Delayed loss of cone and remaining rod photoreceptor cells due to impairment of choroidal circulation after acute light exposure in rats

PURPOSE: To examine the long-term effects of acute photooxidative stress in the retina, retinal pigment epithelium (RPE), and choroid. METHODS: Albino rats injected with either the protective antioxidant phenyl-N-tert-butylnitrone (PBN) or saline 30 minutes before exposure to 5 klx white fluorescent light for 6 hours were kept for up to 3 months in 5 lux cyclic light. Electroretinograms were recorded, and the outer nuclear layer (ONL) and the choroidal thickness and area were measured after hematoxylin-eosin (H&E) staining. The expression of rod, cone, and RPE cell markers was detected by Western blotting, and apoptosis was analyzed by TUNEL staining. Oxidative stress was analyzed by immunohistochemistry against 4-hydroxynonenal (4-HNE)-modified proteins. Retinal and choroidal ultrastructures were observed by transmission electron microscopy (TEM). Choroidal circulation was analyzed by in vivo staining of the choroidal layer by trypan blue. RESULTS: In the saline-injected animals, TUNEL- and 4-HNE-labeling in the ONL, RPE, and choroid were higher 24 hours and 7 days after light exposure, and ERG amplitude, ONL and choroidal thickness and area, and rhodopsin and RPE65 expression were lower 7 or more days after light exposure than in phenyl-N-tert-butylnitrone (PBN)-injected animals. In the saline-injected animals, the expression of mid-wavelength opsin and the presence of cone cells in the ONL and the choroidal circulation were preserved for 7 days after light exposure but started to decrease by 1 month and continued to decrease for 3 months after light exposure. An increase in TUNEL-positive cells was observed in the ONL at the inferior peripheral retina, just behind the iris, by 3 months after light exposure. Delayed loss of cone cells, remaining rod cells, and choroidal circulation were counteracted by PBN treatment. CONCLUSIONS: Although cone cells are resistant to cell damage induced by acute photooxidative stress, progressive loss of cone cells continued for up to 3 months after light exposure. Impaired choroidal circulation is likely to be involved in the mechanism of delayed photoreceptor cell death after light exposure. Preserving choroidal circulation may provide a novel target for preserving the cone and the remaining rod cells in patients with retinal degeneration such as retinitis pigmentosa.     

Dexamethasone ameliorates retinal photic injury in albino rats.

The effect of dexamethasone in two regimens on retinal photic injury was studied in Lewis albino rats that were exposed to 24 hr of continuous green fluorescent light. Under regimen 1, dexamethasone was given at a daily dosage of 1 mg kg-1 for 8 days, starting 6 days before light exposure. Under regimen 2, dexamethasone was given at the same daily dosage for 3 days, started 1 day before light exposure. Pathologic study of the light-exposed retina, morphometric evaluation of the photoreceptor cell loss, cell counts of the macrophages in the subretinal space, and measurements of rhodopsin levels were undertaken in the dexamethasone-treated and control retinas at various times. The administration of dexamethasone in both regimens did not produce pathologic changes in the retina before light exposure, but rhodopsin levels were significantly lowered in both treated groups when compared to corresponding vehicle treated control animals. Under regimen 1, at 6 hr after light exposure, both the treated and the control groups showed comparable loss of photoreceptor cells, degeneration of the photoreceptor elements and retinal pigment epithelium, but a significantly lowered level of rhodopsin in the treated group was noted. At 6 days after exposure, the outer nuclear layer thickness, and the outer and inner segments showed significant preservation in the treated group. Also in the treated group, the number of macrophages was significantly reduced and the retinal pigment epithelial (RPE) vacuolation was markedly less. However, there was no difference in rhodopsin levels. At 14 days after exposure, the outer nuclear layer thickness and rhodopsin levels of the treated rats had significantly higher values than the controls. Under regimen 2, however, at 6 days after exposure, an ameliorative effect in the RPE was observed but there were no differences of rhodopsin levels, the outer nuclear thickness and number of macrophages between the treated and control groups. Regimen 1 was associated with a significantly higher retinal level of dexamethasone when compared with regimen 2. The ameliorative effect of dexamethasone on rat retinal photic injury may be through inhibition of lipid peroxidation, in which a high retinal level of the steroid is required.     

