Pathological opening of blood-brain barrier in disease conditions

Most compounds in blood are blocked from flowing into brain by blood-brain barrier(BBB) to keep central nerve system normal, but this barrier will be open in different diseases with different mechanisms. As these mechanisms are understood more and more clearly, it will do help to protect blood-brain barrier and treat diseases which are correlative to blood-brain barrier. At the same time, it may also be helpful to let drugs entering central nerve system through BBB.