Retinal ganglion cells in two teleost species,Sebastiscus marmoratus and Navodon modestus

Distribution patterns of ganglion cells in the retina were examined in Nissl-stained retinal whole mounts of Sebastiscus and Navodon. The existence of area centralis in the temporal retina in both species suggests binocular vision. In Navodon, another high density area was found in the nasal retina, and a dense band of ganglion cells was observed along the horizontal axis between the two high-density areas. There is an obvious trend for the ganglion cell size to increase as the density decreases. The total number of ganglion cells was estimated to be about 45 × 10⁴ in Sebastiscus and 87 × 10⁴ in Navodon, whereas the total number of optic nerve fibers was about 35 × 10⁴ and 70 × 10⁴, respectively. The retinal ganglion cells labeled with HRP were classified into six types according to such morphological characteristics as size, shape, and location of the soma as well as dendritic arborization pattern. Type I cells have a small round or oval soma in the ganglion cell layer and a small dendritic field in the inner plexiform layer. Type II cells are similar to type I cells, but the dendrites arborize more closely to the ganglion cell layer in the innermost region of the inner plexiform layer. Type III cells have a medium-sized round soma in the ganglion cell layer, and the dendrites extend in an extremely wide area in the inner plexiform layer with few branches. Type IV cells have a large soma which is located in the ganglion cell layer. Dendrites emanate from the soma in all directions, branching out several times within a rather small region in the innermost part of the inner plexiform layer. Type V cells have large somata of various shapes, usually dislocated to the inner plexiform or granular layer. The dendrites extend in every direction and occupy an extremely large area in the inner plexiform layer. Type VI cells have the largest somata, which are also dislocated to the inner plexiform or granular layer. Type VI cells have a characteristic triangular or fan-shaped dendritic field. Soma size and the axon diameter are intimately linked, that is, small somata of type I and II cells give off thin axons, and large somata of type V and VI give off thick axons. Medium-sized somata of type III cells or large somata of type IV cells, which have rather small dendritic fields, give off medium-sized axons. The histograms of the soma areas in the whole retina are quite similar to the histograms of the diameters of the optic nerve fibers.     

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. J. Comp. Neurol. 385:309–323, 1997. © 1997 Wiley-Liss, Inc.     

Morphological classification of retinal ganglion cells in mice

Mice have been used for extensive studies on optic nerves and retinal ganglion cells, but mouse retinal ganglion cells have not been classified morphologically. In the present study, normally placed retinal ganglion cells and displaced retinal ganglion cells in pigmented and albino mice were classified morphologically using horseradish peroxidase. These cells were classified into three types according to the sizes of the soma and the dendritic field: type I cells, large soma and large dendritic field; type II cells, small-to-medium soma and small dendritic field; and type III cells, small-to-medium soma and large dendritic field. Some ganglion cells had both symmetric and asymmetric cells. Each type was further subdivided according to the termination level of dendrites in the inner plexiform layer and the dendritic branching pattern. Except for type III displaced ganglion cells, dendrites of the normally placed ganglion cells and the displaced ganglion cells ramify in the outer two-fifths of the inner plexiform layer (sublamina a) or the inner three-fifths of the inner plexiform layer (sublamina b). Type III displaced ganglion cells ramify only in sublamina a. Dendrites of some normally placed type I ganglion cells ramify in both sublaminae. Displaced biplexiform cells were observed, the dendrites of which ramify in both the inner and the outer plexiform layers. All cell types were found in both mouse strains. © 1995 Wiley-Liss, Inc.     

