Scientific Research and Essay Vol. 4 (1), pp. 013-017, January, 2009 Available online at http://www.academicjournals.org/SRE ISSN 1992-2248 © 2009 Academic Journals Full Length research Paper

Partial septate uterus and tubal implantation: a normal phenomenon in the Eidolon helvum

Samson A. Odukoya1*, Olusola A. Adeeyo2, David A. Ofusori3, Oladele A. Ayoka4, Oladele P.

Oluwayinka5, Adebayo J. Akinyeye6, Gideon B. Ojo1, Adeola E. Ashamu2 and Layi S. Babatunde2

1Department of Anatomy, Faculty of Basic Medical Sciences, Bowen University, Iwo, Osun State, Nigeria.

2Department of Anatomy, Faculty of Basic Medical Sciences, Ladoke Akintola University of Technology, Ogbomoso, Oyo State, Nigeria.

3Department of Anatomy and Cell Biology, Faculty of Basic Medical Sciences, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria.

4Department of Physiological Sciences, Faculty of Basic Medical Sciences, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria.

5Department of Anatomy, College of Health Sciences, Bingham University, Karu, Nasarawa State, Nigeria. 6Department of Environmental Science, School of Natural and Applied Sciences, Igbinedion University, Okada, Edo

State, Nigeria.

Accepted 12 December, 2008

The aim of the study was to investigate the macro and micro-anatomical adaptations in the uterus and the type and nature of implantation found in Eidolon helvum. A total of thirty pregnant bats sampled from Obafemi Awolowo University Campus were used in this study. They were harvested and sacrificed by cervical dislocation after being carefully assessed and confirmed to be presumably healthy. Abdominopelvic incisions were made on the bats to expose and excise their uteri. The uteri were observed macroscopically while some were fixed in 10% formol saline and processed for routine Heamatoxylin and eosine (H&E) staining procedure and Verhoeff-van Giesson’s stain. It was observed that the uterus of E. helvum possesses a partial septum that divides the uterine cavity into two compartments also; the lateral end of either of the uterine limbs was always enlarged or distended more than the other. As the dormant zygote began to develop in either of the uterine limbs, it grew lateromedially causing the particular limb to distend gradually towards the midline of the body. The uterine body did not participate in any way in carrying the developing fetus till term. Tubal implantation- a pathologic condition in some mammals was also observed to be natural in E. helvum. Thus, the presence of partial septate uterus and tubal implantation being a normal phenomenon in the E. helvum shows its primitiveness as a mammal. Key words: Uterine limbs, uterine body, tubal implantation, partial septate uterus, Eidolon helvum.

INTRODUCTION Eidolon helvum are fruit eating bats (Ogunbiyi and Okon, 1976; Okon, 1977) and exist in roosting colony at the Obafemi Awolowo University, Nigeria. Their natural pos-ture (up-side-down) makes it a unique mammal (Kingdon, *Corresponding author. E-mail: davidofus234@yahoo.com. Tel : +2348036153842.

1974; Okon, 1974). It is often recognized that repro-ductive periods of Frugivorous bats are closely linked to and may be triggered by peaks of fruit abundance (Bonaccorso, 1998; Dinerstein, 1986; Faria, 1995). They also exhibit the phenomenon of sperm storage and delayed fertilization and/or delayed implanttation, sometimes due to alter-nation or intermittent periodic development of the male and female gonads per season. There is a delay in the implantation of the embryo in most, but not all, popula-

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Figure 1. Distended limb of the uterus after implantation, signifying the pregnant limb (PL). UB = Uterine Body; NPL = Non Pregnant Limb; and FT = Fallopian Tube. (X5).

tions. The gestation period typically lasts 9 months, but the embryo only takes 4 months to develop. In popu-lations without delayed implantation, births occur just 4 months after mating (Nowak, 1997; Smithers, 1983).

The young are born in February and March. Female gives birth to a single offspring that weighs 50 g at birth (Nowak, 1997). E. helvum has female parental care, like all other mammals. The female nurses her offspring until it is ready to forage on its own. In this species, young are not able to fly at birth and so are considered altricial.

The uterus in mammals consists of a body, a base or fundus, a neck or cervix, and a mouth. Suspended in the pelvis, it lies with the base directed upward and forward and the cervix directed slightly backward. It is connected to the vagina by the cervix. On either side of the uterus lies an ovary (Heath et al., 2009). Eggs produced by the ovaries reach the uterus through the fallopian tubes. In the unimpregnated condition the uterus is about 7.6 cm (about 3 inch) in length, 5 cm (2 inch) in breadth, and 2.5 cm (1 inch) in thickness in E. helvum (Heath et al., 2009).

