From the article:
They implanted capsules under the monkeys' [who’d had their ovaries removed] skin that released estradiol, fooling their brains into thinking there were ovaries at work preparing for ovulation. At the same time, the scientists kept the animals from making any of their own estrogens by inhibiting the work of an enzyme, aromatase, necessary for estrogen production.
Without the help of estradiol produced by the monkeys, the rising release of luteinizing hormone began, but fell short of the full surge required to spark ovulation by about 70 percent compared to animals whose estrogen production wasn’t suppressed.
To zero in on where the estrogen was doing its work, the researchers repeated the process, but blocked estradiol production specifically in the hypothalamus in the monkeys. They watched for the emergence of hypothalamic hormones – called gonadotropin-releasing hormone and kisspeptin – that indicated the key neurons were ramping up to cue the luteinizing hormone surge.
In this case, the releases of all three ovulation-signaling hormones were reduced, indicating that the brain was where the estradiol effects were happening.
“The ovarian estrogen starts the surge, but the brain estrogen allows the surge to continue,” says Kenealy. “When we block the production of brain estrogen, we still start the surge, but basically we cut the top off the mountain and the surge is drastically reduced.”
“This shows the brain’s estrogen is a huge helper, necessary for the release of an egg that makes pregnancy possible”