Rod and cone inputs to bipolar cells in goldfish retina

Spectral sensitivities of seven morphological types of photoreceptors in the retina of the turtle, Geoclemys reevesii

Spectral sensitivities of photoreceptors in the turtle (Geoclemys) retina were studied by intracellular recording, and each cell was filled with Lucifer yellow (LY). Photoreceptors were classified into seven morphological types: rod, four types of single cones, and two members of a double cone. Single cones contained one of four different oil droplets: red, pale-green, orange, and clear. Double cones consisted of two apposed cones; principal members contained yellow oil droplets, while accessory members contained no oil droplet. Spectral sensitivities recorded from these seven types of photoreceptors were classified into one type of rod and three chromatic types of cones. Rods (n = 19) showed peak sensitivity at 520 nm. Single cones containing either a red (n = 51) or a pale-green (n = 9) oil droplet were red-sensitive (lambda max at 620 nm). Single cones containing an orange oil droplet (n = 14) were green-sensitive (lambda max at 540 nm). Single cones containing a clear oil droplet (n = 3) were blue-sensitive (lambda max at 460 nm). Both members of the double cone, principal (n = 22) and accessory (n = 15), were red-sensitive (lambda max at 620 nm). No diffusion of LY was detected between the apposed members of double cones. Red-sensitive cones, therefore, consisted of four different morphological types of cones, and they occupy about 70% of the photoreceptor mosaic in the turtle retina.

Reexamination of photoreceptor-bipolar connectivity patterns in carp retina: HRP-EM and Golgi-EM studies

On- and off-center bipolar cells were identified in the carp retina by means of intracellular recording, intracellular injection of HRP, and Golgi silver-chromate impregnation. Light and electron microscopy revealed that these functionally different bipolar cells make synaptic contacts with both rods and cones, and that both on- and off-center cells can be further divided into two subtypes (I and II) according to the relationship between the position of their dendritic processes and the synaptic ribbons in the photoreceptor terminal. The type I on-center bipolar cell is characterized by a large cell body, a thick primary dendrite, and a big swelling of the axon terminal in the innermost part of the inner plexiform layer (IPL). Dendritic processes of this cell type make predominantly ribbon contacts with rods and nonribbon contacts with cones. The type II on-center cell, having a large dendritic tree in the outer plexiform layer and a large ramification of the axon terminal extending over the inner part of the IPL makes mostly nonribbon contacts with rods and cones. Many of these type II cell processes, however, terminate very close to cone synaptic ribbons. The type I off-center cell shows two varieties in the axon terminal structure; a large terminal swelling or a large flat ramification of the terminal in the outermost part of the IPL. These cells make predominantly ribbon contacts with rods and cones. Usually, but not always, the process of a type I off-center cell runs parallel to the synaptic ridge apex of cones. The type II off-center cell, showing a large ramification of the axon terminal extending over the outer half of the IPL, makes mainly nonribbon contacts with rods and cones. The results from the HRP-EM study generally agree with those from the Golgi-EM study. A few discrepancies between the results obtained with these two techniques are noted and their implication is discussed.

Synaptic organization of substance P-like immunoreactive amacrine cells in goldfish retina

A class of amacrine cells in the goldfish retina displays substance P-like immunoreactivity (SPIR). We studied the synaptic organization of SPIR amacrine cells by electron microscopical immunocytochemistry. Amacrine cells showing SPIR have processes which ramify in a very narrow band in layer 3 of the inner plexiform layer. SPIR is restricted to large dense-cored vesicles (DCVs), which are distributed throughout the dendrites. Processes labeled with SPIR contain a mixture of DCVs and numerous small agranular vesicles. Of 88 synaptic contracts analyzed, SPIR processes occurred as the presynaptic element 57 times and as the postsynaptic element 31 times. SPIR processes made synapses upon amacrine and ganglion cell dendrites with equal frequency and received synaptic input from both amacrine and bipolar cells. The stratification of SPIR amacrine cells in proximal sublamina a suggests that their synaptic interactions are restricted to "off" and "on-off" neurons. However, this is in contrast to published electrophysiological data. Possible explanations for this discrepancy are discussed in detail.

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.