Age-related and light-associated retinal changes in Fischer rats

Morphological changes in retinas of aging Fischer 344 rats were characterized. The numbers of photoreceptor cells gradually decreased as rats aged. The outer nuclear layer was 12 cells thick at 3 months, but was reduced to less than 8 cells by 18 months. The decrease of photoreceptor cells was more pronounced in rats housed under a light intensity of 32-ft-c than in rats housed under a light intensity of 1 ft-c. Inner and outer segments of surviving photoreceptor cells were morphologically normal. A new form of retinal degeneration was discovered in aged Fischer rats characterized by selective degeneration of peripheral retina. Degeneration was characterized by severe loss of photoreceptor cells in the far peripheral retina. Microcystoids were found in about 25% ofthe affected retinas, and the loss of photoreceptor cells was followed by proliferation and vascularization of the retinal pigment epithelium and disorganization of retinal structures. The incidence and severity of peripheral retinal degeneration increased with aged and prolonged exposure to comparatively high-intensity light. All Fischer rats ((5/5) housed under light intensity of 32 ft-c developed severe peripheral retinal degeneration by 24 months. Peripheral retinal degeneration was an age-related change but appeared to be exaggerated by ambient light.     

Localization of retinal calmodulin kinase

The localization of calmodulin kinase II (CaM kinase) was studied in the retina by light and electron microscopic immunocytochemistry, and by enzymatic and immunoblot assay of cellular and subcellular tissue fractions. By light microscopy, both mono- and polyclonal antibodies revealed CaM kinase-like immunoreactivity in the inner and outer plexiform regions (synaptic layers), retinal pigment epithelium (RPE), and ganglion cells. The inner nuclear layer and photoreceptor outer segments stained much less intensely, and the outer nuclear layer did not stain. Electron microscopy confirmed the high concentration of immunoreactive protein in RPE and minimal outer segment staining. In addition, photoreceptor inner segments also contained CaM kinase-like immunoreactivity. Calcium and calmodulin stimulated phosphate incorporation into proteins of retinal cytosol and of isolated and cultured RPE. Calcium- and calmodulin-dependent kinase activity was present to a lesser degree in crude nuclei and synaptic membranes and was absent in isolated rod outer segments. Immunoblot analyses were consistent with enzymatic assays and immunocytochemistry. These data suggest that retinal CaM kinase is ideally located to play an important role in synaptic transmission and modulation of visual processes. Furthermore, its presence in RPE implies that CaM kinase may have a more ubiquitous role in regulating cellular processes than was previously recognized.     

Opsin distribution and protein incorporation in photoreceptors after experimental retinal detachment.

The distribution of opsin was examined immunocytochemically after experimental retinal detachment in adult cats. Retinal detachments were produced by injecting fluid between the retinal pigment epithelium and neural retina. One to 60 days later the animals were killed. Tissue areas from detached and attached retinal regions from the eye with the detached retina, as well as normal (control) retinas, were processed for post-embedding light and electron microscopic immunocytochemistry. In normal and attached retinal regions, anti-opsin labeled the outer segments and Golgi apparatus most heavily, although the entire photoreceptor plasma membrane was labeled at a low level. Beginning at 2 days after retinal detachment, immunolabeling increased in the photoreceptor inner segment, cell body and synaptic terminal plasma membranes. This pattern of anti-opsin labeling continued at all intervals up through the 60-day detachment time-point. Injection of radiolabeled amino acid in detachments from 1 to 30 days show that radiolabeled protein is still transported to the truncated outer segments of the photoreceptor cells. In addition, these outer segment disks label with anti-opsin. These data imply that opsin continues to be transported and incorporated into the outer segments of photoreceptors showing severe degeneration as a result of long-term detachment from the RPE.     

