subfornical organ

The subfornical organ (SFO), situated on the ventral surface of the fornix (the reasoning behind the organ's name), at the interventricular foramina (foramina of Monro), is one of the circumventricular organs of the brain, meaning that it is highly vascularized and does not have a blood-brain barrier, unlike the vast majority of regions in the brain. The SFO is a sensory circumventricular organ responsive to a wide variety of hormones and neurotransmitters, as opposed to a secretory circumventricular organ.