Social influences on cortisol and behavioral responses of preweaning, periadolescent, and adult guinea pigs.

In various species, the presence of an attachment figure can reduce hypothalamic-pituitary-adrenal (HPA) responses. In the guinea pig, the mother reduces HPA elevations of her young both prior to and following weaning. Recently, an unfamiliar female was also found to reduce the HPA responses of postweaning guinea pigs. The present study evaluated the specificity and ontogenetic course of the effect of the unfamiliar female. Experiment 1 found that an unfamiliar adult male did not reduce the cortisol response of periadolescent subjects during novelty exposure. Experiment 2 showed that the effect of the unfamiliar female was present as early as the second week of life. Experiment 3 found that neither an unfamiliar adult female nor male affected the cortisol response in adult guinea pigs. In all experiments, the mother reduced the cortisol elevations of her offspring. The ability to buffer the cortisol response could not be explained by the amount of agonistic behavior subjects received from the stimulus animals. Results indicate that the mother guinea pig has a persisting ability to buffer HPA responses in her developing offspring; that during at least a large portion of the time that the mother can moderate the cortisol response of her young, so too can an unfamiliar adult female, but not an unfamiliar adult male; and that the ability of social partners to moderate HPA activity is not readily predictable from behavioral interactions.