The generation and changing retinal distribution of displaced amacrine cells in Bufo marinus from metamorphosis to adult.

Summary The generation and retinal distribution of displaced amacrine cells (DAs) were studied from metamorphosis to adult in the cane toad Bufo marinus. Displaced amacrine cells were identified by inducing chromatolytic changes in ganglion cells (GCs) following optic nerve section. Cells that did not chromatolyse in the ganglion cell layer (GCL) of the retina were regarded as DAs. The number of DAs increased considerably from an estimated 10000 at metamorphosis to 211000 in the adult toad, and was accompanied by a substantial decrease of average cell density. In contrast to the reported 6:1 cell density gradient of all cells of the GCL in adult toad (Nguyen and Straznicky 1989) only a shallow 1.6:1 density gradient of DAs from the visual streak to the dorsal and ventral retinal margins was detected. Consequently, the incidence of DAs increased from 15% of all cells of the GCL in the visual streak to 30% in the dorsal and ventral peripheral retina. These results indicate that the ratio of the newly generated DAs and GCs at the ciliary margin must be changing during development. More GCs are generated before and around metamorphosis then DAs, in contrast to the relative increase of the percentage of DAs generated after metamorphosis. The possible control of the numbers of DAs in the GCL is discussed.     

Genesis of neurons of the retinal ganglion cell layer in the opossum

Summary In this study, we have examined the genesis of neurons of the retinal ganglion cell layer of the opossum Didelphis marsupialis by [³H]-thymidine autoradiography. Our results suggest that most neurons surviving to adulthood are generated in postnatal life from day 1 to day 23. Cells are generated according to a coarse gradient from the retinal geometric center to the periphery. Regional analysis of soma size distributions in different cohorts suggest that this gradient is actually formed by two partially-overlapping, concentric waves of cell proliferation. Most medium and large ganglion cells are formed during the early wave, whereas most displaced amacrine cells and small ganglion cells are formed during the late wave. Our results confirm the appropriateness of the opossum as a model for studies of development of the mammalian visual system.     

Dendritic morphology and retinal distribution of tyrosine hydroxylase-like immunoreactive amacrine cells in Bufo marinus

Summary Tyrosine hydroxylase-like immunoreactive (TH-IR) amacrine cells (ACs) in the retina of metamorphosing and adult Bufo marinus were visualized, and their retinal distribution established, using immunohistochemistry on retinal wholemount and sectioned material. The somata of TH-IR ACs were located in the innermost part of the inner nuclear layer (INL). Their dendrites branched predominantly in the scieral sublamina of the inner plexiform layer (IPL), with sparse branching also in the vitreal sublamina. In the retinae of metamorphosing animals 592 ± 113 (mean ± S.D.) immunoreactive cells and in adult 5,670 ± 528 cells were found. Usually 1, 2 or 3 stem dendrites arose from the somata of TH-IR cells which branched 2 or 3 times. In the adult retinae the dendritic field sizes of immunoreactive cells were in the range of 0.059 ± 0.012 mm², which resulted in a considerable dendritic overlap across the retina. TH-IR cells were unevenly distributed over the retina, with 72 cells/mm² in the central temporal retina, 45–50 cells/mm² along the naso-temporal axis of the retina and 25 cells/mm² in the dorsal and ventral peripheral retina. The average density was 36 ± 6 cells/mm². A considerable number of TH-IR cells (range 52–133, n=4) were displaced into the ganglion cell layer (GCL) of the retina. The mean soma sizes of immunoreactive cells were significantly higher in the low density (95 ± 13 m²) than in the high cell density areas (86 ± 12 m²). There was also a slight but significant increase of the dendritic field sizes of these cells towards the low cell density areas of the retina. These observations show that the retinal distribution of TH-IR ACs parallels the non-uniform distribution of neurons of the INL demonstrated recently in Bufo marinus (Zhu et al. 1990). The class of TH-IR ACs appears to correspond to a subgroup of morphologically distinct dopaminergic ACs found in a number of other vertebrate species.On leave from Department of Anatomy, Zhanjiang Medical College, Guangdong, People's Republic of China     

