Effects of Cross Fostering on Open-Field Behavior, Acoustic Startle, Lipopolysaccharide-Induced Corticosterone Release, and Body Weight in Lewis and Fischer Rats

Lewis (LEW/N) and Fischer (F344/N) rats differ on a myriad of behavioral and physiological endpoints, some of which have been reported to be affected by maternal experience in outbred rats and other strains. To assess whether epigenetic factors contribute to the differential behavioral responses to stress and pro-inflammatory challenges in these strains, the effects of cross fostering on open-field, acoustic startle, and glucocorticoid reactivity to lipopolysaccharide (LPS) were examined in the present experiment. In the open-field test, although in-fostered female LEW/N and F344/N strains did not differ, female LEW/N rats displayed significantly greater activity than female F344/N rats in the cross-fostered condition. Differences between males of the two strains were increased by cross fostering, with the LEW/N strain displaying greater total activity. In acoustic startle, there was little strain difference between in-fostered or cross-fostered female rats. On the other hand, in-fostered male LEW/N rats had a significantly greater startle response than in-fostered male F344/N rats, an effect that was dramatically reduced by cross fostering. In-fostered female LEW/N rats displayed a blunted corticosterone response relative to in-fostered female F344/N rats, an effect that was reduced by cross fostering. Conversely, although there was no strain difference between male in-fostered rats, cross-fostered male F344/N rats displayed a significantly greater corticosterone response to LPS than cross-fostered male LEW/N rats. Finally, body weight differences between in-fostered LEW/N and F344/N rats were reduced by cross fostering. Together, these data illustrate that maternal factors play a role in the behavioral and physiological responses to stress between the two strains.