Nikkei opened sharply lower Thursday, with the key stock index falling over 2 percent, as investors worry that the spike in the yield on Italy\'s government bonds will worsen the eurozone debt crisis. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average fell 204.16 points, or 2.33 percent, from Wednesday to 8, 551.28. The broader Topix index of all First Section issues on the Tokyo Stock Exchange was down 19.23 points, or 2.57 percent, to 730.17.