Morphological classification and retinal distribution of large ganglion cells in the retina ofBufo marinus

Summary The retrograde transport of horseradish peroxidase (HRP) and cobaltic-lysine complex (CLC) was used to morphologically characterize large ganglion cells (GCs) and to determine their distribution in retinal wholemounts and in sectioned material in the retina ofBufo marinus. Large GCs, amounting to about 0.5% of total GC population, were defined to be those with very large dendritic field sizes varying between 0.1 mm² to 0.6 mm² and cell soma sizes of between 100 m² to 400 m². These cells were subdivided into 3 major groups, Types I, II and III, on the basis of their dendritic field sizes, arborization patterns and the strata of dendritic branching within the inner plexiform layer (IPL). The majority of large neurons (about 90%) were classified as Type I GCs with symmetrical dendritic arbor. These cells had either bistratified branching in the scierai and vitreal sublaminae of the IPL (65% of Type I Cells) or unistratified branching in the scleral (26%) or in the vitreal (9%) sublamina. Their dendritic field sizes increased linearly from the retinal centre from 0.13 mm±0.02 mm² (mean and S.D.) to 0.58±0.11 mm² in the retinal periphery. Type II GCs (about 9% of the large GC population) were characterized by an asymmetrical dendritic arborization directed towards the ciliary margin with unistratified branching in the scierai sublamina of the IPL. The mean dendritic field sizes of these cells were 0.26±0.09 mm². Type III GCs, the least frequent (about 1%) category of large GCs had sparsely branching, elongated dendritic branching aligned approximately parallel with the nasotemporal axis of the retina. The unistratified dendritic branches of these neurons were located in the vitreal sublamina of the IPL with a mean dendritic field size of 0.42±0.11 mm². The dendritic field sizes of Types II and III GCs did not increase with retinal eccentricity. Type I GCs were distributed unevenly across the retina, the density being greatest in the visual streak, along the nasotemporal meridian of the retina. The dendritic field sizes of these cells increased towards the retinal periphery, resulting in a constant dendritic field coverage factor across the retina. Each retinal point was covered by the dendritic fields of 4–5 adjacent GCs. In contrast, Types II and III GCs had only discontinuous dendritic coverage. The identification of morphological types of large GCs with previously described functional classes of GCs in the anuran retina is discussed.On leave from the Department of Anatomy, University Medical School, Pécs, Hungary     

Response of cat retinal ganglion cells to motion of visual texture

Summary Responses of retinal ganglion cells to motion of large fields of visual texture were recorded in the lightly anaesthetised, immobilized cat. Brisk sustained and brisk transient, on- or off-centre, units gave a modulated response to texture motion. The pattern of temporal modulation of the response was dependent upon the particular configuration (sample) of texture crossing the receptive field. The magnitude of the response depended on the size of the receptive field centre. For all units, whether sustained or transient the magnitude of response to a textured field of fixed angular subtense declined as centre-diameter increased from 0.9 deg. For brisk units the response magnitude levelled off for centre sizes smaller than 0.9 deg. Responses to texture were confined spatially to the region of the receptive field, and the overall characteristics of this response were due to interactions between the centre and surround mechanisms of the receptive field. In brisk transient units, no evoked response was evident when texture motion was confined to regions well away from the receptive field of the unit, i.e. no periphery or shift effect could be demonstrated. The results support previous suggestions that the differential sensitivity to texture motion evident in cortical neurones must be due to intra-cortical processing.Supported by Project Grant G978/558/N from the Medical Research Council     

Cell populations of the ganglion cell layer: displaced amacrine and matching amacrine cells in the pigeon retina

