Animal Research International (2019) 16(1): 3137 – 314 3 3137

THE OESOPHAGUS OF THE AFRICAN PALM ( EPIXERUS EBII ): A MICRO ANATOMICAL OBSERVATION

IKPEGBU, Ekele, IBE, Chikera S amuel , NLEBEDUM, Uchenna Calistus and NNADOZIE, Okechukwu Department of Veterinary Anatomy, Michael Okpara University of Agricultu re, Umudike, Abia State, Nigeria .

Corresponding Author : Ikpegbu, E. Department of Veterinary Anatomy, Michael Okpara University of Agriculture, Umudike, Abia State, Nigeria . Email : [email protected]. ng Phone : +234 8060775754

Received: November 17 , 2018 Revised: February 5, 2019 Accepted: February 11 , 201 9

ABSTRACT

The oesophageal micromorphology of the , African Palm Squirrel was investigated to fill the dearth of information on the histol ogy of this organ from available literature and help in understanding its digestive tract biology . The organ after harvesting was subjected to routine histological procedure for light microscopy. The organ microanatomy was typical of the histology of mamma lian tubular organ. The well - developed epithelium was of stratified squamous cells. The laminar propria containing elastic tissue fibres was apparently smaller than the large epithelium and muscularis muco sae. The muscularis mucosae striated muscle was arr anged longitudinally. The small submucosa contained thin regular connective tissue. The tunica muscularis was made up of skeletal muscle cells which were arranged in an inner circular and outer oblique orientation, with the myenteric plexus located between these two muscle layers. The adventitia contained blood vessels. The well - developed epithelium is an adaptation to rough and coarse feed it consumes in the wild especially the fibrous coat of the oil palm fruit and other hard nuts.

Keywords: Histology, M yenteric plexus, African palm squirrel , Elastic fibres , Nigeria

INTRODUCTION et al ., 2010 ) , nature and composition of the lami na propria ( Sukon et al ., 2009 ) , presence or The oesophagus has been described as the absence of the muscularis mucosae, even the transit tube connecting the oro - pharyngeal type of muscle cell ( Nzalak et al ., 2010 ), cavity to the stomach ( Nzalak et al ., 2010; p resence and nature of oesophageal glands Ikpegbu et al ., 2012 ). The morphology of the ( Rossi et al ., 2006 ) and type and orientation of o e sophagus has been described in some the muscles in the tunica muscula ris (Sukon et domestic ( McGeady et al ., 2006 ), al . , 2009 ). As part of continued study of wild African giant rat ( Nzalak et al . , 2012 ) , gopher rodent biology , the finding on the histology of snake ( Khamas and Reeves, 2011 ), camel this is reported . Results of the present (Dellman n et al ., 1968; Jamdar and Ema, 1982), study will serve as a base - line for future laboratory mouse ( Berghes et al. , 2010 ); African reference in rodent oesophageal histology. The catfish ( Ikpegbu et al ., 2012), but none has results will not only fill the knowledge gap, but been documented in the African palm squirrel also help in understanding the digestive tract ( APS ) . biology and its role in adaptation of the African Variations have been reported on the palm squirrel in the wild. Moreover, result of the d ifferent coats of this organ . These include type microstructure of the African palm squirrel of epithelium (Schummer et al ., 1979 ; Berghes oesophagus will serve as a lead for future

ISSN: 1597 – 3115 ARI 2019 16(1): 3137 – 314 3 www.zoo - unn.org Ikpegbu et al . 3138 clinical and therapeutic intervention of diseased granulosu m , stratum spinosum and deep conditions of the digestive tract of the rodent. stratum basale ( F ig ure 2) .

