| dc.description.abstract | The qualitative and quantitative features of the olfactory mucosa of the
domestic dog and sheep were examined at light, scanning and
transmission electron microscopy. Samples were obtained from adult
and young (suckling) male dogs and sheep, each represented by groups
of five animals comprising of dogs aged 15 - 24 months, puppies 4 - 6
weeks, sheep 12 - 19 months and lambs 3 - 6 weeks. The dogs and
puppies were crosses between German shepherd and Rottweiler breeds
while the sheep and lambs were dorpers. Variations in morphometric
parameters between groups were analyzed using the Student's t-test,
considered statistically significant at p < 0.05 and expressed as mean ±
standard deviation (SO)
The olfactory mucosa occupied the caudal roof of the nasal cavity where
it lined the ethmoturbinates, which were relatively longer and with
prominent folds of lamellae in the dogs and puppies. The mucosa
comprised of an epithelium and a lamina propria. The epithelium was
pseudostratified columnar and had the olfactory, supporting and basal
cells as its principal cell types. It comprised of three histological zones
named from the surface inwards as the free, non-nuclear and nuclear
zones. Within the nuclear zone, each cell type established its own layer
of nuclei identified as an upper layer of supporting cells, a middle layer of
olfactory cells and a basal layer of progenitor (basal) cells.
The thickness of the olfactory epithelium varied among the species,
being significantly thicker in the dogs (72.5 ± 2.9 urn) than in sheep (56.8
± 3.1 urn) and in puppies (64.7 ± 1.7 urn) than in lambs (47.8 ± 3.8 urn).
In both species, the thickness of the epithelium increased with age
(between suckling and adult age), with the olfactory cell nuclear layer
contributing more to its thickening in the dog (25.9 %) than in sheep
(13.1 %). Further, cell counts (per square millimeter) showed a
significantly higher number of olfactory cells in the epithelium of the dog
(81,667 ± 7,177 mm") as compared with that of the sheep (46,667 ±
4,924 mm'"), and an insignificant difference in the puppies (66,667 ±
4,924 mrn'") and lambs (63,333 ± 4,924 rnrn").
Within the non-nuclear zone of the olfactory epithelium, the dendrites of
the olfactory cells were identified by their electron-Iuscent appearance
and were joined to the apical segments of the supporting cells by
occluding junctions. On the surface of the epithelium, the dendrites
terminated by forming cilia-bearing knobs, whose width was significantly
greater in the dogs (2.9 ± 0.1 urn) than in sheep (1.9 ± 0.2 urn), though
not significantly different in the puppies (1.8 ± 0.3 urn) and lambs (1.7 ±
0.1 urn). Microvilli arising from the apical surfaces of the supporting cells
intermingled with the dendritic cilia to form a dense tangle of the free
zone of the epithelium, which was significantly thicker in the dogs (4.6 ±
0.3 IJm) than in sheep (3.6 ± 0.3 IJm) and in the puppies (3.3 ± 0.4 IJm)
than in lambs (2.6 ± 0.2 IJm).
Marked interspecies variations were noted with regard to the number,
length and diameter of the cilia sprouting from the dendritic knobs. In the
dog, a thick mesh of cilia whose number averaged 19 in dogs and 18 in
puppies radiated from the entire circumference of the knob while in the
sheep, a bunch with a mean cilia number of 7 in sheep and 9 in lambs
projected from the apical end of the knob. The cilia were significantly
longer in the dog (1.9 ± 0.2 IJm) than in sheep (1.6 ± 0.2 IJm) and in the
puppies (1.7 ± 0.1 IJm) as compared with lambs (1.4 ± 0.1 IJm). Similarly,
the cross-sectional diameters of the cilia were significantly larger in the
dogs (0.29 ± 0.01 IJm) than in sheep (0.23 ± 0.01 IJm) and in the puppies
(0.25 ± 0.01 IJm) than in lambs (0.20 ± 0.01 IJm).
The lamina propria of the olfactory mucosa contained many Bowman's
glands and bundles of olfactory nerve axons. The glands were
tubuloacinar and were mainly located in the superficial region of the
propria. Their acini comprised of pyramid-shaped secretory cells, which
emptied their serous secretion on the surface of the epithelium through
narrow vertical ducts. As depicted by the product of their lengths and
breadths, the acini of the glands were significantly bigger in the dogs
(1,416.8 ± 70.8 urn") than in sheep (1,243.0 ± 45.9 ~m2) and in the
puppies (1,015.8 ± 42.3 urn") than in lambs (718.7 ± 23.5 urn"). On the
other hand, the olfactory bundles were confined to the deep part of the
propria where they were separated by collagen containing clefts and
enveloped by a sheath of fibroblastic processes. Within each bundle, the
axons were packed in hundreds of fascicules, which were in turn
ensheathed by sheets of Schwann cell processes. The cross-sectional
diameters of the bundles were significantly larger in the dogs (73.3 ±
10.3 urn) than in sheep (50.6 ± 6.8 urn) and in the puppies (68.2 ± 9.9
urn) than in lambs (43.8 ± 5.7 urn), Unlike in the sheep and lambs, one
to three blood capillaries were contained within each nerve bundle in the
dogs and puppies.
In conclusion, the morphologic and morphometric results of this study
showed that the mucosa of the dog is structurally more specialized than
that of the sheep. This may partly be explained by the differences in their
feeding and reproductive habits, where the olfactory sense is essential
for both feeding (hunting) and reproduction (mating) in the dog while in
the sheep, olfaction is of main importance only in the control of
reproductive events such as mating, estrus and maternal offspring
recognition. | en |