光损伤对大鼠血-视网膜屏障功能的影响

目的：探讨强光对大鼠血－视网膜屏障功能的影响。方法：大鼠随机分为光照组及对照组,光照组大鼠经散瞳后进行10000lx强光照射（12h光照,12h避光,连续1～14d）,对照组只接受自然光线照射。分别于强光照射后第1、3、7、14 d 摘除相应的光照组和对照组大鼠双侧眼球;并用HE染色观察视网膜各层结构变化,用电镜观察视网膜超微结构变化,用伊凡思蓝（Evans blue,EB）灌注后激光共聚焦显微镜下微循环成像及分光光度法定量检测视网膜微循环通透性变化,来评估血－视网膜屏障变化。结果：大鼠在强光照射1d后就出现视网膜光感受器细胞变性、外节膜盘脱落、外核层厚度变薄等超微结构改变,并随着强光照射持续而逐渐加重,3 d后出现光感受器细胞凋亡,至14 d时外核层厚度已明显变薄、细胞数也明显减少。大鼠在强光照射1 d后视网膜血管就出现EB染料渗漏,至14 d时EB染料渗漏最明显。结论：强光照射可导致大鼠视网膜外核层光感受器细胞变性、凋亡,外核层厚度变薄、细胞数减少,血－视网膜屏障结构、功能破坏。     

Protein modifications by 4-hydroxynonenal and 4-hydroxyhexenal in light-exposed rat retina

PURPOSE: 4-Hydroxynonenal (4-HNE) and 4-hydroxyhexenal (4-HHE) are reactive aldehydes derived from the nonenzymatic oxidation of n-6 and n-3 polyunsaturated fatty acids, respectively. Increasing evidence suggests that protein modifications by reactive aldehydes are involved in various diseases. The present study was undertaken to test whether protein modifications by 4-HNE and 4-HHE increase in retinal tissues after exposure of rats to damaging levels of light. METHODS: Albino rats were exposed to 1 or 5 klux white fluorescent light for 3 hours and, at various times thereafter, the levels and localizations of aldehyde-modified proteins in retinas were assessed by densitometric analysis of semiquantitative Western dot blots and by immunohistochemistry, using 4-HNE- and 4-HHE-specific antibodies. In some rats, the protective antioxidant phenyl-N-tert-butylnitrone (PBN) was injected (50 mg/kg) before exposure to light. To assess retinal damage, outer nuclear layer (ONL) thickness was measured on hematoxylin-eosin (H&E)-stained sections, and apoptosis was semiquantitatively analyzed by TUNEL staining. RESULTS: By dot blot analysis, 4-HNE- and 4-HHE-modified proteins were significantly increased in retina (both by 1.7-fold) and RPE fraction (1.5- and 1.8-fold, respectively) after 5-klux exposure. In retina, increases in 4-HNE- and 4-HHE-modified proteins were more prominent at 3 hours than at 24 hours or 48 hours after exposure to light. In rod outer segments, only 4-HHE-modified proteins increased significantly (1.4-fold). Retinal thinning, TUNEL staining in ONL, 4-HNE-, and 4-HHE protein modifications were all found in the same retinal regions. PBN treatment inhibited the light-induced increase of 4-HNE and 4-HHE modified proteins in retina and RPE fractions. CONCLUSIONS: Exposure to intense light increases 4-HNE and 4-HHE protein modifications in the retina, suggesting that free radical initiated, nonenzymatic reactions are involved in this process. These modifications may be early events that precede photoreceptor cell apoptosis.     

