TH BS. VET . MED . J. 6 SCI . CONF . VOL . 20, NO.1, P .5262 Beni-Suef Veterinary Medical Journal

Light and electron microscopic structure of goat's

S. M. Soliman 1*, Z. A. A. Adam 2, U. K. M. Abd allah 1 1Department of Cytology and Histology and 2 Department of Anatomy and Embryology, Faculty of Veterinary Medicine, Beni-Suef University

The present study was conducting aiming to throw the light on the retinal structure on the level of both light and electron microscope. Eyeballs of 35 adult clinically healthy goats of both sexes were collected from Beni Suef abattoir. The eyeballs were clinically examined before they were dissected and fixed in 10% buffed neutral formalin and in Bouin’s solution for 24 hours. The specimens were then processed for light and transmission electron microscope. The retina (pars optica retinae) of the goats extends rostrally to cover the as pars ciliaris retinae and the as the pars iridis retinae. Pars optica retinae and pars iridis retinae form the light non sensitive parts of the retina, while the sensitive part except at the transition zone; the and the , appeared to be formed of ten layers, named from outward to inward as, retinal pigmented epithelium, rods and cones layer ( layer), external limiting membrane, (cell bodies and nuclei of the photoreceptor cells), , (contained the horizontal, bipolar, Muller and amacrine cells), , ganglionic cell layer, nerve fiber cell layer (unmyelinated nerve fibers) and internal limiting membrane.

The retina which the neural layer of the pathological conditions involving the eyeball eyeball (Tunica nervosa bulbi) is the whitish could be easily diagnosed and managed. membrane forming the innermost portion of the Materials and methods goat's eyeball. It is represented by two parts; a Eyeballs of 35 adult clinically healthy goats sensory photosensitive portion and a non sensory of both sexes were collected from BeniSuef one. The latter extend rostrally to cover the abattoir. The eyeball were bisected and fixed in ciliary body and the iris. The point of transition 10% buffered neutral formalin and in Bouin's from the photosensitive portion to the non solution for 24 hours. The specimens were then photosensitive portion is called ora ciliaris dehydrated in ascending grades of ethanol, retinae in domestic animals and ora serrata in cleared in two changes of xylene, impregnated in human (Banks, 1993). In the available literature, soft paraffin and finally embedded in paraffin it has been found that the structure of the eyeball wax. 46 m thick sections were cut and stained studied in many species of animals including Haematoxyline and Eosin (H&E), Gomori's some laboratory animals as Geunia pigs (Spira reticulin method, Toluidine blue stain, Standard Milman, 1979), rats (Smell et al., 1987), ferrets Sudan black B method and Bielschowsky's silver (Braekevelt, 1982), mouse (Carter–Dawson and stain. The all mentioned stains used for lavil, 1979) and rabbits (Mills and Massey, demonstration the light microsopic structure of 1992); pet animal as dogs (Miyake et al., 2004) the retina and applied as outlined by Bancroft and cats (Braekevelt, 1990) and domestic and Stevens (1996). animals as horse (Altuny, 2000), camels The eyeballs of ten clinically healthy goats, (Derbalah, 2001), cattle (Altuny, 2004), extirpated just after slaughter where 1 3 mm buffaloes (Kassab and Sugita, 2001), sheep thick pieces were excised from the retina and (Nilsson et al., 1973 a,b). The goats received a prefixed in 4% gluteraldhyde in phosphate buffer little attention of the researchers. Furthermore, solution (pH 7.4) at room temperature for 4 none of above mentioned articles have dealt with hours then processed for examination by the structure of the retina at the level of either transmission electron microscope. Semi thin light or transmission electron microscope. sections 0.51 m were cut by a glass knife, and Therefore, the present investigation was stained by Toluidine blue then examined by the conducted aiming to full fill this gap and to optical light microscope for determination of the establish normal standard against which any selected areas (Richardson et al., 1960). Ultra thin sections, 5060 nm thick, of the selected * Corresponding author. Tel.: +20 016 7102575; area were cut, mounted on copper grids and were Fax: +20 082 2327982 Email address: [email protected] (Shehata M. Soliman) 53 BS. Vet. Med. J. 6th Sci. Conf. Vol. 20, No.1

