The Brain’s Gender May Be More Flexible Than Previously Thought

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Scientists have transformed the brain of a female rat to express characteristics more similar to that of its male counterparts. What’s more, the alteration took place outside the supposed time frame for when it was believed such events could occur. 

Scientists have known for some time that male and female brains differ from each other—particularly in the size of certain brain structures and the number of neurons and synapses in various regions of the brain. However, the specifics of how this differentiation occurs are less clear. 

Now, a team of researchers from the University of Maryland School of Medicine has found that giving rats estradiol—a testosterone derivative—‘unsilenced’ certain genes, initiating a gender swap in the brain.

"Physically, these animals were females, but in their reproductive behavior, they were males," said lead researcher Bridget Nugent. The findings are published in Nature Neuroscience.

The researchers initiated this female-to-male swap by injecting newborn rats with Dnmt inhibitors, according to Science Daily. They did this in the preoptic region of the brain, a sexually dimorphic area where there are noticeable differences between males and females. The scientists found that inhibiting the activity of Dnmt enzymes also decreased DNA methylation, a process that can turn genes off with the addition of a chemical called a methyl group.

Essentially, the female rat brains developed the structural characteristics of male brains. This translated to behavioral differences in the female rats, who displayed behavior patterns more typical of males. In another experiment, they deleted the Dnmt gene in female mice, and they too showed sexual behavior mirroring that of males. 

"It was fascinating to see this transformation,” said Nugent. What’s more, the sexual differentiation took place during a window of development in which scientists thought these changes could no longer occur: after the first week of birth.

The concept of gender in regard to the brain is complex, and the research is still in its infant phases. However, studies like this reveal just how flexible the brain’s gender is and, according to Nugent, “gives us a new understanding of how gender is determined in the brain.

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