A study published in the February issue of the journal Endocrinology demonstrates that not only are certain groups of cells different between genders in a part of the sheep brain controlling sexual behavior, but brain anatomy and hormone production may determine whether adult rams prefer other rams over ewes.

"This particular study, along with others, strongly suggests that sexual preference is biologically determined in animals, and possibly in humans," said the study's lead author, Charles E. Roselli, Ph.D., professor in the Department of Physiology and Pharmacology, OHSU School of Medicine. "The hope is that the study of these brain differences will provide clues to the processes involved in the development and regulation of heterosexual, as well as homosexual, behavior."

The results lend credence to previous studies in humans that described anatomical differences between the brains of heterosexual men and homosexual men, as well as sexually unique versions of the same cluster of brain cells in males and females.

"Same-sex attraction is widespread across many different species." said Roselli, whose laboratory collaborated with the Department of Animal Sciences at Oregon State University and the USDA Agricultural Research Service's U.S. Sheep Experiment Station in Dubois, Idaho.

Kay Larkin, Ph.D., an OHSU electron microscopist who performed laboratory analysis for the study, said scientists now have a marker that points to whether a ram may prefer other rams over ewes.

"There's a difference in the brain that is correlated with partner preference rather than gender of the animal you're looking at," she said.

About 8 percent of domestic rams display preferences for other males as sexual partners. Scientists don't believe it's r
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Contact: Jonathan Modie
modiej@ohsu.edu
503-494-8231
Oregon Health & Science University
8-Mar-2004