Four retinal ganglion cell types that project to the superior colliculus in the thirteen-lined ground squirrel (Spermophilus tidecemlineatus)

The morphology of retinal ganglion cells projecting to the superior colliculus (SC) of the thirteen-lined ground squirrel (Spermophilus tridecemlineatus) was studied after retrogradely labeling the cells with cholera toxin subunit B. On the basis of previous reports, labeled cells were classified as small (6–10 μm in soma diameter), medium (11–14 μm), or large (>14 μm). A total of 3,427 cells were studied. Small cells constituted 78% of the population, 21% were medium cells, and only 1% were classified as large. The morphology of medium-sized cells was studied in more detail because large cells were few in number and the staining of the dendritic tree of small cells was not optimal. The best labeled medium-sized cells were classified on the basis of the shape and size of their dendritic tree and the pattern of dendritic ramification. Four types were identified among the medium-sized ganglion cells. Two types were classified as symmetric δ-like and asymmetric δ-like cells considering the relative symmetric or asymmetric distribution of their dendritic branches and their similarities with the δ type of the cat. Approximately 52% of all the medium-sized cells studied were symmetrical δ-like, and 19% were classified as asymmetrical δ-like. These cells were also very similar to the symmetrical and asymmetrical directionally selective ganglion cells described in rabbit retina. Other cells were termed β-like. They had the smallest dendritic tree diameter, and their tree size seemed to be related to retinal eccentricity. Medium β-like cells comprised approximately 21% of all cells projecting to the SC. The fourth type was termed “acute angle” because most of their dendritic branches were relatively straight and formed acute angles (10–45°) at their branching points. These cells were few in number (approximately 8% of all medium-sized cells studied) and did not resemble any reported previously in cats. Thus, a variety of morphological types of retinal ganglion cells projected to the SC. Of these, the symmetrical and asymmetrical δ-like cells appeared to correspond to the directionally selective type described in the ground squirrel (Michael, C.R. [1968] J. Neurophysiol. 31:257–267) and reported in the rabbit retina. J. Comp. Neurol. 396:105–120, 1998. © 1998 Wiley-Liss, Inc.     

Electron microscopic analysis of amacrine and bipolar cell inputs on Y-, X- and W-cells in the cat retina

In the cat retina, bipolar and amacrine cell inputs were analyzed electron microscopically in 5 ganglion cells (two Y-cells, two X-cells and one W-cell) that were well-isolated and had clear morphological features. For Y- and X-cells, subtypes of a and b were further identified according to the sublamina of the inner plexiform layer in which their dendrites extended. Y-a and Y-b ganglion cells had large somas, thick axons, and several thick dendrites that branched extensively with a large dendritic field. X-a and X-b cells had medium-sized somas, medium-sized axons and extremely narrow dendritic fields. The W-cell studied had a medium-sized soma, a medium-sized axon, and extremely thin dendrites that extended widely. For each of the 5 ganglion cells, ultrathin serial sections were made to study relative occurrence of amacrine and bipolar synapses in whole length of dendrites. About 50% of the terminals were bipolar in the Y-a and Y-b cell dendrites, 36-38% in the X-a and X-b cell dendrites, whereas only 19.7% were bipolar in the W cell dendrites. Bipolar terminals tended to make synaptic contacts with the distal dendrites of Y- and W-cells.     

Retinal ganglion cell size groups projecting to the superior colliculus and the dorsal lateral geniculate nucleus in the North American opossum

The retinal ganglion cells projecting to the superior colliculus (SC) and dorsal lateral geniculate nucleus (LGNd) of the North American opossum (Didelphis virginiana) were studied by using the retrograde transport of horseradish peroxidase (HRP). The four ganglion cell size groups recognized previously were found to project in systematically different ways. After injections of HRP into the superior colliculus, labeled cells were seen in nasal retina contralateral to the injection and in temporal retina both ipsilateral and contralateral to the injection. In contralateral nasal retina cells of all size classes were labeled, while in contralateral temporal retina small (8-14 micrometers diameter), small-medium (15-19 micrometers diameter), and large (greater than 24 micrometers diameter) cells were labeled but few, if any, large-medium (20-24 micrometers diameter) cells were labeled. In ipsilateral temporal retina, soma size groups labeled included small-medium, large-medium, and large cells, but very few small cells. A nasal-temporal difference in the soma size of ganglion cells projecting to the SC was found: Labeled cells in temporal retina were 1.7-4.2 micrometers larger than their counterparts in nasal retina. Following injection of HRP into the LGNd, label was seen in contralateral nasal and ipsilateral temporal retina with no label seen in contralateral temporal retina. The labeled cells were small-medium, large-medium, and large. No small ganglion cells were labeled from the LGNd. A small nasal-temporal soma size difference in retinal ganglion cells projecting to the LGNd was seen: labeled cells in temporal retina were 1.0-2.1 micrometers larger than in nasal. It is concluded that all four ganglion cell size groups in the opossum project to the SC, but that only the three largest project to the LGNd.     

