Postnatal experiences influence the behavior in adult male and female Fischer and Lewis rats.

The postnatal environment with the rat pups' dam as the most important regulator, plays a central role in determining developmental processes of the offspring. Early disturbances of the dam-pup-dyade, like separation from the dam for hours (maternal deprivation, MD), or a short period of separation, and exposure to novelty, like the handling stimulation (HA), might induce long-lasting changes within the individual. To further investigate the susceptibility to these postnatal manipulations with regard to both, sex and genetic background, we used male and female Fischer (F344) and Lewis (LEW) rats. F344 and LEW rats were daily subjected to either HA, MD, or were left undisturbed until weaning. The immediate effects of these manipulations were studied using the mother-pup-interaction-test on postnatal days 3-7. At the age of 4 months, animals were subjected to a behavioral test battery, determining activity, exploration, and anxiety-like behavioral parameters. Postnatal manipulations induced significant alterations of the mother-pup-interaction patterns that were more pronounced in F344 dams. MD and HA F344 dams were longer off pups than LEW dams. MD F344 pups were longer groomed than MD LEW pups and HA F344 pups were longer passive nursed than HA LEW pups. In adulthood, F344 rats showed increased anxiety-like behavior compared to LEW rats. Furthermore, females of both strains exhibited more anxiety-like behavior than males. Test independently, MD led to more anxiety-like behavior and less exploratory responses, while handled rats exhibited an anxiolytic-like behavior and increased exploratory responses. In conclusion, postnatal experiences specifically altered the behavioral phenotype in adulthood. While these changes were co-directional in the two strains and in both sexes, the degree of susceptibility varied.