OSU researches ‘male-oriented' behavior in sheep

In the debate surrounding homosexuality and gay rights, the "nature versus nurture" quandary inevitably crops up time and again. Some argue that genetics determine sexual orientation, while others claim it's a matter of social environment or personal choice.

Homosexuality isn't limited to humans; many species in the animal world exhibit same-sex mating preferences and behaviors. Researchers at Oregon State University, Oregon Health & Science University and the U.S. Department of Agriculture's Sheep Experiment Station have found that roughly 8 percent of rams are "male-oriented."

In their efforts to determine why some rams eschew ewes, and whether it's possible to alter brain development in utero to impact sexual orientation, these scientists lend credence to the belief that homosexuality is biologically driven.

So far they've applied their findings just to sheep, but this team believes their investigation has the potential to help explain sexuality in other mammals, including the complex human.

"We're after a basic biological understanding of how the brain works, and the neurons that drive sexual behavior," said Fred Stormshak, distinguished professor of animal science at OSU, and an investigator on the project.

The study, hubbed at an undisclosed site on the OSU campus, drew national media attention this spring, when a drunken Beavers football player absconded with one of the homosexual rams. Although it just recently made headlines, this research project has been going on for a decade.

In 1995, researchers at the federal Sheep Experiment Station in Dubois, Idaho, noticed that some rams refused to mate with female sheep. Of these animals, some showed no interest in males or females, and a fraction preferred to mount other rams.

In the sheep production industry, breeders buy high-quality rams to populate their flocks. These studs can cost upwards of $500, so the owners suffer when breeding rams won't mate with ewes.

"You may as well kiss whatever you've spent on that animal down the drain," Stormshak said.

Stormshak, along with John Resko, retired chairman of physiology at OHSU, and Charles Roselli, OHSU professor of physiology and pharmacology, partnered with the national sheep center to determine what causes homosexuality in ovines.

Stormshak said the ultimate goal of this research from an animal science and sheep production perspective is to find a biological test to determine ovine sexual orientation. That way, breeders can make informed purchases of stud rams.

But in the broader scope, he believes that understanding sexual drives and the continuum of sexual behavior could possibly help explain the scientific basis of sexual assault, put an end to assertions that homosexuality is a lifestyle choice, and lead to a richer understanding of humanity.

OSU gets its homosexual rams from Dubois. The rams are raised and studied on campus, and their brain tissue and blood samples are analyzed at OHSU. In 2001, the project received a three-year grant for about $800,000 from the National Institutes of Health. Roselli and his team renewed the grant in 2004 for another five years and about $2 million.

The researchers found marked differences in the brain anatomy and hormones between male- and female-oriented rams, Stormshak said.

In rams who like other rams, the anterior preoptic area of the hypothalamus was about half the size of this part of the brain in heterosexual rams.

"This was exciting to us because this area of the brain has been found in many species to regulate sexual behavior," Stormshak said.

These findings correlate with a human study conducted by neurobiologist Simon LeVay in 1991.

LeVay looked at the hypothalamus of homosexual men who died of AIDS. He compared these samples to the brains of heterosexual men who died in other ways. LeVay found that the volume of a particular group of neurons called the sexually dimorphic nucleus was significantly smaller in gay men.

LeVay's findings are widely disputed. Other scientists argue that the AIDS virus, and not homosexuality, could have affected the size of the hypothalamus in the gay subjects.

But the work of Stormshak and his colleagues show similar findings when comparing the volume of ovine sexually dimorphic nuclei.

This bundle of cells in the hypothalamus is called the sexually dimorphic nucleus because its size is dependent upon gender. Ewes have smaller nuclei than rams, and homosexual rams have smaller nuclei than their heterosexual counterparts.

The size differential can be linked with fetal androgen deprivation, some experts say. Androgen is a testicular hormone signal. In the sheep he studied, Roselli discovered that male-oriented rams receive lower-than-normal androgen stimulation in the brain.

To explore this issue further, the OSU-OHSU investigation targeted aromatase activity in the hypothalamus. Aromatase is an enzyme that converts androgens such as testosterone into estrogens such as estradiol. In male mammals, estrogen causes masculinization of the brain during gestation.

According to Roselli, the team hypothesized that low levels of aromatase in the brain of the developing fetus somehow keep it from becoming fully masculinized.

"For some reason, and we don't know why, these male-oriented rams aren't completely masculinized during the sexual differentiation process. So their sexual preferences are more like a female than a male," he said.

The team decided to see whether treating pregnant ewes with inhibitors that interfere with the fetus' aromatase would yield more homosexual rams. So far, results have been inconclusive.

They'll continue experimenting with dosage levels and duration of treatment to test their hypothesis.

"We're still hopeful that we're on the right track, but we just haven't found the right conditions for treatment," Roselli said.

One important step was proving that differences in the volume of the sheep's sexually dimorphic nuclei exist in utero, rather than being caused by social interactions during the lamb's early years. On this front, Roselli claimed success.

"This lends further support to the idea that homosexuality has biological underpinnings," he said.

Mary Ann Albright covers higher education. She can be reached at maryann.albright@lee.net or 758-9581.