Morphology of rabbit retinal ganglion cells projecting to the medial terminal nucleus of the accessory optic system

Rabbit retinal ganglion cells were retrogradely labeled following injection of rhodamine-labeled microspheres into the medial terminal nucleus. The small fraction of rhodamine-labeled neurons reached their peak concentration within the visual streak and then decreased with increasing eccentricity until none were encountered in the far periphery. The same rabbits also received injections of the fluorescent tracer Fast Blue into the superior colliculus. No double-labeled neurons were observed, i.e., ganglion cells projecting to the medial terminal nucleus (MTN) had no axon collaterals to the superior colliculus. In fixed retinae rhodamine-labeled ganglion cells were intracellularly injected with the fluorescent dye Lucifer Yellow to reveal their full dendritic arborization. MTN-projecting cells had medium-sized to large somata with thin and frequently branched dendrites. The large dendritic trees had a distinct morphology and were predominantly unistratified in a narrow band that presumably corresponded to the electrophysiologically determined on-sublamina of the inner plexiform layer. Dendritic field sizes were inversely related to ganglion cell density, thus providing an eccentricity-independent, constant dendritic coverage factor. Approximately five to six dendritic fields from neighboring cells cover every point of the retina. Published reports claim that the physiological class of on-direction-selective ganglion cells provides the sole retinal input to the MTN in the rabbit. In this context morphological features of MTN-projecting cells and their presumed functional correlation with on-direction-selective ganglion cells are discussed.     

New metrics for analysis of dendritic branching patterns demonstrating similarities and differences in ON and ON-OFF directionally selective retinal ganglion cells.

The morphology and dendritic branching patterns of retinal ganglion cells have been studied in Golgi-impregnated, whole-mount preparations of rabbit retina. Among a large number of morphological types identified, two have been found that correspond to the morphology of ON and ON-OFF directionally selective (DS) ganglion cells identified in other studies. These two kinds of DS ganglion cell are compared with each other, as well as with examples of class I, class II, and class III cells, defined here with reference to our previous studies. Cell body, dendritic field size and branching pattern are analyzed in this paper and levels of dendritic stratification are examined in the following paper. ON DS ganglion cells are about 10% larger in soma size and about 5 times the dendritic field area of ON-OFF DS ganglion cells, when compared at the same retinal location. These two morphological types of ganglion cell can be said to define the upper and lower bounds of an intermediate range of cell body and dendritic field sizes within the whole population of ganglion cells. Nevertheless, in previous physiological studies receptive field sizes of the two types were shown to be similar. This discrepancy between morphological and physiological evidence is considered in the Discussion in terms of a model of the excitatory receptive field of ON-OFF DS ganglion cells incorporating starburst amacrine cells. A new set of metrics is introduced here for the quantitative analysis and characterization of the branching pattern of neuronal arborizations. This method compares the lengths of terminal and preterminal dendritic branches (treated separately), as a function of the distances of their origins from the soma, viewed graphically in a two-dimensional scatter plot. These values are derived from computer-aided 3D logging of the dendritic trees, and distance from the soma is measured as the shortest distance tracked along the dendritic branches. From these metrics of the "branch length distributions," scale-independent branching statistics are derived. These make use of mean branch lengths and distances, slopes of lines fitted to the distributions, and elliptical indices of scatter in the distributions. By these measures, ON and ON-OFF DS ganglion cells have similar branching patterns, which they share to varying degrees with functionally unrelated class III.1 ganglion cells. The scale of the branching patterns of ON and ON-OFF DS cells and their degree of uniformity are different, however.(ABSTRACT TRUNCATED AT 400 WORDS)     

Morphological types of ganglion cells in the dog and wolf retina.

