# Ependymal Cells: Function, Location, and CSF Production

Ependymal cells are ciliated glial cells that form a single-layer epithelium lining the ventricles of the brain and the central canal of the spinal cord. They separate cerebrospinal fluid (CSF) from the underlying nervous tissue, drive fluid movement with their motile cilia, and contribute to the blood-CSF and CSF-brain interfaces of the central nervous system.

Ependymal cells matter in veterinary practice because they sit at the crossroads of CSF production, flow, and clearance. When ependymal cilia fail, when the ventricular lining is damaged by infection or toxicants, or when an ependymoma arises from this cell layer, the result is hydrocephalus, periventricular edema, or focal neurologic deficits. Understanding this cell type also clears up a common misconception: the ependyma is not the main factory for CSF. That job belongs to the choroid plexus, a specialized derivative of the same cell lineage.

This article is educational and is not a substitute for veterinary diagnosis or treatment.

## What Are Ependymal Cells?

Ependymal cells (also written ependyma cells, singular ependymal cell) are one of the four classical glial cell types of the central nervous system, alongside astrocytes, oligodendrocytes, and microglia. Unlike neurons, they do not fire action potentials. Unlike astrocytes, they do not form a syncytium through gap junctions in the same way. They form a true epithelial sheet, one cell thick, that is polarized: the apical surface faces the CSF, and the basal surface rests on underlying neural tissue or a basal lamina.

The ependyma is a glial epithelium. That phrase captures both its origin and its behavior. It arises from the neuroepithelium of the neural tube, and it retains epithelial features in the adult: apicobasal polarity, junctional complexes, and, in most locations, motile cilia.

### Where Ependymal Cells Are Found

The ependymal lining is continuous with the choroid plexus epithelium at a transitional zone, and the two cell populations form a single contiguous sheet [1]. The main locations are:

- The lateral ventricles, third ventricle, and fourth ventricle of the brain
- The central canal of the spinal cord
- The surface of the choroid plexus (as modified ependymal cells)
- The median eminence and other circumventricular organs, where specialized ependymal cells called tanycytes reside
- The organum vasculosum, subfornical organ, and subcommissural organ

Ependymal cells are heterogeneous. At least three subtypes are recognized, and they are localized to different regions of the central nervous system [2].

## The Three Ependymal Subtypes

### Ciliated Ependymal Cells

Ciliated ependymal cells are the classic ventricular lining cells. Each cell carries a tuft of motile cilia on its apical surface, and these cilia beat in a coordinated, metachronal wave. The coordinated beating is what moves CSF through the ventricular system and helps circulate solutes [3]. Ciliary beat frequency is not fixed. It can be modulated by signaling molecules, including adenosine acting through A2B receptors, which enhances ciliary beat frequency in mouse lateral ventricle ependymal cells [4].

Ciliated ependymal cells line the lateral, third, and fourth ventricles and the central canal. Their cilia are anchored to basal bodies, and the planar polarity of those basal bodies determines the direction of the beat. When that polarity is disrupted, CSF flow becomes abnormal. In zebrafish, mutations that disorganize ependymal polarity and ciliary beating produce hydrocephalus and spinal curvature resembling adolescent idiopathic scoliosis [5].

### Non-Ciliated (Transporting) Ependymal Cells

Non-ciliated ependymal cells lack motile cilia and are found in regions where the primary role is transport rather than fluid propulsion. They are prominent in the choroid plexus, where the epithelium is a specialized, non-ciliated ependymal derivative with epithelial characteristics and barrier properties [1][6]. These cells are the site of the blood-CSF barrier.

Non-ciliated ependymal cells also occur in parts of the ventricular lining where absorptive or secretory transport dominates over ciliary-driven flow. They express aquaporin water channels and transporters that move water and solutes between CSF, blood, and brain interstitial fluid. Aquaporin-1 (AQP1) is expressed apically in choroid plexus epithelial cells, while aquaporin-4 (AQP4) is expressed mainly in ependymal cells and in astrocytic endfeet [1][6][7].

