Classes Of Retinal Ganglion Cells Research Articles

Neuronal Synchronous Discharges and Behavior: Retinal Synchronous Discharges are Essential for Escape Behavior in Frogs

Oscillatory synchronized activities are generated among visual neurons in a manner that depends on certain key features of light stimulation. Although these activities are assumed to play an important role in perceptual integration, their functional significance has yet to be elucidated. We performed behavioral tests and multi-electrode recordings from retinas isolated from the frog. Pharmacological manipulation of the oscillatory synchronized activities in a class of retinal ganglion cells (dimming detectors) induced correlated changes in escape behavior. The retinal oscillatory synchronized activities are likely to encode escape-related information in frogs.

Monocular and binocular thresholds for abruptly and gradually presented illusory contours

Background: In this study, monocular thresholds and binocular summation for abrupt onset/offset versus gradually revealed phantom letter E (illusory contours) stimuli are compared to determine the suitability of these stimuli for assessment of the integrity of two of the major retinal streams: the magnocellular and the parvocellular pathways. Such tests are important in progressive retinal disease where disease severity may differ between the classes of retinal ganglion cells and between the two eyes. Abrupt onset phantom contours have long been considered to activate the magnocellular visual pathway and we propose that gradually revealed high contrast ramped onset/offset stimuli are more likely to promote the more sustained processing of the parvocellular stream.Methods: Contrast discrimination thresholds for monocular and binocular viewing were compared in a counter‐balanced order in 70 young normal subjects, using tests of contrast threshold for a flicker‐defined letter E produced by alternation of light and dark dots. Three onset/offset conditions were used—abrupt onset that was maintained for 34 milliseconds (four frames of 8.5 milliseconds) then discontinued, ramped onset over 34 milliseconds (four frames) with offset over 34 milliseconds and ramped onset over 85 milliseconds (10 frames) with offset over 85 milliseconds.Results: Contrast thresholds for identification of the orientation of the E, when presented with four frames ramped onset and offset when compared to the four frames abrupt onset/offset were three times higher, irrespective of monocular or binocular viewing conditions. Threshold contrasts were seven times higher when the 10 frames ramped onset/offset stimuli were compared to abrupt four frames onset/offset. Binocular contrast thresholds were reduced by approximately 40 per cent compared to monocular thresholds for all conditions. The binocular increase in contrast sensitivity is approximately equal for abrupt transiently presented stimuli and for gradually presented more sustained stimuli.Discussion: The results indicate that the same mechanisms of monocular processing and binocular summation are used for identification of a flickering contrast‐defined phantom contour under presentation conditions, which are characteristic of the temporal and contrast preferences of the primate magnocellular and parvocellular visual pathways. This suggests that the phantom contour E test may be useful for clinical differentiation of the integrity of the M and P retinal ganglion‐derived visual pathways, regardless of whether it is applied monocularly or binocularly.

Dendritic Abnormalities in Retinal Ganglion Cells of Three-Month Diabetic Rats

Purpose: To determine the effect of three-month diabetes on the retinal ganglion cell (RGC) morphology and density. Methods: Experimental diabetes was induced in Sprague-Dawley rats by intraperitoneal injection of streptozotocin (STZ). Retinas from three-month diabetic and age-matched control rats were harvested, and immunohistochemistry with monoclonal anti-Thy-1 antibody was carried out for calculating RGC density. Random RGC labeling with gene gun propelled lipophilic fluorescent dye, DiI, coated particles (DiOlistic method) was done for detailed RGC classification, dendritic field, and soma size measurement. Results: The number of Thy1-labeled RGCs in the three-month diabetic rats was significantly reduced compared with that in the age-matched control. Obvious RGC morphology changes were observed, and the number of RGCs that could not be classified was significantly greater in the diabetic retinas. Among those well-classified RGCs, cells with enlarged dendritic fields were more frequently seen in the RGA group (401±86um, n = 59, P < 0.001), but the soma sizes were unchanged from the controls (P > 0.05). For cells in the groups of RGB and RGC, no significant changes in the dendritic fields and soma sizes were found (P > 0.05). Conclusions: In the three-month STZ-induced diabetic rat, retinal ganglion cell loss is associated with morphology change. The surviving RGCs in the diabetic retina, especially those in RGA group, show significant dendritic field enlargement. This plasticity of the surviving RGC dendrites may represent a compensatory response to the overall loss of RGCs in diabetes.

