实验性大鼠视网膜光损伤与视细胞凋亡的关系

目的 :研究视网膜光损伤与视细胞凋亡的相互关系 ,以探讨视网膜光损伤的发生、发展机制。方法 :所有SD大鼠在循环光环境中适应 7d ,在实验前先行暗适应 36h ,分别于光照 3、6、9、12、15和 18h时灌流固定 ,摘除眼球。光镜标本在常规脱水、透明、石蜡包埋切片后 ,行HE、TUNEL法染色 ,用光镜观察 ;电镜标本在树脂包埋、超薄切片、醋酸 柠收稿日期 :2 0 0 2 -0 7-15 ;修回日期 :2 0 0 2 -10 -2 0基金项目 :辽宁省教育厅资助项目 ( 99172 114 9)。作者简介 :刘学政 ( 1962 -) ,辽宁葫芦岛人 ,医学博士 ,解剖学教授 ,研究生导师。通信作者 :刘学政 (E -mail:xuezheng @hotmail.com)。檬酸铅双重染色后 ,用透射电镜观察 ;应用CIAS 10 0 0图像分析系统定量检测外核层面积和视细胞凋亡指数 ,所得数据做统计学分析。结果 :视网膜出现了光损伤和视细胞凋亡现象 ,随着光照时间的延长 ,视网膜光损伤逐渐加重 ,视细胞凋亡逐渐增多。在外核层 ,透射电镜观察见核染色质浓集 ,而无炎性反应。外核层面积和视细胞凋亡指数做相关性分析 ,显示有显著性意义。结论 :视细胞凋亡是视网膜光损伤的重要机制。光损伤启动了视细胞凋亡的发生 ,外核层细胞核的丢失是视细胞凋亡的结果。视网膜光损伤与视细胞凋亡有着密不可分的联系。     

地塞米松对光损伤大鼠视细胞凋亡的防治作用

目的 :研究地塞米松对光损伤及视细胞凋亡的防治作用 ,以探讨光损伤视细胞凋亡的发生机制。方法 :所有SD大鼠经循环光环境适应 7d ,实验前暗适应 36h。实验A组的大鼠只光照 ,实验B组的大鼠光照 6h后在暗箱中喂养 ,实验a组的大鼠在暗适应后腹腔注射地塞米松再光照 ,实验b组的大鼠光照 6h后在暗箱中喂养 ,且每天应用地塞米松。对经以上处理过的大鼠行灌流固定 ,摘除眼球。光镜标本在常规脱水、透明、石蜡包埋切片后 ,行HE、TUNEL法染色 ,光镜观察。应用CIAS 10 0 0图像分析系统定量检测外核层面积和视细胞凋亡指数 ,所得数据做统计学分析。结果 :在实验A组中 ,随着光照时间的增加 ,视网膜光损伤逐渐加重 ,视细胞凋亡逐渐增多 ,外核层面积逐渐减少。而在实验a组中 ,也出现如实验A组的规律性变化 ,但应用地塞米松后 ,视网膜光损伤程度减轻 ,发生视细胞凋亡的时间延迟 3h。两实验组定量检测结果经统计学分析表明 ,地塞米松对视网膜光损伤及视细胞凋亡有明显的预防作用。实验B组和实验b组的定量检测结果经统计学分析表明 ,地塞米松对视网膜光损伤及视细胞凋亡有明显的治疗作用。结论 :地塞米松在实验性大鼠视网膜光损伤及视细胞凋亡过程中发挥较好的防治作用     

视网膜光化学损伤机制的研究进展

视网膜光损伤已引起人们的特别注意 ,并对其发生机制进行了广泛的研究。目前认为视网膜的光化学损伤是最主要的机制。本文介绍了视网膜光损伤的光源类型 ,着重探讨了有关光性视网膜损伤的病理机制及其进展。     

视网膜光损伤研究的分子生物学进展

光诱导视网膜损伤的概念早在柏拉图时代就已被提出。此后 ,有作者描述了太阳光照后眼部改变的特点。直到 6 0年代中期 ,Noell等才开始实验室研究。近 30年 ,视网膜光损伤的临床和科研研究日益成为眼科医师关注的热点。其意义主要在于 :第一 ,随着眼科光学诊疗器械的日益增多 [1 ] ,过强的光源导致的视网膜损伤不断见诸报道。认识其发病机制和防治方法 ,对于减少医源性光损伤是大有好处的。第二 ,视网膜光损伤是研究视网膜变性类疾病的良好动物模型 [2 ] 。众所周知 ,老年性黄斑变性 (ARMD)是西方社会老年人致盲的重要眼疾 ,而视网膜光损伤…     

