Retinal ganglion cells in the crucian carp (Carassius carassius). II. Overlap, shape and tangential orientation of dendritic trees

The morphological characterization of orientation-biased displaced large-field ganglion cells in the central part of goldfish retina

The vertebrate retina has about 30 subtypes of ganglion cells. Each ganglion cell receives synaptic inputs from specific types of bipolar and amacrine cells ramifying at the same depth of the inner plexiform layer (IPL), each of which is thought to process a specific aspect of visual information. Here, we identified one type of displaced ganglion cell in the goldfish retina which had a large and elongated dendritic field. As a population, all of these ganglion cells were oriented in the horizontal axis and perpendicular to the dorsal-ventral axis of the goldfish eye in the central part of retina. This ganglion cell has previously been classified as Type 1.2. However, the circuit elements which synapse with this ganglion cell are not yet characterized. We found that this displaced ganglion cell was directly tracer-coupled only with homologous ganglion cells at sites containing Cx35/36 puncta. We further illustrated that the processes of dopaminergic neurons often terminated next to intersections between processes of ganglion cells, close to where dopamine D1 receptors were localized. Finally, we showed that Mb1 ON bipolar cells had ribbon synapses in the axonal processes passing through the IPL and made ectopic synapses with this displaced ganglion cell that stratified into stratum 1 of the IPL. These results suggest that the displaced ganglion cell may synapse with both Mb1 cells using ectopic ribbon synapses and OFF cone bipolar cells with regular ribbon synapses in the IPL to function in both scotopic and photopic light conditions.

Stem Cells and Regeneration in the Retina: What Fish Have Taught Us about Neurogenesis

Many species of fish grow for much of their lifetimes and add neurons to the CNS continuously. The retina has proved to be a convenient model in which to study neurogenesis, both the normal variety associated with growth and regeneration in response to a lesion. Initial neurogenesis in the embryonic eye cup begins in a tiny cluster of neuroepithelial cells that steadily enlarges to produce a central disk of neurons. Subsequent growth occurs mainly at the edge of this disk, in the circumferential germinal zone, where the retina adds annuli of new neurons of all varieties except the rod photoreceptors. A few proliferative cells persist to adulthood in central retina and normally produce only rods, but when the retina is damaged, these cells contribute to the production of new neurons of diverse classes. Recent work has revealed two additional populations of dividing cells in central retina; they normally proliferate so slowly that special methods are required to reveal them. We suggest that the three proliferative cell types are related through lineage in a model similar to those described for hematopoiesis. The persistent neurogenesis of fish retina seems to resemble qualitatively the neurogenesis of the mammalian brain, but quantitatively the neurogenesis is much more vigorous in the fish.

A morphological classification of retinal ganglion cells in the Japanese catshark Scyliorhinus torazame

Retinal ganglion cells (GCs) in the Japanese catshark Scyliorhinus torazame were labeled retrogradely with biotinylated dextran amine (BDA3000). First the labeled cells were classified into 5 morphological types (types I-III: small GCs; types IV and V: large GCs) according to the size of the soma and the dendritic arborization pattern as seen in retinal wholemounts. Type I cells were stellate, with dendrites radiating in different directions. Type II cells had bipolar dendritic trees, with 2 primary dendrites extending in opposite directions. Type III cells had a single thick primary dendrite. Type IV cells were stellate, with dendrites covering a large area centered on the cell body. Type V cells were asymmetric, with most dendrites extending opposite to the axon as a large, fan-shaped dendritic field. Subsequently a wholemount was cross-sectioned, and we classified cells further into multiple subtypes according to the level of dendritic arborization within the inner plexiform layer. The present results suggest the existence of many types of GCs in elasmobranchs in addition to the 3 types of large GCs that have been characterized previously. Some of the newly described GC subtypes in the catshark retina appear to be similar to some of those reported in actinopterygians.

Vision in elasmobranchs and their relatives: 21st century advances

This review identifies a number of exciting new developments in the understanding of vision in cartilaginous fishes that have been made since the turn of the century. These include the results of studies on various aspects of the visual system including eye size, visual fields, eye design and the optical system, retinal topography and spatial resolving power, visual pigments, spectral sensitivity and the potential for colour vision. A number of these studies have covered a broad range of species, thereby providing valuable information on how the visual systems of these fishes are adapted to different environmental conditions. For example, oceanic and deep-sea sharks have the largest eyes amongst elasmobranchs and presumably rely more heavily on vision than coastal and benthic species, while interspecific variation in the ratio of rod and cone photoreceptors, the topographic distribution of the photoreceptors and retinal ganglion cells in the retina and the spatial resolving power of the eye all appear to be closely related to differences in habitat and lifestyle. Multiple, spectrally distinct cone photoreceptor visual pigments have been found in some batoid species, raising the possibility that at least some elasmobranchs are capable of seeing colour, and there is some evidence that multiple cone visual pigments may also be present in holocephalans. In contrast, sharks appear to have only one cone visual pigment. There is evidence that ontogenetic changes in the visual system, such as changes in the spectral transmission properties of the lens, lens shape, focal ratio, visual pigments and spatial resolving power, allow elasmobranchs to adapt to environmental changes imposed by habitat shifts and niche expansion. There are, however, many aspects of vision in these fishes that are not well understood, particularly in the holocephalans. Therefore, this review also serves to highlight and stimulate new research in areas that still require significant attention.

