How to do OnMouseUP event for GUI.Button?

I need change a boolean variable, and I need put the OnMouseDown and onMouseUp events for this GUI.Button for move my camera, please can someone help me with that !?

Thanx for your time, thanks for your help, thanks at all :)

Edit: Found out that this was the basic behavior of the buttons :)

Maby you can do something like this

bool buttonDown = false;
if(GUI.Button())
{
    OnMouseDown();
    buttonDown = true;
}
else if(buttonDown)
{
   buttonDown = false;
   OnMouseUp();
}