视网膜视细胞的成片移植

目的 探索用准分子激光切削技术制备视网膜单层细胞植片,经内入路视网膜下腔的单层视细胞成片移植。方法 用准分子激光对大鼠视网膜进行切削,制取单层视细胞植片,此后,按内入路手术方法进行了兔视网膜下腔的异种移植。结果 切削后所得视细胞植片由单层视细胞组成,结构完整,包括外丛状层、外核层和外节层;视细胞植片经明胶包埋后被准确植入宿主视网膜下腔中,移植术后第1,2天宿主观视网膜未能复位,呈脱离状态,移植物没能与视网膜色素上皮层相贴;移植后10天,宿主视网膜复位,视细胞移植片平铺于宿主视网膜下腔中,植片视细胞外节也宿主视网膜色素上皮层相贴;移植后10天,宿主视网膜复位,视细胞移植片平铺于宿主视网膜下腔中,植片视细胞外节与宿主视网膜色素上皮层相贴,未见明显免疫排异现象。结论 准分子激光制备单层视细胞植片方法简单、可行;初步观察到内入路单层视细胞成片移植后,视细胞植片能够在宿主视网膜下腔中以正常生理位置存活;视网膜下腔为理想的视网膜移植的受位。     

Sulforaphane induces thioredoxin through the antioxidant-responsive element and attenuates retinal light damage in mice

PURPOSE: Thioredoxin (Trx) is a multifunctional endogenous redox regulator that protects cells against various types of cellular or tissue stresses. This study was conducted to test whether sulforaphane (SF), a naturally occurring isothiocyanate that is highly concentrated in broccoli sprouts, induces Trx in retinal tissues and whether pretreatment with SF protects against light-induced retinal damage in mice. METHODS: Expression of Trx in mouse retina was analyzed by Western blot and immunohistochemistry. Retinal damage was induced by exposure to white light at 6000 lux for 2 hours. To estimate retinal cell damage, the number of cell nuclei and the percentage of TUNEL-positive cells were counted in the outer nuclear layer and the retinal pigment epithelial (RPE) layer and the electroretinograms recorded. To analyze further the mechanism of Trx induction by SF, cultured human K-1034 RPE cells were used. RESULTS: Both intraperitoneal and oral SF induced Trx protein in the neural retina and RPE. The maximum induction of Trx was observed with intraperitoneal SF 0.5 mg/d for 3 days. After exposure to light, mice pretreated with SF had a significantly lower percentage of TUNEL-positive RPE and photoreceptor cells, a significantly higher number of RPE and photoreceptor nuclei, and greater amplitude of ERG a- and b-waves than in the saline-treated mice. In K-1034 cells, 1 microM SF induced Trx protein, whereas 10 microM SF did not damage cells or augment cellular peroxide production, tested by a lactate dehydrogenase (LDH) release assay and 2',7'-dichlorofluorescein diacetate (DCFH-DA)/flow cytometry, respectively. In the luciferase reporter assay, the antioxidant-responsive element (ARE) played a role in SF-induced Trx expression. In the electrophoretic mobility shift assay, SF induced binding of Nrf2, small Maf, and c-Jun to the ARE of the Trx gene. CONCLUSIONS: SF induced Trx in murine retina and effectively reduced retinal light damage. Evidence suggests that the ARE is involved in the mechanism of Trx induction by SF in RPE cells.     

鼠视网膜光化学损伤中的主要组织化学改变

目的：观察大鼠视网膜光化学损伤的主要组织化学改变。方法：对动物模型进行视网膜超微结构观察、丙二醛含量测定、细胞色素氧化酶及镁激活三磷酸腺苷酶活性的组织化学观察。结果：超微结构发现光照后6小时，光感受器细胞核肿胀，内节线粒体肿胀，外节水肿，视网膜色素上皮(retinal pigment epithelitis,RPE)顶端微绒毛消失，溶酶体增多，6天反应加重。14天光感受器细胞及内节已基本正常，外节再生但盘膜排列稀疏，RPE顶端出现微绒毛。观察到光照后6小时及６天，视网膜细胞色素氧化酶及镁激活三磷酸腺苷酶活性下降，丙二醛含量增高，至１４天均有所恢复。结论：脂质过氧化使光感受器细胞膜系统损伤崩解，引起细胞超微结构及酶活性改变，可能与视网膜光化学损伤的发病有关。 (中华眼底病杂志,1998,14:38-40)     

