Ameritrade Profit Up But Trading Slips  NEW YORK (Reuters) - Internet brokerage Ameritrade Holding  Corp. &lt;A HREF="http://www.investor.reuters.com/FullQuote.aspx?ticker=AMTD.O target=/stocks/quickinfo/fullquote"&gt;AMTD.O&lt;/A&gt; said Tuesday its quarterly profit rose from a  year earlier, though trading revenue fell as investors curbed  trading activity in recent weeks.