Depth segregation of retinal ganglion cells projecting to mouse superior colliculus

The retinotectal projections in the mouse were analyzed with injections of horseradish peroxidase into the superior colliculus and of radioactive amino acids into the eye. At least 70% of the ganglion cells, and possibly all of them, were found to project to the superior colliculus, including ganglion cells of all sizes. Small injections revealed that ganglion cells of different sizes terminate at different levels in the superior colliculus. The small ganglion cells that form the vast majority of all cells project predominantly to the upper stratum griseum superficiale. A small population of mainly medium-sized and large ganglion cells project to the deep stratum griseum superficiale and to the stratum opticum. The ipsilateral projection is restricted to the deep stratum griseum superficiale and stratum opticum and consists predominantly of medium-sized and large ganglion cells.     

Morphological identification and systematic classification of mammalian retinal ganglion cells. I. Rabbit retinal ganglion cells

Retinal ganglion cells (RGCs) convey visual signals to 50 regions of the brain. For reasons of interest and convenience, they constitute an excellent system for the study of brain structure and function. There is general agreement that, absent a complete “parts list,” understanding how the nervous system processes information will remain an elusive goal. Recent studies indicate that there are 30–50 types of ganglion cell in mouse retina, whereas only a few years ago it was still written that mice and the more visually oriented lagomorphs had less than 20 types of RGC. More than 30 years ago, I estimated that rabbits have about 40 types of RGC. The present study indicates that this number is much too low. I have employed the old but powerful method of Golgi-impregnation to rabbit retina, studying the range of component neurons in this already well-studied retinal system. Close quantitative and qualitative analyses of 1,142 RGCs in 26 retinas take into account cell body and dendritic field size, level(s) of dendritic stratification in the retina's inner plexiform layer, and details of dendritic branching. Ninety-one morphologies are recognized. Of these, at least 32 can be correlated with physiologically studied RGCs, dye-injected for morphological analysis. It is unlikely that rabbits have 91 types of RGC, but is argued here that this number lies between 60 and 70. The present study provides a “yardstick” for measuring the output of future molecular studies that may be more definitive in fixing the number of RGC types in rabbit 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.     

Morphological properties of mouse retinal ganglion cells during postnatal development

Quantitative methods were used to assess dendritic stratification and other structural features of developing mouse retinal ganglion cells from birth to after eye opening. Cells were labeled by transgenic expression of yellow fluorescent protein, DiOlistics or diffusion of DiI, and subsequently imaged in three dimensions on a confocal microscope followed by morphometric analysis of 13 different structural properties. At postnatal day 1 (P1), the dendrites of all cells ramified across the vertical extent of the inner plexiform layer (IPL). By P3/4, dendrites were largely confined to different strata of the IPL. The stratification of dendrites initially reflected a retraction of widely ramifying dendritic processes, but for the most part this was due to the subsequent vertical expansion of the IPL. By P8, distinct cell classes could be recognized, although these had not yet attained adult-like properties. The structural features differentiating cell classes were found to follow three different developmental trends. The mean values of one set of morphological parameters were essentially unchanged throughout postnatal development; another set of measures showed a rapid rise with age to adult values; and a third set of measures first increased with age and later decreased, with the regressive events initiated around the time of eye opening. These findings suggest that the morphological development of retinal ganglion cells is regulated by diverse factors operating during different but overlapping time periods. Our results also suggest that dendritic stratification may be more highly specified in the developing mammalian retina than has been previously realized.     

Distribution of ganglion cells in the retina of adult pigmented ferret

The retinal ganglion cell distribution in adult pigmented ferret was mapped in Nissl-stained retinas and in retinas back-filled with HRP after large bilateral injections of the enzyme into the brain. In common with other carnivores the ferret has an area of peak cell density equivalent to the area centralis and a prominent visual streak of high cell density extending horizontally across the retina. The maximum ganglion cell densities for the retinas were estimated to be 3500-5200 cells/mm2 in Nissl-stained, dehydrated retinas and 3300-4300 cells/mm2 in HRP-labelled, undehydrated retinas. Three cell types were distinguished in the HRP-labelled retinas and they appear to correspond to alpha-, beta- and gamma-cell types of cat retina. However, unlike in cat, the retinal ganglion cells of the ferret do not consistently fall into 3 distinct groups with respect to cell size, nor is there a tendency for the cells in the area centralis to be smaller than those in the peripheral retina. Estimates for the total number of ganglion cells of 82,000 and 88,000 were obtained from Nissl-stained retinas, and of 74,000, 75,000 and 78,000 from HRP-labelled retinas.     

