Veronique Greenwood, reporting for BBC Future:
The sense of smell is one of our most powerful connections to the physical world. Our noses contain hundreds of different scent receptors that allow us to distinguish between odours. When you smell a rose or a pot of beef stew, the brain is responding to scent molecules that have wafted into your nose and locked on to these receptors. Only certain molecules fit specific receptors, and when they slot together, like a key in a lock, this triggers changes in cells. In the case of scent receptors, specialised neurons send messages to the brain so we know what we have sniffed. The discovery, in 1991, of around 1,000 genes involved in generating scent receptors was rewarded with the Nobel prize in Medicine over a decade later.
In the last ten years, however, reports have trickled in from bemused biologists that these receptors, as well as similar ones usually found on taste buds, crop up all over our bodies. In 2003, bitter taste receptors were found in sperm. The same year Pluznick came across scent receptors in the kidney, biologists at the University of California, San Diego identified sour receptors in the spine. A smattering of papers over the following few years reported sweet taste receptors in the bladder and the gut, bitter taste receptors in the sinuses, airways, pancreas and brain, and scent receptors in muscle tissue.
This field has exploded in recent years, and few scientists illustrate the surprise and serendipity of it all better than Jennifer Pluznick, a professor at Johns Hopkins University. She stumbled on unusual smell receptors eight years ago when investigating kidney disease. Her initial foray has now morphed into a quest to find scent receptors wherever they are in the body. Go ahead, stop and smell the roses. You may never think about your sense of smell in the same way again.