on mouse exit function not working

i have attached the code below to various gui textures in my heirarchy and i have also populated the variables with assets in my project. when i play the game, the OnMouseOver function gets called and the 2d texture on my screen changes but the OnMouseExit function doesnt seem to run...HELP PLIZ

var buttonExit : Texture2D; var buttonOver : Texture2D;

function OnMouseOver(){

guiTexture.texture =buttonOver;

}

function onMouseExit(){

guiTexture.texture= buttonExit ;

}