function do_mark_read(i,title) {
  toggle_visibility("body_"+i);
  document.getElementById("title_"+ i).innerHTML = "<a onClick='toggle_visibility(\"body_"+i+"\");'>"+ title +"<"+"/a>";
  x_mark_read(i,mark_read_cb); // sajax call to mark read in DB
}
function mark_read_cb(phpData) {
  // ...
}

function toggle_visibility(id) {
  var e = document.getElementById(id);
  if(e.style.display == 'block')
    e.style.display = 'none';
  else
    e.style.display = 'block';
}