视网膜光化学损伤机制的研究进展

视网膜光损伤已引起人们的特别注意，并对其发生机制进行了广泛的研究。目前认为视网膜的光化学损伤是最主要的机制。本介绍了视网膜光损伤的光源类型，着重探讨了有关光性视网膜损伤的病理机制及其进展。     

视网膜光辐照实验模型研究进展

随着电子设备的普及与环境光污染现象的日趋严重, 视网膜光辐照引起的损伤及其对视网膜色素变性、年龄相关性黄斑变性等疾病的致病作用逐渐被关注。光-视网膜组织反应类型以光热反应及光化学反应为主, 其中可见光产生的光化学反应与视网膜疾病关系密切。光辐照参数包括光辐照波长、辐照能量及辐照时间等, 不同参数下光辐照对视网膜细胞的作用还可能受多种外界因素影响。较多视网膜光辐照细胞实验模型建立以研究光辐照, 尤其是蓝光对视网膜色素上皮细胞、光感受器细胞及神经细胞损伤的机制。光辐照会导致视网膜各细胞氧化应激、内质网应激及线粒体损伤激活自噬调控细胞凋亡。炎性小体激活及外泌体也参与调控光辐照对视网膜色素上皮细胞的损伤。也有研究探讨不同波长光源对细胞的潜在治疗作用。本文从光-视网膜组织反应类型、生物学研究中常用的光辐照参数, 以及视网膜色素上皮细胞光辐照模型、视网膜光感受器细胞光辐照模型、视网膜神经节细胞光辐照模型等方面就视网膜光辐照的实验模型, 探讨不同模型间细胞及光辐照参数的差异。     

视网膜光损伤的研究进展

视网膜光损伤及其损伤防御机制和药物性防治的研究一直是数十年来眼科领域一个基础结合临床的重要研究课题。本文回顾了视网膜光损伤的研究历史，从致伤光源的性能，光损伤的影响因素，分子病理机制的研究进展，及其防治措施等方面的研究进展进行综述，指出在视网膜光化学损伤过程中，存在着我种因素的调控与影响，其损伤机制是多层次多方面的，但随着分子生物学在光损伤机制研究中的普遍应用，光损伤确切的分子致病机制可在不久的将     

视网膜光损伤的研究进展

视网膜光损伤及其损伤防御机制和药物性防治的研究一直是数十年来眼科领域一个基础结合临床的重要研究课题。本文回顾了视网膜光损伤的研究历史，从致伤光源的性能、光损伤的影响因素、分子病理机制的研究进展，及其防治措施等方面的研究进展进行综述，指出在视网膜光化学损伤过程中，存在着多种因素的调控与影响，其损伤机制是多层次多方面的，但随着分子生物学技术在光损伤机制研究中的普遍应用，光损伤确切的分子致病机制可望在不久的将来得到阐明     

可见光对视网膜的损伤

光性视网膜损伤已愈来愈受到人们的重视,但是有关损伤机理的研究仍不很透彻。本文综述了大量文献,着重探讨了光性视网膜损伤的致伤光源、视网膜吸收光的部位、光性视网膜损伤的检测手段、光性视网膜损伤的可能机理以及视网膜光性损伤的防护。     

自主感光视网膜神经节细胞与彩色光瞳孔测量

自主感光视网膜神经节细胞（ipRGCs）是除视杆细胞、视锥细胞以外的第三类光感受器细胞,位于视网膜内层,由于其内含黑视蛋白,故具备自主感光能力。瞳孔对光反应（PLR）主要由ipRGCs介导产生。ipRGCs可通过黑视蛋白直接感受光信号产生PLR,也可被来自视杆、视锥细胞的信号激活产生PLR。由于视杆细胞、视锥细胞和黑视蛋白产生的PLR各具特点,可采用不同强度和波长的光信号选择性刺激视杆细胞、视锥细胞和黑视蛋白,通过对产生的PLR进行分析可间接反映视杆细胞、视锥细胞和含黑视蛋白的ipRGCs的功能,这一方法称为彩色光瞳孔测量。现主要对ipRGCs介导PLR的通路、视杆/视锥细胞和黑视蛋白引起的PLR特点、彩色光瞳孔测量及其临床应用作一综述,希冀为相关眼科疾病的诊断及鉴别诊断提供新思路。     