Morphology and spatial arrangement of large retinal ganglion cells projecting to the optic tectum in the perciform fish Pholidapus dybowskii

Using retrograde HRP labeling from the optic nerve (ON) or optic tectum (OT), we have visualized large ganglion cells (LGCs) in wholemounted retinas of the teleost Pholidapus dybowskii and studied their morphology and spatial properties. In all, three LGC types were distinguished. In a previous paper, detailed data were provided on one type, biplexiform cells [Pushchin, I. I., & Kondrashev, S. L. (2003). Biplexiform ganglion cells in the retina of the perciform fish Pholidapus dybowskii revealed by HRP labeling from the optic nerve and optic tectum. Vision Research, 43, 1117-1133]. Here, we present data on the other two confirmed types, alpha(a) and alpha(ab) cells. The types differed in the level of dendrite stratification, dendrite arborization pattern, dendritic field size, and other features, and formed in the retina significantly non-random, spatially independent mosaics. Both types were labeled from the OT, indicating their participation in OT-mediated visual reactions. The comparison of spatial properties of alpha(a) and alpha(ab) mosaics labeled from the ON and OT suggests that the OT is the major or one of the major projection areas of both types. We also describe the morphology of cells resembling alpha(c) cells of other fishes, which were only labeled from the ON. The LGC types presently revealed were similar in their morphology to LGCs found in other teleosts supporting the hypothesis of LGC homology across the teleost lineage.

Morphological features of chick retinal ganglion cells

On average, in chicks, the total number of retinal ganglion cells is 4.9 x 10(6) and the cell density is 10400 cells/mm2. Two high-density areas, namely the central area (CA) and the dorsal area (DA), are located in the central and dorsal retinas, respectively, in post-hatching day 8 (P8) chicks (19000 cells/mm2 in the CA; 12800 cells/mm2 in the DA). Thirty percent of total cells in the ganglion cell layer are resistant to axotomy of the optic nerve. The distribution of the axotomy resistant cells shows two high-density areas in the central and dorsal retinas, corresponding to the CA (5800 cells/mm2) and DA (3200 cells/mm2). The number of presumptive ganglion cells in P8 chicks is estimated to be 4 x 10(6) (8600 cells/mm2 on average) and the density is 13500 and 10200 cells/mm2 in the CA and DA, respectively, and 4300 cell/mm2 in the temporal periphery (TP). The somal area of presumptive ganglion cells is small in the CA and DA (mean (+/- SD) 35.7 +/- 9.1 and 40.0 +/- 11.3 microm2, respectively) and their size increases towards the periphery (63.4 +/- 29.7 microm2 in the TP), accompanied by a decrease in cell density. Chick ganglion cells are classified according to dendritic field, somal size and branching density of the dendrites as follows: group Ic, Is, IIc, IIs, Ills, IVc. The density of branching points of dendrites is approximately 10-fold higher in the complex type (c) than in the simple type (s) in each group. The chick inner plexiform layer is divided into eight sublayers according to the dendritic strata of retinal ganglion cells and 26 stratification patterns are discriminated.

Morphologic analysis and classification of ganglion cells of the chick retina by intracellular injection of lucifer yellow and retrograde labeling with DiI

Retinal ganglion cells (RGCs) of chicks were labeled by using the techniques of intracellular filling with Lucifer Yellow and retrograde axonal labeling with carbocyanine dye (DiI). Labeled RGCs were morphologically analyzed and classified into four major groups: Group I cells (57.1%) with a small somal area (77.5 microm(2) on average) and narrow dendritic field (17,160 microm(2) on average), Group II cells (28%) with a middle-sized somal area (186 microm(2)) and middle-sized dendritic field (48,800 microm(2)), Group III cells (9.9%) with a middle-sized somal area (203 microm(2)) and wide dendritic field (114,000 microm(2)), and Group IV cells (5%) with a large somal area (399 microm(2)) and wide dendritic field (117,000 microm(2)). Of the four groups, Groups I and II were further subdivided into two types, simple and complex, on the basis of dendritic arborization: Groups Is, Ic, and Groups IIs, IIc. However, Group III and IV showed either a simple or complex type, Group IIIs and Group IVc, respectively. The density of branching points of dendrites was approximately 10 times higher in the complex types (18,350, 6,190, and 3,520 points/mm(2) in Group Ic, IIc, and IVc, respectively) than in the simple types (1,890, 640, and 480 points/mm(2) in Group Is, IIs, and IIIs). The branching density of Group I cells was extremely high in the central zone. The chick inner plexiform layer was divided into eight sublayers by dendritic strata of RGCs and 26 stratification patterns were discriminated. The central and peripheral retinal zones were characterized by branching density of dendrites and composition of RGC groups, respectively.

Asymmetric temporal properties in the receptive field of retinal transient amacrine cells

The speed of signal conduction is a factor determining the temporal properties of individual neurons and neuronal networks. We observed very different conduction velocities within the receptive field of fast-type On-Off transient amacrine cells in carp retina cells, which are tightly coupled to each other via gap junctions. The fastest speeds were found in the dorsal area of the receptive fields, on average five times faster than those detected within the ventral area. The asymmetry was similar in the On- and Off-part of the responses, thus being independent of the pathway, pointing to the existence of a functional mechanism within the recorded cells themselves. Nonetheless, the spatial decay of the graded-voltage photoresponse within the receptive field was found to be symmetrical, with the amplitude center of the receptive field being displaced to the faster side from the minimum-latency location. A sample of the orientation of varicosity-laden polyaxons in neurobiotin-injected cells supported the model, revealing that approximately 75% of these processes were directed dorsally from the origin cells. Based on these results, we modeled the velocity asymmetry and the displacement of amplitude center by adding a contribution of an asymmetric polyaxonal inhibition to the network. Due to the asymmetry in the conduction velocity, the time delay of a light response is proposed to depend on the origin of the photostimulus movement, a potentially important mechanism underlying direction selectivity within the inner retina.

