Subcommissural organ

Subcommissural organ
Mesal aspect of a brain sectioned in the median sagittal plane. (Subcommissural organ not labeled, but region is visible, near the pineal gland.)
Details
Identifiers
Latin	organum subcommissurale
MeSH	Subcommissural+organ
NeuroNames	hier-474
NeuroLex ID	Subcommissural organ
Dorlands /Elsevier	o_06/12596276
TA	A14.1.08.511
FMA	72414
Anatomical terms of neuroanatomy []

The subcommissural organ (SCO) is one of the circumventricular organs. It is a small glandular structure formed by ependymal cells and hypendymal cells and is located in the dorsocaudal region of the third ventricle, at the entrance of the cerebral aqueduct. The SCO is one of the first differentiated brain structures to develop. It has its name because of the localization in the brain. The organ's main functions are unknown; nevertheless, some evidences suggest that the organ may participate in different process, such as the clearance of certain compounds and the circulation of the cerebrospinal fluid, and it could also play a role in some morphogenetic mechanisms.

The subcommissural cells, specialized in the secretion of glycoproteins (including ependymin) are arranged into two polarized layers: ependyma and hypendyma. The first one (formed by a very high cylindrical cells) release their secretions into the ventricular cerebrospinal fluid and the hypendyma cells (located under the ependyma), characterized by numerous blood capillaries and glial cells, projects into the local blood vessels and to the subarachnoidal space.

The ependymal cell bodies present a clear zonation, specially marked in certain species: the perinuclear region - the most distinct ultrastructural feature off virtually all species is the presence of large and dilated cisternae of the rough endoplasmic reticulum (RER); intermediate region – constituted mainly by the RER and the Golgi apparatus (it is not certain the involvement of the Golgi apparatus in the secretary process of the subcommissural organ); subapical region – short region, with microtubules, mitochondria and smooth endoplasmic reticulum; and an apical region – projecting a large protrusion into the ventricle.

The ependymal cells of the SCO, are also involved in the production of brain transthyretin, which is a protein involved in the transport of thyroid hormones in blood and also plays a role in transporting the cerebrospinal fluid. Ependymal cells also secrete high molecular mass glycoproteins into the cerebrospinal fluid in which the bulk of them condense to form a filamentous structure, named Reissner’s fiber.