I thought this would make them transexual, since their brains are similar to that of males.
That's what I thought too. This would be most similar to transsexual rats, not lesbian rats.
Because as far as I'm aware, in humans at least, gay males and lesbian females have the same type of brain patterns that heterosexual males and females have. Although for transsexuals, some (most?) studies have shown that their brain patterns match with their perceived gender, but not their body.
But I'm not 100% familiar with all the latest research, so someone can correct me if I'm wrong.
From reading through the article, they can control whether a male sex rat will behave like a female, or vice versa, which is governed by the brains preoptic area(Or POA), and even though it's rats, Humans have the same area.
So in theory, by doing this to babies you can guarantee the gender matches the sex. They don't mention any side effects in the rats(They mention the immune system, but that's tied to governing brain growth..), what this could mean is that gender dysphoria could be prevented before it even happens.
I guess the argument comes in form whether people who would be gender dysphoric should have the right to choose whether they want to be gender dysphoric or not...but the window of applying this injection is only open when the brain hasn't fully formed, right after birth...
..It's a tough question. I'm sure I've read here and there that gender dysphoric people wouldn't want to wish their situation on others(Correct me if I'm wrong), but..I can see how some would think it unethical.
That is a tough question. I'm not sure how people with gender dysphoria will feel about it.