MORPHOLOGICAL STUDY OF THE VAGINA OF THE Myocastor coypus (COYPU)

ESTUDIO MORFOLOGICO DE LA VAGINA DE Myocastor coypus (COIPO)

*	Antonio E. Felipe
*	Alejandra Castro
**	Santiago S. Callejas
**	Jorge A. Cabodevila

 

FELIPE, A. E.; CASTRO, A.; CALLEJAS, S. S. & CABODEVILA, J. A. Morphological study of the vagina of the Myocastor coypus (Coypu). Rev. Chil. Anat., 18(2):231-235, 2000.

SUMMARY: The Myocastor coypus (coypu) is a medium size rodent internationally considered as a species of economic interest because its fur. The aims of this work was realized the morphological study of the vagina of coypu. The vagina of sexually mature coypus appeared as a tubular organ, 10.25±1.40 cm long. The vaginal wall was very thin. It was composed by four layers: mucosa, submucosa, muscularis, and adventitia or serosa (according to the region). The lining epithelium of the mucosa was squamous stratified and without glands. Two layers of smooth muscular tissue with abundance of connective tissue were differentiated in the muscularis. The tunica serosa, formed by connective tissue of dense aspect, had numerous big blood vessels.

KEY WORDS: 1. Vagina; 2. Myocastor coypus; 3. Morphology. INTRODUCTION

The Myocastor coypus (coypu or South-american nutria) is a South-American rodent, member of the Capromyidae family (Catzeflis et al., 1995) that has been internationally bred under semicaptivity and captivity conditions to obtain its fur (Colantoni, 1993). Studies on the reproductive aspects of this species have been made in the northern hemisphere with naturalised populations or with animals from breeding farms (Newson, 1966; Ehrlich, 1966; Gosling, 1974) and in Argentina with native populations (Crespo, 1981) or with populations from breeding farms (Iudica & Alberio, 1995).

Among recent studies on the reproductive apparatus of the coypu there are references to cyclic changes in the vaginal epithelium during the estrual cycle described by exfoliative cytology. A terminology commonly applied to other species has been used to classify the cellular types present in the samples obtained (Cabodevila & Callejas, 1992; Iudica & Alberio).

The situation thus abridged tends to favour comparative analyses, but specific studies on the vaginal anatomy and histoarchitecture of the coypu are still lacking since there are only brief references about this organ in general works on the reproductive apparatus (WEIR, 1974; Kulisek et al., 1988; BURA et al., 1992; FELIPE et al., 1998). A specific analysis of the vagina of the coypu would make possible to interpret the observations in function of its own model.

Therefore, the aims of this work was to contribute with a characterisation of the anatomy and histology of the vagina of the Myocastor coypus at sexual maturity that could be useful as a basic model for the analysis and interpretation of the variations at different reproductive stages.

MATERIAL AND METHOD

Twenty virgin sexually mature females of the Silver and Greenland mutations were used. Their ages were between 6 and 9 months. The females were obtained from a breeding farm with corral system and had an average weight of 4.71±0.29 kg.

The anatomical description was realised "in situ". The complete genital organs were removed to observe the organs in isolation, which allowed deepening in the details and the study of the internal conformation. For the histoarchitectural study the vagina was sectored and fixed in Bouin's fluid. Samples were taken from 7 sectors: 1­ caudal sectors of the vagina parallel to the anal sac, 2 and 3 ­ mid sectors of the vagina between anal sac and bladder, 4 ­ mid sector parallel to the bladder, 5 ­ sector between the bladder and the cervix, 6 ­ sector parallel to the cervix, and 7­ sector of the vaginal fornix. Routine techniques were used to process the samples until embedding in paraffin wax. Semi-serial 5mm-thick cuts of the sectors were made and were stained with haematoxylin/eosin, Mallory´s trichromic, and van Gieson´s trichromic (LYNCH et al., 1980). The schemes and the morphological analysis were made with a Wild M3C stereoscopic microscope equipped with drawing camera. The mean thickness of each tunica and of the epithelial layer of the mucosa was determined. In the epithelial layer the size of each cellular type was determined starting from the mean of two diameters at a right angle. Measurements were taken in each one of the sectors in five cuts every 200 microns. Macroscopical measurements were made with Vernier calliper and microscopical measurements were made with a micrometric ocular. All measurements were expressed as the mean ± sd.

RESULTS

Macroscopic analysis: The vagina of the Myocastor coypus appeared as an elongated tube, dorsoventrally flattened and 10.25±1.40 cm in long. The vagina occupied a mid position in the pelvic cavity, relating towards dorsal with the rectum and separated from it by a peritoneal cul-de-sac, the rectogenital pouch (Figure 1). This last extended until the middle part of the ischium and from that point towards caudal it was related with an area of thick connective tissue, the pelvic fascia. Towards ventral, the vagina was related with the urethra and the bladder (Figure 1).