### Tanycytes

Tanycytes are specialized ependymal cells with long basal processes that extend into the hypothalamus. They are concentrated in the median eminence and the infundibular recess of the third ventricle. Their apical surface contacts CSF, and their basal processes contact portal capillaries and hypothalamic neurons. This arrangement lets tanycytes sample CSF and deliver signals or metabolites to the hypothalamic-pituitary axis.

Tanycytes are best known for their role in neuroendocrine regulation, including the transport of hormones and metabolic signals between CSF and blood. They are part of the circumventricular organ system, which contains homeostatic transporters for secretion and reabsorption at the CSF interface [8].

## Summary Table: Ependymal Subtypes

| Subtype | Primary location | Motile cilia | Main function |
|--|--|--|--|
| Ciliated ependymal cell | Lateral, third, and fourth ventricles; central canal | Yes, tufts of motile cilia | Propel CSF, circulate solutes, maintain local fluid flow |
| Non-ciliated (transporting) ependymal cell | Choroid plexus epithelium; selected ventricular lining | No | Blood-CSF barrier, water and solute transport, CSF secretion |
| Tanycyte | Median eminence, infundibular recess, circumventricular organs | No (or modified) | Neuroendocrine signaling, CSF-to-blood transport, metabolic sensing |

## How the Ependyma Differs from the Choroid Plexus

Students often treat the ependyma and the choroid plexus as the same structure. They are related but distinct.

The choroid plexus is a vascularized, folded structure that projects into the ventricles. It is covered by a specialized epithelium that is derived from ependymal cells but has acquired epithelial barrier properties [1][6]. The choroid plexus epithelium sits on a basal lamina, and its stroma contains fenestrated blood vessels. The ependyma, by contrast, does not have a basal lamina in the same way and does not form a tight barrier [1].

The junctional difference is the key point. Choroid plexus epithelial cells are joined by tight junctions, which form the blood-CSF barrier. Ependymal cells are joined mainly by gap junctions and desmosomes, which allow communication between cells but do not seal the paracellular space. This is why the ependyma is described as a leaky epithelium and the choroid plexus as a tight one.

## CSF Production: Who Makes It?

Most CSF is produced by the choroid plexus epithelium, not by the ependyma itself. The classic figure for total CSF production in humans is roughly 0.3 to 0.4 mL per minute, which corresponds to about 500 to 600 mL per day. Species differences are substantial. Smaller animals turn over their CSF volume faster relative to body size, and absolute production rates scale with brain and choroid plexus mass.

The choroid plexus is described as producing the main part of CSF [6]. Ependymal cells contribute to CSF homeostasis, but their contribution is secondary to the choroid plexus. Aquaporin-4 in ependymal cells supports an extrachoroidal component of CSF formation, meaning water movement between brain capillaries and interstitial fluid that contributes to the overall CSF pool [7].

### The Mechanism of CSF Secretion

CSF secretion by the choroid plexus is an active, energy-dependent process. The steps are:

1. Blood arrives at the choroid plexus through fenestrated capillaries in the stroma.
2. Water and solutes cross the capillary endothelium into the stromal interstitium.
3. Choroid plexus epithelial cells take up ions and water at their basolateral surface.
4. Sodium is actively transported across the epithelium, and water follows osmotically.
5. Carbonic anhydrase and aquaporin-1 facilitate ion and water movement.
6. Fluid exits the apical surface into the ventricular lumen as CSF.

The enzyme carbonic anhydrase IX and aquaporin-1 are both involved in this process, and their expression is regulated by liver X receptors in the choroid plexus epithelium [9]. Atrial natriuretic peptide binds to choroid plexus epithelial cells, generates cGMP, alters ion transport, and slows CSF production, which provides a mechanism for intracranial pressure regulation [10].

### The Blood-CSF Barrier vs the CSF-Brain Interface

The blood-CSF barrier is formed by tight junctions between choroid plexus epithelial cells. These junctions prevent free paracellular movement of solutes from blood into CSF, so the composition of CSF is controlled by selective transport rather than by passive filtration [11].

