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ARS Home » Pacific West Area » Dubois, Idaho » Range Sheep Production Efficiency Research » Research » Publications at this Location » Publication #158647
Title: THE VOLUME OF A SEXUALLY DIMORPHIC NUCLEUS IN THE OVINE MEDIAL PREOPTIC AREA/ANTERIOR HYPOTHALAMUS VARIES WITH SEXUAL PARTNER PREFERENCE

Author
item ROSELLI, CHARLES - OREGON HEALTH & SCI UNIV
item LARKIN, KAY - OREGON HEALTH & SCI UNIV
item RESKO, JOHN - OREGON HEALTH & SCI UNIV
item Stellflug, John
item STORMSHAK, FRED - OREGON STATE UNIV

Submitted to: Endocrinology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/23/2003
Publication Date: 2/1/2004
Citation: Roselli, C.E., Larkin, K., Resko, J.A., Stellflug, J.N., Stormshak, F. 2004. The volume of a sexually dimorphic nucleus in the ovine medial preoptic area/anterior hypothalamus varies with sexual partner preference. Endocrinology. 145:478-483.

Interpretive Summary: Domestic rams display distinct variations in sexual attraction that make them a valuable model to study the biological mechanisms of sexual partner preferences. Approximately 8% of rams exhibit sexual preferences for male partners (male-oriented rams) in contrast to most rams that prefer female partners (female-oriented rams). The region of the brain that is essential for the expression of masculine sexual behavior in most mammalian species is the medial preoptic area of the anterior hypothalamus. This region is steroid sensitive and conversion of circulating testosterone to estradiol is an important part of the mechanism by which androgens facilitate male sexual behaviors. Within this area of the brain from several species, sexually dimorphic cell groups have been identified that are significantly larger in males than in females. However, this is the first demonstration in non-human animals that there is an association between natural variations in sexual partner preferences and brain structure supporting the suggestion that there is a biological basis for sexual partner preference. Female-oriented rams had the largest sexually dimorphic nucleus, male-oriented rams were intermediate, and ewes were smallest. The sexually dimorphic nucleus has been associated with two distinct aspects of male sexual behavior, male copulatory motor patterns and sexual partner preference. Moreover, the presence of aromatase (an enzyme that converts testosterone to estradiol) in the sexually dimorphic nucleus suggests that testosterone metabolism to estradiol occurs in this cell group and may be important for both its development and adult function.

Technical Abstract: Sheep are one of few animal models in which natural variations in male sexual preferences have been studied experimentally. Approximately 8% of rams exhibit sexual preferences for male partners (male-oriented rams) in contrast to most rams, which prefer female partners (female-oriented rams). We identified a cell group within the MPOA/AH of age-matched adult sheep that was three times larger in adult rams than in ewes. This cell group was labeled the ovine sexually dimorphic nucleus (oSDN). In addition to a sex difference, we found that the volume of the oSDN was two times greater in female-oriented rams than in male-oriented rams. The dense cluster of neurons that comprise the oSDN express cytochrome P450 aromatase. Aromatase mRNA levels in oSDN were significantly greater in female-oriented rams than in ewes, while male-oriented rams exhibited intermediate levels of expression. Since the MPOA/AH is known to control the expression of male sexual behaviors, these results suggest that naturally occurring variations in sexual partner preferences may be related to differences in brain anatomy and capacity for estrogen synthesis.