Summary The proportion and size distribution of ganglion and non-ganglion cells in the ganglion cell layer of different areas of the pigeon retina was examined in whole-mounts of the retina by retrograde axonal transport of horseradish peroxidase (HRP) from large brain injections. A maximum of 98% of cells were labelled in the red field and a maximum of 77% in the peripheral yellow field. Unlabelled cell bodies were 30% smaller than labelled ganglion cells and had a mean diameter of 6.2 m and a size range of 4 to 9 m. The morphology of cells in the ganglion cell layer was examined by Golgi staining of retinal whole-mounts. Small glia, displaced amacrine and ganglion cells were found. Displaced amacrine cell bodies were about 30% smaller than ganglion cells and their size distribution was similar to the unlabelled cells in HRP preparations. Displaced amacrine cells had small rounded cell bodies (mean diameter 6.2 m) increasing in size with eccentricity, and a unistratified dendritic tree of fine, nearly radial, varicose dendrites in sublamina 4 of the inner plexiform layer. They had elliptical dendritic fields (mean diameter 66 m) aligned parallel to the retina's horizontal meridian. A population of amacrine cells was found with somas at the inner margin of the inner nuclear layer and soma and dendritic morphology matching those of displaced amacrines. These amacrine cells had unistratified dendritic trees at the junction of sublaminae 1 and 2 of the inner plexiform layer. Pigeon displaced amacrine cells and their matching amacrines are similar to starburst cells of the rabbit retina. They may participate in on and off pathways to ganglion cells and their lamination suggests that they are cholinergic.     

The morphology and distribution of photoreceptors in the retina of Bufo marinus

Summary The number, cell morphology and retinal distribution of rods and cones were determined in the retina of the toad, Bufo marinus. Adult animals were sacrificed, both eyes were removed and prepared for either tangential section across the outer segments of the photoreceptor layer, or transverse section across the whole retina.Cone densities increased from an average of 7000/mm² in the peripheral to a maximum of 25000/mm² in the central retina. The high cone densities extended across the naso-temporal axis of the retina corresponding to the position of the visual streak in the ganglion cell layer. The total number of cones in the retina was estimated to be 1.1 million. Rod density of 21000/mm² in the central retina decreased to 17000/mm² at 1.5–4 mm eccentricity, and then increased to 29000/mm² in the peripheral retina. The total number of rods amounted to about 2 million. The mean of the crosssectional area of rod outer segments was 11.2 ± 1.5 m² (mean ± SD) in the highest and 17.9 ± 4.7 m² in the lowest density areas of the retina. The length of the rod outer segments extended from 28 m in the ventral peripheral retina to a maximum of 89 m in the dorsal retina, dorsal to the visual streak of the ganglion cell layer.The results of the present study showed a differential retinal distribution of photoreceptors, with a peak density in the retinal centre and a higher density along the naso-temporal axis of the eye. We conclude that the area of high photoreceptor density, matched by high neuron densities of the INL and GCL, corresponds to the site of acute vision of the Bufo retina.On leave from Department of Biology, Fujian Teachers University, Fuzhou, Fujian, People's Republic of China.     

CPT-cAMP对成年金黄地鼠视网膜节细胞存活的影响

目的　探讨眼球玻璃体内注射CPT cAMP对切断视神经后视网膜节细胞存活的影响。方法　用荧光素逆行示踪标记法和定量解剖学技术观察视神经切断 5、7和 14d后成年金黄地鼠视网膜节细胞的密度。结果　 (1)正常视网膜节细胞平均密度为 2 0 0 7± 115 /mm2 ;(2 )视神经切断 5、7、14d后 ,视网膜节细胞平均密度分别下降至 :10 10± 131/mm2 、782± 5 5 /mm2 和2 14± 30 /mm2 ;(3)给予DMSO/生理盐水的对照组在上述各时间段视网膜节细胞平均密度与单纯神经切断组结果相似 ;(4)给予CPT cAMP的实验组在 5、7、14d视网膜节细胞的平均密度分别为 1398± 2 45 /mm2 、12 93± 84/mm2 和 5 0 1± 72 /mm2 ,与视神经切断组和DMSO/生理盐水对照组相比在各时间段上均存在显著性差异 (P <0 0 5 )。结论　CPT cAMP可提高视神经切断后成年金黄地鼠视网膜节细胞的存活。     

The topographic organization of the retinal ganglion cell layer of the lizard Ctenophorus nuchalis.