contrasted with uranyl acetate ethanol followed lodged in the apical processes of the pigmented by lead citrate stain (Reynolds, 1963). The epithelium (Fig. 5). sections were examined using JEOL JEM The cone outer segments appear conical in 100CX II transmission electron microscope in shape with tapered free ends and wide bases. the electron microscope unit, Assiut University. They were shorter than the rod outer segments Results and did not reach the pigmented epithelium (Fig. The retina (pars optica retinae) of the 4). goats is the innermost portion of the eyeball Each cone outer segment was consisted of which was sensitive to light and colors. It several parallel double membranous discs extended rostrally to cover the ciliary body as (stalks) separated from each other by narrow pars ciliaris retinae and the iris as the pars iridis regular spaces and the discs were separated from retinae. Both formed the light non sensitive parts the covering plasma membrane (Fig. 6). The of the retina. discs were closely packed and have narrower Light sensitive part. Except at the transition spaces than the corresponding rod outer segment zone; the ora serrata and the optic disc, the goat's discs. retina appeared to be formed of ten layers, The inner segment of both the rods and the named from outward to inward as, retinal cones were composed of two parts; an outer pigmented epithelium, layer of rods and cones ellipsoid and an inner myoid. The myoid of the (photoreceptor cell layer), external limiting rod appeared as electron dense irregular structure membrane, outer nuclear layer, outer plexiform containing rough and smooth endoplasmic layer, inner nuclear layer, inner plexiform layer, reticulum (Fig. 7). The ellipsoid of both ganglionic cell layer, nerve fiber cell layer and contained many vesicles and numerous tubular internal limiting membrane (Fig.1). mitochondria with long filamentous cristae (Fig. The retinal pigmented epithelium. The retinal 8). The mitochondria in cone ellipsoid were pigmented epithelium consisted of a single row more numerous than that of rods. of cuboidal cells resting on a clear basal lamina, The external limiting membrane. The external it contained central, spherical and vesicular limiting membrane appeared as a dark line (euchromatic) nuclei. The nuclei contained well separating the rods and cones layer from the demarcated prominent nucleoli. Numerous dark outer nuclear layer. It contained argyrophilic brown melanin granules (melanosomes) of material (Fig. 9). By electron microscopy, the variable shapes and sizes are aggregated in the external limiting membrane was untrue apical part of the cells (Fig. 2 and 3). membrane. It could be seen as an electron dense The cytoplasm of these cells contained also line representing the close adherence of the scarce amount of rER and numerous sER, zonulae adherences between Müller cells and secretory vesicles, secondary lysosomes as well between them and the inner segments of as electron dense irregular masses resembling the photoreceptor cells. rod's outer segment. Zonula adherent and tight The outer nuclear layer . As shown in (Fig. 10), junctions were seen between the adjacent the outer nuclear layer was formed mainly of cell epithelial cells. Finger like projections were, bodies and nuclei of the photoreceptor cells also, noticed at vitreal end to interdigitate and to arranged in 67 rows. The most superficial row house the rod outer segments. it did not contain constituted the lightly stained cone nuclei and any melanin granules. the reminders were mostly formed of the darkly The basal parts were characterized by the stained rod nuclei. The cone nuclei appeared presence of numerous deep basal infoldings. large, oval to spherical, with peripherally They were rested on a complex basement distributed euchromatin and more electron lucent membrane (Bruch's membrane) which separated nucleoplasm (Fig. 11). On the other hand, the the from the retina. rod nuclei were smaller in size, oval to spherical The photoreceptor layer. Two types of in shape with more centrally distributed photoreceptors could be differentiated in this heterochromatin and more electron dense layer; the rods and the cones. They were nucleoplasm. Connecting fibers and axons of rod considered modified neurons; composed of an and cone cells as well as Müller processes were, outer (photosensitive part) and an