Slow recovery of goldfish retinal ganglion cells' soma size during regeneration

The goldfish optic nerve regenerates after sectioning. Recently both short-term (30 days) and long-term (4 months) recovery of various goldfish behaviors were observed after optic nerve section. Using intracellular injection of Lucifer Yellow (LY) the morphology of regenerating ganglion cells in goldfish retina after optic nerve section over a 4 month period have been investigated. In normal retinas, most cells (96-98%) were 7-10 microm in soma diameter which increased with increasing distance from the optic disc. Only two or three short, thin processes could be traced with LY. The remaining cells (2-4%) were 13-16 microm in soma diameter and all of the long dendritic trees could be traced with LY. The most conspicuous morphological change observed was cellular hypertrophy, which occurred for 20-90 days after axotomy. Neuronal processes were also hypertrophic in this period. The percentage increase in hypertrophy of the central ganglion cells tended to be slightly higher compared to cells from other regions. These morphological changes peaked at 60 days after axotomy and fully disappeared by 120 days after axotomy. The slow recovery of ganglion cells' soma size may reflect the slow return to the normal number of optic axon terminals in the tectum during regeneration.

Morphological classification of ganglion cells in the central retina of chicks

Classification of retinal ganglion cells (RGCs) in the chick central retina was studied by retrograde labeling of carbocyanine dye (DiI) and intracellular filling with Lucifer Yellow. Ganglion cells were divided into 4 groups, Group Ic/Is, Group IIc/IIs, Group IIIs, Group IVc, according to sizes of somal area and dendritic field and dendritic branching pattern. Group I cells had small somal area and small dendritic field. They were further divided into 2 subgroups by complexity (subgroup Ic) and simplicity (subgroup Is) of the dendritic arborization. Group II cells had medium-sized soma and dendritic field. They were also divided into subgroup IIc and IIs by the same definitions as those of subgroup Ic and Is. Group IIIs had medium-sized soma, large and simple dendritic arborization. Group IVc in which all cells had large soma, showed large and complex dendritic arborization. Cell populations of each group were 51.8% (subgroup Ic), 21.1% (subgroup Is), 6.2% (subgroup IIc), 14.6% (subgroup IIs), 4.2% (Group IIIs), and 2.1% (Group IVc). Subgroup Ic cells, which were very similar to beta-cells in the mammalian central area, represented about a half of the ganglion cell population. Cells in subgroup Is and IIs, which were not reported in the mammalian retina, were found in the chick central retina in relatively high population (35.7%). Morphological features of chick RGCs in the central retina were considered in comparison with those of other vertebrates.

Large retinal ganglion cells that form independent, regular mosaics in the ranid frogs Rana esculenta and Rana pipiens

Population-based studies of ganglion cells in retinal flatmounts have helped to reveal some of their natural types in mammals, teleost fish and, recently, the aquatic mesobatrachian frog Xenopus laevis. Here, ganglion cells of the semiterrestrial neobatrachian frogs Rana esculenta and Rana pipiens have been studied similarly. Ganglion cells with large somata and thick dendrites could again be divided into three mosaic-forming types with distinctive stratification patterns. Cell dimensions correlated inversely with density, being smallest in the visual streak. Cells of the alpha a mosaic (< 0.2% of all ganglion cells) had the largest somata at each location (often displaced) and their trees were confined to one shallow plane within sublamina a of the inner plexiform layer. In regions of high regularity, many trees were symmetric. Elsewhere, asymmetric, irregular trees predominated and their dendrites, although sparsely branched, achieved consistent coverage by intersecting in complex ways. Cells of the alpha ab mosaic were more numerous (approximately 0.7%) and had large somata, smaller (but still large) trees, and dendrites that branched extensively in two separate shallow planes in sublaminae a and b. The subtrees did not always match in symmetry, and each subtree tessellated independently with its neighbors. Cells of the alpha c mosaic (approximately 0.1%) had large, orthotopic somata and large, sparse trees (often asymmetric and irregular) close to the ganglion cell layer. Nearest-neighbor analyses and spatial correlograms confirmed that each mosaic was regular and independent. Densities, proportions, sizes, and mosaic statistics are tabulated for all three types, which are compared with types defined by size and symmetry in R. pipiens, by discriminant analysis in R. temporaria, by physiological response in both, and by mosaic analysis in Xenopus and several teleosts. The variable stratification of these otherwise similar types across species is consistent with other evidence that stratification may be determined, in part, by functional interactions.

The cone photoreceptor mosaic of the green sunfish, Lepomis cyanellus

Recent empirical and theoretical evidence has implicated the geometrical birefringence of the double cones of the green sunfish (Lepomis cyanellus) as the biophysical basis of this vertebrate's sensitivity to polarized light. Because of the intimate link between the organization of the cone-photoreceptor mosaic and the psychophysical details of polarization sensitivity, we have examined the structural features of the green sunfish cone-photoreceptor mosaic, in particular the orientation of the elliptical cross sections of the double cones. Our primary observations are that (1) the arrangement of the cone-photoreceptor mosaic is constant across the retina (with two regional exceptions), with double cones arranged in a rhombic mosaic and aligned roughly +/- 45 deg to the nearest retinal margin; (2) the double-cone/single-cone ratio is everywhere the same; (3) cone density is inhomogeneous across the retina, with the highest densities in the temporal hemiretina. These results are discussed as they relate to the animal's retinal growth and visual mechanisms, particularly the sensitivity to polarized light.

