Comparison of the effects of the mother and an unfamiliar adult female on cortisol and behavioral responses of pre- and postweaning guinea pigs

In the guinea pig, the presence of the mother, but not littermates, has bee n found to inhibit hypothalamic-pituitary-adrenal (HPA) responses during br ief (30-60 min) exposure to novel surroundings both prior to and several we eks following the completion of weaning. in the present study, we found tha t an unfamiliar adult female inhibited plasma cortisol and vocalization res ponses of pre- and postweaning guinea pigs during a till-min exposure to a novel environment. However, the presence of the mother still had a greater effect on the cortisol levels of the young, at least during the preweaning period. The moderating influence of the unfamiliar adult female on vocaliza tions and cortisol levels occurred despite behavioral interactions, such as heightened aggression and sexual behavior, not seen during tests with the mother. It is suggested that the unfamiliar adult female's effectiveness in reducing HPA activity during exposure to novelty may facilitate the change in patterns of social interaction occurring in recently weaned animals. (C ) 2000 John Wiley & Sons, Inc.