Estradiol, and Not Increased Calorie Intake, Determines Sexual Behavior in Female Common Marmosets Karli R. Hochstatter¹, Amber K. Edwards¹, David H. Abbott¹˒² ¹Wisconsin National Primate Research Center ²Department of Obstetrics and Gynecology, University of Wisconsin, Madison, WI. Introduction  There is strong evidence of the importance of the hypothalamus in controlling sexual behavior  The hypothalamus has an array of estrogen receptors  Female receptivity (sexual acceptance) is estrogen- dependent  Low levels of circulating estradiol in women are correlated with diminished sexual behavior and increased risks of obesity  Common marmosets (Callithrix jacchus) serve as well established models of the female reproductive system Objective Methods  Confirm that estradiol treatment of female marmosets improves sexual interactions with their male pair-mates 2-5 months following ovariectomy (OVX)  Examine whether estradiol treatments prevent the development of diet-induced obesity, and accordingly, if the obesity affects sexual behaviors in female marmosets 2-5 months following OVX  15 adult female common marmosets ranging from 2-6 years of age  Each female is pair-housed with a testis-intact adult male  Bilaterally OVX and placed into the following groups:  Control Empty Silastic capsules, High Calorie Diet (n=4)  Control Empty Silastic capsules, Normal Calorie Diet (n=4)  Estradiol-filled capsules, High Calorie Diet (n=4)  Estradiol-filled capsules, Normal Calorie Diet (n=3)  Sexual and affiliative behavior of each pair observed at:  2 months after OVX  5 months after OVX  Behavioral Testing: Each study female was placed in a test cage out of sight of her male pair-mate. After 90 minutes, the male pair-mate was introduced into the test cage from a side cage via a remote door. Behaviors were scored for 15 minutes from within a blind behind a one-way screen.  Each female received 2 behavioral tests, one week apart, at both 2 and 5 months after OVX Results  5 months post-OVX, male mounts correlate with:  Female sexual receptivity in estradiol-treated females only (diets combined) (p<0.007)  Female sexual rejection in control females only (diets combined) (p<1.8 x )  Estradiol tends to enhance female total sexual receptivity at 5 months following OVX (p < 0.07 vs. controls (diets combined) at 5 months post OVX)  5 months post-OVX, frequency of female sexual receptive behavior positively correlates with necropsy uterine weight at 6 months post-OVX (all females combined)  Estradiol and high calorie diet treatment of females do not alter frequency of male mounts/attempted mounts  Estradiol, but not high calorie diet, increases female marmoset sexual receptivity (mount acceptance)  Behaviors indicative of female anxiety (scratches and long calls, all females combined) are exclusionary to females accepting mounts at both 2 and 5 months post OVX P < p<0.07 vs. controls (diets combined) at 5 months post OVX Conclusion  Sexual behavior between highly compatible, well- established pairs of marmosets can be increased when females have high levels of estradiol (specifically, females are more willing to copulate with their male mate)  Anxiety reduces sexual behavior  High calorie diet does not diminish female marmoset sexual behavior % Mounts Accepted Time Following OVX (months) Control (empty) capsules Estradiol-filled capsules P-Value 218% (5/28)56% (5/9)p < % (3/34)77% (13/17)p < 3 x Time Following OVX (months) Normal Calorie DietHigh Calorie DietP-Value 236% (4/11)23% (6/26)NS 529% (4/14)32% (12/37)NS NS: non-significant, P-Value > 0.05