close

Вход

Забыли?

вход по аккаунту

?

The presence of fenestrated capillaries in the papillary layer of the enamel organ.

код для вставкиСкачать
The Presence of Fenestrated Capillaries in the
Papillary Layer of the Enamel Organ
PHILIAS R. GARANT AND ROBERTA GILLESPIE
Harvard School of Dental Medicine, Boston, Massachusetts
ABSTRACT
The capillary network of the papillary layer of the enamel organ was
studied with the electron microscope. Mandibular incisor teeth of ten-day old Swiss
albino mice were fixed in formaldehyde-glutaraldehyde, postfixed in osmium tetroxide
and prestained with 0.5% uranyl acetate prior to being embedded in Epon. Examination of ultrathin sections revealed the presence of fenestrations approximately 500 A
to 700A in diameter within the most attenuated regions of the capillary walls. In
most instances the fenestrations appeared to be closed by diaphragms usually consisting of a thin membrane with a thicker centrally located button of electron opaque
material.
The presence of fenestrated capillaries within the papillary region of the enamel
organ lends further support to the concept that papillary cells are engaged in transport
functions during the maturation of enamel.
The development and intimate apposition of a capillary network to the ameloblastic layer of developing teeth has been
the subject of numerous histological studies in a wide variety of species (Addison
and Appleton, '22; Bernick, '60; Glasstone,
'62; Jordan, '21; Jump, '38; Kingery, '24).
In rodent incisor teeth an especially abundant network of capillaries becomes closely
apposed to the enamel organ overlying the
post-secretory ameloblasts (Adams, '62).
This region of the enamel organ, commonly referred to as the papillary layer,
has an architecture of alternating epithelial
ridges and capillaries which provides an
increased surface area for the rapid exchange of metabolites (Reith, '59; Kallenbach, '66).
In the only reported electron microscopic
study of the vascular supply to the enamel
organ, Decker ('67) has described unfenestrated capillaries of the conventional
or continuous type in close proximity to
the external enamel epithelium of the developing rat molar. The present investigation, however, revealed that the capillaries
associated with the papillary layer of the
mouse incisor are of the fenestrated variety. Fenestrated capillaries have been reported within numerous organs, many of
which are specialized for the rapid exchange of metabolites. A few examples
are the kidney (Pease, '55; Yamada, '55;
Rhodin, '62), the lamina propria of intesANAT. REC., 1 6 3 ; 71-80.
tinal villi (Palay and Karlin, '59; Bennett,
Luft and Hampton, '59), parotid gland
(Parks, '61), and the rete mirabile of fish
swim bladder (Fawcett, '63). For a
thorough compilation of the reports of
fenestrated capillaries one should consult
a review of the ultrastructure of the vascular membrane by Majno ('65).
MATERIAL A N D METHODS
Mandibular incisors of ten-day old Swiss
albino mice were dissected free of surrounding tissues in a dish containing a formaldehyde-glutaraldehyde fixative buffered to pH
7.4 with cacodylate (Karnovsky, '65). Upon
completion of the dissection, the incisors
were cut into smaller pieces and transferred to a fresh solution of fixative. After
30 minutes in this fresh solution at room
temperature, the tissues were transferred
through several rinses of 0.1 M cacodylate
buffer and stored overnight in buffer containing 0.25 M of sucrose. Postfixation
was carried out in a 1% collidine buffered
osmium tetroxide solution (pH 7.4) for
45 minutes at 4°C. The tissue blocks were
then stained at room temperature with
0.5% uranyl acetate in acetate-Verona1
buffer for 45 minutes (Farquhar and
Palade, '65). Dehydration was rapidly
carried out in a graded series of ethanol
and the tissues subsequently embedded in
Epon (Luft, '61). Sections were cut on
Received July 19, '68. Accepted Sept. 25, '68.
71
72
PHILIAS R. GARANT AND ROBERTA GILLESPIE
a Porter-Blum microtome equipped with a
diamond knife, stained with lead citrate
and examined in an RCA-EMU-3G electron microscope at 50 kv.
RESULTS
The portions of the enamel organ overlying post-secretory ameloblasts, when
viewed in sections cut perpendicular to the
long axis of the incisor, are arranged into
a series of papillae projecting away from
the ameloblastic layer (fig. 1 ). Capillaries
originating in the connective tissue of the
surrounding dental sac course within the
spaces between adjacent papillae (fig. 1).
Tangential sections through the papillary
layer reveal the complex network of capillaries in close association with the papillary cells of the enamel organ (fig. 2).
