The Sensex at the Bombay Stock Exchange gained 180 points, or 1.1 per cent, to 16,682 within the first five minutes of trade, on Tuesday morning, on fresh buying by investors, triggered by positive regional markets, amid easing concerns about the euro zone debt crisis. But later, after rising more than 260 points at one stage, the Sensex gave up all its initial gains, to stand 39 points, or 0.2 percent in negative territory, at 16,463, in volatile afternoon trade, a short while ago. The 30-share Sensex had lost more than 660 points in the past two trading sessions.Key stock indices in Japan, Indonesia, and Singapore were up by between 0.1 percent and 1.3 percent, today, as anxiety over the European debt crisis calmed a little, following a report that China might buy Italian bonds. Over in the US, the key Dow Jones Industrial Average had gained 0.6 per cent, overnight.