inner segment also, noticed in the outer nuclear layer. (Fig. 4). The rod outer segment was elongated The outer plexiform layer. Is that layer uniform structures which were longer and more separating the outer and inner nuclear layers. It numerous than those of the cone. Its free end could be seen as the axons of the rods and cones SOLIMAN ET AL ., 54 which synapsed with the dendrites of inner extending to the inner plexiform layer. Their nuclear layer. The cone axons appeared to be electron dense cytoplasm contained many ended as large, irregular synaptic pedicles, cone mitochondria, rER and free ribosomes (Fig. 16). pedicles, which synapsed with the cells of the The inner nuclear layer was supplied by inner nuclear layer (Fig. 12). double walled capillaries lined by two types of The terminal end of the rod axon was cells resembling that of the outer plexiform layer observed as a flask–shaped structure, the rod (Fig. 17). spherule, that synapsed with the cells in the inner The inner plexiform layer. The layer was nuclear layer. Such synaptic sites contained located between the inner nuclear and the many synaptic vesicles and numerous large ganglionic cell layer. It contained the rounded to oval mitochondria with their long cytoplasmic processes of the bipolar and the tubular cristae. The area of the outer plexiform amacrine cells that synapsed with dendritic layer was supplied by a special doublewalled processes of the ganglionic cell (Figs. 18). blood capillaries lined by two types of cells; The ganglionic cell layer. The layer was formed endothelial cells and an elongated, flattened, of a single and, occasionally, double rows of two electron dense cells enclosed within the types of cells; large spherical cells and small basement membrane. oval cells. The large spherical cells contained The inner nuclear layer. It was intervening large spherical euchromatic nuclei with between outer and inner plexiform layers. It was prominent eccentric nucleoli. The cytoplasm was thinner than the outer nuclear layer, contained abundant and contained numerous mitochondria, cells of different shapes and sizes and were sER, rER and free ribosomes (Fig. 19). arranged in 34 rows. The cellular components of The optic nerve fiber cell layer. The layer this layer were the horizontal, bipolar, Müller appeared to be formed of unmyelinated nerve and amacrine cells. fibers, belonging to the large ganglionic cells. The horizontal cells were large, oval cells They run parallel to the long axis of the retina contained spherical to oval euchromatic nuclei (Fig. 20). The nerve fibers were supported by with prominent nucleoli (Fig. 13). glia cells, mainly, Müller cells. At the level of The bipolar cells, as shown in Figure (14), the optic disc, the nerve fibers were converged were numerous neurons and appeared in two and crossed the retina to form the optic nerve. forms euchromatic and heterochromatic cells. The internal limiting membrane. The internal The cells were randomly distributed within the limiting membrane was seen just close to the inner nuclear layer. vitreous humour (Fig. 1). Electron microscopic The Müller cells were elongated astrocytes. examination of this membrane showed that it At the outer end, the cells were fused with the was an electron dense osmiophilic, thick rods and cones and at the inner end they were membrane separating the Müller cells from the fused with each other. The cells fulfill the spaces (Fig. 21). Numerous rER and between the various neural elements between the many mitochondria were observed inside the end external and internal limiting membranes. They feets of the Müller's cells. possessed a triangular or angular, more electron Light non sensitive part. The non sensory dense nuclei. Their plasmalemma showed portion of such tunica began at the ora serrata. It extensions lodged between the cell types (Fig. extended anteriorly to cover the ciliary body as 15). the pars ciliaris retinae and the iris as the pars The amacrine cells occupied the innermost iridis retinae. It was a type of stratified portion and formed an incomplete layer at the epithelium. The outer cell is non pigmented and vitreal margin of this layer. They were identified the inner layer was, in contrast, heavily by their deeply indented nuclei. Their rounded pigmented, these pigments masked any details of cell bodies contours and their processes were the above mentioned cells (Fig.22).

