Effect of intermittent light on photoreceptor cells in the rabbit retina

Purpose  

The objective of the present study was to determine what histological changes occur in the photoreceptor layer of male rabbits exposed to intermittent light of different intensities.     

Effects of continuous light exposure on the rat retina and pineal gland

We examined the effects of intense continuous light (400 ftc for 10 days) on the morphology and immunoreactivity of the rat retina and pineal gland. The light treatment caused severe degeneration in the retina, with loss of most photoreceptor cells, and produced a marked decrease in S-antigen immunoreactivity in this organ. Unlike the retina, the light treatment had minimal effects on the histological structure of the pineal gland. However, pineal glands of light-treated rats exhibited a substantial reduction in their S-antigen immunoactivity, as demonstrated immunohistochemically and quantitatively verified by the rocket immunoelectrophoresis technique: pineal glands of light exposed rats had approximately two-thirds of the S-antigen immunoactivity of the untreated controls. Light treatment was also found to reduce both uveoretinitis and pinealitis in rats immunized with S-antigen. Yet pinealitis was not affected by light exposure in rats, as they were enucleated before treatment. This study thus provides new information to support the notion that the mammalian pineal gland is directly associated with light detection by the retina.     

Biochemical studies on the effects of continuous light on the albino rat retina

The causal mechanism of light damage in the albino rat retina has been investigated. Male and female albino Wistar rats weighing 200-300 g and previously maintained in normal room lighting of approximately 15 hr light (0.85 +/- 0.05 X 10(-4) W cm-2) per 9 hr dark cycle were simultaneously exposed continuously to uniform fluorescent light flux of 3.01 +/- 0.5 X 10(-3) W cm-2 for a period of 6-18 hr. The animals were killed immediately after exposure and the retinas analysed for their contents of DNA, protein and lipids. There were significant losses of retinal DNA, protein, total lipid and polyunsaturated fatty acids, particularly docosahexaenoic acid. The losses were progressive with duration of exposure. There were also changes in phospholipid subclasses. These results could indicate altered photoreceptor-membrane viability secondary to continuous illumination. The ultimate effect would be the loss of photoreceptor cells with a concomitant loss of normal physiological function. Generally, gender was found to play no significant role, thus excluding possible endocrine interference. It is suggested that lipoperoxidative reactions could account for the observations made in this study. The danger of over-exposure to radiant flux in the tropics is inferred from these observations.     

Effect of continuous low-intensity light on the lysosomal enzymes in the retina of albino rats

Lysosomal enzyme activities in the retina of albino rats following the exposure to continuous low-intensity light were studied biochemically. The total and free acid phosphatase and β-glucuronidase activities in the continuously exposed neuroretina were higher than those in the control neuroretina exposed to a diurnal rhythm of light. The highest activities were observed in the 9 day-exposed retina. Total and free cathepsin D activities in the retinal pigment epithelium and choroid in experimental eyes were also higher than those in the control tissues exposed to a diurnal rhythm of light. It is suggested that lysosomal enzymes are involved in the damaging process of the continuously exposed retina.     

Mechanisms of light adaptation in rat retina

Green, Dowling, Siegel and Ripps (1975)²¹J. gen. Physiol.65, 483–502 found that both receptors and post-receptoral elements regulate the process of light adaptation in skate retina. As a test of the generality of this conclusion, we repeated their experiments on the retina of the intact albino rat. Increment threshold and intensity-response functions of aspartate-isolated receptor potentials, ERG b-waves and single retinal ganglion cell axons were measured, and all were found to be similar to those described by Greenet al. (1975). In particular, the adaptive properties of the b-wave and ganglion cells were similar to each other, but different from those of the receptor potential. We conclude that the retinal mechanisms of light adaptation are similar in rat and skate.     

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.     

Lateral spread of light adaptation in the rat retina

Recordings from the rat optic tract fibers were used to assess changes in sensitivity under various conditions of adaptation. An adapting background which excites only a small fraction of the rods can yet cause a several-fold change in sensitivity. A small adapting spot much more effectively decreases the cell's sensitivity to a superimposed test than to test spots in positions far from the adapting locus. Thus, adaptation spreads laterally but not uniformly throughout the ganglion cell center. Scattered light does not account for the spread, since a displaced adapting spot can be more effective than one superimposed on the test spot.     

