Functional anatomy of the photoreceptor and second-order cell mosaics in the retina of Xenopus laevis (original) (raw)
Related papers
Structure and function of photoreceptor and second-order cell mosaics in the retina of Xenopus
Elsevier eBooks, 2001
The structure, physiology, synaptology, and neurochemistry of photoreceptors and second-order (horizontal and bipolar) cells of Xenopus laevis retina is reviewed. Rods represent 53% of the photoreceptors; the majority (97%) are green light-sensitive. Cones belong to large long-wavelength-sensitive (86%), large short-wavelength-sensitive (10%), and miniature ultraviolet wavelength-sensitive (4%) groups. Photoreceptors release glutamate tonically in darkness, hyperpolarize upon light stimulation and their transmitter release decreases. Photoreceptors form ribbon synapses with second-order cells where postsynaptic elements are organized into triads. Their overall adaptational status is regulated by ambient light conditions and set by the extracellular dopamine concentration. The activity of photoreceptors is under circadian control and is independent of the central body clock. Bipolar cell density is about 6000 cells/mm2 They receive mixed inputs from rods and cones. Some bipolar cell types violate the rule of ON-OFF segregation, giving off terminal branches in both sublayers of the inner plexiform layer. The majority of them contain glutamate, a small fraction is GABA-positive and accumulates serotonin. Luminosity-type horizontal cells are more frequent (approximately 1,000 cells/mm2) than chromaticity cells (approximately 450 cells/mm2). The dendritic field size of the latter type was threefold bigger than that of the former. Luminosity cells contact all photoreceptor types, whereas chromatic cells receive their inputs from the short-wavelength-sensitive cones and rods. Luminosity cells are involved in generating depolarizing responses in chromatic horizontal cells by red light stimulation which form multiple synapses with blue-light-sensitive cones. Calculations indicate that convergence ratios in Xenopus are similar to those in central retinal regions of mammals, predicting comparable spatial resolution.
The Journal of Comparative Neurology, 1994
The relationship of primate horizontal cells (HC) to cone pedicles was assessed by superimposing the cone inner segment mosaic upon Golgi-impregnated HC dendritic terminal clusters in a light microscope (LM) study. The HI, HII, and HI11 types of HC were identified, hand-drawn, photographed, and analyzed by computer graphics methods. Blue cone (B-cones) inner segments and their projected pedicles were distinguished from red (R-cones) and green (G-cones) cones on morphological criteria. Thus the inclusion or avoidance of B-cone pedicles by the various HC types' dendritic terminal clusters establishes whether there is any color specificity to their connections. In addition, we made counts of the number of dendritic terminals in the clusters going to cone pedicles in the various HCs' dendritic fields and plotted these against distances the cone pedicles lay from the cell body. In this way we could evaluate the weighting of spectral type of cone input.
Bipolar cell-photoreceptor connectivity in the zebrafish (Danio rerio) retina
The Journal of Comparative Neurology, 2012
Bipolar cells convey luminance, spatial and color information from photoreceptors to amacrine and ganglion cells. We studied the photoreceptor connectivity of 321 bipolar cells in the adult zebrafish retina. 1,1'-Dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) was inserted into whole-mounted transgenic zebrafish retinas to label bipolar cells. The photoreceptors that connect to these DiI-labeled cells were identified by transgenic fluorescence or their positions relative to the fluorescent cones, as cones are arranged in a highly-ordered mosaic: rows of alternating blue-(B) and ultraviolet-sensitive (UV) single cones alternate with rows of red-(R) and green-sensitive (G) double cones. Rod terminals intersperse among cone terminals. As many as 18 connectivity subtypes were observed, 9 of which -G, GBUV, RG, RGB, RGBUV, RGRod, RGBRod, RGBUVRod and RRod bipolar cells -accounted for 96% of the population. Based on their axon terminal stratification, these bipolar cells could be further sub-divided into ON, OFF, and ON-OFF cells. The dendritic spread size, soma depth and size, and photoreceptor connections of the 308 bipolar cells within the 9 common connectivity subtypes were determined, and their dendritic tree morphologies and axonal stratification patterns compared. We found that bipolar cells with the same axonal stratification patterns could have heterogeneous photoreceptor connectivity whereas bipolar cells with the same dendritic tree morphology usually had the same photoreceptor connectivity, although their axons might stratify on different levels.
American Journal of Anatomy, 1967
After impregnation of goldfish retina by the rapid Golgi method, two classes each of photoreceptor, bipolar, and horizontal cells were observed by light microscopy. Interconnections between these elements in the outer plexiform (first synaptic) layer were investigated by electron microscopy of ultrathin sections, in which the processes of impregnated cells are easily distinguished. Dendrites of large bipolar cells (Cajal's “bipolaires destineés aux bâtonnets”) appeared to contact the synaptic endings of both rods and cones, while those of small bipolars (Cajal's “bipolaires destinées aux cónes”) appeared to contact only cones. Processes from horizontal cells of the vitread level (Cajal's “cellules horizontaux intermédiaires”) appeared to contact only rods, while those from horizontal cells of the sclerad level (Cajal's “cellules horizontaux externes”) appeared to contact only cones. The structures formerly called “synaptic vacuoles” are the terminals of horizontal cell processes in the goldfish, and by analogy they should be so identified in all vertebrates. Teleostean horizontal cells are not typical of neurons or glia cells, but are morphologically intermediate between them. Their most interesting properties are their unique relationship to photoreceptor synaptic endings and their segregation into rod and cone subsystems along with the corresponding photoreceptor and bipolar cells. Although their specific function is not clear, some role in information processing therefore appears likely.