Independent mosaics of large inner- and outer-stratified ganglion cells in the goldfish retina

Goldfish retinal ganglion cells were filled with horseradish peroxidase and studied in flatmounts. Two regular mosaics of large neurons with many of the properties of mammalian alpha ganglion cells were found, differing from each other in spacing, size, and dendritic stratification. The existence of biplexiform ganglion cells with additional dendrites in the outer plexiform layer was also confirmed. One of the two alpha-like mosaics consisted of giant ganglion cells with thick primary dendrites and large, sparsely branched dendritic trees in the outer sublamina of the inner plexiform layer (IPL). In fish 55-65 mm long, about 300 formed a tessellated array across each retina. Their somata (mean area 277 +/- 6 microns 2) were displaced to varying degrees into the IPL, neighbours in the mosaic often occupying different levels. Their dendrites ramified in one stratum near the inner nuclear layer, at a mean depth of 70.8 +/- 0.5% of the IPL. The other alpha-like mosaic comprised about 900 large ganglion cells, with slightly smaller somata (mean area 193 +/- 4 microns 2) in the ganglion cell layer. Most of their dendrites lay in a narrow stratum at 41.9 +/- 0.5% of the depth of the IPL. However, deviations (usually into more vitread strata) were common, which was not true for similar cells in the distantly related cichlid fish Oreochromis. Measurements of nearest neighbour distance (NND) for 4 outer and 4 inner mosaics showed that they were at least as regular as the alpha cell mosaics of mammals: the ratio of the mean NND to the standard deviation ranged from 4.03 for the least regular outer mosaic to 6.47 for the most regular inner mosaic. The wide phylogenetic distribution of these paired, regular mosaics points to a fundamental role in vision. The presence of some variability in dendritic stratification even within the exceptionally regular inner-stratified mosaic suggests that classifications based entirely on the detailed morphology of individual neurons may not always correlate well with their primary functional roles. Where possible, neuronal morphology and spatial distribution should be studied together.

Alpha ganglion cells in mammalian retinae: common properties, species differences, and some comments on other ganglion cells

A specific morphological class of ganglion cell, the alpha cell, was first defined in cat retina. Alpha cells have since been found in a wide range of mammalian retinae, including several orders of placental and marsupial mammals. Characteristically, they have the largest somata and a large dendritic field with a typical branching pattern. They occur as inner and outer stratifying subpopulations, presumably corresponding to ON-center and OFF-center receptive fields. In all species, alpha cells account for less than 10% of the ganglion cells, their somata are regularly spaced, and their dendritic fields evenly and economically cover the retina in a mosaic-like fashion. The morphology of alpha cells and many features, both of single cells and of the population, are conserved across species with different habitats and life-styles. This suggests that alpha cells are a consistent obligatory ganglion cell type in every mammalian retina and probably subserve some fundamental task(s) in visual performance. Some general rules about the construction principles of ganglion cell classes are inferred from the alpha cells, stressing the importance of population parameters for the definition of a class. The principle, that a functionally and morphologically homogeneous population should have a regular arrangement and a complete and even coverage of the retina to perform its part in image processing at each retinal location, is especially evident across species and across ganglion cell types.

Regular mosaics of large displaced and non-displaced ganglion cells in the retina of a cichlid fish

Large retinal ganglion cells in the tilapid cichlid fish Oreochromis spilurus (standard length 15-54 mm) were filled with horseradish peroxidase and studied in flatmounts. Three types, with distinct patterns of dendritic stratification, formed spatially independent, nonrandom mosaics. One type (about 0.3% of all ganglion cells) resembled the outer (off) alpha cells of mammals. They were very large, with thick primary dendrites and large, sparsely branched planar trees in the outer part of the inner plexiform layer (IPL). About 300 were arrayed regularly across each retina, their exact number and spacing depending on its size. Their somata were often displaced into the IPL, even where neighbours in the mosaic were orthotopic. Another type (0.8%) resembled the inner (on) alpha cells of mammals. These had slightly smaller somata that were never displaced and smaller trees in the middle layers of the IPL. About 800 were arrayed uniformly and regularly across each retina. A rarer type (0.06-0.08%) had two planar trees: one forming a coarse mosaic in the outer part of the inner plexiform layer (co-planar with the trees of outer alpha-like cells) and another in the outer plexiform layer. These "biplexiform" cells were smaller and rounder than alpha-like cells and always displaced. The dendrites were finer and less tapered. Cells in which we could identify an outer plexiform tree failed to cover the retina completely, but were nonrandomly distributed. We draw three main conclusions: (1) some nonmammalian vertebrates have separate inner and outer mosaics of large ganglion cells like those of mammals, (2) the vertical displacement of ganglion cell somata can vary widely within a single mosaic and may thus be functionally irrelevant, and (3) biplexiform ganglion cells exist in fish but differ in morphology from the biplexiform types described in some other vertebrates.

