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Ultrastructural morphology of the normal nasal respiratory epithelium of the mouse.

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Ultrastructural Morphology of the Normal Nasal
Respiratory Epithelium of the Mouse
Anatomy Department, University of Kentucky, Lexington, Kentucky 40506
The nasal respiratory epithelium of the mouse has been studied
at the ultrastructural level. The tissue was found to be a rather typical pseudostratified columnar ciliated epithelium, superficially different but basically similar to tracheal and bronchial epithelium in the same species, and clearly similar
in most respects to that of other mammals. Four cell types were distinguished:
ciliated columnar, secretory (goblet), intermediate, and basal.
The ciliated cells, which exhibited typical surface cilia and microvilli, were
characterized by a distinct stratification in the arrangement of subcellular components in their supranuclear cytoplasm. Beginning at the apical end and proceeding basally, the following strata were seen: an ectoplasmic region relatively
free of organelles; an area rich in vesicular and tubular membrane profiles; a
mitochondria1 zone; a layer rich in ribosomes and polyribosomes; and a stratum
of Golgi complexes.
Secretory (goblet) cells were observed at various stages of secretion droplet
accumulation. Cells in the earliest stage, characterized by a dense content of
sER in the supranuclear cytoplasm, were similar to the “non-ciliated” cells of
the mouse’s lower respiratory tract. Some of the secretory cells contained dilated
cisternae of rER which were engorged with a relatively electron-dense material.
The possible significance of these inclusions is discussed.
Unlike the other cell types, intermediate and basal cells displayed no features
indicative of specialized function.
Increasing scientific interest in the
effects of tobacco smoke and environmental irritants on the respiratory tract
emphasizes the general need for continuing study of the structure and function of
respiratory mucosa. Experimental studies
in the senior author’s laboratory on the
respiratory system of the mouse have
occasioned the specific need for a description of the normal ultrastructure of respiratory epithelium of the nasal chamber in
that species. Although an adequate literature exists concerning the ultrastructure
of the lower respiratory tract of a number
of species, nasal respiratory epithelium
has received little attention, perhaps because of the difficulty or inconvenience of
obtaining tissue samples. Of the two accounts which constitute the available
relevant literature, one (Adams, ’72) deals
with the distribution of olfactory and nonolfactory epithelia of deer mice at the lightand scanning-electron microscopic levels.
ANAT. REC., 176: 65-81.
The other (Casorati et al., ’65) briefly describes certain ultrastructural aspects of
respiratory epithelium in the human nasal
cavity. The present paper is a more complete study of nasal respiratory epithelium
in the mouse and furnishes a reference
description for comparison with the appearance of tissues experimentally altered
by exposure to tobacco smoke.
Fifteen C57B1/6J mice provided by the
Kentucky Tobacco Research Institute were
used in the present study. Nasal respiratory
epithelium was obtained and processed for
electron microscopy by the following
Animals were anesthetized by intraperitoneal injection of 0.3 cm3 of 10%
nembutal. Entire nasal chambers were
quickly removed and placed into a 0.1 M
cacodylate-buffered 3.5% glutaraldehyde
Received Sept. 13, ’72. Accepted Dec. 22, ’72.
fixative (pH 7.4) at room temperature. The
cacodylate buffer contained 0.0032%
MgC1,. Nasal respiratory mucosa from the
dorsal portion of the nasal septum (Adams,
'72) was then carefully dissected while
immersed in this fixative. The remainder
of the 1.5 hour fixation was carried out at
4°C in the same fixative (Gomori, '52;
Sabatini et al., '63). Six 20-minute changes
of fresh 0.1 M cacodylate buffer containing
2% sucrose followed the initial fixation.
The tissues were then post-fixed in cacodylate-buffered 1% osmium tetroxide for one
hour at 4"C, dehydrated in graded ethanol
solutions at 4"C, passed through propylene
oxide at room temperature, embedded in
Epon 812 (Luft, '61, modified), and polymerized at 60°C for 48 hours.
