Get ready to rock

时间:2019-03-07 08:07:09166网络整理admin

By Philip Cohen GIVING mice a very hot sauna protects them from hearing loss caused by blasts of noise similar to those at rock concerts, say biologists in Boston. Sudden, intense sounds can damage the sensory cells in the inner ear and cause permanent hearing loss. Strangely, however, first exposing animals to more moderate levels of sound protects their ears from subsequent damage. But Charles Liberman of Harvard Medical School suspected that sound itself had little to do with this conditioning. “If you take a mouse out of its cage each day and blare noise at it, you stress it out,” says Liberman. He knew of many instances where chemical stress, for example, conditions animals to stand up to more extreme stress later. In these cases, stress activates genes that prepare the animal for greater challenges. Some of the genes activated during stress code for heat shock proteins (HSPs), which protect proteins and refold any damaged ones. To find out if HSPs could protect hearing in mice, Liberman and his team anaesthetised the animals and put them in a tiny sauna, raising their body temperature to a feverish 41.5°C for 15 minutes. Then the mice were exposed to 100 decibels of noise for 2 hours—a damaging level of sound that is regularly endured by, for example, rock musicians. Seven days later, the team tested the mice for permanent hearing loss by working out how intense sounds of different frequencies had to be before they would stimulate a nerve signal. In untreated mice, the most profound loss was at 17.5 kilohertz, where sensitivity dropped by 40 decibels, meaning the sound had to be 10 000 times more energetic to trigger the ear’s nerves. But the mice that had been in the sauna six hours before suffered a loss of only 13 decibels. The researchers also found more than a hundredfold increase in HSP gene expression in the inner ear after the heat treatment, suggesting that these proteins may stabilise fragile sensory cells. If the animals were heated more than 24 hours before being subjected to the noise, however, the protective effect was lost. But for anyone thinking of taking a sauna before their next trip to the clubs, Liberman has a word of warning. “A sauna probably wouldn’t hurt, but don’t try to bring your temperature up to 41°C,