Ganglion cells in the goldfish retina: correlation of light-evoked response and morphology.

Goldfish retinal ganglion cells were intracellularly stained with horseradish peroxidase after recording their responses to a predetermined set of test stimuli. Depolarizing responses were elicited by cells differing in shapes and sizes of their somata and dendritic fields; these cells were mostly bistratified in the inner plexiform layer (sublamina b and distal sublamina a). Hyperpolarizing responses were generated by cells monostratified in a, and by cells bistratified in a and at the a/b border. Responses that were hyperpolarizing to long wavelengths and involving large superimposed depolarizations for short wavelengths were recorded from cells with somata displaced in the inner nuclear layer. The latter cell group had wide, elliptical dendritic fields (confined to the distal sublamina a) and very fine axons. The ganglion cell types recorded are compared with morphological classification schemes proposed from earlier studies. Possible "structure-function" relations are also discussed.     

Displaced horizontal cells and biplexiform horizontal cells in the mammalian retina

We have used the neurofibrillar method of Gros-Schultze to stain the axonless horizontal cells of capybara, agouti, cat, and rabbit retinae. In all of these species, we have found two unusual horizontal cell morphologies: displaced horizontal cells and biplexiform horizontal cells. The displaced horizontal cells have perikarya located in the ganglion cell layer and dendrites branching in the inner plexiform layer. Many dendrites take an ascending trajectory to branch in the outer plexiform layer. The biplexiform horizontal cells are normally placed horizontal cells with descending processes that branch in the inner plexiform layer. Both cell types occur mainly in the retinal periphery, near the ora serrata. They are more numerous in the capybara retina, where they represent as much as 50% of the axonless horizontal cells of the retinal periphery.     

Bipolar cells in the "grouped retina" of the elephantnose fish (Gnathonemus petersii)

To elucidate the specific properties of retinae with grouped photoreceptors the neural pathways in the outer and inner plexiform layer were studied. Photoreceptor bundles in this species consist of more than 100 rods and up to 50 cones, and are usually regarded as functional units. Golgi impregnation in thick and thin sections and light microscopy were used to identify bipolar cell types linking photoreceptors to amacrine and/or ganglion cells. Nine different types were distinguished based on their dendritic morphology and the position of the axon terminal in the inner plexiform layer. Small cells have dendritic fields smaller than the diameter of a photoreceptor bundle and are contacted mostly by cones. The dendritic field size of bushy cells matches that of a photoreceptor bundle; they are contacted mainly by rods. Flat cells receive about equal input from rods and cones; their dendritic field size exceeds the bundle diameter. Within the three major classes there are subtypes addressing three sublaminae of the inner plexiform layer, the proximal On-centre region (sl b), the distal Off-centre region (sl a) and a central sublayer (sl c) probably with transient activity. These observations suggest that cone vision has a spatial acuity better than the "bundle grain". In rod dominated vision the resolution matches that of the bundles; for this pathway, the hypothesis of the bundle as a functional unit is confirmed. The mesopic flat cell pathway has a resolution inferior to the "bundle grain"; it may therefore be dedicated to movement detection.     

Displaced small amacrine cells in the retina of the marine teleost Callionymus lyra L

The displaced small amacrine cells (DSA cells) in the dorsal pure cone part of the retina of the marine teleost Callionymus lyra have been analysed in a combined light and electron microcopical study. These unistratified cells have their dendritic arborization at 70% of the depth of the inner plexiform layer (P5 level). The DSA cells constitute a dense population and have variable dendritic field sizes. The bipolar input occurs in the P5,1 and the P5,2 pattern layer. The short, central DSA dendrites make ribbon synapses with midget mixed di-cone bipolar cells and with two types of pure cone bipolar cells. The amacrine input and output occurs in the fibrous layer that separates both pattern layers. The dendritic arborization is most extensive and the dendrites of neighbouring DSA cells are interconnected. The thick, central DSA dendrites are presynaptic to adjacent DSA cells and possibly to large bistratified and diffuse ganglion cells. The fine, peripheral DSA dendrites receive input from neighbouring DSA cells and probably from large uni- and bistratified and diffuse amacrine cells. A matching population of regularly placed small amacrine cells (RSA cells) has been observed. Their unistratified dendritic arborization is situated at 20% of the depth of the inner plexiform layer. The synaptic relations of RSA cells have not yet been completely analysed in detail. However, results up till now indicate that they most probably receive input from two bipolar cell types, one of which may be a pure cone type. In addition, the large bistratified amacrine and ganglion cells may be synaptically connected to the RSA cells as well as to the DSA cells.     