The morphological types of ganglion cells in the dog and wolf retina were studied by intracellular staining with Lucifer Yellow. These retinae contain a range of ganglion cell types that closely correspond to those found in cat retina: alpha cells with large somata and large, relatively densely branched dendritic trees; beta cells with medium-sized somata and small, densely branched dendritic trees; and a variety of other types with smaller somata and varying dendritic branching patterns and dendritic field sizes. The correspondence of canine and cat ganglion cell types strengthens the view that there is a common set of ganglion cell types in carnivores. Alpha and beta cell dendritic trees of dog and wolf are monostratified in either the inner or the outer part of the inner plexiform layer, suggesting an on/off dichotomy in the response to light. Dendritic field sizes of dog alpha and beta cells increase from the central area to peripheral retina: alpha cell fields from 160-200 microns to about 1,100 microns diameter, and beta cell fields from 25 microns to about 360 microns diameter. These sizes are quantitatively very similar to those found in cat retina. The close qualitative and quantitative morphological correspondence of cat and dog ganglion cells suggests that they are also functionally very similar. It is likely that dog alpha cells have brisk-transient (Y), and dog beta cells brisk-sustained (X) concentric receptive fields. From the smallest beta cell sizes it is concluded that the visual acuity of the dog may be as good as that of the cat.     

Thorny ganglion cells in marmoset retina: Morphological and neurochemical characterization with antibodies against calretinin

In primates, over 17 morphological types of retinal ganglion cell have been distinguished by their dendritic morphology and stratification, but reliable markers for specific ganglion cell populations are still rare. The calcium binding protein calretinin is known to be expressed in the inner nuclear and the ganglion cell layer of marmoset retina, however, the specific cell type(s) expressing calretinin in the ganglion cell layer are yet to be determined. Here, we identified calretinin positive retinal ganglion cells in the common marmoset Callithrix jacchus. Double labeling with the ganglion cell marker RBPMS demonstrated that the large majority (80%) of the calretinin positive cells in the ganglion cell layer are ganglion cells, and 20% are displaced amacrine cells. The calretinin positive ganglion cells made up on average 12% of the total ganglion cell population outside of the foveal region and their proportion increased with eccentricity. Prelabeling with antibodies against calretinin and subsequent intracellular injection with DiI revealed that the large majority of the injected cells (n = 74) were either narrow thorny or broad thorny ganglion cells, 14 cells were displaced amacrine cells. Narrow thorny cells were further distinguished into outer and inner stratifying cells. In addition, weakly labeled cells with a large soma were identified as parasol ganglion cells. Our results show that three types of thorny ganglion cells in marmoset retina can be identified with antibodies against calretinin. Our findings are also consistent with the idea that the proportion of wide‐field ganglion cell types increases in peripheral retina.     

Mudpuppy retinal ganglion cell morphology revealed by an HRP impregnation technique which provides Golgi-like staining