55 BS. Vet. Med. J. 6th Sci. Conf. Vol. 20, No.1

Fig. (1) : A Photomicrograph of goat's retina showing the different layers of the retinal wall; retinal pigment epithelium (RPE), photoreceptor layer (PL), outer nuclear layer (ONL), outer plexiform layer (OPL), inner nuclear layer (INL), inner plexiform layer (IPL), ganglionic cell layer (GCL ), nerve fiber layer (NFL) and internal limiting membrane (ILM). H & E, X 400. Fig. (2): A Photomicrograph of goat's retina showing the retinal pigment epithelium (RPE) in the non tapetal area. Note that the cells are cuboidal containing apically located melanin granules. Notice that both the outer segment (OS), and inner segment (IS) of the photoreceptor layer and the outer nuclear layer (ONL). H&E, X1000. Fig. (3): Transmission electron micrograph of goat's retina showing that the retinal pigment epithelium was formed of low cuboidal cells containing apically situated melanosomes (M) of different shapes and sizes, spherical nucleus (N) and secondary lysosome (L). Notice the photoreceptor outer segment (P). Uranyl acetate and lead citrate, X 2700. Fig. (4): TEM of retina of goat showing that each of the cones and the rods was formed of outer and inner segments. Notice cone outer segment (COS), inner segment (IS), rod outer segment (ROS) and inner segment (IS). Uranyl acetate and lead citrate, X 2700. Fig. (5): TEM of retina of goat showing the rod outer segment (ROS). Notice that the discs were separated from the plasmalemma. Uranyl acetate and lead citrate, X40000. Fig. (6): TEM of goat's retina showing the cone's outer segment (OS), inner segment (IS) and calycal process (arrow). Notice the presence of mitochondria (M) in the inner segment. Uranyl acetate and lead citrate, X 40000. Fig. (7): TEM of photoreceptors of goat's retina showing that the inner segment of either rods or cones was composed of two parts; outer ellipsoid (E) and inner myoid (M).Uranyl acetate and lead citrate, X2700. SOLIMAN ET AL ., 56

Fig. (8): TEM of both rod (RE) and cone (CE) ellipsoid showing several mitochondria (M) and vesicles (V). Uranyl acetate and lead citrate, X10000. Fig. (9): A micrograph of the goat's retina showing the external limiting membrane (ELM). Note fine reticular fibers in plexiform layer (PL). Gomori's reticulin method, X400. Fig. (10): A micrograph of goat's retina showing the outer nuclear layer (ONL) which was formed of euchromatic cone nuclei (C) and heterochromatic rod nuclei (R). Note the outer plexiform layer (OPL) and inner nuclear layer (INL). Toluidine blue, X 1000. Fig. (11): TEM of the retina of goat showing a with a large vesicular euchromatic nucleus (Cn). Note the presence of Müller cell processes (Mp) between the photoreceptor cells. Uranyl acetate and lead citrate, X 8000. Fig. (12): TEM of the outer plexiform layer (OPL) showing a cone pedicle (CP) which synapsed with processes of the inner nuclear layer. Notice the cone nucleus in the outer nuclear layer (ONL). Uranyl acetate and lead citrate, X 2700. Fig. (13): TEM of the inner nuclear layer of the goat's retina showing one the electron lucent horizontal cell with its oval nucleus (N). Note the horizontally oriented processes (P). Uranyl acetate and lead citrate, X4000. Fig. (14): TEM of the inner nuclear layer of the goat's retina showing the two types of bipolar cells; cells with euchromatic (Be) and cells with heterochromatic nuclei (Bh) and Müller cells (M)inbetween. Note the presence of blood vessel (bv). Uranyl acetate and lead citrate, X2700. Fig. (15): TEM in the inner nuclear layer of the goat's retina showing one of the Müller cells (M) lodged between the bipolar cells (B). Notice the numerous mitochondria (M) within the Müller cell cytoplasm. Uranyl acetate and lead citrate, 8000. Fig. (16): TEM in the inner nuclear layer of the goat's retina showing one of the amacrine cells (A). It was characterized by its deep invaginated nucleus (N). Uranyl acetate and lead citrate. X 8000. 57 BS. Vet. Med. J. 6th Sci. Conf. Vol. 20, No.1

Fig. (17): TEM of the inner nuclear layer of the goat's retina showing a double walled blood vessels (bv) lined by two types of cells; normal endothelial cells(1) and electron dense flattened cells (2). One of the bipolar cells (B). Uranyl acetate and lead citrate, X6700. Fig. (18): TEM of the goat's retina showing that the inner plexiform layer (IPL) was formed of the cytoplasmic processes of the inner nuclear layer (INL). Uranyl acetate and lead citrate, X 2700. Fig. (19): TEM of ganglionic layer of the goat's retina showing a ganglionic cell (G) with its large nucleus (N). the latter contained prominent nucleolus (n). Notice the presence of many mitochondria (M). Uranyl acetate and lead citrate, X 6700. Fig. (20): A Photomicrograph of the goat's retina showing the black stained nerve fibers in the nerve fiber layer (NFL). Notice that the fibers run parallel to the surface of the retina. Bielschowsky's silver stain, X400. Fig. (21): TEM in the goat's retina showing the (ILM). Note the end feet of the Müller cells (CPm) which contained many mitochondria (M). Uranyl acetate and lead citrate, X 20000. Fig. (22): A higher magnification of pars ciliaris retinae showing the outer non pigmented epithelium (OL) and the inner heavily pigmented one (IL). H & E, X 1000.