MATERIALS AND METHODS

Five adult African palm of both sexes captured in the wild from Olokoro , Umuahia in Abia State , Nig eri a from March 2013 to September 2014 using metal cage traps, were used for the study. Olokoro , Umuahia is in the rainforest vegetation of southern Nigeria characterized by heavy rains and thick mangrove fores t. The ro dents were immediately transferred to t he Veterinary Anatomy Laboratory of Michael Okpara University of Agriculture , Umudike, for acclimatization. During this period, the animals were fed with grasses, Figure 1: Transverse section of the oesophagus oil palm fruit and water ad libitum. The squirrel s the lumen L, epithelium E, muscularis mucosae were sedated with chloroform and sacrifice d by M, and tunica muscularis TM. Note the lumen L, containing desquamating cells. H & E ( Scale cervical decapitation. A nimal weight was taken bar = 4 µm) with Mettler balance (Model Ohaus Scout PRO -

200) with a sensitivity of 0.1 g. The was placed on dorsal recumbency and cut open through mid - ventral incision from the inguinal region to the mandibula r symphysis. The oesophagus was dissected out and slices fixed in 10 % neutral buffered formalin.

The tissues were p rocessed by firstly, dehydrating them in gr aded ethanol . Thereafter, they were cleared in xylene, impregnated and embedded in paraffin wax. Sections 5 µ m thick were obtained with Leitz Microtome Model 1512.

They were stained with Haematoxylin and Eosin for light microscopy examination (Bancroft and

Stevens, 1990 ) . The slides were examined and Figure 2: Section of oesophagus showing the photomicrographs taken with Motican 2001 epithelium containing stratum corneum C, camera (M otican , UK) attached to Olympus stratum granulosum (white arrow ), stratum microscope. spinosum (black arrow), and stratum basale B. Note the laminar propria LP, muscularis RESULTS mucosae MM, and the desquamating cells (Z - shaped arrow head). H & E ( Scale bar = 40 µm) The APS oesophagus at low magnification presented prominent epithelium, muscularis Polygonal to regularly shaped fibres containing mucosae and tunica muscularis ( Fig ure 1). At desquamating squamous cells were seen higher magnification, the stratified squamous attaching to the apical surface of the epithelial epithelium was composed fro m surface to stratum corneum , hence, becoming the most underlying laminar propriaviz: stratum corneum proximal structure surrounding the oesophageal containing 5 – 8 layers of cell , stratum lumen ( F ig ures 2 and 3 ). The laminar propria contained lymphocytes and elastic fibres which

Animal Research International (2019 ) 16(1): 3137 – 314 3 Micro anatomical observation of the oesophagus of the African palm squirrel 3139 formed pa pillary layer that interdigitated with the epithelial ridges or pegs . The well - developed muscularis mucosae were of skeletal muscle arranged in a longitudinal fashion (F ig ures 2 and 4 ) . The submucosa was relatively small and contained thin layer of reg ular connective tissue fibres (F ig ure 4 ).

Figure 4: Section of the oesophagus showing

the epithel ium E, laminar propria LP, containing elastic fibres (white arrow), and lymphocytes (black arrow), muscularis mucosae MM, containing longitudinally arranged skeletal muscle cells. Note the submucosa SM, containing collagen fibres. H & E (Scale bar = 40 µm) Figure 3: Section of oesophagus showing desquamating cells (black arrow), detaching from the epithelium E. Note that the desquamating cells layer DS, now surrounds the lumen L, directly. H & E (Scale ba r = 40 µm)

The tunica muscularis contained skeletal muscle cells arranged in an inner circular and outer longitudinal to oblique orientation ( F ig ures 4 and 5 ) . No smooth muscle was observed . Myenteric plexu s was observed between the two muscle la yers of t he tunica muscularis (F ig ure 5 ). The tunica adventitia of loose irregular fibrous coat contained blood vessels (F ig ures 5 Fig ure 5 : Section of the oesophagus showing and 6 ). the tunica adventitia TA, skeletal muscles of tunica muscularis arranged in an inner circular layer CM and outer oblique layer OM. Note the DISCUSSION myenteric plexus MP, in - between the two tunica muscularis layers. H & E (Scale bar = 40 This study has attempted to expound the µm) microstructure of the oesophagus of the African palm squirrel. Result of the study showed that The stratified squamous cell is a protective the rodent APS oesophageal histology is typical epithelium against rough food materials ( Sukon of mammalian tubular organs. This finding has et al. , 2009 ). This epithelium type may be been reported in the Chinchilla laniger (C a l a mar related to its feeding habit and the presence of et al. , 2014). desquamating cell layer ( Dellmann and Brown, 19 87).