Fig. 1. Schematic lateral view of the vagina of M. coypus and schemes of transversal sections.

The vagina showed a very thin and transparent wall. The lumen was ovoid in latero-lateral direction, with a dorsoventral diameter of 0.56±0.50 cm and a latero-lateral diameter of 1.57±0.73 cm. In the cranial area of the organ's lumen the projection of the cervix reduced the vaginal lumen, forming a ring-shaped space (fornix), subdivided into five cul-de-sacs separated by short septa. The caudal portion of the vagina, at caudal of the ischiatic arc, inclined ventrally until its opening in the vulva. Here, a marked inflexion with the bodily axis, at an angle of almost 45 degrees, was observed. At first sight, the vaginal mucosa appeared very folded in different directions, giving an irregular and rugose aspect to the internal conformation of the organ. There were no traces of the membrane of vaginal occlusion.

Histoarchitectural analysis: The thickness of the vaginal wall was of 305.6±17.5 µm. Four layers were seen in the vaginal wall: mucosa, submucosa, muscularis, and adventitia or serosa. There was no delimitation between the subepithelial connective tissue, corresponding to the lamina propria of the mucosa, and the connective tissue near the tunica muscularis, equivalent to the submucosal layer.

The lining epithelium was of the squamous stratified type and without glands, having a thickness of 17.8±4.9 µm. In none of the specimens analysed there was mucification of any of the sectors. The following description corresponds with the cellular layers observed in the epithelium of the coypu:

1 ­ Deep layer: it was possible to distinguish two cellular strata. The inner was called stratum of basal cells, and the outer was called stratum of parabasal cells. The stratum of basal cells was composed of a row of prismatic cells, forming a palisade, with big ovoid nuclei and perpendicular to the surface of the epithelium (height of 7.6±1.4 µm and width of 3.8±1.1 µm). The height of the cells was of 14.7±2.2 µm and its width of 5±0.9 µm). The stratum of parabasal cells was formed by two to three rows of ovoid cells, with big and vesicular nucleus (height of 8.2±0.5 µm and width of 5.9±0.7 µm). The height of the cells was of 14.3±1.8 µm and its width of 12.4±1.2 µm.

2 - Intermediate layer: this layer was formed by 6 to 10 cellular rows. The cells nearer to the deep layer were ovoid, with smaller and rounded nuclei, in central or eccentric position, some of them slightly vesicular (width of 5.2±0.5 µm and height of 10.7±1.1 µm). The height of these cells was of 7.1±0.7 µm and their width of 15.9±2.4 µm. The rows of cells nearer to the superficial layer of the epithelium were slightly flattened, with a height of 6.1±0.8 mm and a width of 14.5±1.7 µm. This cells had ovoid nuclei somewhat flattened and of prepyknotic aspect (height of 4.6±0.5 µm and width of 9.5±0.5 µm).

3 - Superficial layer: four to eight rows of flattened cells were observed in this layer. Those cells nearer to the intermediate layer had flattened or pyknotic nuclei, with punctuate and hyperchromatic aspect, and the rows next to the surface showed neither nuclei nor nuclear remains (cariorrexis). The width of the cells of this layer was of 21.3±2.1 µm and their height of 1.9±0.8 µm.

The area represented by the lamina propria and submucosal layer had a thickness of 98.5±16.01 µm, with values that oscillated between 169.6 µm in the widest zones and 39.2 µm in the narrowest ones. The histological appearance of the zone nearer to the epithelium (lamina propria) had some differential characteristics with respect to that nearer to the muscular layer (submucosa). In the subepithelial zone there was abundance of connective tissue, rich in cells and collagen fibres and with abundance of blood vessels of small calibre. The junction between the connective tissue of this layer and the superficial epithelium was very irregular due to the presence of numerous connective papillae that projected towards the base of the epithelium. The submucosal layer was formed by moderately dense, irregular connective tissue near to the previous zone, thickening towards the muscularis and by many blood vessels of various diameters. In all the lamina propria there was a diffuse lymphocytic infiltration but the conformation of lymphoid nodes was not observed.

Two layers of smooth muscular tissue with abundance of connective tissue were differentiated in the muscularis. The muscular layers had little development and were very vascularized. In the internal muscular layer there was an interwoven arrangement of the fibres, with predominance of those orientated in a circular direction. The width was of 82.66±18.77 µm. In the outer layer, 103.66±21.81 µm thick, the fibres arranged longitudinally. In the sections at the vaginal fornix level it was observed the separation of the external muscular layers of the vagina and the uterus by an area of richly vascularized connective tissue. At uterine neck level, the fusion of the longitudinal muscular layers of uterus and vagina appeared already complete, with a marked interweave of muscular fibres. In the caudal region of the vagina the external muscular layer was associated to a layer composed of numerous fibres of striated muscle.

