U.S. stocks closed mostly lower Thursday, under pressure from low oil prices and concerns about the effectiveness of monetary policy following the morning's announcements from the European Central Bank.

    The Dow Jones Industrial Average closed down 5.23 points, or 0.03%, to settle at 16,995.13.    The Nasdaq Composite fell 12.22 points, or 0.26%, to settle at 4,662.16. It fell as much as 66 points in intraday trading but closed well above session lows.

    Meanwhile, the S&P 500 managed to recover from an intraday decline of 1% to squeeze out a gain of 0.31 points, or 0.02%, to close at 1,989.57.