Cold inhibits neurite outgrowth from single retinal ganglion cells isolated from adult goldfish

We have studied the growth of neurites from single retinal ganglion cells isolated from adult goldfish and maintained under various primary cell culture conditions. In 10% Leibovitz's L-15 medium at 23 degrees C, these ganglion cells remained viable for up to 10 days and generated extensive fields of neurites. We found two patterns of neuritic fields. In one, a pair of neurites exited from opposite sides of the cell soma, forming a bipolar pattern. In the second pattern, three to five neurites exited from several points around the soma, forming a multipolar pattern. Characteristically, each neurite of this latter type tapered and branched two to seven times, whereas neurites forming bipolar patterns showed less branching and little or no taper. The fields subtended by the neurites in multipolar patterns ranged in size from 33,000 to 204,000 microns 2. Finally, although these neurites grew as fast as 35 microns hr-1 at 23 degrees C and individually reached lengths of up to 735 microns, they showed essentially no growth at 13 degrees C. Neurite outgrowth at 23 degrees C was vigorous even in cells whose growth had previously been suppressed for as long as 8 hr at 13 degrees C.

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.

Topography and morphology of retinal ganglion cells in the coral trout Plectropoma leopardus (Serranidae): a retrograde cobaltous-lysine study

The retinal topography of the adult coral trout Plectropoma leopardus (Serranidae, Perciformes) is examined in Nissl-stained material and confirmed by means of retrograde labelling with cobalt-lysine from the optic nerve. Concentric isodensity contours surround a temporoventral area centralis of over 1.5 x 10(4) cells per mm2 which lies ventral of the elongated optic nerve head. Peripheral densities of ganglion cells fall to less than 0.25 x 10(4) cells per mm2. A total of 1.17 x 10(5) ganglion cells is found over the entire retina. Silver intensifications of cobalt-lysine-stained cells allow a detailed analysis of ganglion cell morphology. Soma and dendritic field size increase with eccentricity, and within the confines of the area centralis only the smallest cell size is found. Dendritic arbors of peripheral ganglion cells are all oriented parallel to the retinal margin with an axon lying close to the vitreous humor. Nine classes of cells are characterized on the criteria of soma size, dendritic field size, primary and secondary branching patterns, soma position, and dendritic termination areas. Possible morphological homologies with ganglion cells of other teleosts are also discussed.

Ganglion cells in the frog retina: discriminant analysis of histological classes

Neurons in the ganglion cell layer were studied in Golgi-stained flat-mounted frog (Rana temporaria) retinas. Complementary data were obtained from methylene blue- and HRP-stained retinas. On the basis of qualitative criteria, 55 neurons were ordered into six groups, one class of amacrine cell (A1) and five classes of ganglion cells (G1-G5). A discriminant function analysis based on seven morphological variables resulted in a separation of the cell classes in the space of three axes. The A1 cells are small axonless neurons with knotty and dense dendritic trees. The G1 cells are also small, and apparently very numerous, while the G2 cells are medium-sized neurons with two loose dendritic layers, one vitreal and another (less conspicuous) scleral. The rest of the cells are medium-sized to large neurons with sturdy primary dendrites and more distinct dendritic layers, which in some cells (G3) spread both sclerally and vitreally, in other cells in a single either scleral (G4) or vitreal (G5) layer. The relation between our data and the classification of frog ganglion cells recently presented by Frank and Hollyfield is discussed at length, and in that context problems related to statistical classifications are dealt with. A hypothetical identification of the morphological types with the functional cell classes studied in the Helsinki laboratory is discussed.

Orientation and direction tuning of goldfish ganglion cells

Orientation and direction tuning were examined in goldfish ganglion cells by drifting sinusoidal gratings across the receptive field of the cell. Each ganglion cell was first classified as X-, Y-, or W-like based on its responses to a contrast-reversal grating positioned at various spatial phases of the cell's receptive field. Sinusoidal gratings were drifted at different orientations and directions across the receptive field of the cell; spatial frequency and contrast of the grating were also varied. It was found that some X-like cells responded similarly to all orientations and directions, indicating that these cells had circular and symmetrical fields. Other X-like cells showed a preference for certain orientations at high spatial frequencies suggesting that these cells possess an elliptical center mechanism (since only the center mechanism is sensitive to high spatial frequencies). In virtually all cases, X-like cells were not directionally tuned. All but one Y-like cell displayed orientation tuning but, as with X-like cells, orientation tuning appeared only at high spatial frequencies. A substantial portion of these Y-like cells also showed a direction preference. This preference was dependent on spatial frequency but in a manner different from orientation tuning, suggesting that these two phenomena result from different mechanisms. All W-like cells possessed orientation and direction tuning, both of which depended on the spatial frequency of the stimulus. These results support past work which suggests that the center and surround components of retinal ganglion cell receptive fields are not necessarily circular or concentric, and that they may actually consist of smaller subareas.

Responsivity and absolute sensitivity of retinal ganglion cells in goldfish of different sizes, when measured under "psychophysical" conditions

Retinal neurogenesis occurs in adult goldfish, and more rods are added to the retina than any other class of cell as the fish grows. To determine whether the disproportionate addition of rods affects the responsivity and sensitivity of dark adapted retinal ganglion cells, we recorded activity from optic tract fibers in goldfish of different sizes. Experimental conditions were as similar as possible to those used in a separate study in which psychophysical absolute thresholds were measured: large, dim, monochromatic spots 1 sec in duration were projected close to the right eye of alert, self-respiring goldfish. A total of 214 fibers were recorded in small (5.0-5.7 cm), medium (9.5-11.0 cm) and large (13.0-20.0 cm) fish. Neither maintained activity (mean and variance of the discharge rate in darkness) nor responsivity (quantum-to-spike ratios) nor absolute threshold (quantal irradiance required to produce a difference of 1 spike/trial from spontaneous rates) varied reliably with size of fish. However, some Off cells were more active in the dark than On and On/Off cells; these had low QSR's and absolute thresholds, and were found in all sizes of fish. Fifty percent (50%) of Off cells (compared to 8% of On cells) had thresholds comparable to or lower than psychophysical threshold, and Off cell thresholds (but not On cell thresholds) tended to be lower in larger fish. Because psychophysical threshold is closely related to the planimetric density of rods in goldfish, the similarity between Off cell threshold and psychophysical threshold suggests that Off cells may be influenced relatively more than On cells by the addition of new rods to the retina.

