Med.Weter. Ngb in the mammalian retina and provides valuable ported in the current study but differs from the results clues for the study of its function. of Xu et al.(24).The difference may be related to the Adult rabbits.Previous studies have shown that sensitivity of the antibodies and methods used Ngb was positively expressed in all layers ofthe rodent, Immuno-histochemical semi-quantitative analysis dog,and human retinas,excluding the pigmented cor- results showed that Ngb expression in rabbit retina tex and photoreceptors (5,23).The studies further layers has an obvious difference on the strength of the stated that Ngb is highly concentrated in the layers and section in the optic nerve fiber layer,cell layer and expression levels differ.Similarly,the current results inner plexiform layer,outer plexiform layer and opti- reported that Ngb expression was found in these re- cal sensors in segmental positive expression which has gions.The positive distribution of Ngb was observed the highest intensity.This is consistent with what in the outer reticular layer,outer membrane and the Schmidt et al.reports in the retina of mice(21).Studies inner segment of the photoreceptor,while no positive have shown that the optic nerve fiber layer,ganglion expression was observed in the outer segment of the cell layer,inner reticular layer,outer reticular layer and photoreceptor,retinal inner boundary membrane,optic inner photoreceptor segment of the mammalian retina nerve fiber layer,ganglion cell layer,inner reticular are the most concentrated parts of the retina in oxygen layer,and kernel layer.Up to the present,debate on consumption because these regions are the adjacent the exact localization and mechanism of Ngb remains layer of the synaptic connection between neurons and a focus among scientists.A study documented that Ngb mitochondria(27).These neurons are involved in the show sequence variation in vertebrate evolution,sug- passage of information through mutual synapses.The gesting conserved structures and functions,and an photoelectric signal conversion needs to consume large important role in the animal's metabolism(6).Li You amounts of oxygen,and Ngb in these regions is high- (15)et al.utilized immunohistochemistry to confirm ly expressed.These regions and the subcellular local- Ngb expression,and the results reported that the ex- ization of mitochondria are closely related since with pression of Ngb was observed in other layers except the expression of Ngb because the body carrying oxy- for the pigmentation cortex of rats and mice.However, gen can also be used by retinal neurons to satisfy the Ostoji et al.(17)applying similar methods found that demand of oxygen consumption.Additionally,Xu et Ngb was located in the retinae of humans.The expres- al.(24)found that there were more Ngb positive par- sion was mainly located in the upper epidermis of ticles distributed between the synaptic vesicles in the human and dog retinas.In the current study,Ngb presynaptic structure of the adult rat retina,which positive expression was observed in the superior cortex supported the hypothesis that Ngb was related to the of the retinal pigment in adult rabbits which is consis- oxygen consumption of the optic network membrane. tent with the observation of Ding et al.(10).There also This further suggested that Ngb could be secreted and exists a minimum difference in these results and the transported to the synaptic vesicles to complete com- difference may have originated from the sensitivity of plex physiological functions.The present study like- the antibody and the methodology employed. wise found that Ngb also had a high level of positive Additionally,to ensure the functionality of the retina, expression in the retinal pigment superior cortex of humans and most mammals through the retina and rabbits.Studies have shown that the inner folds of the choroid double loop to oxygen in a row,the inner plasma membrane of the pigment epithelial cells can retinal nutrition by the central retinal vascular system. expand the contact area between the pigment epithe- the outer retinal blood supply is mainly supported by lial cells and the choroidal capillaries,which is con- choroid cycle,and the circulation of choroid blood ducive to the selective transfer of nutrients and me- does not directly reach the photoreceptor cell layer, tabolites between the outer layer of the retina and the which must pass through a pigment in the cortex of choroidal capillaries (29).Moreover,epigallocytes oxygen to diffuse to the photoreceptors.This might be have the functions of vitamin A transport and metabo- one of the reasons for different Ngb expression. lism,drug detoxification,synthesis of melanin and Whether the presence of Ngb in the pigment super extracellular matrix,and phagocytosis and digestion cortex is produced by the pigment super cortex cells of membrane plates shed from the outer segments of or the transport and redistribution of Ngb produced in photoreceptors.These functions of pigment epithelial neurons remains to be verified by further experiments. cells all require higher energy requirements on them- As reported in the study of Ding et al.(11).Ngb is selves,suggesting that the high expression of Ngb in distributed in the mammalian retina outer nuclear the pigment epithelial layer may be related to the high layer which differs from the current research report. oxygen consumption needed to maintain normal func- The in situ hybridization histochemistry technique was tional activities.Studies have shown that Ngb plays used by Yan et al.(27)and Ostoji (17)to examine the a crucial role in the dynamic oxygen balance of the expression of Ngb in the inner and outer nuclear layer retina,and its existence can make the optic network in the retinae of human and rat.The results confirmed membrane endure longer under the condition of isch- that strong expression was found in the inner and emia and hypoxia(20).Shi et al.(22)found that Ngb outer nuclear layers which are similar to what is re- was rapidly increased after the lack of blood in theMed. Weter. 