Retinal ganglion cell coding in simulated active vision

The image on the retina is almost never static. Eye, head, and body movements, and externally generated motion create rapid and continual changes in the retinal image ("active vision"). Virtually all vision in animals such as primates, which make saccades as often as 3-4 times/s, is based on information that must be derived from the first few hundred milliseconds after sudden, global changes in the retinal image. These changes may be accompanied by large changes in area mean luminance, as well as higher order image contrast statistics. This study investigated how retinal ganglion cell responses, whose response properties have been typically studied and defined in a stable stimulus regime, are affected by sudden changes in mean luminance that are characteristic of active vision. Specifically, the steady-state responses of retinal ganglion cells to static or moving square-wave grating stimuli were recorded in an isolated, superfused rabbit eyecup preparation and compared to responses after saccade-like changes in luminance. The manner of coding after luminance changes was different for different ganglion cell classes; both suppression and enhancement of responses to patterns following luminance changes were found. Brisk-transient Off cells unambiguously signaled the darkening of the overall image, but were also modulated by the subsequently appearing grating stimulus. Several types of On-center cell behavior were observed, ranging from strong suppression of the subsequent response by luminance changes, to strong enhancement. Overall, most ganglion cells distinguished static patterns after a luminance change via differences in their spike discharges nearly as well as before, although there were clear asymmetries between the On and Off pathways. Changes in mean luminance in some ganglion cells, such as On-Off directionally selective ganglion cells, could create large phase shifts in the response to patterned, moving stimuli, although these stimuli were still detected immediately after luminance changes. The results of this study show that the image dynamics of active vision may be a fundamental challenge for the visual system because of strong effects on retinal ganglion cell function. However, rapid extraction of unambiguous information after luminance changes appears to be encoded in differences in the spike discharges in different retinal ganglion cell classes. Asymmetries among ganglion cell classes in sensitivity to luminance changes may provide a basis by which some provide the "context" for interpreting the firing of others.

Classification of retinal ganglion cells: a statistical approach.

Numerous studies have shown that retinal ganglion cells exhibit an array of responses to visual stimuli. This has led to the idea that these cells can be sorted into distinct physiological classes, such as linear versus nonlinear or on versus off. Although many classification schemes are widely accepted, few studies have provided statistical support to favor one scheme over another. Here we test whether some of the most widely used classification schemes can be statistically verified, using the mouse retina as the model system. We used a cluster analysis approach and focused on 4 standard response parameters: 1) response latency, 2) response duration, 3) relative amplitude of the on and off responses, and 4) degree of nonlinearity in the stimulus-to-response transformation. For each parameter, we plotted its distribution and tested quantitatively, using a bootstrap method, whether it divided into distinct clusters. Our analysis showed that mouse ganglion cells clustered into several groups based on response latency, duration, and relative amplitude of the on and off responses, but did not cluster into more than one group based on degree of nonlinearity-the latter formed a single, large, continuous group. Thus while some well-known schemes for classifying ganglion cells could be statistically verified, others could not. Knowledge of which schemes can be confirmed is important for building models of how retinal output is processed and how retinal circuits are built. Finally, this cluster analysis approach is general and can be used to test other classification proposals as well, both physiological and anatomical.

Intrinsic light responses of retinal ganglion cells projecting to the circadian system.

In mammals, light entrainment of the circadian clock, located in the suprachiasmatic nuclei (SCN), requires retinal input. Traditional rod and cone photoreceptors, however, are not required. Instead, the SCN-projecting retinal ganglion cells (RGCs) function as autonomous photoreceptors and exhibit light responses independent of rod- and cone-driven input. Using whole-cell patch-clamp recording techniques, we have investigated the morphological and electrophysiological properties of this unique class of RGCs. Although SCN-projecting RGCs resemble Type III cells in form, they display strikingly different physiological properties from these neurons. First, in response to the injection of a sustained depolarizing current, SCN-projecting cells fired in a transient fashion, in contrast to most RGCs which fired robust trains of action potentials. Second, in response to light, SCN-projecting RGCs exhibited an intensity-dependent transient depolarization in the absence of rod and cone input. This depolarization reached a peak within 5 s and generated increased spiking activity before decaying to a plateau. Voltage-clamp recordings were used to characterize the light-activated conductance which generated this depolarization. In response to varying light intensities, SCN-projecting RGCs exhibited a graded transient inward current which peaked within 5 s and decayed to a plateau. The voltage dependence of the light-activated current was obtained by subtracting currents elicited by a voltage ramp before and during illumination. The light-activated current displayed both inward and outward rectification and was largely unaffected by substitution of extracellular Na+ with choline. In both respects, the intrinsic light-activated current observed in SCN-projecting RGCs resembles currents carried by ion channels of the transient receptor potential (trp) family, which are known to mediate the light response of invertebrate photoreceptors.

