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Third ventricle suprachoroidal cells.

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THE ANATOMICAL RECORD 202:113-116 (1982)
Third Ventricle Suprachoroidal Cells
Instituto di Cibernetica del CNR, 80072 Arco Felice, Naples, Italy
Using transmission electron microscopy two types of cells on
the choroid plexus of the third ventricle of the frog Rana esculenta have been
located. They lie on the microvilli and cilia of the choroid epithelium. Their free
surface is in contact with the cerebrospinal fluid. One type, Kolmer-like, has
large, dense bodies in its cytoplasm. The cytoplasm of the other type is complete
ly filled by large, ovoidal structures which have a limiting membrane and a
polymorphic filamentous content. Their functional significance is unknown.
Supraependymal cells have often been
reported in the ventricular system of the
vertebrate brain (Coates, 1973; Paull et al.,
1974; Mestres and Breipohl, 1976; Bleier,
1977; Card and Mitchell, 1978; Kemali and
Miralto, 1979), and various interpretations
have been given to their functional role:
Supraependymal cells are believed to be
macrophages, glial or neuronal elements stemming from ependymal cells, to have osmosensitive or neurosecretory functions, and to be
perceptors of the concentration of various
chemical compounds of the cerebrospinal fluid
(CSF). Cells lying on the choroid epithelium
have not been described frequently (Ling,
1979 Baumgarten et al., 1980).Here we report
the Occurrence of suprachoroidal (epiplexus)
cells in the third ventricle of the frog.
choroid epithelium. One is spherical (on the
left), the other is ovoidal in shape (on the right).
The latter shows several filopodial processes
insinuating into the underlying microvilli.
At the electron microscope both types show
a dark nucleus with large, dark, chromatin
masses; they differ, however, in their c y t e
plasmic content.
The cytoplasm of the spherical type is completely filled by large inclusions (Fig. 2a) which
have a polymorphic filamentous content as
shown in detail in Figure 2b. The inclusions,
some ovoidal and some spherical in shape,
seem to have a limiting membrane. Only small
portions of their cell cytoplasm is apparent
among the packed inclusions, where some clear
vesicles are also visible (arrow in Fig. 2b). The
surface of the spherical, large inclusion-
Three adult frogs of the species Rana
esculenta were anesthetized with M S 222
(1:3,000) and were fixed by perfusion for electron microscopy. The fixative used was a mixture of 1% glutaraldehyde and 1% formaldehyde in phosphate buffer at pH 7.4. The
dissected choroid plexus was postfixed in 2%
osmium tetroxide and underwent block staining by uranyl acetate. Ultrathin sections were
counterstained with lead citrate and observed
on a Philips 200 electron microscope.
We have observed two types of cells lying on
the microvilli and cilia of the choroid epithelium of the third ventricle.
In Figure 1-which is a light microscope picture of a semithin section lp thick -both types
are shown lying over the free surface of the
0003-276X/82/2021-0113$01.50 0 1982 Alan R. Liss, Inc.
Fig. 1. Light microscopy of a semithin section, 1, lam
thick, showing the two types of suprachoroidalcellslying on
the microvilli of the choroid plexus. On the f a r left. the
spherical, large inclusion-bearing cell, on the right the
ovoidal Kolrner-like cell with several elongations. X 130.
Received March 2. 1981; accepted May 14,1981
Fig. 2. a. Frog third ventricle suprachoroidal cell showing a dark nucleus and the cytoplasm completely filled by
large inclusions. The free surface of the cell is in contact with
the CSF. X 7,500.b. Detail of the intracytoplasmatic i n c h
sions showing a polymorphic filamentous content. The arrow points to a small portion of the cytoplasm free of inchsions where some clear vesicles are visible. X 45.400.c. Two
types of suprachoroidal cells lying in close contact with
microvilli and cilia. One type, on the left, has a dark nucleus
and the cytoplasm with dark granules (arrows)and a smooth
surface facing CSF. The other type, on the right, shows a
portion of its large inclusion-bearing cytoplasm and has an
angular surface facing CSF. X 16.400.ven=III ventricle.
bearing cell has an angular aspect which
reflects the geometry of the packed inclusions.
The other type of suprachoroidal cell is
ovoidal in shape and contains large dense
bodies in its cytoplasm (Fig. 2c-on the left). It
is Kolmer-type (Kolmer,1921)and is similar to
the monocytetype of Ling (1979).
As shown in Figure 2c, where both types of
cells occur in the same section, they lie in close
contact with the microvillli and cilia of the
choroid epithelium on which they seem to be
anchored. The surface facing the ventricle is
free and in contact with CSF.
