image: Kerstin Lenk, Institute of Neural Engineering, TU Graz. Credit: Fotogenia Women are diagnosed with severe depression about twice as often as men, though the underlying causes remain unclear. One area under investigation is whether the blood-brain barrier functions differently between sexes. This critical barrier, made up of astrocytes (branched brain cells) and endothelial cells (which form the inner lining of blood vessels), defends the brain from harmful substances. When it becomes