The Nikkei stock index jumped over 2 percent early Thursday as exporters were bought on a weaker yen following an anticipated interest rate cut by the U.S. Federal Reserve. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average rose 762.31 points, or 2.10 percent, from Wednesday to 37,142.48. The broader Topix index was up 50.83 points, or 1.98 percent, at 2,616.20.