A morphological classification of ganglion cells in the zebrafish retina

We examined the distribution and morphological types of ganglion cells in the retina of the zebrafish, a model vertebrate genetic organism. Using cresyl violet and methylene blue staining, a prominent central area was observed in the ventral temporal retina. The density of ganglion cell layer neurons averaged from approximately 12,000/mm2 in the dorsal-nasal retina to a peak of approximately 37,000/mm2 in the ventral-temporal retina. Individual zebrafish ganglion cells were labeled by backfilling with DiI through the optic nerve followed by reconstruction using confocal microscopy. The dendritic stratification and branching pattern of each labeled ganglion cell was examined in relation to the borders of the inner plexiform layer (IPL). We identified 11 different morphological types of ganglion cell. The most commonly labeled ganglion cells were two types termed Type III or IV, which displayed highly stratified dendritic arborizations in their respective ON-, OFF-sublaminae of the IPL. Their dendritic branching patterns were highly asymmetric with many thorn-like varicosities that profusely filled the area of arborization. In contrast, Type V cells formed a small simply branching dendritic field in the innermost portion of the ON-sublamina of the IPL. Two large ganglion cell types (Types I and II) with wide monostratified dendritic fields were found in both the ON- and OFF-sublamina of the IPL. Three different types of multistratified/bistratified ganglion cells were found (Types, IX, X, and XI.) whose dendrites occupied different regions of the IPL. The multistratified dendrites of IX cells occupied the whole width of the IPL, while the dendrites of Type XI cells formed vertical claw-like endings in only the ON-sublamina of the IPL. We conclude that zebrafish ganglion cells display a rich variety of types and branching patterns. This study establishes a series of baseline measurements of zebrafish ganglion cells to facilitate examination of genes playing a role in the specification and stratification of ganglion cell types.     

Morphological characterization of substance P-like immunoreactive amacrine cells in the anuran retina

Using substance P immunohistochemistry it was possible to demonstrate a class of morphologically homogeneous group of neurons in the inner nuclear layer (INL) of the retina of two anuran species: Xenopus laevis and Bufo marinus. The number of cells with substance P-like immunoreactivity (SP-LI) was about 250 and 800 in juvenile and 600 and 2500 in adult Xenopus and Bufo, respectively, SP-LI cells had a small soma with one primary dendrite having up to four slender branches, located in the vitreal sublamina of the inner plexiform layer (IPL). Mean dendritic field sizes were 0.12 and 0.30 mm2 in juvenile and 0.29 and 0.65 mm2 in adult Xenopus and Bufo, respectively. The density of SP-LI cells was 40/mm2 in juvenile and 24/mm2 in adult Xenopus compared with 20/mm2 in juvenile and 13/mm2 in adult Bufo. Nearest neighbour distance measurements indicated that SP-LI cells were randomly distributed across the entire retina in both species. The location and the morphology of SP-LI cells indicated that they correspond to a subclass of wide-field amacrine cells, similar to types 20 and 21 described by Golgi techniques in the cat.     

Histogenesis of the cat retina

The development of the retina of the cat was studied with light and transmission electron microscopy from prenatal day 36 (E36) through postnatal day 9 (P9; eye opening), and at the adult stage (1 year). Tissue samples were taken from the posterior pole of the retina. At E36, the optic cup was completely formed, the pigment epithelium was a single cell layer, the retina consisted of an inner marginal fiber layer and an outer layer of neuroblastic cells, and the innermost cells of the neuroblastic cell layer, presumptive ganglion cells (which might still migrate through the inner plexiform layer) were displacing away from the neuroblastic cell mass. At E40, a distinct ganglion cell layer was seen. At E46, primitive horizontal cells appeared within the neuroblastic cell layer. Separation of the neuroblastic cell mass into inner and outer nuclear layers was first evident on E48; by E60, the layers were clearly separate. Conventional synapses were seen in the inner plexiform layer in the week prior to birth. Blood vasculature was observed prenatally as deep as the inner plexiform layer. In the newborn a few discs were seen in some photoreceptor cell outer segments. Synaptic ribbons appeared first in the outer plexiform layer in the newborn and then in the inner plexiform layer by P4.     

