Tokyo stocks opened lower Thursday on the lackluster overnight performance of European and U.S. shares markets, which encouraged investors to lock in recent gains. At 9:15 a.m., the 225-issue Nikkei Stock Average was down 152. 24 points, or 0.94 percent, from Wednesday to 15,969.21. The broader Topix index of all First Section issues on the Tokyo Stock Exchange was down 5.52 points, or 0.42 percent, at 1, 300.71.