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Journal of the Anatomical Society of India

Intra-Epithelial Capillaries In The Neuro-Epithelium Of Vomeronasal Organ In Adult Guinea Pig

Author(s): >Sangari, S.K., Sen Gupta, P., Pradhan, S. & Khatri, K.

Vol. 51, No. 1 (2002-01 - 2002-06)

Department of Anatomy, UCMS & GTB Hospital, Shahdara, Delhi-95. INDIA

Abstract

In adult guinea pig, the olfactory neuro-epithelium of the vomeronasal organ (thickness - 84 ± 3.34 mm) shows intra- epithelial capillaries, whereas the olfactory epithelium lining the rest of nasal cavity (thickness - 62 ± 5.36 mm) is avascular. The epithelial capillaries occupy an area of 0.0225 ± .0138 mm2/mm2 of the neuro-epithelium of the vomeronasal organ. The vascularisation of the neuro-epithelium of the vomeronasal organ and the association of the capillaries with the olfactory neurons may suggest nutritive and neuro-secretory control.

Key words: Vomeronasal organ, intra-epithelial, capillaries, neuro-epithelium.

Introduction:

As a rule, the epithelium is an avascular tissue in adults. However, the vascularity of the epithelium has been reported in growing foetal epithelial tissues like maternal layer of some epithelio-chorial placentae (Fawcett, 1986), neuro-epithelium of the neural tube and developing olfactory mucosa of mouse (Cuschieri & Bannister 1975, Herken et al, 1989). We observed intra-epithelial capillaries in the developing olfactory neuro epithelium in human foetuses whereas at birth the epithelium was avascular (Sangari et al, 2000).

Probably the degree of vascularisation of the embryonic neuro-epithelium constitutes an important developmental step in its functional maturation. (Fenney & Watterson, 1946; Caley & Maxwell, 1970). Persistence of neurogenesis in the adult olfactory neuroepithelium (Nagahara, 1940; Smith, 1951; Mulvaney & Heist 1971, Motulonis, 1974, 1975) prompted us to explore the possibility of vascularization of olfactory neuro-epithelium in a macrosmatic rodent, guinea pig.

Materials & Methods:

The study was conducted on 10 adult guinea pigs of either sex weighing between 200-250 gm. Under ether anaesthesia, the animals were sacrificed by perfusion with 10% formal saline. The nasal cavity was dissected out, decalcified in 10% EDTA and processed for paraffin sectioning. 7mm thick serial coronal sections of the nasal cavity were stained with haematoxylin and eosin, periodic acid Schiff, Van Gieson, Masson’s trichrome and Peter’s protein silver stains. The thickness of the olfactory neuro-epithelium lining the nasal cavity and the vomeronasal organ was measured at random in all the serial sections of the nasal cavity. The area occupied by intra-epithelial capillaries per square micron of the olfactory neuro-epithelium was quantitatively measured with the help of a square grid ocular micrometer and the data was statistically analysed.

Observations and results:

In serial coronal sections of the nasal cavity, the olfactory mucosa lines the posterior part of the roof, upper part of nasal septum and all the ethmoturbinals. The neuro-epithelium has a mean thickness of 62 ± 5.36 mm and is devoid of capillaries even in its thickest part. The vomeronasal organ is seen as a paired tubular structure with a crescentric lumen in the lower bony part of the anterior one third of the nasal septum. It opens into the vestibular part of the nasal cavity anteriorly by a narrow duct, lined by stratified squamous epithelium, whereas posteriorly it ends blindly. Its medial wall as well as the upper and lower margins are lined by olfactory neuroepithelium (mean thickness 84 ± 3.43 mm) while the lateral wall is lined by respiratory epithelium (Fig. 1).

The olfactory neuro-epithelium is pseudostratified columnar (fig. 2). The olfactory cells, sustentacular cells and basal cells of the epithelium rest on a linear basement membrane. The olfactory cells are bipolar neurons and their nuclei are arranged in 2-6 layers. The sustentacular cells are tall columnar cells with elongated heterochromatic nuclei, arranged in a row near the luminal surface of the epithelium. Small occasional basal cells rest on a basement membrane.

Intra- epithelial capillaries are observed only in the neuro-epithelium lining the vomeronasal organ. The basement membrane and the endothelial cells lining the capillaries are clearly outlined (Fig. 2, 3). The adjoining respiratory epithelium of the vomeronasal organ is avascular. The Intra-epithelial capillaries occupy an area of 0.0225 ± 0.0138 mm2/ mm2 of the neuro-epithelium of the vomeronasal organ (Table 1).

