Gay sheep have brain changes

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WASHINGTON (Reuters) - Researchers who found homosexual rams in a herd of sheep say they have found changes in the brains of the "gay" animals.

The results, published in the latest issue of the Journal Endocrinology, tend to support studies in humans that have found anatomical differences between the brains of heterosexual men and homosexual men.

The researchers at the Oregon Health & Science University School of Medicine found certain groups of brain cells were different between rams and ewes in a part of the sheep brain controlling sexual behaviour.

And in rams that preferred to mate with other males, this area was smaller than in males that preferred females.

"There's a difference in the brain that is correlated with sexual partner preference rather than gender of the animal you're looking at," said Kay Larkin, an OHSU electron microscopist who worked on the study.

"This particular study, along with others, strongly suggests that sexual preference is biologically determined in animals, and possibly in humans," added Charles Roselli, a professor of physiology and pharmacology who led the research team.

"The hope is that the study of these brain differences will provide clues to the processes involved in the development of heterosexual, as well as homosexual behaviour."

Animal experts have found that about 8 percent of domestic rams display preferences for other males as sexual partners.

"Same-sex attraction is widespread across many different species," said Roselli, who worked with a team at Oregon State University and the U.S. Department of Agriculture's U.S. Sheep Experiment Station in Dubois, Idaho.

They looked at 27 adult, 4-year-old sheep of mixed Western breeds including eight male sheep that preferred to mate with females, nine that mated mostly with males and 10 ewes.

They found a densely packed cluster of nerve cells in the hypothalamus of the sheep brain, which they named the ovine sexually dimorphic nucleus or oSDN.

The hypothalamus regulates sex hormone secretion, blood pressure, body temperature, water balance, and food intake, and also helps regulate complex behaviours such as sexual behaviour.

The oSDN in rams that preferred females was "significantly" larger and contained more neurons than in male-oriented rams and in ewes. There were also hormonal differences between the brains of homosexual and heterosexual sheep.

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