Structure/function relationships of retinal ganglion cells in the cat

Intracellular recording and horseradish peroxidase (HRP) iontophoresis was used to define structure/function relationships for single retinal ganglion cells in the intact cat eye. Fifteen physiologically characterized cells were labeled as follows. Five W-cells had gamma morphology, 6 X-cells had beta morphology, and 1 Y-cell had alpha morphology, and these relationships support earlier conclusions. However, one cell could not be physiologically classified despite beta morphology, one X-cell was not a beta cell, and one Y-cell was not an alpha cell. Whether these unusual structure/function relationships represent an artifact of methodology or complications to be added to prevailing notions requires further study.     

Morphological properties of chick retinal ganglion cells in relation to their central projections

Morphological properties of chick retinal ganglion cells (RGCs) were studied in relation to their central projections in 23 chicks. A total of 217 RGCs were retrogradely labeled by applying a carbocyanine dye (DiI) to the thalamus and optic tectum. The labeled RGCs were classified into six groups on the basis of their somal areas, dendritic fields, and branching patterns. The dendrites of these RGCs extended horizontally in the inner plexiform layer (IPL) forming eight dendritic strata. The RGCs in each group showed certain specificities in their central projections. Group Ic predominantly projected to the tectum. Groups IIs and IIIs showed a high thalamic dominance. Groups Is and IIc were nonspecific with regard to their tectal and thalamic projections. Group IVc showed tectal‐specific projections. Occurrence rates of the dendritic strata increased progressively toward the inner part of the IPL, i.e., DSs (dendritic strata) 1–4 were scantily distributed, DSs 5 and 6 were moderately distributed, and DSs 7 and 8 were the most frequently distributed. A total of 42 dendritic stratification patterns were identified, and of these, 18 patterns were common to the tectal RGCs (tec‐RGCs) and thalamic RGCs (tha‐RGCs). The common patterns were detected very frequently in the tec‐ and tha‐RGCs (≈85%), and the dendritic strata were largely distributed in the inner part of the IPL (DSs 5–8). In contrast, the remaining 24 noncommon stratification patterns showed low occurrence rates (≈15%); however, these dendritic strata were widely distributed in both the outer (DSs 1–4) and inner (DSs 5–8) IPL. J. Comp. Neurol. 514:117–130, 2009. © 2009 Wiley‐Liss, Inc.     

Morphology and distribution of synapses onto a type of large field ganglion cell in the retina of the goldfish

The morphology and dendritic distribution of terminals that synapse onto a type of large-field ganglion cell in the retina of the goldfish are described. Electron microscopy was combined with retrograde labelling of cells with horseradish peroxidase (HRP). Synapses from both amacrine (four types) and bipolar cells contacted the dendrites (all orders) of these cells. In contrast to a recent report describing the synaptic organization of large-field ganglion cells in the catfish (Sakai et al., '86), the synapses were relatively evenly distributed throughout the dendritic arbor, not clustered at discrete sites, and no presynaptic specializations were seen in the dendrites of the ganglion cells.     

Selective acrylamide-induced degeneration of color opponent ganglion cells in macaques

P beta (color opponent) retinal ganglion cells in macaques were found to degenerate as a result of oral administration of acrylamide. Histological examination, wheat germ agglutinin-horseradish peroxidase transport and cytochrome oxidase histochemistry indicate that other retinal ganglion cells and other neurons in the visual pathways were spared.     

Retinal ganglion cell terminals in the hamster superior colliculus: an ultrastructural study.

The distribution, cross-sectional area, and presynaptic and postsynaptic characteristics of retinal ganglion cell axon terminals in the superior colliculus of normal adult female Syrian hamsters were investigated by quantitative ultrastructural techniques. After an intravitreal injection of horseradish peroxidase, most labelled axon terminals were found in the stratum griseum superficiale and stratum opticum of the contralateral superior colliculus. However, a small proportion (approximately 2%) of retinal ganglion cell axon terminals were located in deeper layers of the superior colliculus between the stratum opticum and the periaqueductal grey matter. Terminals were smaller in the upper two-thirds of the stratum griseum superficiale than in the lower one-third of this layer, the stratum opticum, and the stratum griseum intermedium. Presynaptic characteristics such as the length and number of contacts and the postsynaptic neuronal domains (somata, dendritic spines, or shafts) contacted by retinal ganglion cell axons in the superior colliculus were similar in all layers.     

Displaced ganglion cells in the retina of the rat

The distribution, laterality of projection, and perikaryal sizes of displaced ganglion cells (DGCs) were examined in whole-mounted retinae after massive unilateral injections of horseradish peroxidase along the optic tract in pigmented rats. The DGCs were found predominantly in the lower temporal periphery of the retina. Nearly all DGCs labeled had contralaterally projecting axons. The sizes of the labeled DGCs spanned the range of ordinary ganglion cells, but few middle-sized DGCs were labeled. The results support the hypothesis that displaced ganglion cells are late-developing neurons that do not complete their migration toward the ganglion cell layer during retinal histogenesis.     