Expression of brain-derived neurotrophic factor in cholinergic and dopaminergic amacrine cells in the rat retina and the effects of constant light rearing

Brain-derived neurotrophic factor (BDNF) regulates many aspects of neuronal development, including survival, axonal and dendritic growth and synapse formation. Despite recent advances in our understanding of the functional significance of BDNF in retinal development, the retinal cell types expressing BDNF remains poorly defined. The goal of the present study was to determine the localization of BDNF in the mammalian retina, with special focus on the subtypes of amacrine cells, and to characterize, at the cellular level, the effects of constant light exposure during early postnatal period on retinal expression of BDNF. Retinas from 3-week-old rats reared in a normal light cycle or constant light were subjected to double immunofluorescence staining using antibodies to BDNF and retinal cell markers. BDNF immunoreactivity was localized to ganglion cells, cholinergic amacrine cells and dopaminergic amacrine cells, but not to AII amacrine cells regardless of rearing conditions. Approximately 75% of BDNF-positive cells in the inner nuclear layer were cholinergic amacrine cells in animals reared in a normal lighting condition. While BDNF immunoreactivity in ganglion cells and cholinergic amacrine cells was significantly increased by constant light rearing, which in dopaminergic amacrine cells was apparently unaltered. The overall structure of the retina and the density of ganglion cells, cholinergic amacrine cells and AII amacrine cells were unaffected by rearing conditions, whereas the density of dopaminergic amacrine cells was significantly increased by constant light rearing. The present results indicate that cholinergic amacrine cells are the primary source of BDNF in the inner nuclear layer of the rat retina and provide the first evidence that cholinergic amacrine cells may be involved in the visual activity-dependent regulation of retinal development through the production of BDNF. The present data also suggest that the production or survival of dopaminergic amacrine cells is regulated by early visual experience.     

Photochemical damage of the retina

Visual perception occurs when radiation with a wavelength between 400 and 760 nm reaches the retina. The retina has evolved to capture photons efficiently and initiate visual transduction. The retina, however, is vulnerable to damage by light, a vulnerability that has long been recognized. Photochemical damage has been widely studied, because it can cause retinal damage within the intensity range of natural light. Photochemical lesions are primarily located in the outer layers at the central region of the retina. Two classes of photochemical damage have been recognized: Class I damage, which is characterized by the rhodopsin action spectrum, is believed to be mediated by visual pigments, with the primary lesions located in the photoreceptors; whereas Class II damage is generally confined to the retinal pigment epithelium. The action spectrum peaks in the short wavelength region, providing the basis for the concept of blue light hazard. Several factors can modify the susceptibility of the retina to photochemical damage. Photochemical mechanisms, in particular mechanisms that arise from illumination with blue light, are responsible for solar retinitis and for iatrogenic retinal insult from ophthalmological instruments. Further, blue light may play a role in the pathogenesis of age-related macular degeneration. Laboratory studies have suggested that photochemical damage includes oxidative events. Retinal cells die by apoptosis in response to photic injury, and the process of cell death is operated by diverse damaging mechanisms. Modern molecular biology techniques help to study in-depth the basic mechanism of photochemical damage of the retina and to develop strategies of neuroprotection.     

Understanding the origin of visual percepts elicited by electrical stimulation of the human retina

· Background: The success of a retinal prosthesis for patients with outer retinal degeneration (ORD) depends on the ability to electrically stimulate retinal cells other than photoreceptors. Experiments were undertaken in human volunteers to ascertain whether electrical stimulation of cells other than photoreceptors will result in the perception of light. · Methods: In two subjects, two areas of laser damage (argon green and krypton red) were created in an eye scheduled for exenteration due to recurrent cancer near the eye. In the operating room prior to exenteration, under local anesthesia, a hand-held stimulating device was inserted via the pars plana and positioned over the damaged areas and normal retina. Subjects’ psychophysical responses to electrical stimulation were recorded. · Results: In both subjects, electrical stimulation produced the following perceptions. Normal retina: dark oval (subject 1), dark half-moon (subject 2); krypton red laser-treated retina: small, white light (both subjects); argon green laser-treated retina: thin thread (subject 1), thin hook (subject 2). Histologic evaluation of the krypton red-treated retina showed damage confined to the outer retinal layers, while the argon green-treated area evinced damage to both the outer and the inner nuclear layers · Conclusion: The perception produced by electrical stimulation was dependent on the retinal cells present. Electrical stimulation of the krypton red-ablated area best simulated the electrically elicited visual perceptions of our blind, ORD patients, suggesting that the site of stimulation in blind patients is the inner retinal neurons. Received: 25 February 1999 Revised version received: 25 May 1999 Accepted: 28 June 1999     

