Maternal environment alters social interactive traits but not open-field behavior in Fischer 344 rats

Although it is recognized that the genetic background governs behavioral phenotypes, environmental factors also play a critical role in the development of various behavioral processes. The maternal environment has a major impact on pups, and the cross-fostering procedure is used to determine the influence of early life experiences. The present study examined the influence of maternal environment on behavioral traits in inbred Fischer 344 (F344) rats. F344/DuCrlCrlj and Wistar (Crlj:WI) pups were fostered from postnatal day 1 as follows: Wistar pups raised by Wistar dams, F344 raised by Wistar, Wistar raised by F344, and F344 raised by F344. At 10 weeks of age, rats were randomly assigned to an open-field test and social interaction test. In the open-field test, irrespective of the rearing conditions, the activity during the first 1 min was significantly lower in F344 rats than in Wistar rats. Latency to the onset of movement showed no difference between groups. In the social interaction test, the recognition performance during the first 1 min in F344 raised by F344 was significantly shorter than that in the other groups. The onset of recognition to a novel social partner in F344 raised by F344 was significantly delayed, and the delay disappeared upon cross-fostering by Wistar dams. These results raise the possibility that the behavioral phenotype of F344 rats results from the interplay of genetic factors and maternal environment during early life, and that F344 rats are a strain with high susceptibility to rearing conditions for the formation of their emotionality.