PORTLAND, Ore. Research conducted at Oregon Health & Science University (OHSU) has demonstrated structural brain differences associated with naturally occurring variations in sexual partner preferences. These are the first findings to demonstrate such a correlation in research animals, in this case sheep. The researchers' results confirm and expand upon human studies that compared morphological brain differences between heterosexual men, homosexual men and women. Scientists at Oregon State University and the U.S. Sheep Experiment Station in Dubois, Idaho, collaborated with OHSU on the research. The investigators' results are being presented on Nov. 4 during the annual meeting of the Society for Neuroscience in Orlando, Fla.

Domestic rams were used as an animal model for this research because they display distinct, natural variations in sexual attraction, making them valuable in studying the biological basis for sexual partner preference. Previous studies documented that approximately 6 percent to 8 percent of domestic rams court and mate with other rams exclusively.

Sheep selected for this research were chosen after their sexual partner preference and mating habits were studied for two years. A total of 27 sheep were studied: nine rams that preferred to mate with males, eight rams that preferred to mate with females, and ten ewes. When researchers compared brains among the three groups, they recorded marked differences.

Research was focused on the preoptic hypothalamus, a region of the brain known to be involved in sexual behaviors and partner preferences; researchers identified a group of neurons there called the sexually dimorphic nucleus.

"Interestingly, this bundle of neurons is smaller in ewes and in rams with same-sex preferences than it is in rams that prefer ewes," said Kay Larkin, Ph.D., a postdoctoral fellow in physiology and pharmacology in the OHSU School of Medicine, and lead author of the paper. "We also determi
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Contact: Jim Newman
newmanj@ohsu.edu
503-494-8231
Oregon Health & Science University
4-Nov-2002

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