Constant dendritic coverage by ganglion cells with growth of the goldfish's retina

This study demonstrates that in the retina of the goldfish a type of ganglion cell, whose dendritic development has been well characterized [Hitchcock P.F. and Easter S. S. Jr (1986) J. Neurosci. 6, 1037-1050], is distributed across the retina in a nonrandom pattern, and the dendritic fields of this cell type overlap to completely cover, or "tile" the retina. Further, it is shown that the dendritic coverage of the retina by this cell type is established when the retina is small and is maintained as the retina grows.

The visual system of the channel catfish (Ictalurus punctatus). I. Retinal ganglion cell morphology

Horseradish peroxidase was applied to lesions in the optic nerve of catfish (Ictalurus punctatus). The retinae were processed to reveal HRP-labelled ganglion cells. The histochemical techniques employed allowed fine details of the dendritic arbor to be resolved. Flat-mounted retinae were examined and the following characteristics were noted in individual ganglion cells: Soma area, shape, and depth; number and diameter of major dendrites; shape, area, and depth(s) within the inner plexiform layer (ipl) of the dendritic arbor; origin of the axon (from the soma or a dendrite). On the basis of these characteristics, eleven classes of ganglion cells were delineated: four classes of giant cells (G1-G4) and seven classes of smaller cells (S1-S7). G1 cells had dendrites arborizing in the most distal sublamina of the ipl. G1 cells in the dorsal retina had nasotemporally elongated dendritic arbors. G2 cells had dendrites in the proximal portion of the ipl. G3 cells were almost completely confined to a band running between the nasal and temporal retinal poles, through the center of the retina. In this location, the cells had dorsoventrally elongated dendritic arbors, which were bistratified in the ipl. G4 cells were displaced into the inner nuclear layer. S1 and S4 cells had axons arising from their somata, and dendrites arborizing in the distal and the proximal ipl, respectively. S2 cells were typified by their unstratified dendritic arbors. Similarly, S3 cells were characterised by their bistratified arbors. S5 cells arborized in the most proximal ipl sublamina. S6 cells were small ganglion cells with their somata lying in the inner nuclear layer. S7 cells tended to have complex dendritic arbors, and their axons arose from dendrites.

Formation of new rod photoreceptor synapses onto differentiated bipolar cells in goldfish retina

In goldfish new rods are continuously added to the entire retina at a rate that assures stable rod density, while the densities of other neurons decrease. The b1 bipolar, known to contact every rod within its dendritic domain, was used to determine the fate of these newly formed rods. Golgi-stained b1 bipolars were sectioned serially at 0.5 micron in the plane of the receptor terminals and reconstructions of their rod and cone contacts were prepared from camera lucida drawings. The newly formed rods are accommodated within the dendritic trees of already-formed b1 bipolars at a rate of about one new rod synapse/bipolar/month. During growth from about 6 months to 5 years of age the number of synapses onto each b1 bipolar increases by 50%. Concomitantly the dendritic tree area increases by about 50%, and the density of rod-b1 synapses remains constant at about one synapse/11 micron 2. Assuming a dendritic coverage factor of 1, the b1 bipolars will contact every retinal rod. The numbers of cones contacted and not contacted do not significantly change. The overall dimensions of b1 bipolars increase with retinal growth and new branches are added to their dendritic trees. These observations show that new rods added to adult goldfish retina form synapses with old bipolars. Some functional inferences are also made.

Lateral actions at the inner plexiform layer of the carp retina: effects of turning windmill pattern stimulus

Lateral action from amacrine to ganglion cells was studied in the isolated carp retina by using a truncated windmill pattern (TWP). About 25% of ganglion cells of both "on" and "off" center types were suppressed or enhanced in firing activity in response to TWP turning. The suppressed cells were more sensitive to slow turning velocities of TWP than the enhanced cells. In the "on-off" type amacrine cells, a steady depolarizing or hyperpolarizing component (less than several mV) was maintained by stationary TWP, while the cells were exclusively depolarized by turning TWP at a wide range of velocities. These results suggest that individual responses of ganglion cells induced by both stationary and turning TWP are depending on a balance between two factors: the polarizing direction of steady components of the "on-off" amacrine cells and the polarizing direction of ganglion cells synaptically produced by the amacrine cells.

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 X 10(4) in Sebastiscus and 87 X 10(4) in Navodon, whereas the total number of optic nerve fibers was about 35 X 10(4) and 70 X 10(4), 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.(ABSTRACT TRUNCATED AT 400 WORDS)

The goldfish nervus terminalis: a luteinizing hormone-releasing hormone and molluscan cardioexcitatory peptide immunoreactive olfactoretinal pathway

Antisera to two putative neurotransmitters, luteinizing hormone-releasing hormone (LHRH) and molluscan cardioexcitatory tetrapeptide (H-Phe-Met-Arg-Phe-NH2; FMRF-amide), bind specifically to neurites in the inner nuclear and inner plexiform layers of the goldfish retina. Retrograde labeling showed that intraocular axon terminals originate from the nervus terminalis, whose cell bodies are located in the olfactory nerves. Double immunocytochemical and retrograde labeling showed that some terminalis neurons project to the retina; others may project only within the brain. All terminalis neurons having proven retinal projections were both LHRH- and FMRF-amide-immunoreactive. The activity of retinal ganglion cells was recorded with microelectrodes in isolated superfused goldfish retinas. In ON- and OFF-center double-color-opponent cells, micromolar FMRF-amide and salmon brain gonadotropin-releasing factor ( [Trp7, Leu8] LHRH) caused increased spontaneous activity in the dark, loss of light-induced inhibition, and increased incidence of light-entrained pulsatile response. The nervus terminalis is therefore a putatively peptidergic retinopetal projection. Sex-related olfactory stimuli may act through it, thereby modulating the output of ganglion cells responsive to color contrast.