The Journal of Neuroscience, 1993
While most mammalian retinas are rod dominated, in the tree shrew retina 95% of the photoreceptors are cones. We studied tree shrew horizontal cells to look for features associated with this unusual photoreceptor arrangement. The morphology of horizontal cells was revealed by intracellular injections of Lucifer yellow, and their photoreceptor contacts were assessed by light and electron microscopy. Horizontal cell topography was studied in material stained with a neurofilament antibody and with toluidine blue. The tree shrew has two types of horizontal cell that are basically the same as A-and B-type horizontal cells of other mammals. All the photoreceptor contacts of the larger, axonless, A-type cell and the dendritic contacts of the smaller, axon-bearing, B-type cell are with cones. Both types contact nearly all the cones in their dendritic field and both types synapse with both red and blue cones. There is no anatomical evidence for chromatic selectivity. The sparsely branched B-type horizontal cell axon probably contacts rods as in other mammals. The unusual features of the A-type cell are the profuse dendritic terminal arborizations and the large dendritic field size. These features may be related to the abundance of cones but do not justify the conclusion for a special type of horizontal cell as has previously been supposed. Both types of horizontal cell have a central-peripheral density gradient; at any location B-type cells are up to three times as numerous as A-type cells. There are detailed features of the distributions that differ from those of other mammalian horizontal cells. The density maximum of B-type cells is in inferior retina and roughly coincides with that of the cones; the A-type maximum is located more superiorly. Neither maximum is colocalized with the ganglion cell peak in the central area. The mosaic of B-type cells is much more regular than that of A-type cells.
Color-specific interconnections of cones and horizontal cells in the retina of the goldfish
Journal of Comparative Neurology, 1975
In Golgi preparations of goldfish retina we have observed three types of horizontal cell which receive exclusively from cones and one which receives exclusively from rods. The cone horizontal cells were designated H1, H2 and H3, in order of increasing dendritic spread, increasing separation from the outer synaptic layer, decreasing size of perikaryon, and decreasing density of cone contacts. Slender appendages with knobby terminal enlargements project horizontally from the perikarya and larger dendrites of both rod and cone horizontal cells.We determined patterns of cone inputs to Golgi-impregnated horizontal cells by analyzing serial 1 μm sections with the light microscope. The probable inputs, in terms of visual pigments in the cones which contact them, are: H1, red + green + blue; H2, green + blue; H3, blue. Analysis of previously published work suggests (1) that H1 cells generate monophasic or L-type responses, H2 cells generate biphasic or C1-type responses, and H3 cells generate triphasic or C2-type responses; (2) that H1 cells receive direct functional input at least from red-sensitive cones, H2 cells from green-sensitive cones, and H3 cells from blue-sensitive cones; and (3) that H1 cells constitute pathways from cones to H2 cells, and H2 cells constitute pathways from cones and H1 cells to H3 cells. The precise location and route of the transfers, from H1 to H2 and from H2 to H3, are not yet known.
Specificity of the horizontal cell-photoreceptor connections in the zebrafish (Danio rerio) retina
The Journal of Comparative Neurology, 2009
Horizontal cells (HCs) are involved in establishing the center-surround receptive field organization of photoreceptor and bipolar cells. In many species, HCs respond differentially to colors and may play a role in color vision. An earlier study from our lab suggested that four types of HCs exist in the zebrafish retina: three cone HCs (H1, H2 and H3) and one rod HC. In this study, we describe their photoreceptor connections. Cones are arranged in a mosaic where rows of alternating blue-(B) and ultraviolet-sensitive (UV) single cones alternate with rows of red-(R) and green-sensitive (G) double cones; the G cones are adjacent to UV cones and B cones adjacent to R cones. Two small-field (H1 and H2) and two large-field (H3 and rod HC) cells were observed. The cone HC dendritic terminals connected to cones with single boutons, doublets, or rosettes, whereas the rod HCs connected to rods with single boutons. The single boutons/doublets/ rosettes of cone HCs were arranged in double rows separated by single rows for H1 cells, pairs and singles for H2 cells, and in a rectilinear pattern for H3 cells. These connectivity patterns suggest that H1 cells contact R, G and B cones, H2 cells G, B and UV cones, and H3 cells B and UV cones. These predictions were confirmed by applying the DiI method to SWS1-GFP retinas whose UV cones express green fluorescent protein. Each rod HC was adjacent to the soma or axon of a DiI-labeled cone HC and connected to 50-200 rods.
2000
In most mammals short-wavelength-sensitive (S) cones are arranged in irregular patterns with widely variable intercell distances. Consequently, mosaics of connected interneurons either may show some type of correlation to photoreceptor placement or may establish an independent lattice with compensatory dendritic organization. Since axonless horizontal cells (A-HC's) are supposed to direct all dendrites to overlying cones, we studied their spatial interaction with chromatic cone subclasses. In the cheetah, the bobcat, and the leopard, anti-S-opsin antibodies have consistently colabeled the A-HC's in addition to the S cones. We investigated the interaction between the two cell mosaics, using autocorrelation and cross-correlation procedures, including a Voronoi-based density probe. Comparisons with simulations of random mosaics show significantly lower densities of S cones above the cell bodies and primary dendrites of A-HC's. The pattern results in different longwavelength-sensitive-Land Scone ratios in the central versus the peripheral zones of A-HC dendritic fields. The existence of a related pattern at the synaptic level and its potential significance for color processing may be investigated in further studies.
The Journal of Comparative Neurology, 1994
Connections of the three human horizontal cell (HC) types with overlying cone pedicles have been studied via electron microscopy (EM). Because blue cones (B-cones) can be recognized on distinctive morphological criteria, we could determine their presence by light microscopy (LM) in the mosaic overlying HC dendritic trees. Then we could confirm the presence or absence of dendritic contacts to B-cone pedicles by examining EM serial sections and making reconstructions of examples of the three HC types.