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 an equivalent degree. However, behavioral interactions with the mother and unfamiliar female differed considerably. The offspring exhibited more defensive behavior and were the targets of more agonistic acts when with the unfamiliar female, though one agonistic behavior, kicking, was observed more often in tests with the mother. Males displayed more social/courtship behavior and tumescence with the unfamiliar female. Further, males exhibited higher plasma testosterone levels when with the unfamiliar female than when either with the mother or alone. These data in conjunction with earlier findings suggest that the ability of unfamiliar adult females to moderate hypothalamic-pituitary-adrenal activity fully emerges during the periadolescent period, is not dependent on nurturant behavior by the adult female, and may facilitate the redirection of social behavior from the mother to unrelated adults. Further, mothers appear to inhibit maternally directed sexual behavior and plasma testosterone elevations in their periadolescent sons, effects which likely serve to inhibit inbreeding.