Directionally selective calcium signals in dendrites of starburst amacrine cells.

The detection of image motion is fundamental to vision. In many species, unique classes of retinal ganglion cells selectively respond to visual stimuli that move in specific directions. It is not known which retinal cell first performs the neural computations that give rise to directional selectivity in the ganglion cell. A prominent candidate has been an interneuron called the 'starburst amacrine cell'. Using two-photon optical recordings of intracellular calcium concentration, here we find that individual dendritic branches of starburst cells act as independent computation modules. Dendritic calcium signals, but not somatic membrane voltage, are directionally selective for stimuli that move centrifugally from the cell soma. This demonstrates that direction selectivity is computed locally in dendritic branches at a stage before ganglion cells.

Retinal ganglion cells with NADPH-diaphorase activity in the chick form a regular mosaic with a strong dorsoventral asymmetry that can be modelled by a minimal spacing rule

We have identified a class of retinal ganglion cells in the chick retina that can be labelled by NADPH-diaphorase histochemistry. These cells have a remarkable topographic distribution, being restricted to the dorsal hemiretina, and form a highly regular mosaic, as revealed by the analysis of nearest neighbour distribution and Delaunay triangulation. Autocorrelation analysis of the mosaic of NADPH-diaphorase-positive retinal ganglion cells shows that the mosaic spatial organization could be generated with the single constraint that two elements cannot be closer than a given minimal distance (d(min)), which we confirmed by computer simulations. In contrast with what has been observed in other mosaics, here d(min) varies with cell density. However, the observed variation of the exclusion area is consistent with an original assembly of the mosaic with a constant d(min) (as is the case in other mosaics), followed by differential expansion of the retina during development.

Molecular control of cell diversification in the vertebrate retina.

Any discussion of the molecular mechanisms that are responsible for the generation of cell diversity in the retina requires some consideration of what constitutes neuronal diversity. Traditionally, retinal neurobiologists have classified retinal cell types on the basis of their morphology, in terms both of their laminar position and their dendritic structure, as well as by their electrophysiological properties. While it is generally accepted that there are five basic classes of retinal neurons, photoreceptors, horizontal cells, bipolar cells, amacrine cells, and ganglion cells, there is a considerable amount of debate as to how these basic classes are subdivided. While there are critical differences in gene expression between the classes of cone photoreceptors that determine the wavelength of light to which they respond, there is little difference in their morphology; by contrast, the various classes of retinal ganglion cells have critical differences in their morphology and connectivity, but as yet few molecules have been identified that are differentially expressed in subsets of ganglion cells, and it is not at all clear whether these differences correspond to the morphological subclasses of ganglion cells. Nevertheless, most retinal neurobiologists place the number of retinal cell types somewhere between “70 and the low hundreds (Cook 1996).”KeywordsBipolar CellRetinal CellAmacrine CellRetinal NeuronbHLH Transcription FactorThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Structural organization of parallel information processing within the tectofugal visual system of the pigeon.

Visual information processing within the ascending tectofugal pathway to the forebrain undergoes essential rearrangements between the mesencephalic tectum opticum and the diencephalic nucleus rotundus of birds. The outer tectal layers constitute a two-dimensional map of the visual surrounding, whereas nucleus rotundus is characterized by functional domains in which different visual features such as movement, color, or luminance are processed in parallel. Morphologic correlates of this reorganization were investigated by means of focal injections of the neuronal tracer choleratoxin subunit B into different regions of the nuclei rotundus and triangularis of the pigeon. Dependent on the thalamic injection site, variations in the retrograde labeling pattern of ascending tectal efferents were observed. All rotundal projecting neurons were located within the deep tectal layer 13. Five different cell populations were distinguished that could be differentiated according to their dendritic ramifications within different retinorecipient laminae and their axons projecting to different subcomponents of the nucleus rotundus. Because retinorecipient tectal layers differ in their input from distinct classes of retinal ganglion cells, each tectorotundal cell type probably processes different aspects of the visual surrounding. Therefore, the differential input/output connections of the five tectorotundal cell groups might constitute the structural basis for spatially segregated parallel information processing of different stimulus aspects within the tectofugal visual system. Because two of five rotundal projecting cell groups additionally exhibited quantitative shifts along the dorsoventral extension of the tectum, data also indicate visual field-dependent alterations in information processing for particular visual features.

