Physiology & Behavior, Vol. 34, pp. 123-128.Copyright©PergamonPress Ltd., 1985. Printed in the U.S.A. 0031-9384/84$3.00 + .00 Effects of Oestradiol 17B, Progesterone and Testosterone Upon Proceptivity and Receptivity in Ovariectomized Common Marmosets (Callithrixjacchus) K. M. KENDRICK AND A. F. DIXSON 1 Department of Reproduction, Institute of Zoology, Regent's Park, London NW1 4RY, U.K. Received 2 April 1984 KENDRICK, K. M. AND A. F. DIXSON. Effects of oestradio117B, progesterone and testosterone upon proceptivity and receptivity in ovariectomized common marmosets (Callithrix jacchus). PHYSIOL BEHAV 34(1) 123-128, 1985.--The sexual behaviour of eight pairs of marmosets was observed during blocks of 30 minute tests after the ovariectomized female partners were treated with physiological doses of testosterone, oestradiol and progesterone. The effects of an intra-vaginal progesterone treatment were also investigated. Pre-ovulatory levels of oestradiol significantly increased the females' proceptive and receptive tongue-flicking displays and reduced the percentage of mounts refused. Mid-luteal levels of progesterone, by comparison, virtually abolished proceptive and receptive tongue-flicking and significantly increased mount refusals. Testosterone treatment was without effect. Vaginal application of progesterone unlike subcutaneous implantation of the hormone did not significantly alter the females' sexual behaviour. These results indicate that central actions of oestradiol and progesterone upon proceptivity and receptivity may occur in this primate, although further research using intra-cranlal implants of these steroids is required to test this hypothesis. Marmosets Primate sexual behaviour Proceptivity Receptivity Attractiveness Oestradiol Progesterone Testosterone ATI~EMPTS to study the hormonal control of proceptivity and receptivity in female primates are complicated by the fact that oestrogens and progestagens also alter genital cues and sexual attractiveness in certain species [3, 10, 22]. Changes in sexual activity which occur after ovariectomy or exogenous steroid treatments in monkeys [5, 7, 11] or apes [27] may therefore reflect changes in female attractiveness as well as in proceptivity or receptivity. In the rhesus monkey oestradiol enhances attractiveness via a local action upon the vagina [10,21] which is antagonized by progesterone [2]. Oestradiol may have some central effect on proceptivity in the rhesus monkey [3, 23, 28] but progesterone does not directly influence proceptivity or receptivity unless adminis- tered in supra-physiological doses to the ovariectomized female [2,22]. The common marmoset Callithrix jacchus) is a New World primate which exhibits rhythmic changes in proceptivity and receptivity during its 28 day ovarian cycle [14]. However, female sexual attractiveness does not vary during the cycle or decrease after ovariectomy in this species [ 14,15] in contrast to findings on various Old World Monkeys [4, 12, 24]. The female marmoset uses a proceptive and re- ceptive tongue-flicking display almost exclusively during the periovulatory phase of the ovarian cycle [ 14]. Plasma levels JRequests for reprints should be addressed to A. F. Dixson, MRC U.K. of oestradiol [9] and testosterone [14] reach a peak during this period and may therefore facilitate this behaviour. Equally, both types of tongue flicking behaviour are virtually absent during the female's luteal phase and she also exhibits a greater frequency of mount refusals at this time [14]. These behavioural changes during the luteal phase may be influ- enced by the high plasma progesterone levels at this time. The present investigation has therefore examined the possibility that exogenous treatments with physiological doses of oestradiol, progesterone and testosterone alter the sexual behaviour of ovariectomized marmosets. Effects of intravaginal progesterone treatment were also measured in order to draw comparisons with similar experiments on the rhesus monkey [2]. METHOD Animals The animals used were eight male and eight female sexu- ally experienced, captive born, adult marmosets. The females had been ovariectomized at least six months previ- ously. Feeding and maintenance procedures have been de- scribed elsewhere [16]. Reproductive Biology Unit, 37 Chalmers Street, Edinburgh EH3 9EW, 123