Discussion body as pars ciliaris retinae and the iris as pars

Due to the great importance of the retina in iridis retinae. The above mentioned findings vision sensation and allowing the individual to were augmented by the findings of Samuelson, react with the surrounding environment, the (1999); Hees and Sinowatz, (2000). The latter retina has been widely studied in a variety of authors added that the image formation is the species (Kuwabara, 1979; Altuny, 1997; 2000, primary function of the retina. 2004; Samuelson, 2007). The pars optica retinae of goats resembled that of other mammals as it composed of ten The goat’s retina appeared to be composed layers named from outside to inside as the retinal of a sensory part and a non sensory part. The pigment epithelium, the visual cell layer, the former represented the neuroepithelial tunica that outer limiting membrane, the outer nuclear layer, was sensitive to light while the non sensory the outer plexiform layer, the inner nuclear layer, portion extended anteriorly to cover the ciliary the inner plexiform layer, the gnglionic cell SOLIMAN ET AL ., 58 layer, the optic nerve fiber layer and the inner into rods or cones was originally proposed by limiting membrane. The same findings detected Schultze, (1866) depending on the in many species as bovine (Aly, 2003), camels morphological characters of the cells. Polyak, (Derballah, 2001), canine (Shively et al., 1970) (1957); Duke–Elder, (1958); Aly, (2003) decided and equine (Ehrenhofer et al., 2002). On the that the rods of the photoreceptor cell layer have other hand, Mohammed, (2004) reported that the cylinderical inner and outer segments, while the ostrich’s retina was composed of nine layers cone of the same layer have a shorter conical only as he not considered the outer limiting outer segment and a wider inner segment. membrane as a true layer. The newly advanced techniques, as electron As reported in many vertebrates (Nilsson, microscopy and immunohistochemistry, gave 1978; Altuny, 2007), the present investigation more details about the photoreceptor cells. The revealed that the retinal pigment epithelium was traditional classification into rods and cones was the outermost layer of the retina and was more accurate and adequate (Cohen, 1972; composed of a single row of cuboidal cells. Rodiek, 1973). Moreover; the cells were These cells were provided with numerous basal considered bipolar nerve cells sensitive to light. infoldings. In the opinion of most histologists Each cell was composed of two parts; an outer (Boulton and Day hawBaker, 2001; Altuny, photosensitive part and an inner one containing 2004) the basal infoldings had a great role in the the nucleus (Aly, 2003; Altuny, 2000, 2004, material transport from choriocapillaries to the 2007). In goat's, the outer and inner segments of photoreceptors. The presence of many apical both rods and cones were arranged parallel to processes which interdigitated with the each other and perpendicular to the retinal photoreceptor outer segments were also met in surface. This finding was in agreement with the other mammalian species. These processes were results of Mills and Massey, (1992). necessary for Phagocytosis of outer segment In the present investigation, as recorded in discs (Bok, 1985), for stabilization of other vertebrates, rods outer segments were photoreceptor outer segments (Enoch, 1979), and elongated, uniform structures and more for adhesion of the neurosensory retina numerous than cones outer segments. Their free (Braekevelt, 1988). Unlike the findings of ends were lodged in the apical processes of the Braekevelt, (1988); Boulton and Dayhaw–Baker, retinal pigmented epithelium. Such microscopic (2001) who described two types of processes findings explain the greater role of rod cells with projecting from the pigment cells, only one type process of vision than cone cells (Carter– projections have been recorded in goat's retina. Dawson and Lavil, 1979). Our finding was met with that of the camel’s eye The rod outer