With the exception of the nucleus and
perinuclear cytoplasm, which usually
bulged outward into the lumen of the
capillary, the cytoplasm of the endothelial
cell was extended to form the narrow attenuated capillary wall (fig. 3). The narrowest
portions of the endothelial wall (300 A
to 500 A thick) were frequently interrupted
by fenestrations approximately 500 A to
7 0 0 A in diameter (figs. 4,5,6). The majority of the fenestrations were closed by
diaphragms (figs. 4, 5, 6). In many instances the diaphragms were characterized
by a centrally located button of electron
opaque material surrounded by a tenuous
30 to 4 0 A membrane (figs. 8, 9). This
arrangement was verified by sections cut
tangential to a fenestration (fig. 10). On
occasion similar buttons of electron opaque
material could be detected at the mouths
of forming pinocytotic vesicles (figs. 8, 9).
A basement membrane, approximately
300 to 500A thick, was present adjacent
to the capillary walls and adjacent to papillary cells of the enamel organ (fig. 3).
Small collagen fibrils and material of the
same structure and electron opacity as
that which was observed to constitute the
basement membrane were usually present
within the narrow extracellular space separating the vasculature from the enamel
organ (figs. 3, 8, 9).
As described in greater detail in a previous publication (Garant and Nalbandian,
'68) the papillary cells abutting the capillaries were usually characterized by num-
erous cytoplasmic infoldings and microvilli which serve to increase the surface
area, and, in addition, they contained
numerous well developed mitochondria
and coated vesicles, suggesting a possible
transport function.
DISCUSSION
Because the papillary cells are strategically placed between the ameloblastic layer
and the rich plexus of capillaries located
within the dental sac, it is not surprising
that numerous investigators have hypothesized that they were in some way involved
in the movement and/or concentration of
nutrients needed during enamel formation
(Adams, '62; Addison and Appleton, '22;
Bernick, '60; Marsland, '52; Reith and
Cotty, '62; Williams, '23).
Electron microscopic studies of the papillary layer in both the rat and mouse have
shown that the cells making up this tissue
contain large numbers of mitochondria,
numerous coated vesicles and a rather extensive surface area due to the development of many microvilli and surface plications, all of which suggest a specialization
for transport functions (Elwood and Bernstein, '65; Kallenbach, '66; Garant and
Nalbandian, '68). The presence of a rich
network of fenestrated capillaries in close
association with the cells of the papillary
layer provides additional evidence that this
tissue performs a transport function during amelogenesis.
During the calcification or maturation
phase of enamel formation there is a reported increase in the mineral content
and a decrease in the water and organic
component of the enamel matrix (Weinmann, Wessinger, and Reed, '42; Deakins,
'42)- Electron microscopic studies of postsecretory ameloblasts have suggested that
they are involved in the removal of organic
matrix during enamel maturation (Reith,
'61, '63), and more recently autoradiographic investigations have provided evidence that this component of the matrix
may be a sulfated compound (Reith and
Cotty, '67). Perhaps the cells of the papillary layer are engaged in functions which
lead to the increased mineral and decreased water content found within mature enamel as proposed by Adams ('62).
F E N E S T R A T E D CAPILLARIES OF THE E N A M E L ORGAN
The preferential distribution of fenestrated capillaries to certain organs known
to be involved in the modification of body
fluids suggests that they are structurally
specialized for rapid exchange of fluid and
solutes (Majno, ’65). Glomerular capillaries are known to pass fluid 100 times
more rapidly than the unfenestrated capillaries of striated muscle (Pappenheimer,
Renkin, and Borrero, ’51). It has been
proposed that the fenestrations and the
intercellular clefts represent the morphological equivalent of the physiologist’s
small pore, and that the higher permeability measured in fenestrated capillary beds
is due to the larger and thinner surface
area available for exchange provided by
the diaphragmatic membranes of the fenestrations (Luft, ’65). The manner in which
fenestrations are formed and the nature
and origin of the diaphragms are speculative. Luft (’65) has proposed that the
fenestrations arise by fusion of a cytoplasmic vesicle with the endothelial cell membrane, followed by degeneration of the
inner and middle layers of the membrane,
while the outer layer remains intact as a
thin diaphragm stretched across the mouth
of the vesicle. Contact of the vesicle with
the other surface of the endothelial wall
and rupture of all three layers of the membrane at this site completes the fenestration. The observations of “buttons” or
diaphragms at the mouth of vesicles (fig.
9) and structures interpreted as vesicles
with double diaphragms (fig. 8) in this
study may be interpreted as stages in the
formation of fenestrations according to the
scheme proposed by Luft (’65).