Synaptic patterns and response properties of bipolar and ganglion cells in the cat retina

After intracellular recording, bipolar cells of the cat retina have been stained with HRP and their contacts in the outer and inner plexiform layers examined by electron microscopy. Rod bipolars and cone bipolar cb6 make invaginating, ribbon related contacts with photoreceptors, hyperpolarize in response to light, and have axons terminating in layer b of the IPL. The axon terminal of cb2 ends in layer a of the IPL and its basal contacts with cones mediate hyperpolarizing light-responses. Cone bipolar cb5 is a center-depolarizing type with an axon ending in layer b but its cone contacts are at semi-invaginating basal junctions. Except for the amacrine-contacting rod bipolar cell, all cone bipolar types synapse with both amacrine and ganglion cells in the inner plexiform layer. In addition cb5 contacts AII amacrine cells with large gap junctions, and is physiologically rod dominated.     

Retinal ganglion cells projecting to the optic tectum and visual thalamus of lizards

Retinal ganglion cells projecting to the optic tectum and visual thalamus have been investigated in the lizard, Podarcis hispanica. Injections of biotinylated dextran-amine in the optic tectum reveal seven morphological cell varieties including one displaced ganglion cell type. Injections in the visual thalamus yield similar ganglion cell classes plus four giant ganglion cells, including two displaced ganglion cell types. The present study constitutes the first comparison of tectal versus thalamic ganglion cell types in reptiles. The situation found in lizards is similar to that reported in mammals and birds where some cell types projecting to the thalamus are larger than those projecting to the mesencephalic roof. The presence of giant retino-thalamic ganglion cells with specific dendritic arborizations in sublaminae A and B of the inner plexiform layer suggests that parts of the visual thalamus of lizards could be implicated in movement detection, a role that might be played by the ventral lateral geniculate nucleus, which is involved in our tracer injections.     

Dendritic distribution of two populations of ganglion cells and the retinopetal fibers in the retina of the silver lamprey (Ichthyomyzon unicuspis)

The distribution of ganglion cells in the retina of the silver lamprey, Ichthyomyzon unicuspis, was revealed by retrograde labeling from the optic nerve with horseradish peroxidase (HRP) and fluorescent-labeled dextrans in live animals and with the fluorescent dye DiI in aldehyde-fixed tissue. The majority of ganglion cells (74%) termed the "outer ganglion cells," are multipolar and are located at the vitread boundary of the inner nuclear layer. The remaining ganglion cells (26%), termed the "inner ganglion cells" are bipolar and are distributed in a sublamina within the inner plexiform layer. The dense, dendritic meshwork of the outer ganglion cells is largely restricted to the sclerad half of the inner plexiform layer with some cells possessing dendrites which pass through the inner nuclear layer to terminate within the outer plexiform layer. The dendrites of the inner ganglion cells form a thin, dendritic network apposing the inner limiting membrane. Axons from both populations of ganglion cells originate from dendrites or the soma and form fascicles lying adjacent to the outer ganglion cell somata. Retinopetal fibers, originating from bilaterally distributed neurons of the tegmental midbrain, were thin and varicose and ran parallel to the ganglion cell axons to terminate either with a varicose enlargement or a few short sidebranches in the sclerad third of the inner plexiform layer. The unusual organization of the lamprey retina and outgroup comparison with hagfish suggests that agnathans share a presumably primitive type of retinal ganglion cell organization compared to that of gnathostomes.     

Grid patterns in the retinal organization of the cichlid fish Astronotus ocellatus

Fibrous grid patterns are found in the outer and inner plexiform layers of the retina of the cichlid fish Astronotus ocellatus. The grid in the outer plexiform layer and the outermost grid in the inner plexiform layer have the same orientation and dimensions as the squares of the mosaic formed by the double cones. The innermost grid in the inner plexiform layer is offset from the other grid patterns in the retina by an angle of 45°. Horizontal cell and amacrine cell processes are intimately associated with the plexiform grids. It is likely that these morphological patterns play a role in the processing of visual information within the retina, by orienting processes of horizontal and amacrine cells in specific directions for lateral inhibition or summation, and perhaps also sorting processes from like types of receptor cells for convergence on ganglion cell dendrites.     

Wide-field cone bipolar cells and the blue-ON pathway to color-coded ganglion cells in rabbit retina