Comparison of photoreceptor-specific matrix domains in the cat and monkey retinas

Two lectins, wheat germ agglutinin (WGA) and peanut agglutinin (PNA), were used to compare domains within the interphotoreceptor matrices (IPM) of the cat and monkey, two species where the morphological relationship between the retinal pigment epithelium (RPE) and photoreceptors is distinctly different. In the monkey, PNA labeling was heaviest over the cone outer segments and a discrete region of the interphotoreceptor matrix bordering the cone inner and outer segments--a region which has been termed the cone matrix sheath. Near the apical border of the RPE, the outer margin of the PNA-labeled matrix is surrounded by a circular array of apical microvilli. In the cat retina, PNA labeling was highest over a region of the IPM lying between the outer margin of the cone sheath processes and surrounding rod matrix. In contrast, intracellular labeling of cone inner and outer segments was sparse. The RPE apical processes forming the cone sheath were not labeled. In the monkey retina, WGA preferentially labeled rod outer segments and the region of the IPM around rod inner and outer segments. The cone matrix sheath was not preferentially labeled using this lectin. Rod inner segments and cone inner and outer segments were labeled moderately. In the cat retina, WGA labeling was dense over both rod outer segments and cone outer segments as well as the cone sheath. Rod and cone inner segments, as well as the IPM around both rods and cones, were moderately labeled. These observations suggest that the specialized processes arising from the apical surface of retinal pigment epithelial cells, together with photoreceptor-specific extracellular matrix domains, contribute to the formation of specific microenvironments around rod and cone photoreceptor cells.     

Melatonin increases photoreceptor susceptibility to light-induced damage.

Melatonin is an indolamine hormone synthesized in the retina and pineal gland. It is thought to act as a paracrine neurohormone in the mammalian retina. Pinealectomy has been shown to protect photoreceptors from light-induced damage, and melatonin treatment has been reported to increase the degree of photoreceptor damage in albino rats. To determine how melatonin influences photoreceptor survival, the effect of melatonin administration on light-induced retinal damage was studied. Melatonin was administered to albino rats by intraperitoneal injections at various times before or after light exposure. The rats were exposed to high-intensity illumination (1600 lux) for 24 hr to induce photodamage, then returned to cyclic lighting for 12 days. After this, they were killed, and their eyes were removed and examined histologically. Measurements of the outer nuclear layer (ONL) thickness were taken at 12 different loci around the circumference of the retinal sections. The animals that received daily melatonin injections (100 micrograms) in the late afternoon (3 hr before lights off) for 1-3 days before photodamage showed an approximate 30% greater reduction compared with sham control animals in ONL thickness in the superior quadrant, the area most susceptible to light damage. Melatonin injections given after the photodamage did not affect ONL thickness. Although retinal susceptibility to light damage varied with time of day, the degree to which melatonin increased the degree of damage appeared unaffected by the time of day. These results suggest that melatonin may be involved in some aspects of photoreceptor sensitivity to light damage.     

Transplantation of retinal pigment epithelial cells to immature and adult rat hosts: short- and long-term survival characteristics

Retinal pigment epithelial (RPE) cells isolated from 6-8-day-old pigmented Long-Evans rat eyes were successfully grafted onto Bruch's membrane in albino Sprague-Dawley hosts ranging in age from 10 days postnatal to young adulthood. Injections of RPE cells were made into the subretinal space using a lesion paradigm which penetrates through the dorsal surface of the eye cutting through the sclera and choroid. Suspensions of pigmented RPE cells were labeled with Nuclear Yellow prior to transplantation, and at 1 week after grafting, the transplanted RPE cells were found attached to previously denuded areas of Bruch's membrane. The grafted RPE cells were positively identified by double labeling-only those RPE cells with melanosomes in their cytoplasm showed fluorescent Nuclear Yellow labeling; host albino RPE cells showed no nuclear labeling. The grafted RPE cells developed a normal relationship with photoreceptor cell outer segments as seen by electron microscopy. When compared with intact retinas or host control areas there were no significant differences in the thickness of the outer nuclear layer or in the lengths of photoreceptor inner and outer segments underneath the grafted RPE cells for at least 3 months after transplantation, which was the longest survival time examined.     

