The subfornical organ (SFO) is one of the circumventricular organs of the brain. Its name comes from its location on the ventral surface of the fornix near the interventricular foramina (foramina of Monro), which interconnect the lateral ventricles and the third ventricle. Like all circumventricular organs, the subfornical organ is well-vascularized, and like all circumventricular organs except the subcommissural organ, some SFO capillaries have fenestrations, which increase capillary permeability. The SFO is considered a sensory circumventricular organ because it is responsive to a wide variety of hormones and neurotransmitters, as opposed to secretory circumventricular organs, which are specialized in the release of certain substances.
Anatomy
thumb|Subfornical organ of a mouse. In this [[photomicrograph, the subfornical organ (arrow) is located on the undersurface of the fornix in the upper part of the third ventricle. The cells in this coronal section of the brain were colored with a bluish dye ("Nissl stain"). The thalamus is at the bottom of the photo. The bar at the lower right represents a distance of 200 μm (0.2mm).]]
As noted above, capillaries in some subregions within the SFO are fenestrated, and thus lack a blood–brain barrier. All circumventricular organs except the subcommissural organ contain fenestrated capillaries, The SFO can be divided into six anatomical zones based on its capillary topography: two zones in the coronal plane and four zones in the sagittal plane. Conversely, the rostral and caudal areas have a lower density of capillaries
The subfornical organ contains endothelin receptors mediating vasoconstriction and high rates of glucose metabolism mediated by calcium channels.
General function
The subfornical organ is active in many bodily processes,
Pathology
Hypertension
Hypertension, or high blood pressure, is highly affected by the concentration of angiotensin. Injection of angiontensin has actually been long used to induce hypertension in animal test models to study the effects of various therapies and medications. In such experiments, it has been observed that an intact and functioning subfornical organ limits the increase in mean arterial pressure due to the increased angiotensin.
Dehydration
As stated above, angiotensin receptors (AT1) have been shown to be upregulated due to water deprivation. These AT1 receptors have also shown an increased bonding with circulating angiotensin after water deprivation. These findings could indicate some sort of morphological change in the AT1 receptor, likely due to some signal protein modification of the AT1 receptor at a non-bonding site, leading to an increased affinity of the AT1 receptor for angiotensin bonding.
Research
Feeding
Although generally viewed primarily as having roles in homeostasis and cardiovascular regulation, the subfornical organ has been thought to control feeding patterns through taking inputs from the blood (various peptides indicating satiety) and then stimulating hunger. It has been shown to induce drinking in rats as well as eating.