It can be done using Jquery
<script type="text/javascript">
$(function () {
$("#Button6").click(function (evt) {
evt.preventDefault();
$('#Panel1').slideToggle('slow');
});
});
</script>
<asp:button id="Button6" runat="server" text="Add Comments" xmlns:asp="#unknown" />
<asp:panel id="Panel1" runat="server" height="120px" width="723px" cssclass="panel" xmlns:asp="#unknown">
<br />
<asp:textbox id="TextBox2" runat="server" height="57px" width="719px"></asp:textbox>
<br />
<br />
<asp:button id="Button4" runat="server" text="Submit" height="25px">
Width="95px" onClick="onsubmit" />
<asp:button id="Button5" runat="server" height="25px" text="Cancel">
Width="88px" />
</asp:button></asp:button></asp:panel>
take a datalist for show reply data.
after reply bind datalist again to make changes.(means in onsubmit button click.)