Photoreceptor allografts in a feline model of retinal degeneration

· Background: Photoreceptor transplants provide a potential means to restore function in a degenerate retina and/or rescue degenerating host photoreceptors by trophic influences. We have examined photoreceptor allografts in the Abyssinian cat model of hereditary photoreceptor degeneration to determine the viability and influence of such transplants on the host retina. · Methods: Small pieces of 3- to 5-day-old normal kitten retina containing undifferentiated photoreceptors were injected into the subretinal space of adult Abyssinian cats at an early stage of retinal degeneration using standard vitreo-retinal surgical techniques. The retinas were examined by ophthalmoscopy and fundus photography, then by light and electron microscopy at different times after surgery. · Results: Such allografts survive for at least 6 months after surgery. The photoreceptors develop outer segments, invariably in rosettes. The transplants gradually integrate with the host retina but detach the host photoreceptor layer from the retinal pigment epithelium (RPE), which tends to reduce the number of host photoreceptors over the transplant. There is no slowing of the photoreceptor degeneration in neighboring non-detached retina. Inflammation or rejection was not detected. · Conclusion: Undifferentiated, neonatal photoreceptor allografts survive and develop outer segments in the subretinal space of the Abyssinian mutant feline retina. The allografts gradually integrate with the host neural retina without inducing rejection. In the vicinity of the transplant there is increased loss of host photoreceptors, considered to be due to their detachment from the RPE layer. There is no evidence of any rescue of host photoreceptors elsewhere in this mutant retina. Received: 10 November 1997 Revised version received: 19 March 1998 Accepted: 23 March 1998     

重组人促红细胞生成素对小鼠视网膜光损伤的防护作用

目的　探讨重组人促红细胞生成素(rHEPO)通过小鼠血视网膜屏障的情况及其对视网膜光损伤的保护作用。方法　24只BALB/c小鼠腹腔注射rHEPO,采用酶联免疫吸附测定(ELISA)法检测小鼠视网膜中促红细胞生成素(EPO)的含量; 24只BALB/c小鼠建立光损伤动物模型,通过光镜和核苷酸末端转移酶介导的dUTP缺口标记(TUNEL)法观察实验组小鼠(12只,腹腔注射rHEPO)和对照组小鼠( 12只,腹腔注射生理盐水)视网膜细胞的变化情况。结果　腹腔注射rHEPO后2、4、6及8h小鼠100μg视网膜蛋白中EPO的含量分别为(0 .68±0 .24)、(1 .87±0 .37)、(0. 96±0 .24)及(0. 47±0. 13)mU,差异有统计学意义(F=2 .113,P<0 .05),在腹腔注射药物后4h视网膜中EPO的浓度达到高峰。随光照时间延长,光镜下可见对照组视网膜杆细胞的内、外节破坏明显加重,外核层逐渐变薄,出现核固缩,甚至核碎裂;实验组各观察时间点损伤变化均较轻,仅见感光细胞内、外节排列紊乱,形成空泡,外核层细胞排列稍紊乱,厚度无明显变化。荧光显微镜下观察,对照组视网膜外核层的凋亡细胞随光照时间延长不断增多,至光照后7d凋亡细胞数量减少;实验组视网膜外核层仅见少量凋亡细胞,光照后72h凋亡细胞的数量明显减少,至光照后7d几乎无凋亡细胞。实验组视网膜外核层凋亡细胞的数量     

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。     

Myosin V in the Retina: Localization in the Rod Photoreceptor Synapse

Brain myosin V is a member of a class of unconventional myosins. Using antibodies against brain myosin V, its distribution in the rat retina has been examined. It was detected in the inner and outer plexiform layers, in the somas of cells forming the inner nuclear layer, and in the ganglion cell layer. Faint labeling was also detected in the inner segments of the photoreceptor cells. In semithin retinal sections and isolated rod photoreceptor cells, a bright punctate labeling pattern was observed in the outer plexiform layer, corresponding to the rod photoreceptor synapses. The results found suggest that a major role of myosin V in the outer retina is in these synapses.     

