Nikkei opened higher Monday, as fears over debt problems in Italy receded slightly after a fiscal austerity bill was passed by the Italian parliament last week. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average rose 129.68 points, or 1.52 percent, from Friday to 8,644.15. The broader Topix index of all First Section issues on the Tokyo Stock Exchange was up 10.27 points, or 1.41 percent, to 739. 40.