Automatic characterization and classification of ganglion cells from the salamander retina.

The classification of retinal ganglion cells according to their morphological features is addressed by using a comprehensive set of shape measures and several clustering strategies. The morphological features considered include many common measures (such as dendritic radii and the number of dendritic segments) and three new quantifiable measures: 1) the area of influence of the dendritic tree as calculated in an operator-independent manner by using Minkowski sausages; 2) the complexity of tortuousity along each dendritic segment as represented by the 3D bending energy; and 3) the coverage factor as calculated by using the Bouligand-Minkowski fractal dimension, which is more accurate than the commonly used box-counting algorithm. We evaluated four clustering approaches including the k-means and Ward's hierarchical clustering methods. By using these highly quantifiable methods to group the cells into classes, the present work has extended and reassessed the analysis of 68 ganglion cells from the tiger salamander previously classified by Toris et al. ([1995] J. Comp. Neurol. 352:535-559). Though substantiating the number of classes (5) previously proposed by Toris et al., the results obtained here indicate a number of discrepancies among the members of each class, especially regarding the border between two classes, originally called the medium simple and the medium complex cells. Such an effect has motivated the proposal of new names for the medium simple and medium complex classes, now called small highly complex and medium cells, respectively. Also included in the present article are comprehensive statistics of each class, correlations among all the adopted shape measures, and examples of the cells from each class. The resultant classes that emerged were compared using their electrotonic characteristics and physiological profiles.

Monocular enucleation prevents retinal ganglion-cell loss following neonatal visual cortex damage in cats.

Damage to primary visual cortex (VC) in young cats leads to severe retrograde degeneration of the dorsal lateral geniculate nucleus (dLGN) and selective transneuronal retrograde degeneration of a class of retinal ganglion cells (RGCs) that have a medium-size soma. Previous studies have shown that "programmed" RGC death associated with normal development in one eye can be attenuated by removal of the other eye, suggesting that binocular interactions can influence developmental RGC death. The present study investigated whether removal of one eye also attenuates the ganglion cell loss that accompanies an early VC lesion. Five one-week-old cats received a unilateral VC lesion (areas 17, 18, and 19), and three of these cats also underwent monocular enucleation at the same time. Two normal control animals also were examined. RGC measurements were made from flat-mounted retinae when the animals were 5 weeks old. Sampling was restricted to a retinal area corresponding to the retinotopic representation included in the VC lesion. Results indicate that there is a marked loss of medium-size RGCs in the hemiretinae projecting to the damaged hemisphere in cats that received a VC lesion alone. However, there is no such loss in VC-lesion animals that also have a monocular enucleation. These results indicate that the transneuronal RGC loss that occurs after an early visual cortex lesion can be influenced by binocular interactions.

Neural cell classification by wavelets and multiscale curvature.

A new approach to automatic classification of retinal ganglion cells using multiscale techniques including the continuous wavelet transform, curvature, and standard pattern recognition techniques is described. Each neural cell is represented by its outer contour, and the wavelet transform is calculated from the complex signal defined by the aforementioned contour, leading to the so-called W-representation (Antoine et al. 1996). The normalized multiscale wavelet energy (NMWE) is used to define a set of shape measures associated with the number of details of the shape for a broad range of spatial scales. Next, the more discriminating NMWE coefficients are chosen through a feature ordering technique and fed to statistical classifiers. In addition, the normalized multiscale bending energy (NMBE) is discussed as a means of neural shape description for classification purposes based on the multiscale curvature, i.e. the curvegram, of the neural contour. It is shown that both shape descriptors are suitable for shape classification, presenting similar classification performance. In fact, NMBE has a slightly better recognition rate than NMWE in our experiments. On the other hand, NMWE is less computationally expensive than NMBE, presenting also the potentially useful property of allowing the use of more suitable different analyzing wavelets, depending on the problem under consideration. Therefore, both measures are related and provide a good framework for the design of neural cell description and classification. The methods described in this work have been successfully applied to the classification of two classes of cat retinal ganglion cells, namely alpha and beta (henceforth referred as alpha-cells and beta-cells, respectively), and three statistical classifiers were considered: minimum-distance, k-nearest neighbours and maximum likelihood. The mean recognition rates are near 90%, which is superior to the other shape measures considered. It is argued here that the proposed technique can be adopted as a new general methodology for multiscale shape analysis and recognition, being applicable also to other problems in biological shape characterization in neuroscience and general biomedical image analysis. In the context of analysis of shape complexity, the multiscale energies are coherent with subjective judgements by humans.