segment of the goat's retina (Altuny, 2007). The processes were finger–like was formed of parallel bi membranous discs and extended between the rods and cones separated from each other by narrow irregular processes. spaces. A finding met with that of Aly (2003) The pigmented epithelial cells of goat’s and Altuny, (2000, 2004). On the other hand, retina were found to be connected with each Braekevelt, (1990) in cat recorded regular spaces other by tight junctions and zonula adherents as between the discs. The author mentioned that the it was mentioned in many other mammalian interdisc spaceopen to the exterior that the species (Boulton, 1991; Altuny, 2007). The irregularity in its rod discs was presumed to authors agreed that the lateral junction played a increase the surface area. The cones outer role for the formation of a selective barrier for segments of goat’s retina, in comparison, were metabolites and ion transport. short, conical in shape and their number was The electron microscopic examination of the lesser than that of rod's outer segments (Cohen, goat’s retinal pigment epithelium revealed 1972; Braekevelt, 1998; Aly, 2003). euchromatic nuclei, abundant mitochondria, As mentioned by many authors (Cohen, smooth endoplasmic reticulum and few rough 1960; Braekevelt, 1983b; Aly, 2003), the higher endoplasmic reticulum. These findings agreed content of mitochondria in cone's ellipsoid than with the results of (Altuny, 1997, 2007), and rods explained higher metabolic activities of reflected a high metabolic activity of these cells. cones. On the other hand, Hagins, (1973) stated The second layer of the goat’s retina was the that the presence of a large number of photosensitive layer which appeared as mitochondria in rods than cones was mainly numerous elongated cylindrical segments. The associated with the active sodium pump. The traditional separation of retinal photoreceptors author added that, the mitochondrion in cones 59 BS. Vet. Med. J. 6th Sci. Conf. Vol. 20, No.1

seems likely to have similar function, but it was increased protection of the retina from rupture not clear. Some energy production was and also to support the blood retinal barrier. associated with the rapid pigment turnover at The occurrence of four cell types in the inner high light intensities. The myoid of nuclear layer of retinae of most animal species; photoreceptors of goat's retina was found to horizontal, bipolar, Müller and amacrine cells contain numerous sER and rER. This fact was (Ehrenhofer et al., 2002; Aly, 2003) could be documented in other animals (Braekevelt, 1983a, easily distinguished in goat's retina. 1987). The goat's horizontal cells were large oval The present study revealed that the external cells contained spherical to oval nuclei and limiting membrane of the goat's retina was electron lucent cytoplasm. The dendrites of formed by a series of zonulae adherents between such cells run horizontally parallel to the retinal the Müller cells and the photoreceptors. The surface. These results were in accordance with same findings were also recorded in domestic those of Nilson et al., (1973a); Samuelson, animals (Cohen, 1972; Braekevelt, 1983a, b and (1999); Derbalah, (2001). The latter author found 1987). The later author as well as Aly (2003) and that horizontal cells synapsed with the Altuny, (2007) augmented our results that the photoreceptor cells and bipolar cell processes. external limiting membrane was interrupted by The occurrence of two types of horizontal cells the cytoplasmic processes of the Müller cells. as recorded by Klab et al., (1992) could not be Regarding the outer nuclear layer, there were noticed in the goats. a quite agreement among the histologists that In goat's retina two types of bipolar cells such layer contained many rows of nuclei of rods were recorded; those with euchromatic and those and cones (Samuelson, 1999; Derbalah, 2001; with heterohromatic cells. Stell, (1967); Nilson Aly, 2003). In goats, the outer nuclear layer et al., (1970); Derbalah, (2001) supported