Two blocks from each animal were sectioned with glass or diamond knives on
LKB or Sorval M-2 ultramicrotomes at
thicknesses of 400 to 800 A. Two grids,
sampling different levels of tissue, were
prepared from each of the blocks. Sections
were mounted on 300 mesh or 75 X 300
mesh uncoated grids. One-micron-thick sections stained with toluidine blue were prepared for orientation and light microscopic
Thin sections stained with lead citrate
for two to three minutes were examined
in a Siemens Elmiskop 1 at 60 KV. Exposures were taken at magnifications of 1500
to 13,000 X and enlarged as required.
General observations. The general character and histological arrangement of cellular constituents of the nasal respiratory
epithelium of the mouse is a typical example of pseudostratified columnar ciliated
epithelium. Four cell types were distinguished: ciliated columnar, secretory (goblet ), intermediate, and basal. Underlying
a distinct basal lamina, several strata of
collagenous fibrils formed the classical
basement membrane. The epithelial surface was free of mucus and debris.
Ciliated columnar cells were the most
numerous cell type encountered in nasal
respiratory epithelium. Typical cilia, the
most prominent surface feature of these
cells (figs. 1, 2), were present on a large
central part of the apical cell surface but
absent from a peripheral border area (fig.
1 insert). Microvilli, approximately 150
mp in diameter and considerably shorter
than the cilia, were distributed relatively
uniformly over the entire apical surface,
intermingling with the cilia centrally. Fine
hair-like filaments approximately 80 mp
long and 15 ma in diameter projected at
right angles from the surfaces of the micro*
(fig. l insert). The cilia were devoid of such projections.
The outstanding characteristic of the
supranuclear cytoplasm of ciliated cells
was a rather distinct stratification into five
layers. Immediately beneath the apical
plasma membrane a layer of amorphous
ectoplasmic matrix contained the basal
bodies and rootlets of cilia (fig. 2) and
occasionally a few ribosomes, smoothmembrane vesicles, and microtubules.
Small vesicular and tubular membrane profiles were the major constituents of the
neighboring stratum, which also contained
a scattering of ribosomes and small rough
endoplasmic reticulum (rER) profiles (fig.
2). The third layer was conspicuous for
its rich content of mitochondria (figs. 1,
2). These organelles were round to elongate in shape. Their cristae were irregularly arranged, and in some cases formed
rather unusual honeycomb configurations
(fig. 2 insert). Their matrix commonly
contained electron-dense particles. Among
the mitochondria of this layer numerous
small vesicles, elongate membrane profiles,
ribosomes, polyribosomes, rER, and microtubules were dispersed (fig. 2). In certain
cells this cytoplasmic stratum also contained electron-dense lysosome-like bodies
and multivesicular bodies. A concentrated
aggregation of ribosomes and polyribosomes formed the fourth layer. A number
of large well-developed Golgi complexes
constituted the fifth layer (figs. 1, 2),
which was just above the nucleus. The
cytoplasm below the nucleus contained
typical organelles with no particular pattern of arrangement.
The elongate nuclei, which frequently
exhibited prominent infoldings, were situated in the upper part of the basal half of
the ciliated cells (fig. 1). Their longitudinal
axis was parallel with that of the cells.
Heterochromatin was usually concentrated
near the nuclear envelope. Nucleoli were
small, dense, and rounded in form (fig. 1).
The ciliated cells were related to one another by small tripartite junctional complexes apically and by complex cytoplasmic
interfoliations laterally.
Secretory (goblet) cells were markedly
different in appearance from the more
numerous ciliated cells, resembling them
only by being tall cells with microvilli on
their luminal surface (fig. 3) and by passessing similar multivesicdar and dense
lysosome-like bodies (figs. 2, 3) in addition to the usual complement of organelles.
The ground cytoplasm of secretory cells
appeared darker than that of ciliated cells
(fig. 1 ) . The lateral surfaces of secretory
cells lacked foliate processes; they were
attached to neighboring cells by small tight
junctions apically and by a few desmosomes at lower levels. Although membrane
bounded secretion droplets were of course
the outstanding morphological feature of
this cell type, secretory cells which were
apparently devoid of droplets were easily
recognizable by other cytoplasmic characteristics. Stages of accumulation of secretion droplets ranging from total absence to
extreme abundance were seen in the secretory cell population of every sample of
tissue studied.
