User:Ronodeep.srimani/sandbox

Ronodeep.srimani/sandbox
Mesal aspect of a brain sectioned in the median sagittal plane. (Subfornical organ not labeled, but fornix and foramen of Monro are both labeled near the center.)
Details
Identifiers
Latin	organum subfornicale
Anatomical terms of neuroanatomy

The subfornical organ (SFO), situated on the ventral surface of the fornix, at the interventricular foramina (foramina of Monro), is one of the circumventricular organs of the brain.

General Function

The SFO plays an important role in a variety of functions. Most of these involve fluid balance through the control of the release of some kind of hormone: for example angiotensin or vasopressin.

Cardiovascular Regulation

The SFO's impact on the cardiovascular system is again mostly seen through fluid balance. The SFO plays a role in vasopressin regulation. Vasopressin is a hormone that, when bonded to receptors in the kidneys, increases water retention in the cardiovascular system by decreasing the amount of fluid transferred out of the blood to the urine by the kidneys. This regulation of blood volume has effects on other aspects of the cardiovascular system. Increased or decreased blood volume has an effect on blood pressure, which is regulated by baroreceptors, and can in turn effect the strength of ventricular contraction in the heart, although heart rate is generally not effected by blood volume.

Relationship With Other Circumventricular Organs

Other circumventricular organs are the area postrema in the brainstem and the organum vasculosum of the lamina terminalis (OVLT).

The OVLT and the SFO are both strongly interconnected with the nucleus medianus, and together these three structures comprise the so called "AV3V" region - the region anterior and ventral to the third ventricle. The AV3V region is very important in the regulation of fluid and electrolyte balance, by controlling thirst, sodium excretion, blood volume regulation, and vasopressin secretion.

The SFO is outside the blood–brain barrier, and so neurons in this region can respond to factors that are present in the systemic circulation. The circumventricular organs express high density of Glucagon-like peptide 1 (GLP-1)receptors and participate in the central regulation of energy intake.

Receptors

Neurons in the SFO have receptors for many hormones that circulate in the blood but which do not cross the blood–brain barrier, including angiotensin, atrial natriuretic peptide, endothelin and relaxin. The role of the SFO in angiotensin regulation is particularly important, as it is involved in communication with the nucleus medianus (also called the median preoptic nucleus). Some neurons in the SFO are osmoreceptors, being sensitive to the osmotic pressure of the blood. These neurons project to the supraoptic nucleus and paraventricular nucleus to regulate the activity of vasopressin-secreting neurons. These neurons also project to the nucleus medianus which is involved in controlling thirst. Thus, The subfornical organ is involved in fluid balance.

Relevant Experiments

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 bloodstream (various peptides indicating satiety) and then stimulating hunger. It has been shown to induce drinking in ratsas well as eating.

One study looks at different stimulation current values, to determine if this has an effect on the amount of feeding that occurs. The rats studied were separated into three groups: rats with electrodes in their subfornical organ with no current passing through (sham), rats with stimulated subfornical organs, and rats with areas other than the subfornical organ stimulated. The group with stimulated subfornical organs was separated into groups with 100mA and 200mA stimulations. All rats were satiated (food and drink) before observations/stimulations were done, and were also monitored for general activity. The group with subfornical stimulation at 100mA drank an increased amount, but did not consume any additional food, and the group with 200mA consumed both more water and more food. All groups without subfornical organ stimulation did not eat or drink at all .

Other studies look specifically at drinking, as the SFO is known to have an important role in fluid balance. One such study looked into the connection between the SFO and the median preoptic nucleus. Rats with both partially or fully severed connections to the median preoptic nucleus showed a significantly decreased tendency to drink water when compared to the control group. Then when angiotensin was injected subcutaneously, drinking incidence went back to original levels. These findings are consistent with a model that postulates that osmoreceptors and angiotensin receptors in the SFO send excitatory neural information to the median preoptic nucleus for the mobilization of thirst.