A new technique of retrograde labeling of ganglion cells with horseradish peroxidase (HRP) has been developed, based on orbital injections of HRP combined with a detergent (lysolecithin). When injections are followed by an appropriate survival time, dense staining of a small number of widely scattered cells results in Golgi-like filling of each neuron. This technique, as well as a variation which causes mass staining of ganglion cell somas, has been used to analyze the morphology of mudpuppy retinal ganglion cells. Morphological analysis has relied on computer reconstruction techniques for display, analysis of dendritic sublamination pattern, and morphometric analysis of the dendrites and soma. Based on morphological criteria, the mudpuppy retina contains a rich variety of ganglion cell types which vary according to soma placement, dendritic field size, polar vs. non-polar dendritic fields, dendritic branching pattern, and dendritic sublamination. The mudpuppy retina contains both conventional and displaced ganglion cells: the latter constitute about 15% of the total ganglion cell population. Both conventional and displaced ganglion cells show morphological diversity of dendritic sublamination branching pattern; cells from each group have a dendritic branching pattern confined to either distal or proximal divisions of the inner plexiform layer, whereas other cells have dendrites which branch in both sublaminae. Using morphological criteria, two subtypes of ganglion cells were identified, which have a distinctive branching pattern and dendritic tree size. The size and distribution of ganglion cell somas were analyzed from retinas in which mass staining of ganglion cells was present. The total number of ganglion cells was estimated at approximately 14,500 cells per retina. There was a tendency for soma size and density to decrease near the optic disk. The somas of displaced ganglion cells are smaller than their conventional counterparts, at the same retinal eccentricity. The somas of all HRP filled cells swell when compared to those of unstained fixed and freshly dissected retinas. The degree of swelling is proportional to the length of exposure to HRP. Cell swelling was evident for both retrograde labeling and intracellularly injected HRP. This artifact of HRP staining could influence the interpretation of studies in which quantitative differences in soma sizes are based on the use of HRP labeling.     

Morphology of ganglion cells which project to the dorsal lateral geniculate and superior colliculus in the ground squirrel

We wished to determine whether retinal ganglion cells that have axons terminating in the dorsal lateral geniculate and/or the superior colliculus have specific sizes of somata, comprising only part of the entire size range of ganglion cell somata. If so, then perhaps the specific functional types described by Michael might be associated with morphological types based on soma size. HRP was injected into either the superior colliculus (SC) or dorsal lateral geniculate nucleus (LGd) of thirteen-lined ground squirrels. Soma diameter of labeled ganglion cells was measured and the relation between cell size and frequency determined. After SC injections HRP-filled cells were mostly small and medium-sized. They ranged in diameter from 3 to 14 microns and the mean diameter of labeled neurons was 7.35 microns. Cells labeled after SC injections were often distributed as doublets or triplets in the retina. After LGD injections the majority of labeled cells were medium and large-sized. They ranged from 4 to 18 microns in diameter with a mean of 9.1 microns and were more regularly spaced within the retinal region of labeled cells. Thus, the present results provide reason to believe that functional classes of ganglion cells in ground squirrels may be correlated with particular morphological types.     

Retinal W-cell projections to the medial interlaminar nucleus in the cat: implications for ganglion cell classification

The perikaryal sizes and retinal distribution of ganglion cells labeled after small iontophoretic injections of horseradish peroxidase (HRP) into the medial interlaminar nucleus (MIN) were studied. Injections were also made into the LGNv and the C-laminae of the dorsal lateral geniculate nucleus (LGNd) for comparison. The results are consistent with suggestions that the MIN contains three approximately vertically oriented laminae which, from medial to lateral, receive their input from, respectively, contralateral nasal, ipsilateral temporal, and contralateral temporal retina. Each MIN lamina receives afferents from two distinct groups of retinal ganglion cells (1) cells with large somas (over 25 micron), coarse primary dendrites, large dendritic trees (500-900 micron in diameter), and coarse axons; (2) cells with medium-sized somas (14-20 micron), medium-caliber primary dendrites, large dendritic trees (350-700 micron), and fine axons. The large cells are clearly Y-cells or alpha cells, and they provide approximately 50% of the retinal input to all layers of the MIN. The medium-sized cells, which provide the remaining 50% of the retinal output in the MIN, are, we argue, W-cells, since they do not differ in soma size, dendritic morphology, axon caliber, or receptive field properties from medium-sized W-cells which project to other thalamic or midbrain structures. These results suggest two phylogenetic trends within the W-cell group: (1) the differentiation of thalamic and midbrain components; and (2) the further differentiation of ipsilateral and contralateral projections within the midbrain component. This latter division corresponds to the distinction between W1 and W2 cells described previously (Rowe and Stone, '77, '80).     