The numbers of neurons of the ganglion cell layer (GCL) and their distribution in the retina of an Australian lizard Ctenophorus nuchalis were investigated. Retinal wholemounts and sections were prepared for light microscopic and optic nerves for electron microscopic study. Counts of cell numbers in the GCL from wholemounts varied from 200,000 to 380,000. Neurons in the GCL were non-uniformly distributed, forming a high cell density streak along the naso-temporal axis of the retina. Neurons of the GCL formed 2 to 9 layers in the visual streak and a single layer in the rest of the retina. The number of neurons of the GCL in this area was estimated at about 2,100,000. Although the visual streak represented only 16% of the total retinal surface area, it contained about 90% of all neurons of the GCL. Optic axon counts yielded 147,000 myelinated and 2,643,000 unmyelinated fibres. The estimated optic fibre number of 2,790,000 was 18.2% less than the total number of neurons counted from sections in the GCL of the same eye. The unexpected high number of neurons in the area of the visual streak indicates that cell numbers obtained only from wholemount preparations may vastly underestimate the total neuron numbers in the GCL of the lizard retina.     

The survival of neonatal rat retinal ganglion cells in vitro is enhanced in the presence of appropriate parts of the brain

Summary The enzyme horseradish peroxidase (HRP) was injected into the visual centres of the brains of neonatal rats. Following dissociation of retinae into tissue culture, the ganglion cells could be identified by appropriate histochemical staining for HRP reaction product. Cultures were prepared of dissociated retinae from rats aged 2–6 days postnatal. After 3 h the cultures were fixed, and HRP-labelled cells visualized and counted. Estimates were made of the number of ganglion cells per retina at each age. Results indicated a loss of ganglion cells during the first few postnatal days. This loss paralleled that observed in vivo. It was further found the retinal ganglion cells died rapidly in vitro when cultured in a minimal medium. Only 50% of ganglion cells originally plated remained viable after 24 h. However, the survival rate could be increased to 100% by coculturing the cells with diencephalon and mesencephalon; these contain the retinorecipient nuclei. Coculturing with cerebellum did not result in such an enhanced survival rate. Ganglion cells could be maintained over longer periods of time by reinoculating the cultures with additional tissue containing diencephalon and mesencephalon. These results support the hypothesis that developing neurons require trophic factors from their target tissues in order to survive.Supported by the O.P.S.M. Research Foundation, the A.R.G.C. and the N.H. & M.R.C.     

Response of X and Y cat retinal ganglion cells to moving stimuli

Summary Single optic tract fibers in the cat were classified as X or Y cells by a contrast reversal stimulus. A slit of light was then moved across the receptive field at velocities from 10–1000 ° /s. The preferred velocity was that velocity which elicited the strongest response from the cell. The maximum velocity was the highest velocity target to which a cell could respond. Y cells as a group both preferred and could follow faster targets than X cells, and were more broadly tuned to the preferred velocity.This study was supported by Public Health Service Grant EY 00701 and NEI Grant EY 00376     

Amblyopia occurs in retinal ganglion cells in cats reared with convergent squint without alternating fixation

Summary The spatial resolving power, contrast sensitivity, and receptive field properties of retinal ganglion cells were studied in cats reared with either convergent or divergent squint in one eye. Sustained-X cells in the area centralis of the squinting eye of the cats with esotropia without alternating fixation showed significantly poorer spatial resolution, and reduced contrast sensitivity compared with cells in the area centralis of the normal eye. These amblyopic sustained-X cells in the area centralis of the squinting eye had receptive field characteristics similar to those found in immature cells of young kittens. They had a shallow sensitivity gradient within a relatively widespread centre zone and a weak and widespread inhibitory surround. In contrast, the sustained cells in the area centralis of the normal eye revealed a typical, well defined, small centre zone with its sensitivity gradient extremely steep and its inhibitory surround strong and confined. A minor degree of amblyopia was also found in transient Y-cells in the area centralis of the squinting eye of these cats.However, no loss of resolving power was found in the cells in the area centralis of the squinting eye of the cats with esotropia or exotropia which showed alternating fixation. Thus, amblyopia occurs in those eyes which have lost the use of the area centralis as the normal visual axis during early postnatal development, and its organic lesion is already apparent in the retinal ganglion cells — the third order neurone in the afferent visual system. It is suggested that the loss of the ability to fixate results in inadequate stimulation of the central retinal ganglion cells due to the habitual presence of blurred images at the area centralis which prevents their full development during the critical period.This work was supported by grants from MRC and St. Thomas's Hospital to H. Ikeda     

