Consequences of the presence of the mother or unfamiliar adult female on cortisol, ACTH, testosterone and behavioral responses of periadolescent guinea pigs during exposure to novelty

Periadolescent guinea pigs were exposed to a novel environment for 10, 30, 60, or 90 min while either alone or with either their biological mother or an unfamiliar adult female. Both classes of females reduced plasma cortisol , ACTH and vocalization responses to the novel environment, and did so to a n equivalent degree. However, behavioral interactions with the mother and u nfamiliar female differed considerably. The offspring exhibited more defens ive behavior and were the targets of more agonistic acts when with the unfa miliar female, though one agonistic behavior, kicking, was observed more of ten in tests with the mother. Males displayed more social/courtship behavio r and tumescence with the unfamiliar female. Further, males exhibited highe r plasma testosterone levels when with the unfamiliar female than when eith er with the mother or alone. These data in conjunction with earlier finding s suggest that the ability of unfamiliar adult females to moderate hypothal amic-pituitary-adrenal activity fully emerges during the periadolescent per iod, is not dependent on nurturant behavior by the adult female, and may fa cilitate the redirection of social behavior from the mother to unrelated ad ults. Further, mothers appear to inhibit maternally directed sexual behavio r and plasma testosterone elevations in their periadolescent sons, effects which likely serve to inhibit inbreeding. (C) 2000 Elsevier Science Ltd. Al l rights reserved.