Cortisol and behavioral responses to separation in mother and infant guinea pigs.

In Experiment 1, lactating guinea pigs 3 days postpartum exhibited an elevation of plasma levels of cortisol when their litters were taken from the home cage and placed out of auditory range for 30 min. If pups were left within auditory range during the period of separation, or if the litter was disturbed but not removed, no increase in plasma cortisol levels was observed. In Experiment 2, 11/12- and 18/19-day-old guinea pig pups placed alone in a novel environment for 30 min displayed levels of plasma cortisol and vocalizations that were greater than those of pups tested in the same environment but with their mother. Pups tested with littermates but not with their mother exhibited plasma cortisol levels that were as great as those of pups tested alone. Pups tested with littermates vocalized much less than pups tested alone but more than pups tested with their mother. These results indicate that brief mother-infant separation can activate the pituitary-adrenal system in mother as well as infant guinea pigs and they provide further evidence for the existence of a reciprocal mother-infant attachment in this species.