Drop down list selected Index on page load

I have a page with 2 drop down lists, and two text boxes.  I want the selectedItem.ToString() to appear in the text boxes.  When the page loads, the first value in the datasource to which the dropdown is bound is selected, and Selected Index Changed does not fire.  I tried setting SelectedIndex to -1 on the page load event, but that had no effect.  If the user does not change the initial selection in the dropdown list, nothing gets written to the text box.  I'd like to know what event I need to catch to be able to capture the initially selectedItem when the page loads.

 

Thanks
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