rd1小鼠视网膜退变中期节细胞功能的变化

 目的:探讨视网膜色素变性模型rd1小鼠视网膜退变中期各类视网膜节细胞(retinal ganglion cells, RGCs)功能的变化情况。方法:运用多电极阵列(multi-electrode arrays,MEA)记录方法,记录视网膜退变中期(出生后20 d,P20)的rd1小鼠或正常对照小鼠视网膜中多个节细胞动作电位的发放,并比较自发发放和光反应特征等指标,评价幸存的节细胞功能变化。另外,采用免疫组化染色方法验证视网膜感光细胞的退化情况。结果:免疫组化的结果表明rd1小鼠视网膜感光层的厚度显著低于正常小鼠。根据节细胞光反应特性的不同,可以将其分成6类:ON sustained、ON transient、ON-OFF sustained、ON-OFF transient、OFF sustained和OFF transient RGCs,但OFF sustained RGCs所占比重极小(1.0%~3.1%)。rd1小鼠视网膜中保持光反应的节细胞比例显著低于正常小鼠。rd1小鼠节细胞的自发发放显著高于正常小鼠,而不同类型的节细胞变化情况有所不同。rd1小鼠视网膜各类节细胞的光反应强度及光敏感度均显著低于正常小鼠。结论:在rd1小鼠退变的中期,视网膜感光层明显退变;rd1小鼠退变中期的视网膜节细胞发生明显的功能退变,而且不同类型的节细胞变化情况有所不同。     

The changing distribution of neurons in the inner nuclear layer from metamorphosis to adult: a morphometric analysis of the anuran retina

Summary The generation and changing distribution of neurons of the inner nuclear layer (INL) in the retina of two anuran species, Bufo marinus and Xenopus laevis, were studied from metamorphosis to adult. Morphometric studies were undertaken at six developmental stages in Bufo and four in Xenopus. The number and thickness of neurons in the INL were established in 29 predetermined retinal locations from serial sections of the eyes cut vertically or horizontally. The total number of neurons in the INL increased from metamorphosis to adult from 826000 ± 185 to 18760000 ± 562 (mean ± SD) in Bufo and from 308000 ± 25 to 877000 ± 31 in Xenopus. Over the same period the surface area of the INL increased about 50-fold from 2 mm² to 96 mm² in Bufo and 5-fold from 2.5 mm² to 13 mm² in Xenopus. In Bufo the difference between the highest cell number (centraltemporal retina) and the lowest cell number in a sample area (dorsal and ventral peripheral retina) was 2.11 at metamorphosis. This ratio increased to 3.41 in the adult. Both the cell number and cell density per sample area in the INL was found to be higher along the nasotemporal meridian of the eye overlying the visual streak of the ganglion cell layer (GCL) of the retina. The retinal distribution of neurons in the INL did not change significantly during postmetamorphic growth in Xenopus. At metamorphosis a 1.71 difference was found between the highest neuron number (retinal ciliary margin) and lowest neuron number (retinal centre) decreasing to 1.51 in the adult. Retinae were labelled with ³H-thymidine in 15 mm Bufos and examined 2, 6, 12 and 18 weeks later. Higher rates of cell addition to the nasal and temporal poles of the INL were found compared with that at the dorsal and ventral poles. The retinal radial growth at the ciliary margin of the dorsal, ventral, nasal and temporal poles between the time of isotope injection and 18 weeks survival was found to be uneven; more radial elongation occurred at the nasal, dorsal and ventral poles and less at the temporal pole. These observations suggest that (a) the neuron distribution of the INL in adult animals approximates that of the GCL and (b) the visual streak-like area of the INL in Bufo develops by a sustained differential cell addition at the temporal and nasal poles of the retina.On leave from the Department of Anatomy, Zhanjiang Medical College, Guangdong,People's Republic of China     