our appeared to be formed of 67 layers of nuclei. results. The role of bipolar cells as interreceptor The most superficial layer represented the cone contact between the photoreceptor and the nuclei while the others formed the rods nuclei. ganglionic cells was a constant function of These findings were in accordance with those of bipolar cells in the opinion of most Braekevelt (1990); Samulson, (1999); histophysiologists. Ehrenhofer, (2002). There were a great The Müller cells in the present investigation resemblance between goats and other vertebrates appeared as elongated or angular cells with many in the electron microscopic picture. Whereas, the cytoplasmic processes that extended between the cone nuclei were large in size and euchromatic, external and internal limiting membranes. The the rod nuclei were smaller in size and same description was reported in most heterochromatin (Shively et al., 1970; Derbalah, vertebrates by Samuelson, (1999); Derbalah, 2001; Aly, 2003). According to the fact that the (2001); Ehrenhofer et al., (2002). The authors more euchromatic nuclei, the increased activity agreed that Müller cells were mainly supportive of the cells, the cone cells was believed to be the in function. Uga and Smelser, (1973); Nishizono more active than the rod cells. This conclusion et al., (1993) added that the vitreal part of the supports our results of the presence of more Müller cells processes end feet which had the numerous mitochondria in cone inner segments ability to phagocytose any foreign substances than those in rods. reached the area. The present investigation revealed that the As stated by many authors, the amacrine outer plexiform layer was formed of axon cells could be easily identified in the goat's retina terminals of rods and cones. These results pass in by their deeply invaginated nuclei (Nilson et al., line with that of Cohen, (1972), Dellman and 1973a; Samuelson, 1999). Their cell bodies were Collier, (1987); Samuelson, (1999). As stated by present in the innermost zone of the inner Derbalah, (2001), the cone pedicles were larger nuclear layer. On the contrary, Ehrenhofer et al., than the rod spherule. The outer plexiform layer (2002) mentioned that the amacrine cells formed of canine retina (Shively et al., 1973) resembled rows of cells closest to the and they were that of goat's retina as it showed synapse identified by their exceptionally wide between axons of photoreceptors, horizontal cytoplasmic rim. There was a quite agreement cells and bipolar cells. that the amacrine cells played an important role The appearance of a double walled blood in the interreceptor connection in the retina. The vessels in the outer plexiform layer of bovine inner nuclear layer contained double – walled (Aly, 2003) was also met in the goat's retina. It capillaries. They considered a direct continuation SOLIMAN ET AL ., 60 in the outer plexiform layer and have the same The retinal nerve fiber layer runs parallel to importance. the long axis of the retina and was supported by Our study revealed that the inner plexiform supportive glia cells mainly Müller cells, these layer was formed mainly of the cytoplasmic results came in accordance with (Dellman and processes of bipolar, amacrine and ganglionic Collier, 1987; Samuelson, 1999). cells. Dowling and Boycott, (1967) could References identify synaptic ribbon containing processes in Altuny, H. (1997): keçilerde retina pigment epiteli, Bruch's the human inner plexiform layer as a bipolar membrani ve koriokapilris' in ince yapisi. Ankara Univ. terminals. The same author described the most Vet. Fak. Derg., 44:183191. typical synapse as a dyad where the bipolar Altuny, H. (2000): Fine structure of the retinal pigment terminal formed a presynptic condition with two epithelium, Bruch's membrane and choriocapillaries in the horse. Anat. Histol. Embryol., 29:135139. processes, one being a ganglionic cell process Altuny, H. (2004): Fine structure of the retinal epithelium, and the other was process. In this