Wide-field cone bipolar cells with sparse dendritic branching and proposed connectivity to blue cones were first identified in rabbit and cat. In rabbit, these were subdivided into type a (wa) and type b (wb), with axonal branching in sublamina a, and sublamina b, respectively, of the inner plexiform layer (IPL). Recent studies in rabbit support the earlier hypothesis of exclusive blue/short wavelength cone connectivity for both types. The homologues of wb cells (but not wa cells) have been identified in other mammals. The axonal branching of wa cone bipolar cells is shown to co-stratify with the dendrites of the "fiducial," type a starburst amacrine cell, although a few branches extend into sublamina b. The axon terminal of wb cone bipolar cells is shown to be narrowly stratified in stratum 5alpha, deep to the dendrites of the type b starburst amacrine cell. Rabbit ganglion cells postsynaptic to wa cells are unknown, but may include class III.2a cells, similarly stratified in the IPL. The wb axon terminal is shown here to co-stratify with and to make close, likely synaptic, contacts with the dendrites of a recently described morphological subtype of class II ganglion cell in rabbit retina, IIb2. Recent morpho-physiological correlation indicates that class IIb2 cells correspond to the blue-ON-center-X or ON-brisk-sustained ganglion cells, defined physiologically in rabbit. In contrast, the wb cell in cat retina must innervate the physiologically identified blue-ON-center-sluggish-sustained ganglion cell. In monkey retina, the wb-like bipolar cells apparently innervate a small, partly bi-stratified ganglion cell. Mammals share a common pathway from short-wavelength-sensitive (S/blue) cone photoreceptors to ON-center ganglion cells in sublamina b of the IPL, in the form of wb or wb-like cone bipolar cells, but the type of ganglion cell innervated appears to be particular, and may serve different functional roles in different mammalian orders.     

Interplexiform cells in macaque monkey retina

The presence of interplexiform cells in primate retina has been disputed, with the dopaminergic interplexiform cell in the New World monkey being the most fully understood. We have examined interplexiform cells in the Old World monkey using immunocytochemistry with the peroxidase-antiperoxidase method of visualization. In several species of macaque retina, two types of interplexiform cells are found. One stains with antisera to tyrosine hydroxylase, a biosynthetic enzyme for dopamine, and the other stains with antisera to gamma aminobutyric acid (GABA). The cell bodies of these two populations of interplexiform cells are located among the amacrine cells in the inner nuclear layer, and they send processes into both the inner and outer plexiform layers. GABA-positive interplexiform processes to the outer plexiform layer arise from the cell body while tyrosine hydroxylase-positive interplexiform processes most often originate from the heavily tyrosine hydroxylase-stained sublamina one of the inner plexiform layer. Cell-body diameter measurements and morphology suggest that these are different neuronal populations.     

Immunocytochemical localization of glycine in the retina of the turtle (Pseudemys scripta)

We have localized glycine-like immunoreactivity to provide new anatomical detail about glycinergic neurons in the turtle retina. A rabbit antiserum directed against a glycine/albumin conjugate was used with standard fluorescent and avidin-biotin labeling techniques. Some processes in the outer plexiform layer and many processes in the inner plexiform layer, numerous somata in the inner nuclear layer, and isolated somata in the ganglion cell layer were immunoreactive. The vast majority of labeled neurons were amacrine cells. One class of amacrine cells had well-labeled somata near the inner nuclear/inner plexiform layer border, which gave rise to thick primary processes that entered the inner plexiform layer and arborized near the border of strata 1 and 2 and in stratum 3. A second class of glycinergic neurons, consisting of putative interplexiform cells, was unique in that it gave rise to dendritic arborizations in both the outer plexiform layer and the inner plexiform layer. Some of the immunoreactive neurons in the ganglion cell layer were apparently displaced amacrine cells, while others were probably true ganglion cells because they gave rise to labeled axons, and many labeled axons were visible in the ganglion cell axon layer. These results suggested that glycine played an extensive role in the turtle retina, and that it was involved in many diverse synaptic interactions in both the outer plexiform layer and the inner plexiform layer.     

Dye coupling in horizontal cells of developing rabbit retina

In the mature rabbit retina, two classes of horizontal cells, A type and B type, provide lateral inhibition in the outer plexiform layer (OPL) and spatially modify the activation of bipolar cells by photoreceptors. Gap junctions connecting homologous horizontal cells determine the extent to which this inhibitory activity spreads laterally across the OPL. Little is currently known about the expression of gap junctions in horizontal cells during postnatal development or how cell-cell coupling might contribute to subsequent maturational events. We have examined the morphological attributes and coupling properties of developing A and B type horizontal cells in neonatal rabbit retina using intracellular injections of Lucifer Yellow and Neurobiotin. Prelabeling with DAPI permitted the targeting of horizontal cell bodies for intracellular injection in perfused preparations of isolated retina. A and B type horizontal cells were identifiable at birth although their dendritic field sizes had not reached adult proportions and their synaptic contacts in the OPL were minimal. Both cell types exhibited homologous dye coupling at birth. Similar to that seen in the adult, no heterologous coupling was observed, and homologous coupling among A type cells was stronger than that observed among B type cells. The spread of tracer compounds through gap junctions of morphologically immature horizontal cells suggests that ions and other small, bioactive compounds may likewise spread through coupled, horizontal networks to coordinate the subsequent maturational of emerging outer plexiform layer pathways.     

