The sun’s ultraviolet(UV) rays can do more a tan(棕褐色) or burn. Indeed, their influence goes more than skin deep, a new study finds. It showed that exposure to ultraviolet light causes mice to make a feel-good chemical, and this chemical may explain why so many people want to get a tan. The study may also help explain why people flock o beaches and coasts for relaxation, Steven Feldman said. He studies public health and skin diseases.
High-energy, UV rays come from the sun and the special lights used in tanning booths. Even though people know UV radiation can be dangerous, they continue to risk sunburns for a tan. Rates of skin cancer have been going up. David Fisher wanted to know why. He is an oncologist- a doctor who treats people with cancer- at Massachusetts General Hospital in Boston. “We know UV light is dangerous,” Fisher says, but many people choose not to protect themselves.
Fisher and his colleagues exposed mice to a moderate amount of UV light five days a week, for six weeks. The scientists shaved the mice so the light would reach their skin. The animals received an exposure to UV light that was similar to what a fair-skinned person gets after 20 or 30 minutes in the Florida sun. After just a week of the UV treatment, mice had higher levels of molecule in their blood called beta-endorphin (内啡肽) than mice not exposed to this radiation did. Similar to drugs such as heroin and opium, beta-endorphin activates feel-good processes in the brain. Previous studies had found beta-endorphin in the skin. This new study showed the molecule also ends up in the blood. UV light didn’t boost beta-endorphin for very long, though. Levels returned to normal a week after the UV treatments stopped. And the mice didn’t seem to have wanted those treatments to end. In fact, they showed signs of an addiction to this light.
Fisher’s group gave a drug, called naloxone(Naa-LOX-ohn), to the UV-treated mice. Doctors prescribe this drug to people who have been abusing heroin. It blocked the places in the brain where heroin triggers the feel-good response. When a heroin addict receives naxolone, the drug can set off withdrawal symptoms within minutes. In the UV-treated mice, the drug seemed to block the feel-good effects of UV exposure. It also caused chattering teeth and shaking in the animals. Those symptoms looked similar to what people go through when they are suffering from withdrawal from heroin.
The new data is “fascinating”, David Fisher said. Still, she says, the new study falls short of proving the mice had become addicted to UV light. “Addiction” means craving, loss of control and tolerance,” he explains. And the new study “didn’t look at any of those things.”
(1) By saying their influence goes more than skin deep, the writer means UV rays can __________.