EFFECTS OF NEONATAL TESTICULAR SUPPRESSION WITH A GNRH ANTAGONIST ON SOCIAL-BEHAVIOR IN GROUP-LIVING JUVENILE RHESUS-MONKEYS

Twenty-four male and eight female I-year-old rhesus monkeys (Macaca mu latta) were observed for social interaction with Ether yearlings and w ith their mothers. The males comprised three groups which differed in the level of neonatal androgen exposure. One group received the GnRH a ntagonist Antide during their first four neonatal months (Antide n = 8 ), which suppressed pituitary LH secretion resulting in peak neonatal T levels < 0.7 nmol/liter. A second group received Antide treatment co mbined with a long-lasting testosterone replacement (Ant/And n = 8), w hich resulted in peak neonatal T levels of 29.1 +/- 3.8 nmol/liter. Th e third group (Vehicle n = 8) received the Antide and androgen vehicle s and had intermediate peak T levels of 5.2 +/- 1.0 nmol/liter. Behavi or of males was compared to that of unmanipulated control females livi ng in the same social group (Control Female n = 8) when androgen level s were uniformly low (< 0.7 nmol/liter) in all male groups. Subjects r eceived 12 weekly 30-min focal observations by an observer blind to th e neonatal treatments. Marked sex differences were found in several ca tegories of sociosexual behavior. All three groups of males engaged in significantly more sexual and play behavior than females, with the ex ception of quiet solitary play, which females exhibited significantly more frequently. In addition, females exhibited significantly more int erest in infants than did any male group. There were no differences be tween groups in agonistic behavior or time spent in contact with other individuals, but females spent significantly more time than any male group in proximity to other animals. Both females and Antide males ini tiated proximity and followed animals significantly more frequently th an Ant/And males, but not Vehicle males. Proximity durations with moth ers initiated and terminated by yearlings were longer for females than for any male group and for Antide males than for Ant/And males. Antid e males were groomed significantly longer than any other group. These results demonstrate effects of neonatal testosterone exposure on socia l behavior in yearling rhesus. Suppression of neonatal T did not affec t sexually dimorphic patterns of play and sexual behavior, but altered the character of interactions with their mothers. Whether this reflec ts a delay in the development of maternal independence or a fundamenta l alteration in patterns of social interaction remains to be resolved. (C) 1995 Academic Press, Inc.