In pregnancy the fertilized egg implants itself in the lining of the uterus, where it grows to maturity; the walls of the uterus are elastic and stretch during pregnancy to hold the developing child. In mammals, when the Graafian follicle bursts, the egg falls toward the interior of the abdominal cavity. The oviduct (known in higher mammals as the fallopian tube) has an open, funnel-shaped end located near the ovary, and the mature egg is drawn into the funnel by peristaltic ciliary action (Odukoya, 2008). Occasionally, the egg misses the open end of the oviduct and falls into the abdominal cavity; such eggs are capable of being fertilized, resulting in ectopic pregnancies. In animals lower than marsupials the oviducts open directly into the cloaca; in marsupials and placental mammals, the oviducts, two of which are normally present, fuse at their cloacal ends to form a thick, muscular organ, the uterus or womb, in which the

young develop, and a thinner channel, the vagina, which opens exteriorly (Odukoya, 2008).

With the disappearance of the zona pellucida, the outer surface of the trophoblast of the blastocyst makes a direct contact with the endometrium and becomes attached to it; this process is referred to as implantation. Initially during the phase in which mammalian morula is converted into a blastocyst, the zona pellucida becomes thin, prior to this, after fertilization has occurred in the ampulla of the uterine tube; the zona pellucida keeps the blastomeres together during cleavage and also prevents the adherence of the “sticky” blastomeres to the epithet-lium of the uterine tube during the tubal passage of the cleaving egg (Banerjee and Karim, 1982; Donald et al., 2005).

Prior researches had it that mammals have a peculiar reproductive system to suit their reproductive life (Odukoya, 2008). We therefore set to verify the macro and micro-anatomical adaptations in the uterus and investigate the type and nature of implantation that the E. helvum has adopted to suit its reproductive life. MATERIALS AND METHODS Care of animal A total of thirty pregnant bats (E. helvum) were sampled from the Obafemi Awolowo University Campus, Nigeria. The bats were identified in the Department of Zoology, Obafemi Awolowo University, Nigeria, and acclimatized for two weeks in the Animal Holdings of the Department of Anatomy and Cell Biology before sacrifice. The bats were fed with ripe bananas and water. The animals were physically assessed, screened and confirmed to be presumably healthy. All animals were treated in accordance with the “Guide for the Care and Use of Laboratory Animals” prepared by the National Academy of Sciences and published by the National Institutes of Health (1985). Excision of the abdominopelvic region The animals were sacrificed by cervical dislocation after pento-barbital administration. Abdominopelvic incisions were made to expose and excise their uteri (Figure 1). These uteri were imme-diately washed in physiological saline and blotted dry using filter paper. Some of the uteri were immediately fixed in 10% formol saline for histological analysis while others were studied macro-scopically adopting a Celestron dissecting Microscope. Histological procedures The harvested uteri were immediately fixed in 10% formol-saline limiting the post-mortem time to approximately 2 min. Tissues were fixed for a minimum period of 24 h before further processing. The tissues were dehydrated through graded alcohol and cleared in 3 changes of xylene (1.5 h each). Tissues were then infiltrated with molten paraffin wax at 56°C for 2 h each in 2 changes of paraffin wax. Embedding was done in paraffin wax for a period of 24 - 48 h. Sectioning was done at 5 µm thickness on a Rotary microtome and then subjected to Haematoxylin and eosine (H&E) staining proce- dure of Luna (1968) and Verhoeff-van Giesson’s stain.

Figure 2. Cross section of the uterine body showing its two compartments (C) and the anteroposterior septum (S) with the endometrial projections (EP). H and E stain, (X220).

Figure 3. The septum (S) showing the smooth muscles (SM) of the uterus. The compact nature of the endometrium (E) is an indication of the resting phase in the uterine cycle. H and E stain, (X400).

RESULT The uterus was bicornuate and symmetrical (Figure 1), but the internal arrangement observed was more of a partial septate type of uterus. It contains a septum attached to the body of the uterus in the uterine lumen anteroposteriorly, separating the uterine body into two lumina- right and left, which was continuous with the lumen of the corresponding uterine limbs (Figures 4 and 5). The septum is incomplete at the cranial end leaving a gap for communication between the lumina at the fundiac region (Figures 6 and 7). Implantation was observed to be tubal in nature in the E. helvum (Figure 1). The histo-logical arrangement of the uterus was in the following order from the inside out; the endometrium, the myome-

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Figure 4. A longitudinal section of the whole uterus showing the rounded, rod-like cranial end of the septum, the free space is the region of communication between the uterine compartments and the uterine limbs. Verhoeff-van Giesson’s stain, (X800).

