Female mice are able to smell male pheromones only when ready to mate

The investigators analyzed female mice at various stages of the ovulation cycle and found that when a female is not ready for reproduction, her hormones (specifically progesterone) block her ability to sense the smell of male pheromones. These hormones diminish during ovulation, eventually allowing a female mouse to smell a potential partner. When ovulation ends, the cycle repeats, and she is again rendered "odor-blind" to males.

"Here we find--in the mouse--that the nose is not simply a sense organ, passively vacuuming up all stimuli and transmitting that information to the brain," says senior author Lisa Stowers of the Department of Molecular and Cellular Neuroscience at The Scripps Research Institute in La Jolla. "Instead, hormonal signals from the body act directly on the nose to make a decision about what information to send to the brain. It is quite surprising that the nose, and not the brain, would be making such important decisions."

She notes that humans are not known to detect pheromones, but her research team is investigating whether human olfactory neurons are similarly able to sense internally circulating hormones.

"We are also currently looking to see if the nose has the ability to make any other behavioral decisions that vary with other internal-state hormone profiles such as stress," Stowers says.