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.     

Cells accumulating 3H-Glycine in the goldfish retina

Glycine accumulating neurons occur among amacrine cells of the goldfish retina with processes distributed in the inner plexiform layer. Similar cells also occur, although much more rarely, among the horizontal cells and in the outer plexiform layer. The latter cells are readily observable only after heavy labelling. They may emit processes ending close to the photoreceptor terminals.     

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.     

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.     

Amacrine cells,bipolar cells and ganglion cells of the cat retina: A Golgi study

Neuronal types contributing to the inner plexiform layer of the cat retina are described based primarily on light microscopy of Golgi-impregnated retinal whole-mounts. Cells have been characterized on morphological criteria that include dendritic branching patterns, dendritic tree sizes, cell body sizes and stratification of processes in the inner plexiform layer. Nine different types of bipolar cell, 22 different types of amacrine cell and 23 different types of ganglion cell can be distinguished using one or more of these morphological criteria. The significance of the different morphological types of cells is discussed, particularly in relationship to the functional bisublamination of the cat inner plexiform layer.     

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.     

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.     

Distribution of synaptic inputs onto goldfish retinal ganglion cell dendrites

Retinal ganglion cells in the goldfish were labeled by retrograde transport of horseradish peroxidase, and areas near the optic disk where the dendrites appeared to be completely filled were analyzed by electron microscopy. Only 6% of their inputs were ribbon synapses from bipolar cells; the other 94% of the inputs were conventional synapses mostly or entirely from amacrine cells. There were three strata of the inner plexiform layer with high densities of inputs to ganglion cells, the first centered at approx. 50% and the second at approx. 80% of the inner plexiform layer depth, as measured from the ganglion cell layer to the inner nuclear layer. These two strata comprised 25% of the volume but contained 41% of the inputs to ganglion cells. There were also two strata with very low densities of ganglion cell inputs located near the boundaries of the inner plexiform layer, from 0- to 15% and 90- to 100% of the depth. These strata, which also comprised 25% of the volume, contained only 7% of the inputs to retinal ganglion cells. These strata near the boundaries of the inner plexiform layer also contained 81% of the processes with large, dense-cored vesicles characteristic of peptidergic neurons. We concluded that each of the two sublaminae, a and b, identified previously by physiological criteria, could be further divided into at least two strata, one near the boundary of the inner plexiform layer with abundant peptidergic terminals and very few ganglion cell synapses and another near the center of the inner plexiform layer with numerous ganglion cell synapses. We also propose a hypothesis that could explain the functions of these additional strata.     

VIP (vasoactive intestinal polypeptide) -like immunoreactive amacrine cells in the retina of the rat

Vasoactive intestinal polypeptide (VIP) -like immunoreactivity was demonstrated in the rat retina, using the peroxidase anti-peroxidase (PAP) method. VIP-like immunoreactivity was observed in the cytoplasm of amacrine cells of the inner nuclear layer (INL) and their varicose processes ramifying in the inner plexiform layer (IPL). VIP-like immunoreactive amacrine cells were present in both central and peripheral retinal regions.In some sections fine ramifications of varicose processes in the IPL could be clearly traced. VIP-like immunoreactivity was detected in both ‘stratified’ and ‘diffuse’ amacrine cells. VIP-like immunoreactive amacrine cells were classified into four types.     

Bipolar cells of the frog retina: a Golgi study.

The morphology of Golgj-impregnated bipolar cells of the frog (Rana temporaria) retina has been investigated. Several new kinds of bipolar cells, in addition to the main types of bipolars described by Ramon y Cajal, have been discovered: small outer cells, large inner cells with Landolt club, several varieties of inner bipolar cells without Landolt club. Probable synaptic contacts of different kinds of bipolars with manifold receptors are discussed. Large (up to 7 μm) swellings of main dendrites of inner bipolars have been revealed in the outer zone of the inner nuclear layer. Several varieties of bipolar axon terminals have been observed in the inner plexiform layer, not represented in the study of Ramon y Cajal, as well as axo-somatic synapses of bipolar axons with the perikarya of ganglion cells. The Golgi findings are discussed in connection with recent electron microscopic studies.     

