Elevating a model in rats' brains blunted cocaine use Little things can make a big difference in the brain. Case in point: A tiny snippet of RNA may help guard cocaine-using rats against addiction to the drug, a new study shows. The minuscule molecular guard is a hairpin-shaped piece of RNA known as a microRNA. Raising levels of a microRNA called miR-212 in the brains of cocaine-using rats led the animals to take less of the drug than rats with normal microRNA levels, researchers report in the July 8 Nature. Similarly, blocking the microRNA’s action increased the rats’ cocaine use....