Figure 5. Cross section of the uterine body showing a region of single lumen (L) at its cranial end, that is, the region of the fundus. H and E stain, (X200).

shown in Figures 4 and 5. A single lumen extended from the vagina, through the cervix to the inferior margin of the uterus where a septum was attached to the anterior and posterior walls of the uterine body dividing the uterine lumen into two, a right and left compartments as seen in Figure 2.

However, the septum was more or less an extension of the myometrium containing essentially the inner longitui- nal and middle circular muscle fibres (Figures 4 and 5). The septum did not extend to the cranial and caudal margins of the uterine wall (the fundus and cervix respectively) permitting some degree of communication between the two uterine compartments and the uterine limbs, giving the terminal end of the septum a rounded, rod-like appearance (Figures 6 and 7).

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Figure 6. Overstretched myometrium (M) of the pregnant limb during pregnancy. C – Chorion. H and E stain, (X225).

DISCUSSION We investigated the macro and micro-anatomical adap-tations in the uterus and the type and nature of implant-tation the E. helvum has adopted to suit its reproductive life. The uterus in the E. helvum has been previously des-cribed as having an anteroposterior septum that separates the uterine body into a right and a left compart-ment (bicornuate), a description that fits into what could be described as septate uterus in agreement with Heinonen, (2006) and Perez-Brayfield et al. (2002).

Our investigation however revealed that the junction between the two uterine limbs and the uterine body, the septum is deficient that is; at the cranial end of the uterine body, leaving a communicating gap between the two uterine limbs, the terminal end having a rod-like rounded appearance. The same gap exists at the caudal end, making the cervical and vaginal passage thorough. This also fits into what could be described as a partial septate uterus (Heinonen, 2006; McNutty, 1996). The uterus in the E. helvum needs a more proper classify-cation, considering the fact that it possesses a septum that partially divides the uterine cavity into two compart-ments as opposed to the description of a bicornuate uterus.

One lateral end of either of the two uterine limbs was always distended while the other was flattened out; this is suggestive of the delayed implantation phenomenon. It was apparent that the distended limb was the one that eventually carried the fetus to term, which could either be the right or the left uterine limb.

Tubal implantation referred to as ectopic pregnancy in advanced mammals which has very fatal anatomical and physiological implications appears to be a normal phenomenon in the Straw coloured fruit bat (E. helvum). The fetus implants in the uterine limb at its lateral extremity and gradually grows toward the uterine body along the medial path. The partial septate uterine body

Figure 7. The non pregnant uterine limb in the pregnant bat showing numerous glands (G) and increased vascularization (BV). H and E stain, (X200).

may have hormonal and metabolic contributions, but it did not participate in the carriage of the fetus during preg-nancy.

Histologically, the myometrium in the uterine limbs and body appeared very thick and compact in a non pregnant state. It was made up of smooth muscles interlaced with areolar tissues. The septum partially demarcating the uterus is an extension of the myometrium. The smooth muscles were well arranged, having an inner longitudinal, middle circular and outer circular and longitudinal outline (Cormack, 1997). Also, there was a mixture of elastic and collagen fibres but, the prevalent fibre was the elastic type. In the pregnant limb, collagen fibres are much more aboundant as seen in Fig. 6 in conformity with earlier investigations (Cormack, 1997; Gulia et al., 2003; Jarret and Matthews, 1973). The non pregnant limb become highly vascularized with numerous glands (Figure 7) sug-gesting that it has a supporting role for the pregnant limb.

Conclusion

The histoarchitecture of the uterus has been well elabo-rated and it is better classified as a partial septate uterus than a bicornuate type of uterus. Implantation in the uterine limbs is subject to a random natural selection or attached to a yet hidden cause. A comprehensive hormo-nal and ovarian investigation may hold more revealing answers to the cause(s) of the non specific preference in zygote implantation in the two uterine limbs. Thus, partial septate uterus and tubal implantation is a normal phenomenon in the E. helvum. All these observations indicate the primitiveness of the animal in agreement with Odukoya (2008). ACKNOWLEDGMENT The authors wish to express their profound gratitude to

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