Bruch's membrane and choriocapillaries in the Ostrich. respect, the present study could differentiate Anat. Histol. Embryol., 33: 3841. between the process of bipolar cells that contain Altuny, H. (2007): Fine structure of the retinal pigment epithelium, Bruch's membrane and choriocapillaries in the vesicles and ganglionic cell process which was camel. Anat. Histol. Embryol., 36(2):116120. free from them. This was, also, stated by Nilson Aly, K. (2003): Glycohistochemical, immunohistochemical et al., (1973a); Samuelson, (1999); Aly, (2003). and electron microscopic examination of the bovine The ganglionic cell layer in the present eyeball.Ph.D., Fac. Vet. Med. Ludwig Maximilians investigation resemble that described by Harman Munich Univ. Bancroft, J. and Stevens, A. (1996): Theory and Practice et al., (2001); Derbalah, (2001); Ehrenhofer et of Histological techniques. 4th Ed., Churchill Livingstone, al., (2002) as it contains two types of cells Edinburgh, London, Melbourne, New York. arranged in one row; one large spherical cells Banks, W. J. (1993): Applied Veterinary Histology. 3rd Ed. having a large vesicular nucleus with prominent Mosbyyear book. St. Louis, Baltimore, Boston, Chicago, London, Philadilphia, Sydney & Toronto PP. 481484. nucleolus and abundant organelles and smaller Bok, D. (1985): Retinal photoreceptor – pigment ganglionic cells with smaller nuclei. On the other epithelium interactions.Invest. Ophthalmol. Vis. Sci., 26: hand, Boycott and Wassals, (1974) described 1659 1694. three types of ganglionic cells; α, β and γ. The Boulton, M. (1991): Ageing of the retinal pigment smaller cells in the ganglionic layer of goat's epithelium. In: progress in the retinal research, II (N. N. Osbsrnea and G. J. chader, eds). Oxford; Pergamon press. retina have a great morphological resemblance to PP. 125 151. Müller cells a finding which was recorded, also, Boulton, M. and Dayhaw –Barker, B. (2001): The role of by Ehrenhofer et al., (2002) in equine. the retinal pigment epithelium: Topographical variation and There was a general agreement that, in all ageing changes. Eye 15:384389. Boycott, B. B. and Wassle, H. (1974): The morphological animal species, the retinal nerve fiber layer types of ganglionic cells in the domestic cat's retina. Am. J. represented the axons of ganglionic cells which Physiol. 226: 397400. coalesced to form the optic nerve. In goats, our Braekevelt, C.R. (1982): Fine structure of the retinal study revealed that the intraocular nerve fibers, epithelium, Bruch's membrane (Complexus basalis) and which represented the scleral, the chroidal and choriocapillaries in domestic ferret. Acta. Anat., 113: 117 127. the retinal parts, were totally unmyelinated as it Braekevelt, C.R. (1983a): Fine structure of was in canine (Shively et al., 1970); camels choriocapillaries, bruch's membrane and retinal epithelium (Derbalah, 2001) and bovine (Aly, 2003). On in the sheep. Anat. Embryol. 166: 415425. the contrary, Miyake et al., (2004) in dogs Braekevelt, C.R. (1983b): Retinal photoreceptor fine structure in the domestic sheep. Acta Anat. (Basel). reported that the scleral and the chroidal sections 116(3): 665 675. consisted largely of myelinated fibers. The Braekevelt, C.R. (1987): photoreceptor fine structure in the failure of myelination in the intraocular fibers vervet monkey (Cercopithecus aethiopos). 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درا ا و او ا ا

أ ه ارا ض اآ ا ا ا ا و ها اض د ٣٥ راس ا ا ا ه ا . ات ر ا ة و اآ ه ااض وا ان وات ٢٥ هة ان و ل ار ادل ول ان ة ٢٤ ٢٤ ات ا . و أت ١٠ ت اى و ل ااه ٤% وت او ا اآ ا ا . و أت ا أن ا ا ن اء اس ا اا ا و اا وا ن ١٠ ت ا ا : : ا ا ا : ون ه ا وا ا ا ا ى ا آو ا وت وا ا وار ، ون هة ا د آ ا و د ا ار . . اء اد ار : ها اء آ اد ا ا ا و ا ار وا ار . ا ار : ه ا ا ا وار . ا ا ار : ن ه ا ات ا وار . ا ا ا : ى ه ا ار ااع ا وه ، ا ا ، ا ا و اوا ا . ا ا ار : ن ه ا ات ا ا اا ا او ا ا وا ا وات ا ا ا . ا ا : ه ا وا او و إ ا ، آة و إ آو ا و اى ة ا و ا . اف ا اى : ون ه ا از اف ا ا اور ا ا ا . اء اد اا : ها اء ام ا او ات ا و ا ا.