The supranuclear cytoplasm of secretory cells containing few or no secretion
droplets was characterized by a dense content of round and elongate profiles of sER
(fig. 3 ) . It also contained numerous mitochondria, a number of lysosome-like inclusions, and a scattering of rER and free
ribosomes. Golgi complexes, some well developed, were located just above the nucleus (fig. 3 ) . The nuclei of these cells contained prominent nucleoli and were
rounded or elongate in shape. The elongate
ones were situated with long axis parallel
to that of the cell. Most of their heterochromatin was located adjacent to the nuclear envelope but some was scattered
throughout the nucleoplasm. The infranuclear cytoplasm, which contained some rER
plus a number of mitochondria presented
no unusual features.
Cells which appeared to be in relatively
early stages of droplet accumulation
showed increased amounts of rER in the
supranuclear cytoplasm. A large supranuclear Golgi complex embracing secretion
droplets of various sizes was seen occasion-
ally but not frequently. The complement of
dense sER in these cells was relatively reduced in amount, and now occupied only
the apical half of the supranuclear cytoplasm. Intermediate stages of droplet accumulation were characterized by a considerable increase in supranuclear rER the
large flat cisternae of which was densely
packed in parallel arrangement. The main
mass of droplets in these cells were located
in the most apical region (fig. 4 ) , an area
formerly occupied almost exclusively by
sER and mitochondria. The surfaces of
many of these droplets showed minute
continuities with those of neighboring
droplets (fig. 4 ) , possibly reflecting an
early stage of droplet fusion and possibly
reflecting a fixation artifact.
In advanced stages of accumulation the
secretion droplets were numerous enough
to distend the supranuclear half of the cell
laterally and apically (fig. 1). The secretory material generally exhibited two degrees of density. Most cells which were full
of secretion antecedents possessed a large
number of lighter or clearer droplets and a
smaller number of darker or denser ones
(figs. 1, 6 ) . Other cells contained droplets
where secretion material appeared dense
in the center and clear at the periphery
(figs. 1,5).
The above description applies to the
majority of secretory cells in nasal respiratory epithelium of the mouse. Some of the
cells of this type exhibited an additional
noteworthy feature in the form of dilated
cisternae of rER containing a relatively
homogenous, electron-dense material (fig.
7). These dilated cisternae or sacs varied
considerably in size, some being smaller
than secretory droplets while others were
many times larger. Large and small inclusions of this type were usually dispersed
randomly in the cells (fig. 7), but smaller
sacs were sometimes concentrated near
the apical surface. Numerous examples of
the continuity between dilated sacs and
ordinary flat cisternae were evident (fig.
8). The matrix density of the rER-bound
material was somewhat similar to that of
the denser homogenous material in the
secretory droplets (figs. 8, 10).
In most cells the dilated rER sacs were
intermingled with ordinary flat rER profiles (figs. 7, 8). Occasionally, however,
they were in very close association with
mitochondria (fig. 9). Various sizes of
dilated rER sacs were also intermingled
with ordinary secretory droplets (fig. 10).
In places the larger rER sacs seemed to be
constricting to form vesicles of a size comparable to that of secretory droplets (fig.
11). However, coalescence of smaller droplets to form larger sacs cannot be ruled
out. Not all cells containing secretory droplets contained rER-bound pools of material,
but cells in which rER-bound pools were
observed usually contained ordinary secretory droplets. It was also noted that in
some animals the population of cells containing the dilated rER sacs was greater
than in other animals.
Basal and Intermediate cells. The basal
cells were often difficult to distinguish
from basal parts of secretory cells since
the density of cytoplasm was similar in
both cell types (fig. 1). However, in general
the basal cell profiles were triangular and
were located in the most basal region of
the epithelium adjacent to the basal lamina
(fig. 12). In most cases the axes of their
somewhat elongate nuclei were oriented in
the horizontal plane (fig. 12) rather than
vertically as was the case with all other
cell types within this epithelium. Relatively
large amounts of heterochromatin were
present in the nuclei, The nucleoli contained electron-dense particles similar in
size to the cytoplasmic ribosomes (fig. 12).
