How a Brain's 'Gender' May be More Flexible Than Once Thought

The brains of most animals develop specifically male or female characteristics during prenatal development. Now, a new study has shed some light on the details about this process, and show that a brain's "gender" may be flexible.

In order to better understand how a brain develops gender, the researchers studied the brain development in newborn rats. They injected DNA methyltransferases (Dnmt) inhibitors into a specific region of the female rat brains known as the preoptic area, or POA. In every species that's been studied, including humans, the POA plays a key role in governing male sexual behavior. The injections occurred after the first week of birth.

So what did the researchers find? The preoptic area in these animals was transformed and took on structural characteristics of a male rat. The female rats also behaved differently, displaying sexual behavior typical of male rats. When the researchers genetically deleted the Dnmt gene in female mice, the animals also showed male behavior patterns.

"Physically these animals were female, but in their reproductive behavior, they were males," said Bridget Nugent, one of the researchers, in a news release. "It was fascinating to see this transformation."

The researchers also discovered that inflammatory immune cells, known as microglia, appear to play a role in masculinization in part through their production of prostaglandins, a neurochemically normally associated with illness. It appears that the immune system is important for establishment of sex differences in the brain.

"Nobody has ever shown that this is how the process looks," said Margaret McCarthy, one of the researchers. "This gives us a new understanding of how gender is determined in the brain."

The findings are published in the journal Nature Neuroscience.

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