Physiology&Behavior, Vol. 34, pp. 1007-1008. Copyright©Pergamon Press Ltd., 1985. Printed in the U.S.A. 0031-9384/85 $3.00 + .00 BRIEF COMMUNICATION Brief Separation Elevates Cortisol in Mother and Infant Squirrel Monkeys MARK E. STANTON AND SEYMOUR LEVINE Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Stanford, CA 94305 Received 27 August 1984 STANTON, M. E. AND S. LEVINE. Briefseparation elevatescortisolin motherand infant squirrel monkeys. PHYSIOL BEHAV 34(6) 1007-1008, 1985.--The pituitary-adrenal response of mother and infant squirrel monkeys was assessed under basal conditions and after 5, 10, or 20 min of separation followed by 30 min of reunion. All separation conditions produced equal increments of cortisol (approximately 50%) in both mothers and infants. These increments were lower than would have occurred in the absence of reunion. These results extend previous reports that reunion ameliorates the psychoendo- crine effects of separation and indicate that mother-infant attachment can be studied with shorter periods of separation than have been used customarily. Mother-infant Separation Reunion Cortisol Squirrel monkeys THE response of the pituitary-adrenal system has proven to be a valuable dependent measure for studying the process of attachment in nonhuman primates (see [1] for review). At- tachment between mother and infant is evident both in the way maternal separation increases cortisol levels as well as in the way maternal reunion reduces, or inhibits increases in, cortisol levels [2]. Recently, it has been postulated that cog- nitive/learning processes may influence the adrenocortical and behavioral responses to separation stress in the squirrel monkey [4], as has been shown for other types of stress in a variety of species [3]. In future work, the role of learning processes within the separation paradigm could be studied by Pavlovian conditioning experiments in which maternal separation serves as an unconditioned stimulus (US). Such experiments could more easily be accomplished if US dura- tions are shorter than 30 min, the minimum period of separa- tion that has been shown to increase cortisol levels in mother and infant squirrel monkeys. Therefore, it is necessary to determine whether cortisol secretion can be increased by relatively brief periods of separation: Momentary separation does not substantially elevate cortisol levels after 30 min of reunion [5,6], whereas 30 min of separation does [2]. In order to further characterize the temporal dynamics of the ad- renocortical response to separation, the present study exam- ined the effects of different durations of separation between zero and 30 rain. Mother-infant squirrel monkey dyads were separated for either 5, 10, or 20 min, allowed 30 min of re- union and then blood sampled. METHOD Animals Six mother-infant pairs of Bolivian squirrel monkeys (Saimiri sciureus) were used in this study. The mothers were wild-born. The infants were laboratory-born and -reared, and were approximately 4 months of age at the start of the experiment. During the experiment, mother-infant pairs were housed in stainless steel Wahmann primate cages (64×74×68 cm). These cages were set in a temperature- controlled colony building having large windows which pro- vided a natural light-dark cycle. All experimental manipula- tions occurred between 0900 and 1100 hr. Wayne Monkey Diet and water were continuously available. Fresh fruit and vitamin-enriched cherry drink were provided twice each week. Procedure The 6 mother-infant pairs were tested in three replications of 2 pairs each. The experiment began by transferring mother-infant pairs from group cages to individual cages where they were left undisturbed for 2-4 weeks. This was followed by four blood samples at weekly intervals. The first of these was a basal sample. Mother and infant were taken from the home cage and, within 3-4 rain, were anesthetized with ethyl ether, and their blood was collected into heparinized syringes via cardiac puncture. The next three blood samples occurred immediately after a 30-min reunion period which was preceded by 5, 10, or 20 min of separation (the order in which these three separation intervals were encountered was counterbalanced across subjects to control for repeated sampling effects). Separation consisted of re- moving the infant from the home cage and placing it in a wire mesh cage (46x46x61 cm) situated within a sound- attenuating chamber in an adjacent room. The separation interval and the 30-min reunion period were timed with a stopwatch. Within each replication, only 1 of the 2 mother- infant pairs was separated on a given day. Further details of 1007