Retinal light damage: Mechanisms and protection

By its action on rhodopsin, light triggers the well-known visual transduction cascade, but can also induce cell damage and death through phototoxic mechanisms – a comprehensive understanding of which is still elusive despite more than 40 years of research. Herein, we integrate recent experimental findings to address several hypotheses of retinal light damage, premised in part on the close anatomical and metabolic relationships between the photoreceptors and the retinal pigment epithelium. We begin by reviewing the salient features of light damage, recently joined by evidence for retinal remodeling which has implications for the prognosis of recovery of function in retinal degenerations.  We then consider select factors that influence the progression of the damage process and the extent of visual cell loss. Traditional, genetically modified, and emerging animal models are discussed, with particular emphasis on cone visual cells. Exogenous and endogenous retinal protective factors are explored, with implications for light damage mechanisms and some suggested avenues for future research. Synergies are known to exist between our long term light environment and photoreceptor cell death in retinal disease. Understanding the molecular mechanisms of light damage in a variety of animal models can provide valuable insights into the effects of light in clinical disorders and may form the basis of future therapies to prevent or delay visual cell loss.     

视网膜光损伤机制的研究进展

视网膜是一种高度专业化的组织,具有独特的结构及适应性,在所有不同类型的视网膜细胞中保持动态平衡对于维持视力至关重要。视网膜可能会暴露在各种环境损伤中,如光诱导的损伤,在进化过程中,视网膜细胞对各种损伤产生了适应性反应,这些反应共同恢复了细胞的动态平衡,并增加了组织对进一步损伤的抵抗力。然而过度光照则会导致视网膜组织内光感受器细胞、视网膜神经节细胞(RGC)、视网膜神经胶质细胞及视网膜色素上皮细胞(RPE)发生一系列病理改变,包括线粒体内活性氧(ROS)和Ca²⁺浓度增加、细胞凋亡、内质网应激、细胞自噬和炎症等,从而导致视网膜发生不可逆损伤。本文将对视网膜光损伤的发病机制和相关研究进展进行详细阐述,为未来防治视网膜光损伤提供研究方向。     

Retinal damage produced by intraocular fiber optic light.

We exposed the maculas of owl monkey eyes to light from an intraocular fiber optic light source similar to that used for human pars plana vitrectomy. Retinal irradiance was calculated at 0.22 W/cm2. Eyes were exposed for time intervals ranging from 30 minutes to five minutes and were observed after light treatment by fundus photography and fluorescein angiography. Tissue was obtained for light and electron microscopy by animal killing at one hour, 24 hours, one week, and four weeks. Fundus lesions were seen ophthalmoscopically as early as five hours following 30 minutes of light exposure. Significant damage to the photoreceptor layer and less damage to the pigment epithelium was present by light and electron microscopy as early as one hour after 30 minutes of light exposure. By one month complete loss of photoreceptors with Müller cell junctions between inner retina and flattened abnormal retinal pigment epithelium cells was observed. Fluorescein angiography revealed significant staining of the pigment epithelium and outer retina 24 hours after 30 minutes of light exposure. No leakage from retinal vessels occurred. At one month following light treatment, transmission of choroidal fluorescein through window defects in the pigment epithelium was present with no retinal staining. The threshold for ophthalmoscopically visible fundus lesions in this study was 15 minutes of light exposure. Ten minutes of light treatment was the threshold for microscopic changes. Short light exposures damaged the outer retina and spared the pigment epithelium. Removing a substantial amount of the infrared light from our light source did not protect the retina from damage. Removal of light between 400 and 500 nm is probably more helpful in protecting the retina. Intermittent light exposure of the retina seemed as harmful as uninterrupted illumination for the same cumulative period of time. We speculate that the retinal damage caused by intraocular fiber optic light has primarily a photic mechanism. Damage to the retinal pigment epithelium may be secondary to outer retinal damage. The present levels of intraocular light used for human pars plana vitrectomy are probably safe in most instances. Lengthy preretinal membrane stripping procedures during vitrectomy, however, may pose a threat of light damage to the retina. This damage must be appreciated as continued efforts are made to produce brighter sources of intraocular light for human pars plana vitrectomy.     

