The Sensex at the Bombay Stock Exchange rose 53 points, to 18,571 in opening trade, this morning, on bargain-hunting by investors. But the Sensex later surrendered all its initial gains, to stand 154 points, or 0.8 percent in the negative zone, at 18,365 in afternoon deals, a short while ago. The 30-share index had lost 353 points in yesterday's session.Stock markets in China, Hong Kong, South Korea, Japan and Singapore were trading mixed, today. Over in the US, the Dow Jones Industrial Average had ended 0.7 per cent lower, overnight.