Tokyo stocks dropped on Thursday morning in volatile trading with initial gains eroded as the yen continued to rally against the U.S. dollar, denting exporters. The 225-issue Nikkei Stock Average fell 359.61 points, or 0.90 percent, from Wednesday to 39,731.17. The broader Topix index was down 6.58 points, or 0.24 percent, at 2,724.09. The dollar briefly dropped to the mid-148 yen zone from the lower 149 range following its weaker tone overnight, as expectations grew that the Bank of Japan may end its negative interest rate policy at a meeting later this month. The U.S. currency met selling pr…