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oesophagus when large volume of food is consumed. This elasticity will help reduce friction on the epithelium, thus a compensatory adaptation for lacking secretory glands. It is also possible that the documented salivary glands products may be aidin g in food softening in the oral cavity before transit through the tube ( Parillo et al ., 2005; Selvan et al ., 2008; Nzalak et al ., 2010; Ikpegbu et al ., 2013) , but more work should be done on the sal ivary glands organ - volume ratio to ascertain this suggesti on. Oesophageal l amina propria mucous glands have been described in the bird Rhynchotus Figure 6: Section of oesophagus showing the rufescens (Rossi et al ., 2006). Tunica adventitia TA containing artery A, and vein V. Note the tunica muscularis containing The well - developed longitudinally circular skeletal muscle. H & E (Scale bar = 40 oriented skeletal musculari s mucosae relative to µm) smaller submucosa may be an adaptation to re - enforce the contraction of the predominant This type of keratinized epithelium has been circular skeletal muscle of the tunica muscularis described in ruminants , horse and , but and the outer oblique muscle . This non - kreatinized stratified epithelium as seen in complimentary contraction under voluntary this study, has been reported in the humans, control will ensure uniform but regular dogs, cats and African giant rat ( Schummer et peristaltic movement from all directions during al ., 1979 ; DeNardi and Riddell, 1991; Fawcett deglut ition . This will reduce incidence of food and Raviola, 1994, Nzalak et al ., 2 010 ) . A stasis in the tube, a phenomenon if it occurs will simple columnar to psuedostratifed columnar be dangerous in the wild where the animal must epithelium has been described in the gopher consume enough food in a short time because snake Pituophis catenifer ( Khamas and Reeves, of prey - predator relationship and also 2011 ), while a ciliated columnar epithelium with competition from man that conside rs their mucous secreting goblet cells has been reported foraging habit as pest activity. This observation in Varanus niloticus (Ahmed et al ., 2009). agree d with t he Sarosiek and McCallum (2000) , O es ophageal gland was not seen in this who stated that this organ is highly specialized study . This could be the reason for the observed for the thrust of food from the mouth to the luminal desquamating cells, which represents stomach. Absence of muscularis mucosae has high cellular turnover. Also, the absence of the been reported in the African giant rat (Nzalak et oesophageal glands resulted to the al ., 2010). Oesophageal muscularis mucosae unavailability of intr a - regional lubricant to containing smooth muscle cells have been ingesta on transit through the tube. The reported (Dellmann and Brown, 1987). absence of oesophageal submucosal gland as Variations exist in the type and seen in this study has been reported in the orientation of muscle cell of the tunica gopher snake ( Khamas and Reeves, 2011 ), muscularis. In humans, hor ses, cats and pigs, laboratory mouse ( Berghes et al ., 2010 ) , African the upper and lower portions of the esophagus giant rat (Nzalak et al ., 2010), but its presence are composed of striated and smooth muscles, has been report ed in the oe sophageal anatomy respectively, with a mixed portion between of the Llama – Lama glama (Sukon et al ., them (Schummer et al ., 1979). In dogs, 2009) , where it is associated with increased ruminants and rodents including mice, rats and buffering capacity and absorption of volatile hamsters, the mu scle layer of the esophagus fatty acids . consists mostly of striated muscle fibers The presence of elastic fibres in the ( McGeady et al ., 2006 ). I n the laboratory lamina propria will allow some elasticity of the mouse, the inner circular and outer longitudinal

