Scientists may have discovered how to safely open and close the blood-brain barrier to deliver drug therapies for Alzheimer’s disease, multiple sclerosis, and cancers of the central nervous system. The research focuses on adenosine, a molecule produced by the body that signals trauma and other physiological functions. Adenosine can modulate the entry of large molecules into the brain. When adenosine receptors are activated on cells that comprise the blood-brain barrier, a gateway into the blood-brain barrier can be established.