The Kolmer-type is considered in the literature to be a phagocytic cell and the other type,
the large inclusion-bearing cell might also
belong to the same functional type. In fact,
Bleier and Albrecht (1980) described
supraependymal macrophages of the third
ventricle which contain many membrane
bound inclusions of various sizes within their
cytoplasm and that may constitute a resident
macrophage system of the ventricles of the
Although the large inclusion-bearing cells
have also a somewhat ultrastructural similarity in their cytoplasmic content to basophilic
leucocytes and mast cells (see the Cell Fine
Structure atlas of Lentz, 1971),we are unable
to say if they also share possible functional
The suprachoroidal cells described here are
features of the adult frog since they have not
been observed in the third ventricle choroid
plexus of the tadpole (Kemali and Gioffre,
The functional role of these suprachoroidal
cells is unknown and we do not know if it is the
same for both types. However, we might suppose that they participate in the functional
events which occur at the level of the third ventricle choroid plexus.
The choroid plexus plays a role in the production of CSF and in the regulation of its composition. The choroid epithelium secretes the
constituents of the CSF from blood to ventricle
Stazione Zoologica of Naples
and, at the same time, it absorbs a variety of
solutes from CSF into the blood with an active for the use of their Philips 200 electron
transport mechanism (Wright, 1979). I t has microscope.
been shown that the third ventricle choroid
plexus plays an important role in maintaining
the circadian rhythm of melatonin levels in
CSF and blood (Smulders and Wright, 1980). Baumgarten, F. v., H.G. Baumgarten, and H.G.
Schlossberger (1980)The disposition of intraventricularly
These authors suggest that melatonin reaches
injected "C-5. 6-DHT-Melanin in, and possible routes of
the CSF directly from the pineal gland, either
elimination from the rat CNS. Cell Tissue Res., 212:
by diffusion from systemic circulation or by
local vascular compartment. This hormone, Bleier, R. (1977)Ultrastructure of supraependymal cells and
ependyma of hypothalamic third ventricle of mouse. J.
through an active transport process located at
Comp. Neurol., 174359-376.
the brush border surface of the choroid
R., and R. Albrecht (1980) Supraependymal
epithelium, then returns to the blood where it Bleier,
macrophages of third ventricle of hamster: Moris metabolized by the liver and excreted in the
phological, functional and histochemical characterization
in situ and in culture. 3. Comp. Neruol, 192489-504.
The level of melatonin in the CSF might, in Card, J.P., and J.A. Mitchell (1978) Electron microscopic
demonstration of a supraependymal cluster of neuronal
addition, be regulated by the suprachoroidal
cells and processes in the hamster third ventricle. J.
cells. In fact, Baumgarten et al. (1980) have
Comp. Neurol., 18e43-58.
demonstrated that epiplexus cells are able to Coates. P.W. (1973)Supraependymal cells in the recesses of
the monkey third ventricle. Am. J. Anat., 136533-539.
accumulate synthetic melanin by phagocyKemali. M., and A. Miralto (1979) Light- and electrontosis.
microscopic structure of e l l s protruding into the
We have observed the large inclusionmesencephalic ventricle of Scyllium stellare (Elasmobranchii, Selachii). Cell Tissue Res., 200.153-157.
bearing cell type also in the layer separating
the pineal parenchima from the habenular com- Kemali, M., and D. Gioffrb (1981)Development of the third
ventricle choroid epithelium of the frog: An electron
missure in the frog epiphysis (Kemali, unmicroscopic study. Zool. Jb. Anat., 105r353-361.
published observation). However, on a purely Kolmer, W. (1921) Uher eine eigenartige Beziebung von
Wanderzellen zu den Choroidealplexus des Gehirns der
morphological basis, we cannot say if the
Wirbeltiere. Anat. Am. 54:15-19.
suprachoroidal cells are involved in melatonin
T.L. (1971) Cell Fine Structure. W.B. Saunders Co.,
regulation. We are also unable to say if both Lentz,
types of epiplexus cells described here play the' Ling. E.A. (1979) Ultrastructure and origin of epiplexus
cells in the telencephalic choroid plexus of postnatal rats
same role.
studied by intravenous injection of carbon particles. J.
Anat., 129:479-492.
Mestres, P., and W. Breipohl (1976) Morphology and
distribution of supraependymal cells in the third ventricle
of the albino rat. Cell Tissue Res.. 168:303-314.
Paull, W.K., D.E. Scott, and W.G. Boldosser (1974) A
cluster of supraependymal neurons located within the in-
fundibular recess of the rat third ventricle. Am. J. Anat.,
SmuMers, A.P., and E.M. Wright (1980) Role of choroid
plexus in transport of melatonin between blood and brain.
Brain Res., 191:555-558.
Wright. E.M. (1979) Relations between thechoroidplexuses
and the cerebrospinal fluid. Trends Neurosci., 2;13-15.
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