Although the fenestrations observed
within the capillaries of the papillary layer
of the mouse enamel organ are fewer in
number per available surface area than
those reported within renal capillaries
(Rhodin, ’62), it can be assumed that they
provide for more rapid exchange than continuous or unfenestrated capillaries. Thus
the papillary layer is closely apposed to a
capillary network containing the morphological characteristics usually equated with
one specialized for increased permeability.
This evidence further substantiates the
current concept that the extra-ameloblastic
portions of the enamel organ are engaged
73
in some transport activity during the maturation of enamel.
ACKNOWLEDGMENTS
The authors wish to express their thanks
to Dr. John Nalbandian for his critical
evaluation of the manuscript and to Mr.
Allen Peeler for his technical assistance.
This work was supported in part by
U.S.P.H.S. research grant DE 01766 and by
training grant DE 00111 from the National Institute of Dental Research, National Institutes of Health.
LITERATURE CITED
Adams, D. 1962 The blood supply to the
enamel organ of the rodent incisor. Arch.
oral Biol., 7: 279-286.
Addison, W. H. F., and J. L. Appleton 1922
The vascularity of the enamel organ in the developing molar of the albino rat. Am. J. Anat.,
31: 161-189.
Bennett, H. S., J. H. Luft and J. C. Hampton
1959 Morphological classification of vertebrate
blood capillaries. Am. J. Physiol., 196: 381-390.
Bernick, S. 1960 Vascular supply to the developing teeth of rats. Anat. Rec., 137: 414-451.
Deakins, M. 1942 Changes in the ash, water,
and organic content of pig enamel during
calcification. J. dent. Res., 21: 429-435.
Decker, J. D. 1967 The development of a vascular supply to the rat molar enamel organ:
a n electron microscopic study. Arch. oral Biol.,
12: 453-458.
Elwood, W. K., and M. H. Bernstein 1965
Ultrastructure of the cells of the papillary layer
in the rat incisor. Anat. Rec., 151: 486.
Farquhar, M. G., and G. E. Palade 1965 Cell
junctions i n amphibian skin. J. Cell Biol., 26:
263-29 1.
Fawcett, D. W. 1963 Comparative observations
on the fine structure of blood capillaries. In:
The Peripheral Blood Vessels, edited by J. L.
Orbison and D. Smith. Baltimore: Williams &
Wilkins, pp. 1744.
Garant, P. R., and J. Nalbandian 1968 The
fine structure of the papillary region of the
enamel organ. Arch oral Biol., (in press).
Glasstone, S. 1962 Vascularization of enamel
organ in the rabbit and some rodents. Odont.
Tidskr., 70: 80-87.
Jordan, H. E. 1921 The comparative histology
of the enamel organ of the mammalian tooth
with special reference to its blood supply. Am.
J. Anat., 29: 379405.
Jump, E. B. 1938 Vascularity of the human
enamel organ. J. dent. Res., 17: 505-518.
Kallenbach, E. 1966 Electron microscopy of the
papillary layer of rat incisor enamel organ
during enamel maturation. J. Ultrastruc. Res.,
1 4 : 518-533.
Karnovsky, M. J. 1965 A formaldehyde-glutaraldehyde fixative of high osmolarity for use
in electron microscopy. J. Cell Biol., 27: 137A.
74
PHILIAS R. GARANT AND ROBERTA GILLESPIE
Kingery, H. M. 1924 The blood supply of t h e Pease, D. C. 1955 Electron microscopy of the
vascular bed of the kidney cortex. Anat. Rec.,
enamel organ in developing molar teeth of
121: 701-721.
mammals. Am. J. Anat., 33: 175-195.
Luft, J. H. 1961 Improvements in epoxy resin Reith, E. J. 1959 The enamel organ of the
rat’s incisor, its histology and pigment. Anat.
embedding methods. J. Biophys. Biochem.
Rec., 133: 75-90.
Cytol., 9: 409-414.
1961 The ultrastructure of ameloblasts
1965 The ultrastructural basis of capilduring matrix formation and the maturation
lary permeability. In: The Inflammatory Procof enamel. J. Biophys. Biochem. Cytol., 9:
ess, edited by B. W. Zweifach, vol. I, Chap. 3.
825-840.
pp. 121-159.
1963 The ultrastructure of ameloblasts
Mejno, G. 1965 Ultrastructure of the vascular
during early stages of maturation of enamel.
membrane. In: Handbook of Physiology, SecJ. Cell Biol., 18: 691-696.
tion 2, vol. 3, pp. 2293-2375, Am. Physiol.