Structural basis of orientation sensitivity of cat retinal ganglion cells

We investigated the structural basis of the physiological orientation sensitivity of retinal ganglion cells (Levick and Thibos, '82). The dendritic fields of 840 retinal ganglion cells labeled by injections of horseradish peroxidase into the dorsal lateral geniculate nucleus (LGNd) or optic tracts of normal cats. Siamese cats, and cat deprived of patterned visual experience from birth by monocular lid-suture (MD) were studied. Mathematical techniques designed to analyze direction were used to find the dendritic field orientation of each cell. Statistical techniques designed for angular data were used to determine the relationship between dendritic field orientation and angular position on the retina (polar angle). Our results indicate that 88% of retinal ganglion cells have oriented dendritic fields and that dendritic field orientation is related systematically to retinal position. In all regions of retina more that 0.5 mm from the area centralis the dendritic fields of retinal ganglion cells are oriented radially, i.e., like the spokes of a wheel having the area centralis at its hub. This relationship was present in all animals and cell types studied and was strongest for cells located close to the horizontal meridian (visual streak) of the retina. Retinal ganglion cells appear to be sensitive to stimulus orientation because they have oriented dendritic fields.

Regional difference in density of monoamine-accumulating cells of carp and catfish retinas

By means of a histofluorescence technique, a comparative study was conducted on the regional density of dopaminergic (DA) and indoleamine-accumulating (IA) cells in carp (Cyprinus carpio) and catfish (Ictalurus punctatus) retinas. In order to enhance detection of fluorescent cells, noradrenaline (NA; 5.0 micrograms) or a mixture of NA (2.5 micrograms) and 5,6-dihydroxytryptamine (5,6-DHT; 2.5 micrograms) was intravitreally injected into the eyes 2-3 hr before enucleation. DA and IA cells were counted systematically in space on flat-mounted preparations. Both classes of cells were found to be distributed similarly in the two species of fish; the cell density is highest in the circumferential margin of the retina, and is slightly higher in a region dorsal to the optic disc than in the surrounding area. Differences in the distribution pattern of the cells between carp and catfish retinas were as follows: (a) the DA cell density is higher over the whole retinal field in carp (the mean density +/- SD = 34 +/- 16 cells/mm2) than in catfish (13 +/- 7 cells/mm2); (b) the region where the density is slightly higher than in the surrounding area is restricted to a small area immediately dorsolateral to the optic disc in carp, while it is relatively broadly placed dorsal to the optic discs, forming a horizontal band in catfish; (c) the density ratio of DA cells to IA cells is 1:1 in carp but 1:2 in catfish; and (d) catfish DA cells seem to be more irregular than carp DA cells in shape, size, dendritic arborization, uptake preference for monoamines intravitreally injected, and also in depth location seen in radial cryosections.

Errant optic axons in the normal goldfish retina reach retinotopic tectal sites

Optic axons in the goldfish retina generally run radially from their origins to the optic nerve. However, horseradish peroxidase (HRP), introduced into small groups of axons through lesions in the tecta of normal fish, consistently filled some which ran parallel to the retinal margin for long distances before turning centrally. Since all the HRP-filled ganglion cells lay close together, their axons evidently reached adjacent tectal sites by these widely divergent routes.

Dendritic tree structure and dendritic hypertrophy during growth of the crucian carp eye

The areas of the ganglion cell dendritic trees were determined in Golgi-stained, flatmounted retinas of crucian carp ranging in age from one summer to 7 years. The dendritic trees of small ganglion cells (S-GC), forming the majority of retinal ganglion cells, add new branches as the retina grows. The increase in dendritic tree area exactly compensates for the decrease in ganglion cell density during growth of the eye so that the number of dendritic trees covering a particular point remains constant. While the retinal diameter increases by a factor of 2.5, the mean diameter of the S-GC dendritic fields increases by a factor of 1.9 and the visual angle covered by one S-GC dendritic tree decreases from 1.6 degrees to 1.2 degrees. The number of branching points of the S-GC dendrites is significantly higher in the ventral retina than in the dorsal. In general the dendrites of the S-GCs tend to grow towards the retinal margin. Dendritic orientation patterns of large (LGC) and large displaced (LDGC) ganglion cells closely resemble those of the amacrines, being oriented parallel to the retinal margin over a wide peripheral region, while the SGCs rapidly lose their tangential orientation. The dendrites of the SGCs are restricted mainly to the proximal sublayer of the inner plexiform layer, suggesting they are ON-cells, while LGC, LDGC, and amacrine cell dendrites are distributed in depth bimodally. As determined from Golgi-stained sections the crucian carp has the same basic IPL organization as the carp and cat.

