WASHINGTON — Catnip is known to hold a special place in the hearts of felines, who often respond by rubbing their face and head in the plant, rolling around on the ground, then zoning out in a state of intoxicated repose. But the biological mechanisms by which it works its magic, and whether it confers any additional benefits to cats, had remained unanswered questions until now. An international team of researchers recently published a study in Science Advances, finding that catnip and silver vine, an even more potent herb found in the mountains of Japan and China, ward off mosquitoes. They also identified nepetalactol as the main compound of silver vine responsible for inducing an euphoric state, and discovered that it activates the brain's opioid reward system. The substance is similar to nepetalactone, the key psychoactive compound in catnip.