How to track Collapse/ Expand event of AJAX Collapsible Panel Extender to call javascript ?

Hi

I am working with AJAX Panel Collapsable panel extender.

The Panel which is to be collapsed/Expanded using AJAX panel Extender contains one custom control, containing 3 Radio buttons one of them is set checked through a javascript function when page loads. I have kept the default property of AJAX collapsable panel as Collapsable.

Script for AJAX Collapsible Panel Extender is as follow. 

 <ajax:CollapsiblePanelExtender ID="cpeSOP" runat="Server" CollapseControlID="pnlCollapsable"
   CollapsedSize="0" Collapsed="True" CollapsedImage="~/public/img/arrowRightWhite.gif"
   ExpandControlID="pnlCollapsable" ExpandDirection="Vertical" ExpandedImage="~/public/img/arrowDownWhite.gif"
   ImageControlID="Image1" SuppressPostBack="true" TargetControlID="pnlSearchCriteria">
  </ajax:CollapsiblePanelExtender>

But problem is that when page loads, collapsible panel gets collapsed but it resets the radio buttons in custom control. i.e. First radio button does not get checked. Script for Collpsable panel is as follow. I want to call some javascript code when the panel is Collapsed or Expanded. Is there any way to track Collapse / Expand event (client side / server side) of AJAX Collapsable Panel Extender ?

 If so it will be my pleaseure to know this as early as possible, as i am fighting on this problem since long time. I searched for this, but found nothing for events.

Thank you.

Sarang Deshpande