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.     

Frog sympathetic ganglion cells have local axon collaterals

Amphibian autonomic ganglia have been used as simple models for studies involving the physiology of synaptic transmission. These models assume an anatomical simplicity where the ganglion is a simple relay for central nervous system output to peripheral autonomic targets. Cholinergic preganglionic fibers innervate the soma and proximal axon of the unipolar ganglion cells, which were thought to relay the information to the periphery with little ganglionic processing. However, several different types of synaptic potentials occur in response to preganglionic stimulation. Also, a variety of neuropeptides are found in both preganglionic fibers and ganglion cells; at least one of the peptides found in preganglionic fibers is known to act as a neurotransmitter in the ganglion. Finally, there may be communication between ganglion cells. In the present study, we have explored the morphology of lumbar sympathetic chain ganglion cells by intracellular injection with horseradish peroxidase to determine whether an anatomical substrate exists for processing information within these ganglia. We have shown that 39% of these cells have axons that branch within the ganglion. While both major classes of ganglion cells (B cells and C cells) had intraganglionic axon collaterals, there was a marked difference in the frequency: 65% of the C cell axons had collaterals while only 19% of the B cell axons collateralized within the ganglion. Ultrastructural examination of labeled axon collaterals indicated that these collaterals receive synaptic input; whether the collaterals also make synapses has not been definitively established.     

Topography of pig retinal ganglion cells

In the present work we analyzed the distribution of retinal ganglion cells (RGCs) in the pig retina. RGCs were retrogradely labeled in vivo by injecting Fluoro-Gold into the optic nerve. RGC density and the distribution of RGCs in terms of soma size were analyzed. Different regions of the porcine retina were identified following analysis of the distribution of RGCs in terms of cell density and soma size: in the central retina, we found a high-density horizontal RGC band lying dorsal to the optic disc. Moreover, in this region, a high proportion of RCGs with small soma size was observed. From the central to the more peripheral retina, we observed a decrease in RGC density, together with a greater presence of RGCs with larger somas. The results of this study should prove to be useful as a foundation for future studies with the porcine retina as a model in ophthalmic research. The study also highlights the necessity to label the RGC population specifically with retrograde tracers in order to quantify precisely alterations in the cell population associated with experimental treatments.     

Morphological and functional evaluation of the superior salivatory nucleus in rabbits

Horseradish peroxidase (HRP) was applied to the submandibular ganglion of the rabbit to determine the locus of the parasympathetic preganglionic neurons in the medulla. Labeled cells were recognized in the ipsilateral bulbar reticular formation at the level between the caudal end of the facial genu and the caudal part of the root of the facial nerve. The size of the labeled cells were distributed from 150 to 1150 μm² with a variety of forms such as spindle shape, triangular, and polygonal. Moreover, these cells of different sizes and forms were evenly scattered in the superior salivatory nucleus. To evaluate the physiologic functions of the bulbar salivatory nucleus, electrical stimulation was applied to the medulla, and salivary secretion and thermal change of the submandibular gland were measured simultaneously after bilateral cervical sympathectomy. A very good parallelism between the volume of salivary secretion and the magnitude of temperature change at each stimulating point suggests that secretory and vasodilator cells are intermingled with each other in the salivatory nucleus.     

Dendritic remodelling of retinal ganglion cells during development of the rat

Investigation of the morphology of ganglion cells in the cat retina has shown that a remarkable reduction in the number of dendritic spines and branches occurs during development of the alpha and beta cell classes. To learn whether dendritic remodelling represents a generalized mechanism of mammalian retinal ganglion cell development, we have examined the morphology of ganglion cells in the retina of the developing rat. The present study has concentrated on type II cells, which retain a great number of dendritic spines and branches in the adult and comprise a large proportion of the population of rat retinal ganglion cells. To reveal fine dendritic and axonal processes, Lucifer yellow was injected intracellularly in living retinae maintained in vitro. Size and complexity of the dendritic trees were found to increase rapidly during an intial stage of development lasting from late fetal life until approximately postnatal day 12 (P12). Dendrites and axons of immature ganglion cells expressed several transient morphological features comprising an excessive number of dendritic branches and spine-like processes, and short, delicate axonal sidebranches. The following developmental stage was characterized by a remarkable decrease in the morphological complexity of retinal ganglion cells and a slowed growth of their dendritic fields. The number of dendritic branches and spines of types I and II retinal ganglion cells declined after P12 to reach a mature level by the end of the first postnatal month. Thus, even cells that retain a highly complex dendritic tree into the adult state undergo extensive remodelling. These results suggest that regressive modifications at the level of the dendritic field constitute a generalized mechanism of maturation in mammalian retinal ganglion cells. © 1993 Wiley-Liss, Inc.