The CSF-brain interface, sometimes called the CSF-brain barrier, is formed by the ependyma. It is not a tight barrier. Ependymal cells are connected by gap junctions, which allow intercellular communication and permit some movement of small molecules between CSF and brain interstitial fluid [11]. This difference explains why substances injected into the CSF can reach periventricular brain tissue relatively easily, while the same substances in blood are excluded from CSF by the choroid plexus tight junctions.

Subependymal astrocytes form a glial plate around blood vessels entering the choroid plexus, and this plate is strongly positive for aquaporin-4 [6]. The transition zone between ependyma and choroid plexus is therefore a region of active water transport, and increased AQP4 expression there may be a compensatory response to reduced CSF production in the aging brain [1].

## How Ependymal Cells Are Studied

### Histology

On routine hematoxylin and eosin sections, ependymal cells appear as a single layer of cuboidal to columnar cells with basally located nuclei and a ciliated apical border. The cilia are best seen with special stains or with electron microscopy. In veterinary histopathology, the ependymal lining is examined for loss of cilia, vacuolation, and inflammatory infiltrates.

### Electron Microscopy

Transmission electron microscopy reveals the ultrastructure of ependymal cilia, including the microtubular axoneme and basal bodies. In mouse models of Bardet-Biedl syndrome, a ciliopathy, electron microscopy showed disruptions of the microtubular structure of the axoneme and electron-dense material along the ciliary shaft in the choroid plexus, subfornical organ, and ventricular ependyma [12]. These structural defects were associated with ventriculomegaly.

### Immunohistochemistry

Aquaporin expression is mapped by immunofluorescence. AQP1 is found apically in choroid plexus epithelial cells, and AQP4 is found mainly in ependymal cells and subependymal astrocytes [6]. Immunolabeling for dystrophin and AQP4 overlaps in the glial plate but not in AQP4-positive choroid plexus epithelial cells [6].

### Functional Imaging

In research settings, phase-contrast MRI and 4D flow MRI measure CSF flow and choroid plexus perfusion. Choroid plexus volume increases with age, while perfusion decreases, and net cranial-to-caudal CSF flow decreases across the adult lifespan [13]. These techniques are used to study CSF dynamics in hydrocephalus and neurodegenerative disease.

### Gene Delivery Studies

Intraventricular injection of adeno-associated virus vectors transduces ependymal cells and choroid plexus epithelium, which can then secrete therapeutic proteins into CSF for months [14]. This approach has been used to deliver lysosomal enzymes and is a research tool for studying ependymal [cell biology](/blog/careers/cell-biology).

## Comparative and Clinical Relevance

### Hydrocephalus

Hydrocephalus is the most direct clinical consequence of ependymal and choroid plexus dysfunction. Ciliary defects in the ependyma and choroid plexus are associated with ventriculomegaly in mouse models of ciliopathy [12]. In zebrafish, ependymal polarity defects cause hydrocephalus and scoliosis before multiciliated ependymal cells fully mature [5]. In congenital human hydrocephalus, aquaporin-4 levels are elevated in CSF, particularly in communicating hydrocephalus, which suggests that AQP4 moves from ependymal cells into CSF when the ependyma is destabilized [15].

### Ependymoma

Ependymoma is a tumor that arises from ependymal cells. It can occur anywhere along the ventricular system and the central canal, including the fourth ventricle, lateral ventricles, and spinal cord. In [veterinary medicine](/blog/careers/veterinary-medicine-careers-from-clinical-practice-to-public-health), ependymomas are reported in dogs and cats, most often in the brain and spinal cord. They are a relevant differential for animals with progressive neurologic signs and imaging evidence of an intraventricular or intramedullary mass. The tumor is named for its cell of origin, which is why understanding ependymal anatomy helps localize the lesion.

