Giving up all its initial gains, the Sensex at the Bombay Stock Exchange stood 122 points, or 0.8 percent in the negative zone, at 15,257, in afternoon deals, amid volatile trade, a short while ago. Earlier in the morning, however, the Sensex had opened 69 points, or 0.4 per cent in positive territory, at 15,448, on the back of firm regional bourses. The 30-share Sensex has already lost more than 620 points in the past four trading sessions.But other regional markets in Japan, China, Hong Kong, Taiwan and South Korea were up by between 0.1 per cent and 0.9 per cent, as they staged a modest pullback rally after yesterday's losses.In the US, the Dow Jones Industrial Average had dropped 0.8 per cent overnight.