远志皂苷元对氧化应激损伤的视网膜神经节细胞的保护作用

目的: 观察远志皂苷元(senegenin,Sen)对氧化应激损伤的视网膜神经节细胞(retinal ganglion cells,RGCs)的影响并初步探讨其作用机制。方法: 采用上丘荧光金逆行标记RGCs后,体外原代RGCs混合细胞培养,随机分为control组、H₂O₂组、Sen+H₂O₂和Sen组。检测带荧光金荧光细胞的活力。同上述分组处理视网膜,用Hoechst 33258 染色后观察视网膜细胞核形态的变化,Western blotting检测视网膜细胞cleaved caspase-3、细胞色素C及Bcl-2蛋白的表达。结果: 与control组比较,Sen浓度在10、20和40 μmol/L时, RGCs活力无明显变化(P>0.05),但Sen浓度达到80和160 μmol/L时,RGCs活力明显下降,差异显著(P<0.01)。25、50、100和200 μmol/L H₂O₂明显降低RGCs活力(P<0.05)。Sen浓度在10、20和40 μmol/L时,对50 μmol/L H₂O₂损伤的RGCs有较好的保护作用(P<0.05),其中40 μmol/L Sen保护作用最为明显。Hoechst 33258染色表明Sen可以减少H₂O₂引起的视网膜细胞凋亡。Western blotting结果表明Sen促进Bcl-2蛋白的表达,降低线粒体细胞色素C的释放,下调cleaved caspase-3的表达。 结论: Sen保护RGCs对抗氧化应激引起的损伤,其机制可能与其增强Bcl-2蛋白表达和减少氧化应激引起的细胞凋亡有关。     

Modulation of breathing by phasic pulmonary stretch receptor feedback in an amphibian, Bufo marinus

This study examined the role of phasic pulmonary stretch receptor (PSR) feedback in ventilatory control, breath clustering and breath timing in decerebrate, paralysed and artificially-ventilated cane toads (Bufo marinus) under conditions designed to minimise tonic PSR feedback. Fictive breathing was recorded as trigeminal motor output to the buccal musculature. Artificial tidal ventilation, with hypercarbic gas mixtures, was either continuous or activated by the fictive breaths and was manipulated to provide differing amounts/patterns of phasic PSR feedback. The results demonstrate that increased amounts of phasic PSR feedback increase overall breathing frequency. Within multi-breath episodes there was an increase in the instantaneous breathing frequency during the later stages of the episode. The temporal relationship between a fictive breath and lung inflation influenced the duration of the pause between fictive breaths. The data indicate that phasic PSR feedback stimulates breathing by enhancing the occurrence of breathing episodes in this species but does not appear to modify the instantaneous breathing frequency during an episode.     

Nogo-A在小鼠胚胎新生视网膜节细胞及其轴突的表达

目的 研究小鼠胚胎阶段Nogo-A在视网膜节细胞(RGCs)及其轴突上的表达及时程变化. 方法 取不同发育阶段的小鼠胚胎,采用免疫荧光染色,以激光扫描共焦显微镜观察Nogo-A在视觉传导通路中的表达.并采用免疫双标染色确定视网膜中表达Nogo-A蛋白的细胞类型. 结果 在视网膜发育的早期阶段(E12),Nogo-A密集表达于具有放射状形态的细胞上,Nogo-A免疫阳性产物出现在胞质、胞膜以及轴突上.Nogo-A与Tuj-1双标染色显示,此阶段的视网膜中几乎所有RGCs及其轴突都表达有Nogo-A;在稍晚的发育阶段(E13),视网膜中表达Nogo-A的RGCs数量明显减少,且仅出现在节细胞层以外的室周带和睫状体边缘区.在视网膜的神经纤维层,大部分RGCs轴突不再表达Nogo-A,仅有少量视觉纤维为Nogo-A免疫阳性;RGCs的神经发生基本完成后(E15), 视网膜中几乎检测不到Nogo-A免疫阳性的细胞,但视网膜纤维层仍有少量表达Nogo-A的节细胞轴突.与之类似,视神经盘、视茎、视交叉和视束都观察到少量Nogo-A免疫阳性的轴突.值得注意的是,视束中表达Nogo-A的纤维集中位于表浅部位,而此处恰为新近到达轴突的通过部位. 结论 Nogo-A在视网膜RGCs以及轴突上表达的时程变化和位置特点提示,新生RGCs及其轴突表达Nogo-A,成熟后RGCs内Nogo-A的表达则下调.推测新生RGCs及其轴突中表达的Nogo-A可能与减少轴突分叉等细胞的内在功能有关.     