In the cranial sector (vaginal fornix and area parallel to the external ora) there was a tenuous serous layer. An adventitial layer lined the rest of the vagina. This layer, formed by connective tissue of thick aspect had many big blood vessels, particularly in the cranial sector. In this same sector of the vagina and within the adventitial layer, there were isolated muscular bunches. Between the adventitia and the muscular layer there was a vascular stratum. There was no demarcation between the vaginal adventitia and the corresponding to the neighbouring structures and organs (pelvic wall, rectum, anal sac, bladder and urethra).

DISCUSSION

The vagina of the Myocastor coypus, as in other mammal species (Arthur, 1982; DYCE et al., 1987), appeared as a tubular organ with extremely thin and transparent wall, flattened in the dorsoventral direction. As in other hystricomorph (WEIR, 1971 a, b and c), the vagina of the coypu is long, but unlike them it does not become sharp in its vulvar end, but keeps the same diameter until the end.

The neighbouring structures and organs to the vagina of coypu (pelvic wall, rectum, anal sac, bladder and urethra) were similar to the reported for other species by BASSET (1983) (cow, goat and sow), and BARONE (1983) (dog and rabbit).

Vaginal closure membrane was presents in all hystricomorph that have been examined by ROOD & WEIR (1970) (Cavia aperea, Galea musteloides and Microcavia australis) and WEIR (1971 b and c) (Lagostomus maximus and Dasyprocta aguti). Coinciding with that reported by WEIR (1974), in sexually mature coypus, there was no membrane of vaginal occlusion. Neither there was a partition nor vaginal septum as that described in the plains viscacha by WEIR (1971 b). The mucosal layer of the coypu was irregularly folded. The presence of longitudinal and transversal folds is a characteristic of the vagina of rodents (Parakkal, 1974; CENTOLA, 1978; KRESS et al., 1989), adult lagomorphs (Kanagawa et al., 1972) and domestic animals (BARONE).

Histologically, the vagina was a fibromuscular sheath and four distinctive layers formed their wall. A similar finding was observed by BURA et al.

Mucification was not determined in the vaginal epithelium unlike other hystricomorph rodents like Dasyprocta aguti (WEIR, 1971 c).

In conclusion, this work contributes with a characterisation of the anatomy and histology of the vagina of the Myocastor coypus at sexual maturity that is useful as a model for the analysis and interpretation of the variations at different reproductive stages.

RESUMEN: Myocastor coypus es un roedor de tamaño mediano, considerado internacionalmente como una especie de interés económico por sus cualidades peleteras. El estudio morfológico de su vagina reviste importancia en el marco de investigaciones de su fisiología reproductiva. La vagina de coipos sexualmente maduros se presentó como un órgano tubular, de 10,25 ± 1,40 cm de longitud. La pared vaginal fue muy delgada, distinguiéndose en ella cuatro túnicas: mucosa, submucosa, muscular y adventicia o serosa (según la región). Su epitelio de revestimiento era de tipo escamoso estratificado y aglandular. En la túnica muscular se diferenciaron dos capas de tejido muscular liso con abundancia de tejido conectivo. La serosa, conformada por tejido conectivo de aspecto denso, presentó numerosos y grandes vasos sanguíneos.

PALABRAS CLAVE: 1. Vagina; 2. Myocastor coypu; 3. Morphology.

^*Area de Ciencias Morfológicas, ^** Area de Reproducción, Núcleo FISFARVET, Facultad de Ciencias Veterinarias, UNCPBA, Argentina.

Dirección para correspondencia:
Prof. Dr. Antonio E. Felipe
Depto. de Ciencias Biológicas
Facultad de Ciencias Veterinarias
UNCPBA
(7000) Tandil
Buenos Aires
ARGENTINA

Recibido : 12-07-2000
Aceptado: 14-09-2000

REFERENCES

ARTHUR, G. H. Veterinary Reproduction and Obstetrics. 5^th ed., Philadelphia, Lea and Febiger, 1982.         [ Links ]

BARONE, R. Anatomia comparata dei mammiferi domestici. Splacnologia. 2. ed., Bologna, Bortolami, Edagricole, 1983. V. 4.         [ Links ]

BASSET, E.G. The comparative anatomy of the pelvic and perineal regions of the cow, goat and sow. N. Z. Vet. J., 19:277-90, 1983.         [ Links ]

BURA, M.; SINCAI, M.; GLUHOVSCHI, N. & BOTAREL, S. Studiul histologic al aparatului genital femal la nutrie (Myocastor coypus). Lucr. Stiin. Zootech., 25:53-4. 1992.         [ Links ]