Displaced amacrine cells of the mouse retina

The aim of this study was to characterize and classify the displaced amacrine cells in the mouse retina. Amacrine cells in the ganglion cell layer were injected with fluorescent dyes in flat-mounted retinas. Dye-filled displaced amacrine cells were classified according to dendritic field size, horizontal and vertical stratification patterns, and general morphology. We identified 10 different morphological types of displaced amacrine cell. Six of the cell types identified here are novel cell types that have not been described previously in the mouse retina, to the best of our knowledge. The displaced amacrine cells included four types of medium-field cells, with dendritic field diameters of 200-500 microm, and six types of wide-field cells, with dendritic fields extending over 500 microm. Narrow-field displaced amacrine cells, with dendritic field diameters smaller than 200 microm, were not encountered. The most frequently labeled displaced amacrine cell type was the starburst amacrine cell. At least three cell types identified here have nondisplaced counterparts in the inner nuclear layer as well. Displaced amacrine cells display a rich variety of stratification and branching patterns, which surely reflect the wide range of their functional roles in the processing of visual signals in the inner retina.     

Subgroup of alpha ganglion cells in the adult cat retina is immunoreactive for somatostatin.

We have previously shown that two types of cells in the ganglion cell layer of the adult cat retina are immunoreactive for somatostatin (White et al., '90). One of the types was identified by morphological criteria as a wide-field amacrine cell. The other cell type had a large, angular soma that resembled the alpha ganglion cell, but evidence was not available to identify it definitively as a ganglion cell. Both cell types were distributed preferentially in the inferior retina. In this report, we demonstrate that the two types of cell are, indeed, displaced amacrine cells and alpha ganglion cells. First, when retrograde tracers were injected into central visual targets, the immunoreactive large cells but not the displaced amacrine cells were found to be labeled. Second, after unilateral section of the optic nerve, the immunoreactive large cells disappeared from the retina on the lesioned side, but the displaced amacrine cells occurred in the same numbers in both retinae. In the periphery, the large cells ranged in diameter from 33 to 47 microns, comparable only to alpha ganglion cells (Boycott and W?ssle, '74). An antiserum to parvalbumin was used to visualize the dendrites (R?hrenbeck and W?ssle, '88) of somatostatin-immunoreactive large cells. Based on dendritic stratification within the inner plexiform layer (Famiglietti and Kolb, '76), the somatostatin-immunoreactive large cells were found to include both on-center cells and off-center cells, but were predominantly of the off-center type. Within a local region, they were found to be arrayed with greater regularity than the overall population of alpha ganglion cells. These results indicate that alpha ganglion cells of the cat retina can be subdivided on the basis of their immunoreactive staining for somatostatin and suggest that the diversity of ganglion cells in the cat retina may be greater than has been recognized on the basis of morphological criteria alone.     

A neurofilament protein antibody selectively labels a large ganglion cell type in the human retina.

An antibody (SMI-32) raised against the non-phosphorylated form of the neurofilament protein triplet (NFP) revealed immunoreactivity in the soma and dendritic arborization of a group of large ganglion cells in the human retina. In addition, a population of smaller somas was also faintly labeled with this antibody in the ganglion cell layer. The completely stained cells amounted to 44,000 and were non-uniformly distributed across the retina with a peak density of 100 cells/mm2 in the retinal periphery. The soma sizes increased about two-fold and dendritic field sizes about 3-fold with retinal eccentricity. The immunoreactive dendrites branched in the vitread sublamina of the inner plexiform layer. The dendritic branching pattern of these cells indicated that they correspond to the previously described shrub cells. Antibodies against NFP and neuropeptide Y showed colocalization of these markers in all of the completely stained cells.     