Persistence of retinal dopamine cells in the degenerated eye of the cave salamander, Proteus anguinus L

The Proteus anguinus L. is a blind cave perennibranch amphibian whose visual system undergoes an important morphogenetic degeneration in adulthood. The eyeball becomes atrophied and disappears under the fat tissue of the head. However, a retina can still be identified and a photophobic behavior of the animal indicates a remaining photosensitivity. In the oldest animal observed, some photoreceptor cells are still present as well as other types of retinal neurons. Characteristic synapses are observed in both the inner and outer plexiform layers. Dopaminergic amacrine cells, with processes in the inner plexiform layer, can be identified by their tyrosine-hydroxylase immunoreactivity. Taken together, these results indicate a possible functional role of the remaining retina. Since dopamine is especially involved in light adaptation from darkness, the residual retina could act in triggering the turning behavior of Proteus in response to lightening.     

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.     

Connexions between retinal neurons with identified neurotransmitters

Dopaminergic and indoleamine accumulating neurons can be demonstrated both in the light and the electron microscopes. Considerable differences have been found between different animal species. There are two types of dopaminergic neurons, the interamacrine cells and the interplexiform cells. The interamacrine cells contact only other amacrine cells. They receive synapses from other amacrine cells which are likely to operate with, e.g. GABA or glycine as neurotransmitter. The dopamine turnover in the dopaminergic interamacrine cells is very rapidly activated by light. Dopaminergic interplexiform neurons are known only in teleost fish and New World monkeys. They have approximately the same contacts in the inner plexiform layer as the interamacrine cells, but, in addition, send processes to the outer plexiform layer and there contact both horizontal cells and bipolar cells. The function of the dopaminergic neurons has not been determined. The indoleamine accumulating amacrine neurons are in Cebus monkeys, cats and rabbits contacted by bipolar cells in dyads and form reciprocal synapses with them. They are also contacted by amacrine cells and make synapses on other with them. They are also contacted by amacrine cells and make synapses on other amacrine cells and on ganglion cells. The contacts are different in teleost fish, where the indoleamine accumulating cells mainly contact other amacrine cells only. The transmitter of the indoleamine accumulating neurons is debated in mammals but is most likely 5-hydroxytryptamine in other vertebrates.     

Peptide immunoreactive neurons in the human retina

The distribution of peptide-immunoreactive neurons in the human retina was investigated. Neurons displaying immunoreactivity towards substance P, vasoactive intestinal polypeptide (VIP), somatostatin, neuropeptide Y (NPY) and peptide histidine-isoleucine (PHI) were found in amacrine cells with cell bodies situated in the innermost part of the inner nuclear layer and nerve fibers ramifying in the inner plexiform layer in a manner differing according to the peptide investigated. Two other cell types were found. In the middle of the inner plexiform layer cell bodies showing immunoreactivity towards substance P, VIP and PHI were found. In the ganglion cell layer there were cell bodies showing immunoreactivity towards substance P, somatostatin, VIP and NPY. Substance P immunoreactive, somatostatin and NPY immunoreactive fibers situated at the border between the inner nuclear and outer plexiform layers and traversing the inner nuclear layer were also found.     

A review of the neurophysiology of the turtle retina III. Amacrine and ganglion cells

Amacrine and ganglion cells are two large classes of inner retinal neurons of the vertebrate retina. Amacrine cells are a morphologically and neurochemically diverse class of axonless neurons, which are primarily involved in lateral retinal processing. In the inner plexiform layer, they engage in complex, often inhibitory, interactions with bipolar and ganglion cells. Two physiological classes of amacrine cells, transient and sustained types, have been distinguished. Ganglion cells in turtle retina comprise many functional subtypes including ON, OFF and ON-OFF types. Many ganglion cells in turtle retina display complex receptive field properties, responding to movement, orientation and direction. Neural mechanisms underlying direction selective responses in retinal ganglion cells have come under particular scrutiny and are discussed in detail.     

