can not reference objectbuttons within frame

On an Excel 2003 spreadsheet I already have two option buttons. I need to add two additional optionbuttons. I placed them within a frame so that they will function independently of the other buttons. Specifically, I created Frame1, selected Frame Object-->Edit, select Toolbox, add Optionbutton3 and Optionbutton4, exit Design mode.

The new Optionbuttons correctly toggle their values when out of design mode . When I re-enter design mode and double-click to take me to the VBA code, it however only shows me Frame1_Click(). Within Frame1_Click() I have tried adding the code

Frame1.OptionButton3.Value = True

, but when it is triggered I get the error message "Object doesn't support this property or method". When I look in Object Browser, I see Frame1 and Frame1_Click, but not Optionbutton3 or Optionbutton4. How do I reference these optionbuttons within the frame?

Thanks,
Cory