### Multiple Sclerosis and Periventricular Pathology

In multiple sclerosis, damage is most severe adjacent to CSF-contacting surfaces, including the periventricular regions. Ependymal cilia are critical for circulating CSF solutes and regulating local fluid flow, and damage to these cilia can modify CSF homeostasis and contribute to periventricular damage [3]. This surface-in pattern of pathology links ependymal function to immune-mediated disease.

### Toxicologic Injury

The choroid plexus-CSF-ependyma-brain nexus is a conduit for infectious and xenobiotic agents. Amoscanate, an anti-helminthic, potently injures rodent ependyma [8]. Piperamide distorts choroid plexus epithelial ultrastructure by producing hydropic vacuoles, which reflects phospholipidosis and altered lysosomal metabolism [8]. Structurally perturbed choroid plexus allows solutes to penetrate the ventricles, where CSF-borne pathogens and xenobiotics may permeate the ependyma and harm neurogenic stem cell niches [8].

### Aging

Choroid plexus volume increases with age while perfusion decreases, and net CSF flow decreases [13]. Increased AQP4 expression in the choroid plexus-ependyma transition zone may be a compensatory mechanism for reduced CSF production in the aging brain [1].

## Clinical Relevance, Limitations and Common Mistakes

The clinical relevance of ependymal cells centers on CSF dynamics, barrier function, and neoplasia. When CSF flow is obstructed or cilia fail, ventriculomegaly and periventricular edema follow. When the ependymal lining is damaged, the CSF-brain interface becomes more permeable, and solutes that would normally be excluded can reach periventricular tissue.

Common mistakes students make:

1. **Assuming the ependyma makes most CSF.** The choroid plexus epithelium makes the main part of CSF [6]. Ependymal cells contribute to CSF homeostasis, particularly through aquaporin-4, but they are not the primary secretory epithelium [7].

2. **Confusing the blood-CSF barrier with the blood-brain barrier.** The blood-CSF barrier is at the choroid plexus and is formed by tight junctions between choroid plexus epithelial cells [11]. The blood-brain barrier is at cerebral capillaries and is formed by tight junctions between endothelial cells. The ependyma forms neither barrier in the tight sense.

3. **Treating all ependymal cells as ciliated.** Non-ciliated transporting ependymal cells and tanycytes are distinct subtypes with different locations and functions [2].

4. **Forgetting that ependymal junctions are gap junctions.** Tight junctions seal the choroid plexus epithelium. Gap junctions connect ependymal cells and allow intercellular communication [11].

5. **Overlooking species differences in CSF production.** The human figure of roughly 0.3 to 0.4 mL per minute is a reference point, not a universal constant. Production rates scale with brain size and metabolic rate.

6. **Missing the clinical significance of ciliary defects.** Ciliary dysfunction in the ependyma and choroid plexus is associated with ventriculomegaly and hydrocephalus in animal models [12].

Individual cases require a veterinarian for diagnosis and treatment. The information here describes general principles, not a diagnostic protocol.

## Quick Review

- Ependymal cells are ciliated glial cells forming a single-layer epithelium lining the ventricles and central canal.
- Three subtypes exist: ciliated ependymal cells, non-ciliated transporting ependymal cells, and tanycytes.
- Ciliated cells line the ventricles and drive CSF flow with motile cilia.
- Non-ciliated cells are found in the choroid plexus and form the blood-CSF barrier.
- Tanycytes sit in the median eminence and link CSF to hypothalamic neuroendocrine function.
- Most CSF is made by the choroid plexus epithelium, not the ependyma. The classic human figure is roughly 0.3 to 0.4 mL per minute.
- Choroid plexus cells have tight junctions. Ependymal cells have gap junctions.
- Ependymoma is a tumor of ependymal cells and is a differential for intraventricular or intramedullary masses.

## Frequently Asked Questions

### What do ependymal cells do?

Ependymal cells line the brain ventricles and spinal canal, separate CSF from nervous tissue, and use motile cilia to help circulate CSF. They also contribute to water and solute transport at the CSF-brain interface.