Morphology of bipolar cells and their participation in spatial organization of the inner plexiform layer of jack mackerel retina

Morphology of bipolar cells in the jack mackerel retina [Trachurus mediterraneus ponticus (Aleev)] was investigated by the Golgi method. Eight types of bipolar cells are described. It is the first time that cells with an unbranched main dendrite are found in fish retina. It is shown that the inner plexiform layer of the jack mackerel retina contains regular lattices, located at 5 levels and conserted in a characteristic way with the cone mosaic. These lattices are formed by swellings of bipolar cell axons. It is shown that only bipolar cells with small dendritic aborizations (less than or equal to 14 micron dia) take part in this organization.

Bipolar cells in monkey retina selective for the cones likely to be blue-sensitive

Bipolar cells are a class of retinal interneurone with dendrites in the outer plexiform layer that contact photoreceptors, and axons terminating in the inner plexiform layer where they convey the centre responses of ganglion cells. In the monkey, many of whose ganglion cells respond to stimuli selective for each of the three different cones. There are five types of cone bipolar cells: flat and invaginating midget; diffuse, flat and invaginating cone; and giant, bistratified. Although many of the monkey's ganglion cells are specific for one of the three different cone mechanisms, none of the bipolar cells are known to connect to the morphologically identified counterparts of the different spectral types of cones as in teleost retina. Here, however, I describe a bipolar cell found in Golgi preparations of the rhesus monkey retina which displays an apparently selective and patterned distribution of its dendritic contacts with cone pedicles in the outer plexiform layer. The intercone spacing of dendritic contacts and their distribution match the intercone spacing and proportion of cones thought to be blue-sensitive.

Synaptic contacts between bipolar and photoreceptor cells in the retina of Callionymus lyra L

A combined light and electron microscopic study of Golgi-impregnated retinas of the marine teleost Callionymus lyra L. revealed mixed bipolar cells (M types) contacting rods and cones and pure cone bipolar cells (C types). Five types of mixed bipolar cells can be differentiated on the basis of their synaptic contacts. Two out of the five mixed bipolar cell types contact double cones, single cones, and rods (mixed, dark, pale, single [Mdps and midget-Mdps]). Their endbuds make narrow cleft junctions, with each type of photoreceptor, and in addition, two endbuds end centrally in the synaptic ribbon complexes of the dark and pale double-cone pedicles. Three types of mixed bipolar cells contact only double cones and rods. The endbuds of one type (mixed, dark, pale, ribbon [Mdpr]) end centrally in the synaptic ribbon complexes of the dark and pale double-cone pedicles as well as of the rod spherules. The endbuds of two types (Mdp and midget-Mdp) make wide cleft junctions in dark and pale double-cone pedicles and in rod spherules. All pure cone bipolar cell types contact cones exclusively with narrow cleft junctions. Four types are seen: a type that contacts predominantly pale double-cone pedicles but also a few dark double-cone pedicles (Cp), a type that is connected with dark and pale double-cone pedicles in about equal numbers (Cdp), a type that makes synaptic contacts with pale double-cone pedicles and single-cone pedicles (Cps), and a type that is connected with both types of double cones and to single-cone pedicles (Cdps). A resemblance between the ultrastructural features of mixed bipolar cell synapses in Callionymus and in Carassius auratus is noted.

Rod input to amacrine cells in dace retina

Intracellular recordings in dace retina demonstrate a type of amacrine cell whose responses to flashes of light were characteristically a transient depolarization at the onset of light, followed by a slow decay toward the dark level, similar to rod-dominated, AII amacrine cells described in cat retina. Electron microscopy of HRP-filled dace AII-like amacrine cells suggested that they receive significant rod inputs through rod-dominated bipolar cells.

Connections between photoreceptors and horseradish peroxidase-injected bipolar cells in the carp retina

We describe two physiologically and morphologically distinct types of on-center bipolar cell in the carp retina. These cells can be distinguished from one another in the following respects: (1) "type I" cells respond to moderate light intensities with a transient depolarization followed by a plateau, while the response of "type II" cells is approximately rectangular in shape; (2) latency of type II cell responses is shorter than that of type I cell responses; (3) mean diameter of type II cell dendritic fields (114 micron) is larger than that of type I cell dendritic fields (65 micron) in the outer plexiform layer; (4) mean diameter of type II cell bodies (7 micron) is smaller than that of type I cell bodies (9 micron); (5) axons of type II cells show extensive arborizations (51 micron), while those of type I cells show a single swelling with a few short collaterals (31 micron) in the proximal half of inner plexiform layer. HRP-injected on- and off-center bipolars were examined by electron microscopy. The dendrites of these bipolar cells invaginate into rod spherules and often occupy the central position of the triad. The dendrites of such bipolar cells also invaginate into cone pedicles, but in quite distinct patterns. Type I on-center bipolars do not send processes to the synaptic ribbons. In contrast, off-center bipolars and type II on-center bipolars send processes to the synaptic ribbons. The dendrites of off-center bipolars occupy the central position of the triad. Although type II on-center bipolar dendrites approach the ribbon very closely, there is usually a process from an off-center bipolar interposed between them.