Table 1 : Area of intraepithelial capillaries in neuroepithelium of vomeronasal organ in adult guinea pig.

Serial No.
of Animals
Mean area
of capillaries
(mm2)/mm2 of
the vomeronasal
neuroepithelium
Standard
Deviation
±mm)
1. 0.0240 .0086
2. 0.0154 .0127
3. 0.0288 .0120
4. 0.0160 .0103
5. 0.0279 .0248
6. 0.0238 .0111
7. 0.0225 .0125
8. 0.0274 .0132
9. 0.0185 .0122
10. 0.0166 .0020
Total 0.0225 .0138

The underlying lamina propria is highly vascular but does not form vascular papillae. There are no interdigitations between the epithelium and the underlying lamina propria. The capillaries of the underlying lamina propria of the neuro-epithelium of the vomeronasal organ are seen piercing the basement membrane of the olfactory neuroepithelium and lie in close association with the olfactory neurons in the epithelium.

Discussion:

In the adult guinea pig, vascularisation is only seen in the neuro-epithelium lining the vomeronasal organ (mean thickness 84 ± 3.43 mm), whereas the olfactory epithelium lining the rest of the nasal cavity (mean thickness 62 ± 5.36 mm) is avascular even in its thickest part. The vascularity of the neuro-epithelium of the vomeronasal organ has also been reported by Cuschieri & Bannister (1975) in mouse and Breipohl et al (1981) in rat but there is no literature available on the quantitative estimation of the area of the neuro-epithelium occupied by the capillaries. In the present study, the epithelial capillaries occupy an area of 0.0225 ± .0138 mm2/ mm2 of the neuro epithelium of the vomero-nasal organ, In our previous study on human fetuses, we observed a statistically significant increase in the area occupied by capillaries in the olfactory neuroepithelium from 0.047 ± 0.01 mm2/mm2 of the neuro-epithelium at 12 weeks of gestation to 0.10 ± 0.02 mm2/mm2 at 24 weeks of gestation whereas at birth, neuro-epithelium was avascular (Sangari et al, 2000). Probably the vascularisation is related to the functional maturation of the neurons and the postnatal retreat of the vasculature to the underlying lamina propria may indicate direct gaseous exchange between the epithelium and the atmosphere. In contrast the vomeronasal organ in adult guinea pig is a paired tubular structure in the nasal septum and opens anteriorly into the main cavity by a narrow duct. Its comparatively thicker neuro-epithelium is not able to meet the metobolic demands by direct gaseous exchange and retains its blood supply throughout life for proper nutrition. Well developed vomeronasal organ in macrosmatic animals and its close association with the faculty of smell and olfacto-endocrine control, especially with reproductive behaviour is well documented. (Estes, 1972, Fleming et al., 1979; Meredith et al., 1980 & Kimmelman, 1993). Peripheral de-afferentation of the vomeronasal system, produces several sexual and maternal behavioural deficits (Powers and Winans, 1979; Fleming et al., 1979, Claney et al., 1984). The concentration of electron dense material in the smooth endoplasmic reticulum and collection of inclusion bodies in the nuronal perikarya of the vomeronasal organ suggests the neuro-secretory activity of the neuronal elements of the vomeronasal organ (Breipohl et al., 1981). It is further strengthened by the immuno-cytochemical and immunoelectron microscopic localization of the Salmon type ganadotropic releasing hormone in the olfactory neurons, olfactory nerves and olfactory bulb by Kudo et al in 1994. The presence of capillaries in close association with olfactory neurons could be an expression of the neurosecretory activity of the neuronal elements of the vomeronasal organ for the transport of secretion.

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Fig. 1 Photomicrograph showing the vomeronasal organ in guinea pig, olfactory epithelium (OE) lining the medial wall and respiratory epithelium (RE) lining the lateral wall. Masson’s Trichrome X 75.

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Fig. 2 Photomicrograph of olfactory neuro-epithelium of the vomeronasal organ olfactory neurons (ON), sustantacular cells (SC) and Basal cell (BC) resting on a basement membrane. The arrows show intraepithelial capillaries. The basement membrane of the capillaries and the lining endothelial cells are clearly visible. Haemotoxylin and Eosin X 300.

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Fig. 3 Photomicrograph of olfactory neuroepithelium of vomeronasal organ. Arrow points to the intraepithelial capillary. Periodic acid Schiff. X 750.

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