快速减压后大鼠视网膜形态和胶质反应变化

目的观察快速减压对大鼠视网膜形态学结构、胶质反应和细胞凋亡的影响。方法24只大鼠随机分为6组,即正常对照组、安全减压组、快速减压处理后0h、6h、24h、48h组。安全减压组、快速减压处理各组实验动物暴露于加压舱内,舱内气压在30s内升至1．0MPa,维持5．5min,快速减压组打开放气阀55s减至常压,安全减压组采用动物安全减压方案减到常压。采用HE染色观察视网膜组织结构和神经节细胞密度变化情况,采用TUNEL染色观察视网膜内细胞凋亡的分布和比例,采用免疫组化方法观察视网膜胶质细胞胶质纤维酸性蛋白（GFAP）和波形蛋白（vimentin）表达变化。结果大体观察发现快速减压后视网膜水肿明显,其中部分血管闭塞,视网膜内点片状出血。HE染色发现快速减压后24h内随时间延长,视网膜水肿逐渐加重,其中神经节细胞层、神经纤维层、内丛状层和外丛状层水肿明显。快速减压后48h视网膜水肿较24h组减轻,神经节细胞数量减少,视锥视杆细胞减少,内核层、外核层变薄、核溶解、坏死,结构较紊乱。减压后24h神经节细胞密度为（6．41±1．39）个／100um,开始明显降低,减压后48h细胞密度为（5．31±1．94）个／100um,与正常对照组（8．62±1．75）个／100um和安全减压组（9．03±2．66）个／100um相比显著降低（P〈0．05）。GFAP和vimentin在快速减压后24h和48h表达最强,正常对照组表达最弱,安全减压组介于两者之间。TUNEL染色显示快速减压后24h和48h时视网膜节细胞层及内、外核层均有大量浓染的阳性细胞。结论快速减压可造成视网膜缺氧,导致多种病理改变,其中主要病变特点是神经元细胞凋亡和胶质细胞反应增强。     

Effect of light on dopamine turnover and metabolism in rabbit retina

Some neurochemical responses of dopaminergic neurons in the rabbit retina have been measured during prolonged light or dark adaptation. Light adaptation produced small increases (20%) in dopamine levels but larger increases (50-100%) in the two metabolites, 3,4-dihydroxyphenylacetic acid and homovanillic acid. Light also significantly increased tyrosine hydroxylase activity; the increase was more pronounced when activity was measured in vivo than in vitro. Dopamine turnover, was faster in the light than in the dark. All these data support the suggestion that light leads to the activation of dopaminergic neurons in the rabbit retina.     

光照节律改变对大鼠视网膜中Cry2表达的影响

背景 Cry2存在于哺乳动物视网膜上,是生物钟振荡器环路中重要的调控因子. 目的 探讨光照节律改变对大鼠视网膜中Cry2表达的影响.方法 将清洁级健康无眼疾SD大鼠30只按随机数字表法分成2个组,正常对照组大鼠在自然昼夜光线照明下喂养,实验组大鼠饲养在光照控制室内,大鼠活动平面光照度为(533±16) lx,设定每日光照明(6:00 ～24:00)、暗(24:00 ～6:00)循环交替时间为18 h/6 h,持续时间为3个月.于实验后3个月时在光学显微镜及透射电子显微镜下观察大鼠视网膜组织结构和超微结构的改变,采用免疫组织化学法检测各组大鼠视网膜中Cry2蛋白的表达,采用实时荧光定量PCR法检测Cry2mRNA在视网膜组织中的表达变化.结果 光学显微镜下可见,正常对照组大鼠喂养3个月时视网膜各层结构清晰,排列整齐,而实验组大鼠视网膜萎缩变薄,排列紊乱.透射电子显微镜下观察表明,正常对照组大鼠光感受器细胞外节膜盘结构清晰,内节线粒体嵴连续,外核层细胞核形态规则,但实验组大鼠光感受器内外节结构紊乱,外节膜盘间隙增大,出现溶解、空泡变,光感受器内节线粒体空泡变,视网膜外核层细胞核染色质浓集,部分出现核碎裂、边集,核膜皱缩、内陷.免疫组织化学检测显示,2个组大鼠Cry2蛋白均在视网膜节细胞及内核层部分细胞的细胞质和核膜阳性表达,实验组大鼠Cry2蛋白表达评分为(0.833±0.197)分,明显低于正常对照组的(1.700±0.245)分,差异有统计学意义(P=0.009).实时荧光定量PCR定量检测结果显示,正常对照组大鼠视网膜中Cry2 mRNA表达量为0.962±0.125,实验组为0.615±0.100,差异有统计学意义(P=0.006).结论 533 lx的光照强度长期节律性照射可导致大鼠视网膜组织结构损伤,其机制可能与视网膜中Cry2的表达下调有关,调整Cry2的表达是否是临床上稳定生物节律的一个重要环节值得探讨.     