Reith, E. J., and V. F. Cotty 1962 Autoradio.
SOC.,Washington, D. C.
graphic studies on calcification of enamel.
Arch. oral Biol., 7: 365-372.
Marsland, E. A. 1952 Histological investigation
1967 The absorptive activity of ameloof amelogenesis i n rats. 11. Maturation. Brit.
blasts durine the maturation of enamel. Anat.
Dznt. J., 92: 109-119.
Rec., 157: 577-588.
Prlay, S. L.,and L. J. Karlin 1959 An electron
microscopic study of the intestinal villus. 11. Rhodin, J. A. G. 1962 The diaphragm of capillarv endothelial fenestrations. J. Ultrastruc.
The pathway of f a t absorption. J. Biophys.
Re;., 6: 171-185.
Biochem. Cytol., 5: 373-384.
Weinmann, J. P., G. D. Wessinger and G. Reed
Pzppenheimer, J. R., E. M. Renkin and L. M.
1942 Correlation of chemical and histologBorrero 1951 Filtration, diffusion and moleical investigation on developing enamel. J.
cular sieving through peripheral capillary
dent. Res., 21: 171-182.
membranes. A contribution to the pore theory Williams, J. L. 1923 Disputed points and unof capillary permeability. Am. J. Physiol., 167:
solved problems in the normal and pathological
13-46.
histology of enamel. J. dent. Res., 5: 27-107.
Pr.rks, H. F. 1961 On the fine structure of the Yamade, E. 1955 The h e structure of the
parotid gland of mouse and rat. Am. J. Anat.,
renal glomerulus of the mouse. J. Biophys.
108: 303-329.
Biochem. Cytol., 1: 551-566.
-
PLATE 1
EXPLANATION OF FIGURES
Light micrographs of the papillary layer of the mouse incisor cut perpendicular (fig. 1) and parallel (fig. 2) to the developing enamel surface.
1 Alternating papillary projections of epithelial cells ( P ) and capillaries
( C ) overlying the reduced (post-secretory) ameloblasts (A). DS, dental sac; E, enamel. x 720.
2 Close apposition of the papillary cells (P) with the rich network of
capillaries (C). X 730.
FENESTRATED CAPILLARIES OF THE ENAMEL ORGAN
Philias R. Garant and Roberta Gillespie
PLATE 1
PLATE 2
EXPLANATION OF FIGURES
Electron micrographs of a portion of a fenestrated capillary in the
papillary region of the enamel organ.
76
3
Low power electron micrograph illustrating the attenuated endothelial wall ( E ) and portions of the closely apposed papillary cells (P).
Outlined rectangular areas are presented at higher magnifications
in figures 4, 5, and 6. BM, basement membranes; L, lumen; hl,
mitochondria; MV, microvilli; RBC, red blood cell. x 15,600.
4-6
High power electron micrographs of the endothelial wall containing
randomly spaced fenestrations (arrows). Note the presence of thin
diaphragms stretched across the fenestrations. Figures 4 and 5,
x 60,000. Figure 6, X 63,000.
FENESTRATED CAPILLARIES O F THE ENAMEL ORGAN
Philias R. Garant and Roberta Gillespie
PLATE 2
77
PLATE 3
EXPLANATION OF FIGURES
High power electron micrographs of the fenestrated endothelial wall.
7
The continuity of the capillary wall is interrupted by numerous
fenestrations (arrows). Note the many microvilli ( M V ) which increase the surface area of the adjacent papillary cell. x 40,000.
8 Portion of the endothelial wall containing two fenestrations (arrows)
one of which appears to be closed by a double diaphragm. BM,
basement membrane; Col, collagen fibers; L, lumen. X 45,000.
9
Two fenestrations (arrows) each with a centrally located button of
electron opaque material. Vesicle ( V ) possessing a similar diaphragm
and button ( B ) across its mouth. BM, basment membrane material;
L, lumen. x 114,000.
10 Fenestrations cut a t different angles illustrating their circular structure and centrally located button. CS, cross section; OS, oblique section; TS, tangential section. X 101,000.
78
FENESTRATED CAPILLARIES OF THE ENAMEL ORGAN
Philias R. Garant and Roberta Gillespie
PLATE 3
79
Документ
Категория
Без категории
Просмотров
0
Размер файла
711 Кб
Теги
presence, capillaries, papillary, layer, enamel, organy, fenestrated
1/--страниц
Пожаловаться на содержимое документа