Pheromones: the key ingredient missing from on-line communication

The vomeronasal organ (VNO), also called Jacobson's organ, is a chemoreceptor organ thought to be involved with the perception of certain scents and pheromones. It is named for its closeness to the vomer and nasal bones, and is particularly developed in animals such as cats and horses.

The VNO is a small, paired tubular structure embedded in the nasal epithelia of amphibians, reptiles, and many mammals. In mammals, the VNO is located on the septum dividing the two nostrils. Recent research has shown that in humans this structure is largely inactive, having lost its connection with the brain - to the dismay of perfume companies worldwide.

In mice, the VNO has a pore that opens into the nasal cavity. When the animal sniffs in a breath of fresh air, the VNO pulsates and draws nasal fluid over the chemoreceptors embedded in its walls. Through the transmission of action potentials, this information then travels to an accessory olfactory bulb in the brain.

In a study by Dr. Ivanka Savic published in Proceedings of the National Academy of Sciences, researchers investigated a testosterone-derived product in men's sweat and an estrogen-like compound in women's urine. Remarkably, the estrogen-like compound activated smell-related regions in women but triggered a response in the male hypothalamus. The hypothalamus governs sexual behavior and indirectly (through the pituitary) regulates the hormonal sate of the body. As one might expect, the testosterone-derived compound stimulated smell-related neuronal processes in the male but led to increased activity in the hypothalami of women. Dr. Savic's group also found that gay men responded via the hypothalamus to testosterone-related compounds. While gay women were also studied, the data obtained were complex and not as easily reduced to an overall trend. Further research is required to determine whether these differences are the cause or effect of variations in sexual orientation.