Tokyo stocks opened sharply higher Thursday, with the Nikkei topping the 42,000 mark for the first time, as technology issues tracked overnight gains in their U.S. peers amid hopes for an early interest rate cut by the Federal Reserve. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average rose 491.02 points, or 1.17 percent, from Wednesday to 42,323.01. The broader Topix index was up 26.71 points, or 0.92 percent, at 2,935.91. Every industry category on the top-tier Prime Market except services and securities houses gained ground, led by electric appliance, metal product and p…