CABODEVILA, J. & CALLEJAS, S. Determinación del ciclo estral de la nutria (Myocastor coypus) mediante colpocitología exfoliativa. XIII Congreso Panamericano de Cs. Veterinarias, Abstracts, 15, 1992.         [ Links ]

CATZEFLIS, F. M.; HANNI, C.; SOURROUILLE, P. & DOUZERY, E. Molecular systematics of histricognath rodents: the contribution of Sciurognath mitochondrial 12 Sr RNA sequences. Mol. Philogenet. Evol., 4 (3): 357-60, 1995.         [ Links ]

CENTOLA, G. M. Surface features of exfoliated vaginal epithelial cells during the oestrus cycle of the rat examined by scanning electron microscopy. J. Anat., 127:553-61, 1978.         [ Links ]

COLANTONI, L.O. Ecología poblacional de la nutria (Myocastor coypus) en la Provincia de Buenos Aires. Fauna y Flora Silvestres, 1 (1):1-25, 1993.         [ Links ]

CRESPO, J.A. Observaciones sobre la reproducción de la nutria en estado silvestre. In: La experiencia argentina en la cría de la nutria, Myocastor coypus. México, Pider SARH, 1981.         [ Links ]

DYCE, K.M.; SACK, W.O. & WENSING, C.J.G. Textbook of veterinary anatomy. 2. ed. Philadelphia, W. B. Saunders, 1987.         [ Links ]

EHRLICH, S. Ecological aspects of reproduction in nutria, Myocastor coypus. Mol. Mammalia, 30:142-52, 1966.         [ Links ]

FELIPE, A. E.; CALLEJAS, S. & CABODEVILA, J. Anatomohistological Characteristics of female genital tubular organs of the south american nutria (Myocastor coypus). J. Vet. Med.: Anatomia, Histologia, Embryologia, 27 (4):245-50, 1998.         [ Links ]

GOSLING, L. M. The coypu in East Anglia. Trans. Norfolk Norwich Nat. Soc., 23:49-59, 1974.         [ Links ]

HILLEMANN, H. B.; GAYNOR, A. I. & STANLEY, H. P. The genital system of nutria (Myocastor coypus). Anat. Rec., 130:515-31, 1958.         [ Links ]

IUDICA, C. E. & ALBERIO, R. H. Preliminary study of the sexual cycle of the South-American nutria (Myocastor coypus) by the method of exfoliative colpocitology. Scientifur, 19(1):33-42, 1995.         [ Links ]

KANAGAWA, H.; HAFEZ, E.S.E.; PITCHFORD, W.C.; BAECHLER, C.A., & BARNHART, M.I. Patterns in the reproductive tracts of the rabbit observed by scanning electron microscopy. Anat. Rec., 174:205-26, 1972.         [ Links ]

KRESS, A.; SPORNITZ, U.M. & ZOBRIST, R. Scanning microscopy of the developing vagina in postnatal gerbils. J. Morphol., 201:301-14, 1989.         [ Links ]

KULISEK, V.; JAKUBICKA, Y.; BARTA, M.; ZAVODNY, L. & ZEMANOVIC, Y. Anatomical description of the female sexual system of nutria (Myocastor coypus). Polnohospodarstvo, 34 (7):655-60, 1988.         [ Links ]

LYNCH, M.J.; RAPHAEL, S. S.; MELLOR, L.D.; SPARE, P. D. & INWOOD, M. J. H. Medical Laboratory Technology. 2. ed. Philadelphia, W. B. Sawnders, 1980.         [ Links ]

NEWSON, R. M. Reproduction in the feral coypu (Myocastor coypus). Symp. Zool. Soc. Lond., 15: 323-34, 1966.         [ Links ]

PARAKKAL, P. F. Cyclical changes in the vaginal epithelium of the rat seen by scanning electron microscopy. Anat. Rec., 178:529-38, 1974.         [ Links ]

ROOD, J. P. & WEIR, B.J. Reproduction in female wild guinea pigs. J. Reprod. Fert., 23:393-409. 1970.         [ Links ]

WEIR, B. J. Some observations on reproduction in the female green acouchi, Myoprocta pratti. J. Reprod. Fert., 24: 193-201, 1971a.         [ Links ]

WEIR, B. J. The reproductive organs of the female plains viscacha. Lagostomus maximus. J. Reprod. Fert., 25: 365-73, 1971 b.         [ Links ]

WEIR, B. J. Some observations on reproduction in the female agouti, Dasyprocta aguti. J. Reprod. Fert., 24:203-11, 1971 c.         [ Links ]

WEIR, B. J. Reproductive characteristics of Hystricomorph rodents. Symp. Zool. Soc. Lond., 34:265-301, 1974.         [ Links ]