Subfornical organ

Subfornical organ is a collection of neuronal cells which is situated in the anterior wall of the third ventricle, on the dorsal aspect of the lamina terminalis.

Being a circumventricular organ, it lacks a blood-brain barrier, and can therefore sample the systemic circulation for various body fluid constituents, including angiotensin II, sodium, potassium, calcium, and fluid osmolality. In response to this systemic sensory information, the subfornical organ sends efferent neuronal impulses to the hypothalamic nuclei. These include the supra-optic and (magnocellular part of the) paraventricular nuclei, which secrete anti-diuretic hormone and oxytocin, respectively. Through these endocrine and neuronal connections, the subfornical organ plays an important role in maintenance of body fluid homeostasis and mineral balance.

Additional efferents from the subfornical organ also get projected to the parvocellular component of paraventricular nucleus, which synapses with neuronal cell bodies in the median eminence, medulla oblongata and spinal cord.