神经生长因子对激光致视网膜损伤后bFGF蛋白表达的影响

目的观察神经生长因子（NGF）对激光致视网膜损伤后内源性碱性成纤维细胞生长因子（bFGF）蛋白表达的影响，以探讨激光致视网膜损伤的分子病理机制。方法Wistar二级大鼠，分为3组，即损伤对照组、生理盐水对照组、NGF组，分别于倍频Nd：YAG激光损伤后，玻璃体内注射NGF，用免疫组织化学、Western blot方法、苏木精-伊红染色及视觉电位仪测量视网膜电图（ERG）b波幅值，观察视网膜bFGF蛋白表达量的变化及对视网膜组织结构、视功能的影响。结果激光损伤视网膜后玻璃体内NGF组3dbFGF蛋白的表达明显低于损伤对照组（P〈0．01）；NGF组28d感光细胞结构的恢复较损伤对照组差，NGF组的b波幅值在各时间点与对照组比较差异均无统计学意义（P〉0．05）。结论外源性NGF减少了激光视网膜损伤后bFGF产物，不利于感光细胞结构和功能的修复。     

缺血再灌注损伤对鼠视网膜细胞膜结构和功能的影响

目的观察缺血及再灌注损伤对视网膜细胞膜结构和功能的影响。方法３２只ＳｐｒａｇｎｅＤａｗｌｅｙ大鼠随机分为缺血对照组,再灌注３小时、３０小时、５天组计四组,每组８只。采用提高眼压法造成视网膜缺血后,恢复眼压形成血流再灌注。用定磷法测定Ｎａ＋－Ｋ＋－ＡＴＰ酶,荧光探针ＤＰＨ标记细胞膜并测定其流动性。结果再灌注初期,细胞膜结构和功能的损害进行性加重;缺血时间愈长,再灌注损伤愈严重。结论Ｎａ＋－Ｋ＋－ＡＴＰ酶受损的机制在于再灌注过程中产生的过氧化物质、兴奋性氨基酸等可直接造成Ｎａ＋－Ｋ＋－ＡＴＰ酶的损害,还可通过对细胞膜脂质的作用引起膜流动性升高,导致其稳定性下降,从而影响Ｎａ＋－Ｋ＋－ＡＴＰ酶蛋白的活性。     

光明液对视网膜光损害模型大鼠的疗效观察

目的:探讨光明液对实验性视网膜光损害大鼠模型的治疗作用。方法:SD大鼠32只随机分为4组:光明液组、模型组、正常组和VitE组。采用手术显微镜光源(Lux为30000±50)照射SD大鼠右眼30min,建立急性光损伤模型。分别采用光明液、VitE滴丸及等量蒸馏水进行灌胃治疗7d,观察细胞凋亡率、Caspase-3活力、NO含量变化及视网膜外核层厚度改变。结果:光明液可以明显降低视网膜细胞的凋亡率,有效地抑制细胞凋亡中的关键酶—Caspase-3蛋白酶的活力,还可一定程度减缓视网膜外核层厚度的改变,对具有细胞毒性和氧化作用的NO也有较强的降低作用。与抗氧化剂VitE相比,光明液的疗效要优于前者。结论:复方中药光明液是一种治疗视网膜光损害性疾病的有效的中药复方制剂。     

Identification of microglia cell of the rat retina by light and electron microscopy

Distribution of microglia cells was studied in the normal retina of Wistar rats kept in a specific-pathogen-free condition, using a combined technique of light and electron microscopy with the weak silver carbonate staining method of del Rio-Hortega. Typical microglia cells were found mainly in the inner plexiform layer. By electron microscopy these cells were easily identified by metallic deposition in the cells, and had a small oval nucleus with a prominent chromatin pattern, which was one of the most characteristic features of the cell. Based upon these fine structures, microglia cells were identified in the nonimpregnated, ordinarily prepared retina by electron microscopy. These cells contained lysosomes, lipofuscin granules, Golgi apparatus, and long, narrow cisternae of rough-surfaced endoplasmic reticulum mainly at both sides of the perikaryon. These features were identical with those of microglia cells in the central nervous system. Microglia cells were found to be widely distributed in the inner portion of the retina, most of the cells locating closely to ganglion cells or capillary walls, and occasionally in the inner plexiform layer. The nuclear feature of the cell was also recognizable by light microscopy in 1-micron-thick Epon sections stained with toluidine blue. Serially cut thick sections of the retinal ribbon revealed that microglia cells were widely distributed from the peripapillary to the ora serrata region. From the present study, it is concluded that the microglia cell can be considered a component of the normal retina. This is the first report on the precisely described fine structures of the retinal microglia cells.     

The effect of oxygen and light on the structure and function of the neonatal rat retina

The neonatal rat is born with its eyes closed and an immature visual system, that some say is equivalent to that of a human fetus at 26 weeks of gestation. From birth, the visual system of the newborn rat will gradually mature, the first manifestation of that being the opening of the eye which usually take place at postnatal day 14. Complete maturation of the retina and visual pathways is normally reached at the end of the first month of life. The neonatal rat model thus represents a unique paradigm to study the normal and abnormal maturation of the primary visual pathways that normally occurs in utero in human subjects. Our laboratory has, over the past decade, developed two animal models of postnatally induced retinopathy, namely the Oxygen-Induced Retinopathy (OIR) that share several common features with the human Retinopathy of Prematurity (ROP) and the Light-Induced Retinopathy that is viewed by some as a valid model of some forms of Retinitis Pigmentosa (RP). The following pages review what is known of the pathophysiological processes taking place and suggest possible therapeutic avenues that could be explored in order to halt the degenerative process.