li.toplevel_page_laboratory .wp-menu-image a img  { display: none; }
#wpwrap li.toplevel_page_laboratory.current div.wp-menu-image, #wpwrap li.toplevel_page_laboratory:hover div.wp-menu-image, #wpwrap li.toplevel_page_laboratory.wp-has-current-submenu div.wp-menu-image  { background-position: 0 top; }