Retinal light damage in rats exposed to intermittent light. Comparison with continuous light exposure

Visible light-induced photoreceptor cell damage resulting from exposure to multiple intermittent light-dark periods was compared with damage resulting from continuous light in albino rats maintained in a weak cyclic-light environment or in darkness before light treatment. The time course of retinal damage was determined by correlative measurements of rhodopsin and visual cell DNA at various times after light exposure, and by histopathological evaluation. The effect of intense light exposures on rhodopsin regeneration and on the level of rod outer segment docosahexaenoic acid was also determined. For rats previously maintained in weak cyclic light, 50% visual cell loss was measured 2 weeks after 12 1 hr light/2 hr dark periods, or following 24 hr of continuous light. A comparable 50% loss of visual cells was found in dark-reared rats after only 5 hr of continuous illumination or 2-3 hr of intermittent light. As judged by histology, cyclic-light-reared rats incurred less retinal pigment epithelial cell damage than dark-reared animals. In both experimental rat models intermittent light exposure resulted in greater visual cell damage than continuous exposure. Visual cell damage from intermittent light was found to depend on the duration of light exposure and on the number of light doses administered. Measurements of rhodopsin and DNA 2 hr and 2 weeks after light exposure of up to 8 hr duration revealed that visual cell loss occurs largely during the 2 week dark period following light treatment. The loss of docosahexaenoic acid from rod outer segments was also greater in rats exposed to intermittent light than in animals treated with continuous light. It is concluded that intermittent light exposure exacerbates Type I light damage in rats (involving the retina and retinal pigment epithelium) and the schedule of intense light exposure is a determinant of visual cell death.     

The cone-specific visual cycle

Cone photoreceptors mediate our daytime vision and function under bright and rapidly-changing light conditions. As their visual pigment is destroyed in the process of photoactivation, the continuous function of cones imposes the need for rapid recycling of their chromophore and regeneration of their pigment. The canonical retinoid visual cycle through the retinal pigment epithelium cells recycles chromophore and supplies it to both rods and cones. However, shortcomings of this pathway, including its slow rate and competition with rods for chromophore, have led to the suggestion that cones might use a separate mechanism for recycling of chromophore. In the past four decades biochemical studies have identified enzymatic activities consistent with recycling chromophore in the retinas of cone-dominant animals, such as chicken and ground squirrel. These studies have led to the hypothesis of a cone-specific retina visual cycle. The physiological relevance of these studies was controversial for a long time and evidence for the function of this visual cycle emerged only in very recent studies and will be the focus of this review. The retina visual cycle supplies chromophore and promotes pigment regeneration only in cones but not in rods. This pathway is independent of the pigment epithelium and instead involves the Müller cells in the retina, where chromophore is recycled and supplied selectively to cones. The rapid supply of chromophore through the retina visual cycle is critical for extending the dynamic range of cones to bright light and for their rapid dark adaptation following exposure to light. The importance of the retina visual cycle is emphasized also by its preservation through evolution as its function has now been demonstrated in species ranging from salamander to zebrafish, mouse, primate, and human.     

Increased metallothionein in light damaged mouse retinas

Oxidative stress plays a role in human age-related macular degeneration and in the light damage model of retinal degeneration. Metallothionein (MT), an antioxidant, has been reported to protect retinal pigment epithelial cells against apoptosis and oxidative stress. The purpose of this study was to evaluate changes in MT expression level and retinal localization following light damage. To accomplish this, Balb/c mice were exposed to cool white fluorescent light (10,000 lx) for 7 hr. In three independent experiments, at several intervals after the light injury, retinal MTs were studied at the protein level by immunohistochemistry (IHC) and Western analysis, and at the mRNA level by quantitative PCR with isoform-specific primers. Western analysis and IHC indicated an increase in metallothionein protein following light damage. MT localized to the retinal pigment epithelium and several layers of neural retina. Quantitative PCR identified the expression of MT I-III isoforms, not the MT IV isoform in the mouse retina, and, following light damage, showed increased expression of retinal MT-I and MT-II mRNAs by 8- and 22-fold, respectively. Increased expression of the antioxidant MT in the light damaged mouse retina suggests that upregulation of MT is an important acute retinal response to photo-oxidative stress.