Neuronal addition and retinal expansion during growth of the crucian carp eye

Using standard paraffin technique the addition of new cells in crucian carp retinas was examined. Between eye diameters 4.4 and 10.0 mm the number of ganglion cells increases from 103,000 to 205,000, INL cells from 1.5 to 3 million, comes from 250,000 to 900,000, and rods from 2 to 9 million. Concomitantly retinal area increases fivefold and the cell densities decrease by 37% for the cones, 57% for the INL cells, and 58% for the ganglion cells, while the rod density remains stable. In relation to the rods the cell ratios at different retinal loci undergo marked changes during growth. The contributions to retinal growth by addition of new neurons and by expansion of the retina have been determined for the different retinal layers. The layer of rods grows exclusively by addition of new rod mosaic. In the cone layer 81% of growth is due to addition of new cone mosaic. In the inner nuclear layer (INL) 56% of growth is due to addition of new cells and in the ganglion cell layer 52% is due to cell addition. In each case retinal expansion accounts for the remainder of increase in retinal area. On morphological grounds six cone types can be found in the crucian carp retina. Their ratios are constant during retinal growth and at different retinal loci.

Retinotopic and temporal organization of the optic nerve and tracts in the adult goldfish

In order to investigate the role of the different factors controlling the pathways and termination sites of growing axons, selected optic fibers were traced from the eye to the tectum in adult goldfish either by filling them with HRP, or by severing a group of fibers and tracing their degeneration in 2 micrometers plastic sections stained with toluidine blue. Some fish received more than one lesion and others received both lesions and HRP applications. Two major rearrangements of the optic fibers were identified, one at the exit from the eye, the other within the optic tracts. Near the eye the optic fibers appear to be guided by the conformation of the underlying tissue planes that they encounter. The most recently added fibers, from the peripheral retina, grow over the vitread surface of the older fibers toward the blood vessel in the center of the optic nerve head. Behind the eye the fibers follow this blood vessel until it leaves the side of the optic nerve, and the fibers from peripheral retina are left as a single group on the ventral edge of the optic nerve cross section. As a consequence of this pattern of fiber growth the fibers form an orderly temporal sequence in the optic nerve, with the oldest fibers from the central retina on one side of the nerve and the youngest from peripheral retina on the other. In addition, the fibers are ordered topographically at right angles to this central-to-peripheral axis, with fibers from ventral retina on each edge of the nerve, dorsal fibers in the center, and nasal and temporal fibers in between. This arrangement of the optic fibers continues with only a little loss of precision up to the optic tracts. A more radical fiber rearrangement, seemingly incompatible with the fibers simply following tissue planes occurs within the optic tracts. Each newly arriving set of fibers grows over the surface of the optic tracts so that the older fibers come to lie deepest in the tracts. This segregation of fibers of different ages ensures that the rearrangement is limited to each layer of fibers. The abrupt reorganization of the fibers occurs as the tracts split around the nucleus rotundus to form the brachia of the optic tracts. The fibers are then arranged with temporal fibers nearest the nucleus rotundus and nasal fibers on the opposite edges of the brachia. From this point the fibers grow out over the tectal surface to their termination sites with only minimal rearrangements. Therefore the optic fiber rearrangements show evidence of several different sorts of constraints acting on the fibers at separate points in the optic pathway, each contributing to the final orderly arrangement of the fibers on the optic tectum.

Spatial distribution of catecholaminergic cells in the fish retina

The cell density, distribution pattern, and morphology of catecholaminergic (CA) cells have been studied by fluorescence microscopy of retinal flat-mounted preparations from various species of fresh water, estuary, and marine is lowest in the central region surrounding the optic disc, slightly higher in the intermediate region, and highest in the periphery. The size of CA-cells is smaller the higher their density. Following administration of L-Dopa, dompamine, or noradrenaline, the density of CA-cells approximately doubled, due to the appearance of small fluorescent cells. CA-cells are arranged in rows along radial lines which fan out from the optic disc. In large cells of the central and intermediate regions three to five processes arise from the some and extend and ramify irregularly in the inner plexiform layer, while in small cells from the intermediate and peripheral regions two processes arise from opposite poles and extend regularly in a direction perpendicular to the rows of cells and parallel to the retinal margin. In the retina of the marine fish Holocentrus sp CA-cells are fewer in number compared to other fish studied and their processes extend without any regular pattern. In the toad their size and density are homogenous throughout the retina, and their processes show a regular arrangement.

Retinal ganglion cells in the crucian carp (Carassius carassius). I. Size and number of somata in eyes of different size

Ganglion cell somata were drawn, measured and counted in flat-mounted crucian carp and goldfish retinas stained with cresyl violet or methylene blue. Some diameter histograms suggest that the ganglion cells can be divided into two populations with overlapping soma sizes: a large group of small cells and a small group of large cells, the latter constituting 2.5-5% of all ganglion cells. With increasing distance from the optic disc the mean soma diameter increases while the ganglion cell density decreases. In a peripheral growth zone close to the margin the ganglion cells become smaller again. The total number of ganglion cells in retinas of different size was calculated from the areas of the flat-mounted preparations and the cell densities in two representative regions. In the crucian carp population used in this work the total number of ganglion cells per retina was found to increase from roughly 140,000 (mean of 8 scattered value) to a full 200,000 between eye diameters 4 and 10 mm, this increase taking place mainly between eye diameters of 4 and 6.5 mm. Thus, due to a drastically decreasing cell density, the total number of ganglion cells increases only by a factor of about 1.5 while the retinal area becomes sixfold. During the same growth period the mean soma diameter increases by a factor of about 1.3 and the soma volume more than doubles. The optic nerve of a small crunated and myelinated axons were found. The axons in the optic nerve are, on an average, considerably thicker than the axons on the retinal surface.