The ratio of nucleoplasm to cytoplasm was
larger in basal cells than in any of the
other cell types.
The most numerous subcellular structures in basal cells were ribosomes, polysomes, and mitochondria (fig. 12). The
membranes of some cells were irregular
and interdigitated with adjacent cells. In
several instances a solitary cilium was seen
projecting from the basal cell into the intercellular space. Desmosomes between
basal and adjacent cells were observed
(fig. 12), but they were sparse and poorly
Intermediate cells were wedge-shaped,
taller, and considerably more slender than
the basal cells (fig. 1 ). The cell nuclei were
oriented in a vertical plane. In all other
respects the intermediate cells were similar
to those of the basal cells.
In this investigation the nasal respiratory epithelium of the mouse was found to
be a rather typical example of respiratory
epithelium, similar in many respects to
that of tracheae (Osada, '64; Cirili, '66;
Komadova, '66a,b, '67; Rhodin, '66; Hansell and Moretti, '69) and bronchi (Watson
and Brinkman, '64; Frasca et al., '68;
Baskerville, '70) of various mammals including the mouse. At the same time, however, it has revealed some differences and
some interesting features.
CiZiated cells of the nasal respiratory
epithelium were similar to those described
for the tracheae (Rhodin, '66; Hansell and
Moretti, '69) and bronchi (Frasca et al.,
'68; Baskerville, '70) of various species,
especially in point of relative abundance,
dimensions of cilia and microvilli, and arrangement of intracellular components.
Stratification of subcellular components in
the supranuclear cytoplasm is a conspicuous feature of the nasal ciliated cell of the
mouse. A similar preferential arrangement
of components is noted with varying degrees of emphasis by other authors: e.g.,
Frasca et al., ('68) describe four strata in
bronchial ciliated cells in the dog; Hansell
and Moretti ('69) remark that mitochondria are concentrated beneath the cilia and
that the Golgi complex is apical to the
nucleus in tracheal cells of the mouse;
Baskerville ('70) calls attention to the
supranuclear location of numerous mitochondria in bronchial cells of the pig. The
functional significance of this stratification, apart from that suggested by the
relatively close relationship between mitochondria (energy sources) and cilia (energy consumers), is not immediately apparent.
Cytoplasmic glycogen stores, present in
bronchial ciliated cells in the pig (Baskerville, '70) and dog (Frasca et al., '68),
were sparse or absent in nasal ciliated cells
of the mouse. Hansell and Moretti ('69)
likewise apparently did not find appreciable amounts of glycogen in ciliated cells
of the trachea of the mouse.
Nasal respiratory epithelium of the
mouse contained no "dark" ciliated cells
corresponding to those found by Hansell
and Moretti ('69) in the trachea of the
same species. It did not contain elements
corresponding to the “special-type’’ cells
described in the bronchi of dogs (Frasca
et al., ’68) and the trachea of humans
(Miani et al., ’71). Nor did it contain any
of the brush cells that occur in the tracheae
of man (Rhodin, ’66) and the rat (Rhodin
and Dalhamn, ’56) or chemoreceptor cells
of the sort described by Lucian0 et al.
(’68). The basal cells displayed no noteworthy features. Intermediate cells differed
from their counterparts in human trachea
(Rhodin, ’66) by touching the connective
tissue substratum instead of resting on the
upper surfaces of basal cells.
It will be recalled that several stages of
accumulation of secretion droplets were
found in the secretory cell population of
the nasal respiratory epithelium under
study. This observation accords with the
general description of nasal respiratory
epithelia by Schaeffer (’28) and is therefore probably a general feature of such
epithelia. It also contains the basis for reconciling a rather conspicuous apparent
difference between nasal and lower-tract
epithelia in the mouse. Tracheal (Hansell
and Moretti, ’69) and bronchiolar (Karrer,
’56; Kotin et al., ’66) epithelium in this
species are virtually devoid of goblet cells
but contain numerous “non-ciliated” cells
which are probably secretory in function.
