inhibits aggression. In adulthood, even after dietary changes, the resident male showed less aggression toward UFCs when the UFCs were swabbed with the cage mate's urine, which was collected before a dietary change, indicating that individual information was not affected by dietary conditions in adulthood. In a habituation-dishabituation test, resident mice could discriminate among all pairs of mouse urine from each group. These results suggest that olfactory cues containing individual information are shared among littermates, and both the pre- and postnatal environments are important for formation of the information that inhibits aggressive behavior. This individual information might differ from the odor that is used for discriminating in the habituation-dishabituation test.