Tokyo stocks opened lower Wednesday, tracking overnight losses on Wall Street amid a cautious mood ahead of the outcome of the Federal Reserve's policy meeting. In the first 15 minutes of trading, the 225-issue Nikkei Stock Average fell 250.70 points, or 0.56 percent, from Tuesday to 44,651.57. The broader Topix index was down 29.25 points, or 0.92 percent, at 3,139.11. On the top-tier Prime Market, the main decliners were electric power and gas, insurance and securities house issues. At 9 a.m., the U.S. dollar fetched 146.40-41 yen compared with 146.42-52 yen in New York and 146.88-90 yen in ...