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.     

Autoradiography of (3H)-5-hydroxytryptamine uptake in the retina of some mammals

The uptake of indoleamines into the retina of rats, rabbits, cows, pigs, baboons, Cynomolgus monkeys, and man was studied by fluorescence microscopy and autoradiography. Indoleamines were either injected intravitreally or the retinas were incubated with them. Fluorescence microscopy failed to show any indoleamine accumulating neurons in all species investigated except rabbit, confirming previous observations. However, autoradiography showed uptake in a distinct class of neurons in cows and pigs. These neurons had their cell bodies among the amacrine cells and most of their processes branched in the middle of the inner plexiform layer. This is in contradistinction to the dopaminergic neurons, which in cows and pigs have all their processes in the outermost sublamina of the inner plexiform layer. The fluorescence microscopy is quite sensitive to small variations in the indoleamine molecule. The discrepancy between the results with fluorescence microscopy and autoradiography therefore suggests that there is an active uptake mechanism for indoleamines in cows and pigs but that the substances are rapidly transformed to compounds not possible to detect in the fluorescence microscope. No specific indoleamine accumulating mechanism was detected in the retina of rats, baboons, cynomolgus monkeys, or man.     

Substance P-immunoreactive neurons in hamster retinas.

Light-microscopic immunocytochemistry was utilized to localize the different populations of substance P-immunoreactive (SP-IR) neurons in the hamster retina. Based on observation of 2505 SP-IR neurons in transverse sections, 34% were amacrine cells whose pear-shaped or round cell bodies (7-8 microm) were situated in the inner half of the inner nuclear layer (INL) or in the inner plexiform layer (IPL), while 66% of SP-IR somata (6-20 microm) were located in the ganglion cell layer (GCL) which were interpreted to be displaced amacrine cells and retinal ganglion cells (RGCs). At least three types of SP-IR amacrine cells were identified. The SP-IR processes were distributed in strata 1, 3, and 5 with the densest plexus in stratum 5 of the inner plexiform layer. In the wholemounted retina, the SP-IR cells were found to be distributed throughout the entire retina and their mean number was estimated to be 4224 +/- 76. Two experiments were performed to clarify whether any of the SP-IR neurons in the GCL were RGCs. The first experiment demonstrated the presence of SP-IR RGCs by retrogradely labeling the RGCs and subsequently staining the SP-IR cells in the retina using immunocytochemistry. The second experiment identified SP-IR central projections of RGCs to the contralateral dorsal lateral geniculate nucleus. This projection disappeared following removal of the contralateral eye. The number of SP-IR RGCs was estimated following optic nerve section. At 2 months after sectioning the optic nerve, the total number of SP-IR neurons in the GCL reduced from 4224 +/- 76 to a mean of 1192 +/- 139. Assuming that all SP-IR neurons in the GCL which disappeared after nerve section were RGCs, the number of SP-IR RGCs was estimated to be 3032, representing 3-4% of the total RGCs. In summary, findings of the present study provide evidence for the existence of SP-IR RGCs in the hamster retina.     

Anatomical pathways for color vision in the human retina

The major neurons and neural circuits that are involved in the transmission of color signals through the human retina to produce the color and spatially opponent P cell or midget ganglion cell responses are described. The older findings of single cone to midget bipolar connectivity is reviewed, and the single midget bipolar cell to midget ganglion cell connectivity as revealed by a recent serial section electron microscope study is described in detail. Our present knowledge concerning the discrimination of the blue-cone subtype from the other longer wavelength cones in the human at the outer plexiform layer is summarized, and our most recent findings concerning horizontal cell connectivity to the different spectral types of cones are discussed. Finally, a hypothetical pathway is proposed for color-opponent surrounds of midget ganglion cells using both horizontal cells at the outer plexiform layer and amacrine cell pathways at the inner plexiform layer.