Organization of the inner retina following early elimination of the retinal ganglion cell population: effects on cell numbers and stratification patterns.

The present study has examined the effects of early ganglion cell elimination upon the organization of the inner retina in the ferret. The population of retinal ganglion cells was removed by optic nerve transection on the second postnatal day, and retinas were subsequently studied in adulthood. Numbers of amacrine and bipolar cells were compared in the nerve-transected and nerve-intact retinas of operated ferrets, while stratification patterns within the inner plexiform layer were compared in these and in normal ferret retinas. Early ganglion cell elimination was found to produce a 25% reduction in the population of glycine transporter-immunoreactive amacrine cells, and 18 and 15% reductions in the populations of parvalbumin and calbindin-immunoreactive amacrine cells, respectively. GABAergic amacrine cells were also reduced by 34%. The number of calbindin-immunoreactive displaced amacrine cells, by contrast, had increased in the ganglion cell-depleted retina, being three times their normal number. Other amacrine and bipolar cell types were unaffected. Despite these changes, the stratification patterns associated with these cell types remained largely intact within the inner plexiform layer. The present results demonstrate a class-specific dependency of inner retinal neurons upon the ganglion cell population in early postnatal life, but the ganglion cells do not appear to provide any critical signals for stratification within the inner plexiform layer, at least not after birth. Since they themselves do not produce stratified dendritic arbors until well after birth, the signals for stratification of the bipolar and amacrine cell processes should arise from other sources.     

Dendritic morphology of a class of interstitial and normally placed amacrine cells revealed by intracellular Lucifer yellow injection in carp retina

The dendritic morphology of a class of interstitial amacrine (ISA) and normally placed amacrine cells was investigated in carp retina. We first identified their fluorescent nuclei after preloading with 4,6-diamidino-2-phenylindole (DAPI) in living or aldehyde-fixed retinal wholemounts and then injected them iontophoretically with Lucifer Yellow (LY) under microscopic control. Although DAPI appeared to be accumulated nonspecifically by amacrine and ganglion cells, ISA cell nuclei were discriminated by focusing between the amacrine and ganglion cell layers. The fusiform cell bodies of LY-injected cells were located in the middle of the inner plexiform layer (IPL), and the 4-5 stout primary dendrites were monostratified in sublamina b of the IPL and decorated with spines and long thin processes. The average spatial properties of these cells were approximately: density, 6.0 cells/mm2; intersomatic distance, 400 microns; dendritic field size, 0.27 mm2; dendritic coverage, 1.6. The dendritic interconnections were made of tip-to-tip or tip-to-side contacts between dendrites and between a dendrite and thin process, forming many closed loops. The ISA cells belong to a morphological type Fnb. A class of normally placed amacrine cells with dendritic morphology similar to that of the ISA cells was also found by LY injection in wholemounts. These cells belong to a morphological type Fna, with dendrites monostratified in sublamina a of the IPL in a 0.35-mm2 dendritic field. The ISA (Fnb) and Fna cells appear to represent a matched pair of cell types that are similar in structure but complementary in function.     

Glucagon immunoreactive neurons in the retina of different species

Neurons displaying glucagon immunoreactivity were detected among the amacrine cells in the retina of goldfish, frog and pigeon. Nerve cell bodies were located in the inner nuclear layer with their processes ramifying in 2–3 more or less well-defined sublayers in the inner plexiform ayer. The distribution of cell bodies and processes varied with the species. In pigeon retina two separate populations of glucagon immunoreactive neurons were found among the amacrine cells. In frog retina glucagon immunoreactivity was also discerned in cell bodies in the ganglion cell layer. These cell bodies sent processes outwards to the inner plexiform layer. No glucagon immunoreactive neurons were detected in the retina of the rat, rabbit, cat, pig or cow.     

A morphological classification of retinal ganglion cells in Chinese hamsters]

Retinal ganglion cells in Chinese hamsters were morphologically classified into alpha, beta and gamma cells by the horseradish peroxidase labeling method. The alpha cells had large somatic and dendritic fields. The beta cells were small to medium in somatic size and had small dendritic field size. The gamma cells had small to medium somatic and large dendritic fields. Each cell type had either symmetrical or asymmetrical dendrites arising from the soma. The dendrites of alpha, beta and gamma cells extended into either the internal or external stratum of the inner plexiform layer.