Nasal secretory cells in the earliest phases
of droplet accumulation were observed to
be very similar if not identical to the “nonciliated cells of the lower respiratory passages of the mouse. It thus appears that the
difference between upper- and lower-tract
secretory cells is not one of kind but one
of degree of development, cells of the secretory type developing freely into goblet
cells in the upper tract but failing to do
so in the lower. This being the case, the
nasal passages of the mouse exhibit the
structural basis for a typical “mucus escalator” mechanism while the lower tract
does not. Hansell and Moretti (’69) adduce
grounds, however, for a reasonable presumption that non-ciliated cells in the
trachea of the mouse fulfill the functional
role of goblet cells in the tracheae of other
Nasal goblet-type cells in the mouse resembled goblet cells in respiratory epithelia
of other species in a number of respects.
A similar electron-density of the ground
cytoplasm is also found in other animals,
e.g., dog (Frasca et al., ’68), pig (Baskerville, ’70), and man (Rhodin, ’66). Differing degrees of density of secretion droplets within individual cells are generally
depicted if not described in respiratory goblet cells of other species.
An unusual feature of the goblet-type
cell population in the nasal mucosa of the
mouse suggests the possibility that there
may be two sub-types of goblet cell in this
epithelium. Some of the goblet cells had
dilated cisternae or sacs of rER which were
engorged with a relatively dense, presumably proteinous material. The content of
these inclusions resembled that of the
denser secretion droplets in electron-density and was often found in spheroidal vesicles of a size similar to that of ordinary
secretion droplets. Such observations suggest that these inclusions may represent
stages of a secretory process in which secretory material formed in the rER bypasses the Golgi complex. Given the fact
that only morphological data are available
at present it would not be profitable to enlarge on this possibility. More extensive
studies addressed to a similar possibility in
the pancreatic beta cell (Legg, ’67; Nakayama et al., ’71) and the fibroblast (Porter,
’64; Ross and Benditt, ’65; Ashhurst, ’68)
have not yet removed all traces of controversy. A perhaps equally plausible “explanation” for the engorged rER inclusions is
that they result from a defect in the mechanism by which materials are transported
from rER to Golgi complex. A similar problem of interpretation has also been encountered by Williams and Jew (’71) in
sheath cells (cells of Schwann) in sympathetic ganglia. It is of interest in this
connection that Frasca et al. (’68) describe the “usual” rER-Golgi relationship
in canine bronchial goblet cells, in which
cisternae of rER, containing a dense material, extend “smooth-surfaced outpocketings” toward the adjacent Golgi complex.
In any event the significance of the engorged rER cisternae in some of the goblet cells of the nasal mucosa of the mouse
can only be speculated upon at present. It
is hoped that autoradiographic studies currently in progress in the senior author’s
laboratory will shed light on this problem.
Legg, P. G.
1967 The fine structure and inner-
vation of beta and delta cells in the islets of
The present investigation was supported
Lanperhans of the cat. 2. Zellforsch., 80:
by the Kentucky Tobacco and Health Re307-321.
search Institute grant 124-05-83230-24028. Luciano, L., E. Reale and H.Ruska 1968 tfber
eine “chemorezeptive” senneszelle in der
The authors wish to express their gratitude
trachea der ratte. 2.Zellforsch., 85: 350-375.
to Mrs. M. G. Birk for her highly skilled
Luft, J. H. 1961 Improvement in epoxy resin
technical assistance.
Adams, D. R. 1972 Olfactory and non-olfactory epithelia in the nasal cavity of the mouse.
Peromyscus. Am. J. Anat., 133: 37-50.
Ashhurst, D. E. 1969 Fibroblast -Vertebrate
and Invertebrate. Chap. XIX. S. M. McGeeRussell and K. F. A. Ross, eds. Edward Arnold
Pub. Ltd., London, pp. 237-249.
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bronchial epithelium of the pig. Souder. Zentra.