视网膜神经节细胞凋亡对延迟整流钾电流的影响

目的:观察视网膜神经节细胞(retinal ganglion cells,RGCs)凋亡对延迟整流钾电流(delayed rectifier K~+ currents,I_K)的影响。方法:将原代培养2~3 d的SD乳大鼠RGCs分为对照组、加压0.5 h组、加压1 h组、加压1.5 h组和加压2 h组,对照组为常规培养6 d;其它各组常规培养6 d后用自行设计的加压装置加压80 mmHg,时间分别为0.5 h、1 h、1.5 h和2 h,通过连续波长多功能微孔板检测仪检测各组RGCs线粒体的荧光强度;通过全细胞膜片钳技术观察各组细胞膜电容(membrane capacitance,C_m)的变化,观察对照组与加压1 h组I_K、V_(1/2)、k和G_(max)的变化。结果:对照组RGCs线粒体的荧光强度与加压0.5 h组比较差异无统计学显著性,而加压1 h、1.5 h和2 h各组RGCs线粒体的荧光强度显著低于对照组(P0.05);对照组RGCs的细胞Cm与加压0.5 h组比较差异无统计学显著性,其余各组RGCs的细胞C_m显著低于对照组(P0.05)。与对照组比较,加压1 h能使电流幅度显著增加,在刺激电位为-10 m V~60 m V时,加压1 h组的电流密度明显大于对照组(P0.05)。加压1 h组的G_(max)值明显高于对照组(P0.05),V_(1/2)显著小于对照组(P0.01),两组间比较k值的差异无统计学显著性。结论:视网膜神经节细胞凋亡伴有I_K通道电导增加,I_K增大。     

Classification of cat retinal ganglion cells into X- and Y-cells with a contrast reversal stimulus

Summary A contrast reversal (alternating phase) stimulus was used to study the responses of 150 retinal ganglion cells from 15 adult cats. Because the majority of the cells did not show perfect linear spatial summation, a ratio of the firing rates at two time periods was used to express the degree of nonlinearity. Y-cells showed a high degree of nonlinearity, and their mean null ratio was significantly lower than that of X-cells. With the stimulus at the null position, X-cells had an unmodulated discharge rate which was significantly higher than maintained activity, while the firing rate of Y-cells was lower than maintained activity. With the stimulus placed at an eccentric position in the receptive field, X-cells responded in a sustained manner, while Y-cells respond transiently. Because of these observations, we conclude that X-cells correspond to the sustained cells, while Y-cells correspond to the transient cells.     

Neurophysiological properties of the retinal ganglion cell classes of the cuban treefrog,Hyla septentrionalis

Summary The properties of the retinal ganglion cell classes in the cuban treefrog Hyla septentrionalis were studied qualitatively and quantitatively. In the superficial layers of the optic tectum three main classes of afferent optic nerve fibers could be distinguished, class-1^*, class-3 and class-4 neurons. Hyla displays a more classical organization of the receptive fields in class-1^* neurons and a weaker inhibitory surround and lower thresholds with respect to velocity, size and contrast than in Bufo or ranid frogs. The functions for velocity, contrast, size of stimulus, neuronal adaptation and adaptation to background luminance level were evaluated. Experiments with monochromatic light spots are mentioned. The results are compared to those of other amphibia and the diversity of the retinal ganglion cell properties in the different species is stressed as an important factor in the processing of the various ganglion cell types at the tectal level.