The U.S. dollar topped the 123 yen line Monday for the first time since December 2015 after the Bank of Japan announced an emergency bond-buying operation, while the Nikkei stock index ended lower, snapping a nine-day winning streak. The 225-issue Nikkei Stock Average ended down 205.95 points, or 0.73 percent, from Friday at 27,943.89. The broader Topix index of all First Section issues on the Tokyo Stock Exchange finished 8.1 points, or 0.41 percent, lower at 1,973.37. Decliners were led by nonferrous metal, marine transportation and service issues.