Scientists have known for years that when vampire bats tear through an animal's skin with their razor-sharp teeth, their noses guide them to the best spots – where a precise bite will strike a vein and spill forth nourishing blood. But nobody knew exactly how bats knew where to bite. By investigating wild vampire bats in South America, researchers at the University of California, San Francisco and Instituto Venezolano de Investigaciones Científicas in Caracas, Venezuela have discovered their secret: a sensitive, heat-detecting molecule（分子，微粒） covering nerve endings on their noses called TRPV1. A number of pharmaceutical and biotech companies are working on developing new pain medications that target molecules like TRPV1.

"Vampire bats feed on blood, and it's useful for them to have an infrared detector to be able to find the circulation," said David Julius, PhD, the Morris Herzstein Chair in Molecular Biology & Medicine at UCSF, who led the research.

Similar TRPV1 molecules can be found on pain sensing nerve fibers in human tongue, skin or eyes. They allow people to detect the chemical capsaicin（辣椒素） in chili peppers and experience the burning tinge（淡色，风味） of spicy food.

Described this week in the journal Nature, the discovery highlights how small changes to genes in the genome of a species can contribute to major evolutionary adaptations over time – in this case, allowing the vampire bat to detect infrared heat from their prey, helping them efficiently find and feed on blood.

The work also adds a piece to a larger puzzle related to human health and drug design because these same molecules are involved in pain sensation, such as that associated with touching a hot object, or hypersensitivity to heat after injury and inflammation – as occurs with sunburn.

"There is a double-edged sword with pain," Julius said. "Pain is necessary as a warning system to let us know when we are in danger of injury but, at the same time, pain can outlive（活得长） its usefulness as a warning system when it fails to resolve and becomes chronic and debilitating（使虚弱） "