Tokyo stocks ended lower Thursday after giving up earlier gains, as the yen firmed to a one-month high against the U.S. dollar on growing speculation that the Bank of Japan may end its negative interest rate policy as soon as this month. The 225-issue Nikkei Stock Average ended down 492.07 points, or 1.23 percent, from Wednesday at 39,598.71, after hitting a record high of 40,472.11. The broader Topix index finished 12.13 points, or 0.44 percent, lower at 2,718.54. On the top-tier Prime Market, decliners were led by transportation equipment, rubber product and electric appliance issues. The do…