Retinal dystrophy in Wistar-Furth rats

A form of retinal degeneration in the Wistar-Furth strain of rat is described. The changes observed was classified as either mild or severe, depending on the severity of the dystrophy seen by light and electron microscopy. In the mild stage, there was a slight decrease in the number of photoreceptor nuclei in the outer nuclear layer (ONL) and there were pyknotic nuclei in the inner nuclear layer. A few photoreceptor outer and inner segments showed focal swellings. The basal infoldings of the retinal pigment epithelium (RPE) were distributed irregularly, creating spaces that contained collagen-like fibrils. However, the interepithelial tight junctions remained impermeable to intravenously injected peroxidase. In severely dystrophic retinas, there was a further decrease in the width of the ONL, and the photoreceptor outer and inner segments were degenerated. In extreme cases, the photoreceptor cell disappeared completely and the inner retina abutted the RPE. Further changes were also noted in the basal membrane of the RPE; in some regions the membrane was totally flat while in others it formed exaggerated infoldings. In addition, the RPE was frequently vascularized by vessels that originated from the retina. The endothelium of those intra-RPE vessels located near Bruch's membrane was frequently fenestrated. Alterations also occurred in the retinal capillaries; some were degenerated, while others showed increased tortuosity or focal thickenings of the basal lamina. In addition, there were focal increases in the amount of stroma between Bruch's membrane and the choriocapillaris.     

Light-induced retinal damage in mice. Hydrogen peroxide production and superoxide dismutase activity in retina.

The oxidative mechanism in retinal damage due to exposure to intense light was investigated histochemically and biochemically. SMA mice (albino mice) of 2 to 3 months of age were exposed to intense light (1000-1400 lux). In the cyclic light-reared group (without dark adaptation), the outer and inner segments of the photoreceptor cells were damaged after 3 days of exposure, and severe outer nuclear layer damage was observed after 5 to 7 days of exposure. Hydrogen peroxide (H2O2) production in the outer nuclear layer increased with the progress of retinal damage. In the dark-reared group (dark adaptation of 16-18 hours), outer and inner segment damage was noted after 4 hours of light exposure, and severe outer nuclear layer damage was noted after 12 hours of light exposure. H2O2 production increased in the outer nuclear layer with retinal damage. Superoxide dismutase (SOD) activity did not change before the occurrence of retinal damage, and decreased by 25% after 3 days of exposure to light in the cyclic light-reared group. The decrease in total SOD activity corresponded to that of manganese-SOD (Mn-SOD). In the dark-reared group, SOD activity did not change, even after 1 day of exposure. There appears to be some relationship between retinal light damage and H2O2 production in the outer nuclear layer. Superoxide dismutase activity failed to provide protection against retinal oxidative damage due to intense light exposure.     

大鼠实验性视网膜光损伤中的视细胞凋亡

目的 进一步探讨视网膜光损伤的发病机制。 方法 20只Wistar大鼠分为实验组、对照组,分别在光照后12,24,36小时摘除眼球,视网膜组织行HE染色和核苷酸末端转移酶介导的DUTP缺口翻译法(TdT-mediated dUTP nick end labelling method,TUNEL)标记凋亡细胞。 结果 光照后12小时,视杆细胞外节出现少量空泡变性;24小时后,外核层出现明显的细胞核破碎、浓染和DNA裂解;36小时后,视杆细胞内、外节溶解,外核层大量细胞核丢失。 结论 视细胞凋亡是大鼠实验性视网膜光损伤的重要机制之一。 (中华眼底病杂志, 1999, 15: 167-169)