Spatial asymmetries in cat retinal ganglion cell responses.

Enroth-Cugell and Robson (1966) first proposed a classification of retinal ganglion cells into X cells, which exhibit approximate linear spatial summation and largely sustained responses, and Y cells, which exhibit nonlinearities and transient responses. Gaudiano (1992a, 1992b, 1994) has suggested that the dominant characteristics of both X and Y cells can be simulated with a single model simply by changing receptive field profiles to match those of the anatomical counterparts of X and Y cells. He also proposed that a significant component of the spatial nonlinearities observed in Y (and sometimes X) cells can result from photoreceptor nonlinearities coupled with push-pull bipolar connections. Specifically, an asymmetry was predicted in the ganglion cell response to rectangular gratings presented at different locations in the receptive field under two conditions: introduction/withdrawal (on-off) or contrast reversal. When measuring the response to these patterns as a function of spatial phase, the standard difference-of-Gaussians model predicts symmetrical responses about the receptive field center, while the push-pull model predicts slight but significant asymmetry in the on-off case only. To test this hypothesis, we have recorded ganglion cell responses from the optic tract fibers of anesthetized cat. The mean and standard deviations of responses to on-off and contrast-reversed patterns were compared. We found that all but one of the cells that yielded statistically significant data confirmed the hypothesis. These results largely support the theoretical prediction.

Activation and inactivation properties of voltage-gated calcium currents in developing cat retinal ganglion cells

The correlated activity of developing retinal ganglion cells is essential for the reorganization and refinement of retinogeniculate projections. Previous studies have uncovered marked changes in the spiking properties of retinal ganglion cells during this period of reorganization; however, a full understanding of the changes in the underlying ionic conductances has yet to be obtained. To this end, the whole-cell configuration of the patch-clamp technique was used to record currents conducted by voltage-gated calcium channels in 83 dissociated cat retinal ganglion cells obtained from animals aged between embryonic day 34 and postnatal day 105. Calcium currents, magnified by using barium as the major charge carrier, were isolated by substituting choline for Na + in the bathing solution and Cs + for K + in the electrode solution. Three voltage-gated Ca 2+ conductances were identified based on their voltage dependence and kinetics of activation and inactivation: a transient low-voltage-activated conductance, a transient high-voltage-activated conductance and a sustained high-voltage-activated conductance. During the developmental period examined there were significant increases in the densities of all three conductances, as well as significant changes in some of their activation and inactivation properties. These findings, together with those reported previously for the voltage-gated Na + and K + conductances, are related to the generation of excitability in developing retinal ganglion cells during a period critical to the normal development of the visual system. Furthermore, while the sustained high-voltage-activated conductance was present in all of the retinal ganglion cells observed, only about 72% expressed the transient high-voltage-activated current. During the developmental period examined, there was also an increase in the proportion of cells expressing the transient low-voltage-activated conductance. This, along with our previous finding that retinal ganglion cells heterogeneously express different types of voltage-gated K + channels, strongly suggests that the spiking patterns observed in different classes of retinal ganglion cell may be due, in part, to their intrinsic membrane properties.

Synchronizing Retinal Activity in Both Eyes Disrupts Binocular Map Development in the Optic Tectum

Spatiotemporal correlations in the pattern of spontaneous and evoked retinal ganglion cell (RGC) activity are believed to influence the topographic organization of connections throughout the developing visual system. We have tested this hypothesis by examining the effects of interfering with these potential activity cues during development on the functional organization of binocular maps in the Xenopus frog optic tectum. Paired recordings combined with cross-correlation analyses demonstrated that exposing normal frogs to a continuous 1 Hz of stroboscopic illumination synchronized the firing of all three classes of RGC projecting to the tectum and induced similar patterns of temporally correlated activity across both lobes of the nucleus. Embryonic and eye-rotated larval animals were reared until early adulthood under equivalent stroboscopic conditions. The maps formed by each RGC class in the contralateral tectum showed normal topography and stratification after strobe rearing, but with consistently enlarged multiunit receptive fields. Maps of the ipsilateral eye, formed by crossed isthmotectal axons, showed significant disorder and misalignment with direct visual input from the retina, and in the eye-rotated animals complete compensatory reorientation of these maps usually induced by this procedure failed to occur. These findings suggest that refinement of retinal arbors in the tectum and the ability of crossed isthmotectal arbors to establish binocular convergence with these retinal afferents are disrupted when they all fire together. Our data thus provide direct experimental evidence that spatiotemporal activity patterns within and between the two eyes regulate the precision of their developing connections.