### Where are ependymal cells located?

They line the lateral, third, and fourth ventricles and the central canal of the spinal cord. Specialized forms cover the choroid plexus and sit in the median eminence and other circumventricular organs.

### Do ependymal cells produce cerebrospinal fluid?

They contribute to CSF homeostasis, but the choroid plexus epithelium produces most CSF. Ependymal aquaporin-4 supports an extrachoroidal component of fluid movement.

### What is the difference between ependymal cells and choroid plexus cells?

Choroid plexus cells are specialized ependymal derivatives with tight junctions that form the blood-CSF barrier. Ependymal cells are joined mainly by gap junctions and do not form a tight barrier.

### What is an ependymoma?

An ependymoma is a tumor arising from ependymal cells. It can develop in the ventricles or spinal canal and is a differential for animals with progressive neurologic signs and an intraventricular or intramedullary mass.

### What happens when ependymal cilia stop working?

Disrupted ciliary beating and ependymal polarity defects impair CSF flow and are associated with hydrocephalus and ventriculomegaly in animal models.

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## Sources

1. [Shifting from ependyma to choroid plexus epithelium and the changing expressions of aquaporin-1 and aquaporin-4.](https://pubmed.ncbi.nlm.nih.gov/37975746/)
2. [Roles of Ependymal Cells in the Physiology and Pathology of the Central Nervous System.](https://pubmed.ncbi.nlm.nih.gov/37008045/)
3. [Cerebrospinal fluid-driven ependymal motile cilia defects are implicated in multiple sclerosis.](https://pubmed.ncbi.nlm.nih.gov/41277219/)
4. [Activation of adenosine A2B receptors enhances ciliary beat frequency in mouse lateral ventricle ependymal cells.](https://pubmed.ncbi.nlm.nih.gov/19922651/)
5. [Ependymal polarity defects coupled with disorganized ciliary beating drive abnormal cerebrospinal fluid flow and spine curvature in zebrafish.](https://pubmed.ncbi.nlm.nih.gov/36862758/)
6. [Aquaporin-1 and Aquaporin-4 Expression in Ependyma, Choroid Plexus and Surrounding Transition Zones in the Human Brain.](https://pubmed.ncbi.nlm.nih.gov/36830582/)
7. [AQP1 and AQP4 Contribution to Cerebrospinal Fluid Homeostasis.](https://pubmed.ncbi.nlm.nih.gov/30813473/)
8. [The distributional nexus of choroid plexus to cerebrospinal fluid, ependyma and brain: toxicologic/pathologic phenomena, periventricular destabilization, and lesion spread.](https://pubmed.ncbi.nlm.nih.gov/21189316/)
9. [Liver X receptors regulate cerebrospinal fluid production.](https://pubmed.ncbi.nlm.nih.gov/26324101/)
10. [Atrial natriuretic peptide: its putative role in modulating the choroid plexus-CSF system for intracranial pressure regulation.](https://pubmed.ncbi.nlm.nih.gov/16671503/)
11. [Immunodistribution of amyloid beta protein (Aβ) and advanced glycation end-product receptors (RAGE) in choroid plexus and ependyma of resuscitated patients.](https://pubmed.ncbi.nlm.nih.gov/22212919/)
12. [Structural defects in cilia of the choroid plexus, subfornical organ and ventricular ependyma are associated with ventriculomegaly.](https://pubmed.ncbi.nlm.nih.gov/23046663/)
13. [Choroid plexus perfusion and bulk cerebrospinal fluid flow across the adult lifespan.](https://pubmed.ncbi.nlm.nih.gov/36200473/)
14. [Targeted gene transfer into ependymal cells through intraventricular injection of AAV1 vector and long-term enzyme replacement via the CSF.](https://pubmed.ncbi.nlm.nih.gov/24981028/)
15. [Aquaporin-4 expression in the cerebrospinal fluid in congenital human hydrocephalus.](https://pubmed.ncbi.nlm.nih.gov/23659378/)