The Nikkei stock index opened higher Thursday, supported by Wall Street gains overnight that sent the Dow Jones index to a record high. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average rose 221.74 points, or 0.61 percent, from Wednesday to 36,341.66. The broader Topix index was down 1.79 points, or 0.07 percent, at 2,548.16. On the top-tier Prime Market, gainers were led by iron and steel, and transportation equipment shares, while electric power and gas, and land transportation issues were the main decliners. At 9 a.m., the U.S. dollar fetched 148.08-11 yen compared with…