Med.Weter. optic network membrane,indicating that Ngb is very a similar method Ostojic I(17,18)showed that Ngb sensitive to hypoxia,suggesting that Ngb may play an is observed in all retina layers,especially the cortex important role in the adaptive protection of retinal of retina pigment in the human and dog.Despite these hypoxia,while Ding et al.(10)showed that in the acute reported references,there are still limited reports on the ischemic and hypoxic state the main concentration of retina of adult Tibetan sheep.The results of this study Ngb content in the retina of rats was the ganglion cell showed that there were positive distributions of Ngb in layer,and a small amount of Ngb content was also the inner boundary membrane,optic nerve fiber layer, found in the inner and outer netted layer.In addition, ganglion cell layer,inner reticular layer,inner layer, Yan et al.(27)explained that the expression of Ngb in outer reticular layer,outer membrane and an inner seg- the retinal tissues of rabbits was higher than that in the ment of the photoreceptor of the adult sheep retina but plain and subalpine environments under the hypoxic no positive expression was found in the outer segment environment,while Ngb in the plain area was only of the photoreceptor,pigment super cortex,and optic weakly expressed in the inner and outer plexus layers network membrane which is consistent with the find- and the inner segment of photoreceptors.The present ings of Bentmann et al.(2),but different from the ob- research results show that the expression of Ngb in the servation results of Ostojic et al.(17).The expression in optic nerve fiber layer and ganglion cell layer and inner these regions has shown to be strongly expressed with plexiform layer,outer plexiform layer,photoreceptor white mRNA of mixed-signal.Yan et al.and Ostojic inner segment and the intensity of expression of the et al.(18,27)also applied the immunohistochemistry highest in areas such as the pigment in the cortex, method to obtain the expression of Ngb and immune expressed in the kernel layer strength is weak,prompt response in the retina of rats and humans.The Ngb retinal optic nerve fiber layer and ganglion cell layer distribution in both rats and humans was consistent but and inner plexiform layer,outer plexiform layer and in their study Xu et al.(25)did not observe any Ngb optical sensors in segmental oxygen consumption,such distribution in the outer nuclear layer sub-cells of the as the concentration of the highest place on the degree adult rat retina.Similarly,the current reports also ob- of sensitivity of ischemia hypoxia,cortex cell me- served no positive Ngb expression in the outer nuclear tabolism active pigment,with special phagocytosis.At layer of adult sheep retina.To ensure the network of the same time,it also performs the function of bio- membrane function,human and most mammalian filtration of the sensory layer of the retina,which re- retina and choroid membrane double loop to continue quires a higher energy supply,so it is sensitive to the flow of oxygen.Central retinal nutrition blood ischemia and hypoxia the highest.Additionally,the pipe system and outer retinal blood supply are mainly inner core layer acts as a pathway for transmitting supported by the choroid cycle,and the circulation of photoreceptor cell impulses to ganglion cells,both of choroid blood does not directly reach the photoreceptor which have large oxygen consumption requirements. cells layer,which must pass through a pigment in the The sensitivity of ischemia and hypoxia was also cortex of oxygen to diffuse to the light receptors.The higher,while the areas with negative Ngb expression, results of the immuno-histochemical semi-quantitative such as the outer nuclear layer and the outer segment analysis showed that there were significant differences of the photoreceptor,were the least sensitive to hy- in the expression of Ngb in different layers of the sheep poxia.Therefore,the difference of Ngb expression in retina.The positive expression intensity was recorded each layer of the retina may also be correlated with as the highest in the dimension layer,the inner reticular the sensitivity of each layer to ischemia and hypoxia layer,the outer reticular layer,and the inner segment injury. of the photoreceptor.which was similar to the study Adult sheep.Existing research has shown that Ngb results of Schmidt et al.(21)who studied Ngb expres- is solely expressed in rodent,dog,and human retinae sion in the retinae of mice.Mammalian retinal nerve excluding the pigment in the cortex and light sensor fiber layer,inner plexiform layer,outer plexiform layer, section which contain no expression of Ngb.A study and optical sensors are the most important parts of conducted on the mouse retina found that Ngb is ex- oxygen consumption in retinal tissue(2,3),due to the pressed in all neurons especially the plexiform layers great amount of synaptic coupling between adjacent and the ellipsoid region of the photoreceptor inner seg- layer neurons and mitochondria.The neurons send ment(5),which is consistent with the current research information through mutual synapses and releasing the that showed expression in the plexiform layers.Ostojic photoelectric signal conversion.This process requires et al.studied the retina in canines (dog)and reported a large amount of oxygen consumption and the expres- that Ngb is solely expressed in the ganglion cell layer, sion of Ngb was showed to be higher in these regions inner and outer nuclear layers,inner and outer plexi- which are related to the subcellular localization of form layers,photoreceptor inner segments,and retinal mitochondria.The oxygen transported can be utilized pigment epithelium.By using immuno-histochemical by retinal neurons to satisfy the high oxygen demand Schmidt (21)and Li(15)confirmed that Ngb is not of the four layers.In the subcellular structure,the Ngb expressed in the layer of the skin color but can be found protein is not found in the mitochondria but around in other layers of the small rat retina,but by applying them,which has important implications for further8 Med. Weter. optic network membrane, indicating