7 Ngb in the mammalian retina and provides valuable clues for the study of its function. Adult rabbits. Previous studies have shown that Ngb was positively expressed in all layers of the rodent, dog, and human retinas, excluding the pigmented cor￾tex and photoreceptors (5, 23). The studies further stated that Ngb is highly concentrated in the layers and expression levels differ. Similarly, the current results reported that Ngb expression was found in these re￾gions. The positive distribution of Ngb was observed in the outer reticular layer, outer membrane and the inner segment of the photoreceptor, while no positive expression was observed in the outer segment of the photoreceptor, retinal inner boundary membrane, optic nerve fiber layer, ganglion cell layer, inner reticular layer, and kernel layer. Up to the present, debate on the exact localization and mechanism of Ngb remains a focus among scientists. A study documented that Ngb show sequence variation in vertebrate evolution, sug￾gesting conserved structures and functions, and an important role in the animal’s metabolism (6). Li You (15) et al. utilized immunohistochemistry to confirm Ngb expression, and the results reported that the ex￾pression of Ngb was observed in other layers except for the pigmentation cortex of rats and mice. However, Ostoji et al. (17) applying similar methods found that Ngb was located in the retinae of humans. The expres￾sion was mainly located in the upper epidermis of human and dog retinas. In the current study, Ngb positive expression was observed in the superior cortex of the retinal pigment in adult rabbits which is consis￾tent with the observation of Ding et al. (10). There also exists a minimum difference in these results and the difference may have originated from the sensitivity of the antibody and the methodology employed. Additionally, to ensure the functionality of the retina, humans and most mammals through the retina and choroid double loop to oxygen in a row, the inner retinal nutrition by the central retinal vascular system, the outer retinal blood supply is mainly supported by choroid cycle, and the circulation of choroid blood does not directly reach the photoreceptor cell layer, which must pass through a pigment in the cortex of oxygen to diffuse to the photoreceptors. This might be one of the reasons for different Ngb expression. Whether the presence of Ngb in the pigment super cortex is produced by the pigment super cortex cells or the transport and redistribution of Ngb produced in neurons remains to be verified by further experiments. As reported in the study of Ding et al. (11). Ngb is distributed in the mammalian retina outer nuclear layer which differs from the current research report. The in situ hybridization histochemistry technique was used by Yan et al. (27) and Ostoji (17) to examine the expression of Ngb in the inner and outer nuclear layer in the retinae of human and rat. The results confirmed that strong expression was found in the inner and outer nuclear layers which are similar to what is re￾ported in the current study but differs from the results of Xu et al. (24). The difference may be related to the sensitivity of the antibodies and methods used. Immuno-histochemical semi-quantitative analysis results showed that Ngb expression in rabbit retina layers has an obvious difference on the strength of the section in the optic nerve fiber layer, cell layer and inner plexiform layer, outer plexiform layer and opti￾cal sensors in segmental positive expression which has the highest intensity. This is consistent with what Schmidt et al. reports in the retina of mice (21). Studies have shown that the optic nerve fiber layer, ganglion cell layer, inner reticular layer, outer reticular layer and inner photoreceptor segment of the mammalian retina are the most concentrated parts of the retina in oxygen consumption because these regions are the adjacent layer of the synaptic connection between neurons and mitochondria (27). These neurons are involved in the passage of information through mutual synapses. The photoelectric signal conversion needs to consume large amounts of oxygen, and Ngb in these regions is high￾ly expressed. These regions and the subcellular local￾ization of mitochondria are closely related since with the expression of Ngb because the body carrying oxy￾gen can also be used by retinal neurons to satisfy the demand of oxygen consumption. Additionally, Xu et al. (24) found that there were more Ngb positive par￾ticles distributed between the synaptic vesicles in the presynaptic structure of the adult rat retina, which supported the hypothesis that Ngb was related to the oxygen consumption of the optic network membrane. This further suggested that Ngb could be secreted and transported to the synaptic vesicles to complete com￾plex physiological functions. The present study like￾wise found that Ngb also had a high level of positive expression in the retinal pigment superior cortex of rabbits. Studies have shown that the inner folds of the plasma membrane of the pigment epithelial cells can expand the contact area between the pigment epithe￾lial cells and the choroidal capillaries, which is con￾ducive to the selective transfer of nutrients and me￾tabolites between the outer layer of the retina and the choroidal capillaries (29). Moreover, epigallocytes have the functions of vitamin A transport and metabo￾lism, drug detoxification, synthesis of melanin and extracellular matrix, and phagocytosis and digestion of membrane plates shed from the outer segments of photoreceptors. These functions of pigment epithelial cells all require higher energy requirements on them￾selves, suggesting that the high expression of Ngb in the pigment epithelial layer may be related to the high oxygen consumption needed to maintain normal func￾tional activities. Studies have shown that Ngb plays a crucial role in the dynamic oxygen balance of the retina, and its existence can make the optic network membrane endure longer under the condition of isch￾emia and hypoxia (20). Shi et al. (22) found that Ngb was rapidly increased after the lack of blood in the