AQP4 and major depressive disorder: Furthermore, the lack of AQP-4 positive endfeet observed in the PFC of post mortem brains from MDD patients prompted us to hypothesize that either the endfeet of astrocytes were primarily morphologically affected, becoming only secondarily devoid of AQP-4 expression, or AQP-4 was dyslocalized, although astrocyte processes remained unaffected.