But Mimtragul says they were too late - about 30 hours after ovulation - due to delays waiting for a team of panda reproduction experts to arrive from Bangkok, Thailand, and for hormone test results.

He thought it might be necessary to test women more often as they got older to monitor if hormone levels dropped off, an indication menopause was imminent.

Valentino and her colleagues analyzed the brains of rats as they responded to a swim stress test, aimed to trigger the release of the CRF hormone.