Infertility

The human reproductive system is regulated like a thermostat, with a number of hormones and factors produced along the "reproductive axis" acting via feedback loops to keep the body's hormones within the optimal range for fertility and successful mating.

The head of the axis is the brain's GnRH-producing hypothalamus, which communicates via a blood portal with the anterior pituitary and stimulates production of the hormones gonadotropin, luteinizing hormone and follicle stimulating hormone.

These hormones are dumped into the bloodstream and make their way to the gonads, where in males they stimulate production of testosterone and the maturation of sperm.

In females, the hormones stimulate production of estradiol, a sex steroid hormone and the body's main form of estrogen, and regulate ovulation, the production of fertile eggs.

Estradiol and testosterone, in turn, feed back on the pituitary to shut down production of pituitary hormones, establishing feedback that keeps the body's sex hormones on an even keel.

Estradiol also works higher in the brain, on the hypothalamus, to ramp down production of GnRH, but how this works has been a relative mystery.

The new study provides an answer: Estradiol stimulates cells in the dorsomedial ...

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