Stages in the structural differentiation of retinal ganglion cells

Using a cultured wholemount technique we have studied the morphological differentiation of ganglion cells in the retina of the rat and cat, during normal development. In both species the differentiation of ganglion cells begins in embryonic life, before embryonic day (E) 17 in the rat and E36 in the cat. It is useful to describe the morphological differentiation of ganglion cells as occurring in three stages. In the first stage, each germinal cell becoming a ganglion cell extends an axon into the fibre layer of the retina and towards the optic disc, and the soma of the cell moves towards the ganglion cell layer. As the soma approaches the ganglion cell layer, the processes that attach its poles to the inner and outer surfaces of the retina are withdrawn. When the soma reaches the ganglion cell layer, a stage of active dendritic growth begins, which lasts until shortly before birth in the cat and until several days after birth in the rat. The cell extends stem dendrites that branch profusely and are commonly tipped by growth cones. The major morphological classes of ganglion cell become distinct in the latter part of stage 2, as do the centroperipheral gradients in ganglion cell size apparent in the cat. During the third stage, the dendritic trees of ganglion cells no longer branch or extend by means of active growth cones. Very considerable growth of all parameters of the cell (soma size, dendrite calibre and length, axon calibre) occurs nevertheless, presumably by interstitial addition of membrane throughout the cell.     

A distinct type of displaced ganglion cell in a mammalian retina.

The morphology, dendritic stratification and laminal position of the soma of retinal ganglion cells were analyzed in Golgi preparations and in other rabbit retinas containing cells backfilled from the superior colliculus. Only one type, among 40 Golgi-impregnated types identified, always had its cell body displaced to the amacrine cell sublayer of the inner nuclear layer. The displaced ganglion cell of rabbit retina has a small cell body, very wide dendritic field with sometimes unbranched dendrites extending up to a millimeter from the cell body. The dendritic tree is narrowly stratified just under the amacrine cell bodies in stratum 1, and therefore does not co-stratify with starburst (cholinergic) amacrine cells, but rather with dopaminergic amacrine cells. Its correlate among ganglion cells backfilled from tectum is apparently a very sparse population of small-bodied cells mixed with a variable population of misplaced ganglion cells of varying size and type. The authentic displaced ganglion cell of rabbit retina, unlike the large displaced ganglion cell of birds, is apparently not a directionally selective ganglion cell, and its functional role in vision is presently unknown.     

Distribution and morphology of retinal ganglion cells in the Japanese quail

A ganglion cell density map was produced from the Nissl-stained retinal whole mount of the Japanese quail. Ganglion cell density diminished nearly concentrically from the central area toward the retinal periphery. The mean soma area of ganglion cells in isodensity zones increased as the cell density decreased. The histograms of soma areas in each zone indicated that a population of small-sized ganglion cells persists into the peripheral retina. The total number of ganglion cells was estimated at about 2.0 million. Electron microscopic examination of the optic nerve revealed thin unmyelinated axons to comprise 69% of the total fiber count (about 2.0 million). Since there was no discrepancy between both the total numbers of neurons in the ganglion cell layer and optic nerve fibers, it is inferred that displaced amacrine cells are few, if any. The spectrum in optic nerve fiber diameter showed a unimodal skewed distribution quite similar to the histogram of soma areas of ganglion cells in the whole retina. This suggests a close correlation between soma areas and axon diameters. Retinal ganglion cells filled from the optic nerve with horseradish peroxidase were classified into 7 types according to such morphological characteristics as size, shape and location of the soma, as well as dendritic arborization pattern. Taking into account areal ranges of somata of each cell type, it can be assumed that most of the ganglion cells in the whole retinal ganglion cell layer are composed of type I, II and III cells, and that the population of uniformly small-sized ganglion cells corresponds to type I cells and is an origin of unmyelinated axons in the optic nerve.