Distribution, size and number of axons in the optic pathway of ground squirrels.

The present study has examined the distribution of axons of differing sizes in the optic pathway of the ground squirrel. Axon diameters were measured from electron micrographs at various locations across sections of the optic nerve and tract, and total distributions and numbers were estimated. In both the nerve and tract, roughly 1.2 million optic axons were present. The population of optic axons had a unimodal size distribution, peaking at 0.9 microm in diameter and having an extended tail toward larger diameters. Local axon diameter distributions in the optic tract indicated distinct (though partially overlapping) axon diameter classes, including one of fine sizes peaking at 0.8-0.9 microm, a second of medium sizes peaking around 1.7-1.8 microm, and a third composed of the larger fibers with diameters up to 4.8 microm. The fine-caliber axons were found at all locations in the tract, and were the only axons present immediately adjacent to the pia, while the medium- and coarse-caliber axons were found at deeper locations. Curiously, the larger axons were found primarily in the medial parts of the tract, where axons from the dorsal retina normally course. A similarly restricted distribution of the larger axons was observed in the dorsotemporal parts of the optic nerve, suggesting that this difference in the tract may relate to an asymmetric distribution of ganglion cells on the retina giving rise to these axons. Measurements of axonal size taken within the optic fiber layer in dorsal and ventral parts of the retina confirmed this asymmetry, consistent with previous demonstrations of soma size differences in the dorsal versus ventral retina. The partial segregation of axons by size in the optic tract of the ground squirrel then reflects both the asymmetric distribution of retinal ganglion cell classes and the chronotopic reordering of optic axons that occurs within the chiasmatic region.

Injuries in less industrialised countries: what do we know?

Development of visual system circuitry requires the formation of precise synaptic connections between neurons in the retina and brain. For example, axons from retinal ganglion cells (RGCs) form synapses onto...

Retinal ganglion cells in the albino rat: Revised morphological classification

Rat retinal ganglion cells were traditionally classified on the basis of soma size and the morphology of their dendritic fields. However, in the past, techniques used to label ganglion cells (horseradish peroxidase, Golgi, or the neurofibrillar stain) did not always stain the axon and/or the entire dendritic field. In the present study, we have labelled retinal ganglion cells in the adult albino rat with the carbocyanine dye 1,1'-dioctadecyl-3,3,3',3'-tetramethylindo-carbocyanine perchlorate (DiI) or have intracellularly injected them with Neurobiotin. Such procedures enabled us to completely fill these neurons, and our findings prompted us to modify the existing retinal ganglion cell classification in the rat. First, cells were categorised into three groups on the basis of soma and dendritic field size: Group RG(A) cells have large somata and dendritic field diameters, Group RG(B) cells have small somata and dendritic field diameters, whereas Group RG(C) cells have small to medium-sized somata and medium-to-large dendritic field diameters. On the basis of dendritic field morphology and presence across the retina, each Group was then subdivided into subgroups. The significance of our results in terms of retinal ganglion cell function is discussed.

Retinal ganglion cells in the albino rat: Revised morphological classification

Rat retinal ganglion cells were traditionally classified on the basis of soma size and the morphology of their dendritic fields. However, in the past, techniques used to label ganglion cells (horseradish peroxidase, Golgi, or the neurofibrillar stain) did not always stain the axon and/or the entire dendritic field. In the present study, we have labelled retinal ganglion cells in the adult albino rat with the carbocyanine dye 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindo-carbocyanine perchlorate (DiI) or have intracellularly injected them with Neurobiotin. Such procedures enabled us to completely fill these neurons, and our findings prompted us to modify the existing retinal ganglion cell classification in the rat. First, cells were categorised into three groups on the basis of soma and dendritic field size: Group RGA cells have large somata and dendritic field diameters, Group RGB cells have small somata and dendritic field diameters, whereas Group RGC cells have small to medium-sized somata and medium-to-large dendritic field diameters. On the basis of dendritic field morphology and presence across the retina, each Group was then subdivided into subgroups. The significance of our results in terms of retinal ganglion cell function is discussed. J. Comp. Neurol. 385:309–323, 1997. © 1997 Wiley-Liss, Inc.