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1965 Ultrastruttura della porzione respiratoria della mucosa nasale umana. Ann. 1st.
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des epithels der oberem luftwege der ratte. Zeit.
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principles and practice. Chicago, Illinois; Univ.
Chicago Press.
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1966b A study of the involution of
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1967 Ultrastructure of the tracheal
epithelium in children. Cesk Pediat., 22: 25-28.
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Ross, R., and E. P. Benditt 1965 Wound healing and collagen formation. V. Quantitative
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1963 Cytochemistry and electron microscopy.
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the Nasal Cavity and the Paranasal Sinuses.
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Pseudostratified nasal respiratory epithelium depicting ciliated columnar cells (C), secretory cells (S), wedge shaped intermediate cells
( I ) and basal cells (B). Insert depicts microvilli (Mi) between two
ciliated cells. Note the hair-like projections (arrow) of the latter.
Double arrows indicate sharp indentations of nuclei in ciliated cells.
Secretory droplets, Sd; rough endoplasmic reticulum, rER; basal
lamina, B1; lysosome-like bodies, L. x 4,350,insert X 16,500.
Daniel H. Matulionis and Harold F. Parks
Ciliated columnar cells depicting areas of concentrated subcellular
structures; ectoplasmic region, E; smooth membrane and vesicle
area, SV; mitochondrial zone, M Z ; ribosome and polyribosome zone,
RP; and Golgi complex region, G. Insert depicts unusual honeycomb
arrangement of mitochondrial cristae arrangement (arrow). Lysosomelike body, L; multivesicular body, Mb; ciliary basal body, BB; Rootinsert x 19,600.
lets, R. ><16,500,
Daniel H. Matulionis and Harold F. Parks
Immature secretory cell without secretory droplets. Note the extensive
smooth endoplasmic reticulum (sER). Mitochondria, M; ribosomes,
R; lysosome-like bodies, L; Golgi complex, G; microvilli, Mi; heterochromatin, H; lumen of the nasal chamber, Lu. x 16,500.
Mature secretory cells with m a n y secretory droplets (Sd) some of
which are fusing (arrow). Lumen of the nasal chamber, Lu. x 23,600.
Daniel H. Matulionis and Harold F. Parks
Secretory droplets (Sd) in the apical portion of a secretory cell. Note
the more electron dense centers and somewhat manular oeriuheral
areas of the droplets. Some of the droplets have fused- (arrow).
X 16,500.
Secretory cell in the process of secretion, depicting secretory material
(SM) which has fused into large continuous masses. Electron dense
secretory droplet, Sd. X 6,850.
Secretory cells ( S ) depicting various sizes of unusual variations of
rough endoplasmic reticulum (UER).Ciliated cells, C; secretory droplets, Sd; rough endoplasmic reticulum, rER. x 4,350.
Daniel H. Matulionis and Harold F. Parks
Secretory cell depicting a continuity of normal rough endoplasmic
reticulum (rER) with the unusual dilated sacs (UER). Note the
similar density of material in the dilated sacs of rough endoplasmic
reticulum (UER) and the secretory droplets (Sd). x 23,600.
9 Secretory cell depicting a large pool of rER bound material (UER)
closely associated with mitochondria ( M ) . Nuclear envelope, Ne.
10 Apical region of a secretory cell depicting a close association between
rough endoplasmic reticulum bound pools of material (UER) and
secretory droplets (Sd). Note the similar density of material in the
two structures. X 25,600.
Daniel H. Matulionis and Harold F. Parks
Supra-nuclear region of a secretory cell depicting many profiles of
dilated rER sacs (UER). Some of the larger sacs might be pinching
off into smaller rER bound vesicles (arrow). x 19,700.
12 Triangular basal cell adjacent to the basal lamina (Bl) depicts
nucleolar particles (arrow) which are similar in size to the cytoplasmic ribosomes. Desmosome, D; ciliated cell, C. x 19,700.
Daniel H. Matulionis and Harold F. Parks
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ultrastructure, morphology, epithelium, respiratory, mouse, nasal, norman
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