that Ngb is very sensitive to hypoxia, suggesting that Ngb may play an important role in the adaptive protection of retinal hypoxia, while Ding et al. (10) showed that in the acute ischemic and hypoxic state the main concentration of Ngb content in the retina of rats was the ganglion cell layer, and a small amount of Ngb content was also found in the inner and outer netted layer. In addition, Yan et al. (27) explained that the expression of Ngb in the retinal tissues of rabbits was higher than that in the plain and subalpine environments under the hypoxic environment, while Ngb in the plain area was only weakly expressed in the inner and outer plexus layers and the inner segment of photoreceptors. The present research results show that the expression of Ngb in the optic nerve fiber layer and ganglion cell layer and inner plexiform layer, outer plexiform layer, photoreceptor inner segment and the intensity of expression of the highest in areas such as the pigment in the cortex, expressed in the kernel layer strength is weak, prompt retinal optic nerve fiber layer and ganglion cell layer and inner plexiform layer, outer plexiform layer and optical sensors in segmental oxygen consumption, such as the concentration of the highest place on the degree of sensitivity of ischemia hypoxia, cortex cell me￾tabolism active pigment, with special phagocytosis. At the same time, it also performs the function of bio￾filtration of the sensory layer of the retina, which re￾quires a higher energy supply, so it is sensitive to ischemia and hypoxia the highest. Additionally, the inner core layer acts as a pathway for transmitting photoreceptor cell impulses to ganglion cells, both of which have large oxygen consumption requirements. The sensitivity of ischemia and hypoxia was also higher, while the areas with negative Ngb expression, such as the outer nuclear layer and the outer segment of the photoreceptor, were the least sensitive to hy￾poxia. Therefore, the difference of Ngb expression in each layer of the retina may also be correlated with the sensitivity of each layer to ischemia and hypoxia injury. Adult sheep. Existing research has shown that Ngb is solely expressed in rodent, dog, and human retinae excluding the pigment in the cortex and light sensor section which contain no expression of Ngb. A study conducted on the mouse retina found that Ngb is ex￾pressed in all neurons especially the plexiform layers and the ellipsoid region of the photoreceptor inner seg￾ment (5), which is consistent with the current research that showed expression in the plexiform layers. Ostojic et al. studied the retina in canines (dog) and reported that Ngb is solely expressed in the ganglion cell layer, inner and outer nuclear layers, inner and outer plexi￾form layers, photoreceptor inner segments, and retinal pigment epithelium. By using immuno-histochemical Schmidt (21) and Li (15) confirmed that Ngb is not expressed in the layer of the skin color but can be found in other layers of the small rat retina, but by applying a similar method Ostojic I (17, 18) showed that Ngb is observed in all retina layers, especially the cortex of retina pigment in the human and dog. Despite these reported references, there are still limited reports on the retina of adult Tibetan sheep. The results of this study showed that there were positive distributions of Ngb in the inner boundary membrane, optic nerve fiber layer, ganglion cell layer, inner reticular layer, inner layer, outer reticular layer, outer membrane and an inner seg￾ment of the photoreceptor of the adult sheep retina but no positive expression was found in the outer segment of the photoreceptor, pigment super cortex, and optic network membrane which is consistent with the find￾ings of Bentmann et al. (2), but different from the ob￾servation results of Ostojic et al. (17). The expression in these regions has shown to be strongly expressed with white mRNA of mixed-signal. Yan et al. and Ostojic et al. (18, 27) also applied the immunohistochemistry method to obtain the expression of Ngb and immune response in the retina of rats and humans. The Ngb distribution in both rats and humans was consistent but in their study Xu et al. (25) did not observe any Ngb distribution in the outer nuclear layer sub-cells of the adult rat retina. Similarly, the current reports also ob￾served no positive Ngb expression in the outer nuclear layer of adult sheep retina. To ensure the network of membrane function, human and most mammalian retina and choroid membrane double loop to continue the flow of oxygen. Central retinal nutrition blood pipe system and outer retinal blood supply are mainly supported by the choroid cycle, and the circulation of choroid blood does not directly reach the photoreceptor cells layer, which must pass through a pigment in the cortex of oxygen to diffuse to the light receptors. The results of the immuno-histochemical semi-quantitative analysis showed that there were significant differences in the expression of Ngb in different layers of the sheep retina. The positive expression intensity was recorded as the highest in the dimension layer, the inner reticular layer, the outer reticular layer, and the inner segment of the photoreceptor, which was similar to the study results of Schmidt et al. (21) who studied Ngb expres￾sion in the retinae of mice. Mammalian retinal nerve fiber layer, inner plexiform layer, outer plexiform layer, and optical sensors are the most important parts of oxygen consumption in retinal tissue (2, 3), due to the great amount of synaptic coupling between adjacent layer neurons and mitochondria. The neurons send information through mutual synapses and releasing the photoelectric signal conversion. This process requires a large amount of oxygen consumption and the expres￾sion of Ngb was showed to be higher in these regions which are related to the subcellular localization of mitochondria. The oxygen transported can be utilized by retinal neurons to satisfy the high oxygen demand of the four layers. In the subcellular structure, the Ngb protein is not found in the mitochondria but around them, which has important implications for further