Animal Research International (2019 ) 16(1): 3137 – 314 3 Micro anatomical observation of the oesophagus of the African palm squirrel 3139314 1 muscle coats are entirely striated muscle that BANCROFT , J . D . and STEVENS , A . ( 1990 ) . changes to smooth muscle at oesophageal Theory and Practice of Histological sphincte r ( Berghes et al. , 2010 ) , in the African Techniques . Third Edition , Churchill catfish it is entirely striated muscle (Ikpegbu et Livingstone, London . al ., 2012). In this study, the tunica muscularis BERGHES, C., COMAN, T., PETRUT, T., PARVU, was composed of mostly inner circula r and M. and DAMIAN, A. (2010). smaller outer obliquely oriented striated muscle , Contributions to the study of the the arrangement reporte d in the cranial two - esophagus and stomach morphology in thirds of horse oesophagus is the inner circular laboratory mouse. Bulletin of the and outer longitudinal (Schummer et al ., 1979) ; University of Agricultural Sciences and in ruminant, and camel, the arrangement of the Veterinary Medicine Cluj - Napoca. tunica muscularis striated muscle fibers in the Veterinary Medicine , 67 (1): 17 – 23. inner and outer layers is mixed, oblique an d CALAMAR, C. D., PATRUICA, S., DUMITRESCU, spiral (Gett y, 1975; Jamdar and Ema , 1982) . G., BURA, M., DUNEA, I. B. and T he myenteric plexus observed in the NICULA, M. (2014). Morpho - histological study was very prominent like that reported in study of the digestive tract and the the cattle ( Vittoria et al ., 2000; Teixeira et al ., annex glands of Chinchilla laniger . 2001 ), but in the camel and Ilama , it was Scientific Papers Animal Science and reported to be scant and difficu lt to locate Biotechnologies , 47 (1): 269 – 274. (Jamdar and Ema, 1982; Sukon et al ., 2009 ). CLOUSE, R. E. and DIAMANT, N. E. (2006). Though the nature of function of the striated Motor Function of the Esophagu s. Pages esophageal muscle myenteric plexus is still 913 – 926. In : JOHNSON, L. R. (Ed.), largely unknown ( Diamant, 1989; Conklin and Physiology of the Gastrointestinal Tract. Christensen, 1994; Wörl and Neuhuber, 2005; 3 rd Edition, Raven Press, New York, Clouse and Diamant, 2006; Sukon et al ., 2009 ; USA . Shiina and Shimizu, 2012 ), but recent reports in CONKLIN , J . L . and CHRISTENSEN , J . ( 1994 ) . literature have indicated dual i nnervation from Motor functions of the pharynx and both nerve fibers from the vagus and the esophagus . Pages 903 – 928. In : myenteric plexus on the endplates of JOHNSON, L. R. (E d.), Physiology of the oesophageal skeletal muscle in the guinea - pig Gastrointestinal Tract . 3 rd Edition, Raven and rat (Zhou et al ., 1996; Neuhuber et al. , Press , New York, USA. 2001). DELLMANN , D. H and BROWN , E . M . ( 1987 ) . Histology of the digestive system . Pages ACKNOWLEDGEMENTS 229 – 247. In : Textbook of Veterinary Histology . Third Edition, Lea and We wish to acknowledge the technical Febiger, Phila delphia, USA. assistance of Agbakwuru , Isaiah in preparing DELLMANN, D. H., BLIN, P. C. and FAHMY, M. F. the histological slides in this study . We want to A. (1968). Contribution à l'étude de thank the Department of Veterinary Anatomy, l'anatomie microscopique du tube Michael Okpara Un iversity of Agriculture digestif chez le chameau. Revue Umudike, for providing the equipment and D’élevage et de Médecine Vétérinaire reagents used for this research. des pays Tropicaux , 21 (1): 1 – 32. DENARDI , F . G . and RID DELL , R . H . ( 1991 ) . The REFERENCES normal esophagus. Am erican J ournal of Surg ery and Pathol ogy , 15: 296 – 309. AHMED, Y. A., EL - HAFEZ, A. A. E. and ZAYED , DIAMANT , N . E . ( 1989 ) . Physiology of esophageal A . E . ( 2009 ) . Esophagus, stomach and motor function. Gastroenter ology Clinics small intestines of Varanus niloticus . of North America , 18(2): 179 – 194. Journal of Veterinary A natomy , 2(1): 35 FAWCETT , D . W . and RAVIOLA , E . ( 1994 ) . The – 48. esophagus and stomach. Pages 593 –

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