Mechanisms of synaptic transmission in the retina

This paper reviews the mechanisms of transmitter release, the kinetics of synaptic transfer, the mechanisms for the production of conductance changes by transmitters, and the nature of the conductance changes at synapses in vertebrate retina. A method for the culturing of adult retinal cells is described, together with preliminary experiments on the identification of cells in culture.

Physiological and morphological identification of two types of on-center bipolar cells in the carp retina

Two types of on-center bipolar cells, rod- and cone-dominant bipolars have been identified in the dark-adapted retina of the carp by means of intracellular recordings and Lucifer-yellow dye injection. They differ physiologically and morphologically in the following respects: 1) responses of rod-dominant cells to bright lights are characterized by a transient depolarization followed by a smaller sustained depolarization, while those of cone-dominant cells are approximately rectangular; 2) the cone-dominant cells are about 1.5 log units less sensitive to light than the rod-dominant cells; 3) the latency of the response is shorter in the cone-dominant cells than in the rod-dominant cells; 4) the mean diameters of the cone-dominant cell receptive field (0.7 mm) and dendritic field (90 micrometers) are larger than those of the rod-dominant cell receptive field (0.5 mm) and dendritic field (56 micrometers); 5) the mean diameter of the cone-dominant cell soma (8 micrometers) is smaller than that of the rod-dominant cell soma (13 micrometers); and 6) the terminations of the cone-dominant cell axons form a ramification (67 micrometers mean diameter) in contrast to a big terminal swelling of the rod-dominant cell axons (37 micrometers mean diameters). At least two ionic mechanisms are responsible for generating the depolarizing response of on-center bipolar cells, one having a reversal at a positive potential and the other at a negative potential. Responses with a negative reversal potential only are obtained from some of cone-dominant cells and responses with a positive reversal potential only are obtained from some other cone-dominant cells and the rod-dominant cells. There are a large number of bipolar cells that respond by both ionic mechanisms, although the ratio between them varied considerably in different cells.

Localization of synaptic and nonsynaptic nicotinic-acetylcholine receptors in the goldfish retina

The localization of nicotinic-cholinergic receptors in the inner plexiform layer (IPL) of goldfish retina was studied by electron microscopic analysis of the binding pattern of a conjugate or horseradish peroxidase and alpha bungarotoxin (HRP-alpha BTx). Specific HRP reaction product (blockade by 1mM curare) was found at both synaptic and nonsynaptic sites. Synaptic binding sites for HRP-alpha BTx, which accounted for only 16% of the total specific reaction product sites, always involved an amacrine process as the presynaptic element, whereas amacrine, ganglion, and bipolar cells could be post-synaptic elements at labeled synapses. Only 17.5% of the total number of amacrine synapses were labeled by HRP-alpha BTx. Labeled synapses showed the same distribution in the IPL as unlabeled synapses: bimodal for amacrine-to-bipolar synapses with peak concentrations at the 20% and 80% layers and unimodal for amacrine-to-nonbipolar synapses with a peak concentration at the 60% layer. Nonsynaptic binding sites for HRP-alpha BTx (84% of total) were seen on the dendrites of ganglion, amacrine, and bipolar cells. The distribution of the nonsynaptic sites in the IPL largely accounts for the trilaminar binding pattern of 125I-alpha BTx as observed in light microscopic autoradiographs. If, as appears likely, the distribution of synapses is the relevant variable in determining the sites of neuronal interaction for a given transmitter system, then this study further illustrates the importance of distinguishing synaptic from nonsynaptic binding when using receptor-ligand probes to localize sites of chemical synaptic transmission.

Selective potentiation of retinal horizontal cell responses to L-glutamate by D-aspartate

1. L-Glutamate and L-aspartate depolarize type H1 horizontal cells in the isolated retina of goldfish, but only at millimolar concentrations. 2. When applied in the presence of D-aspartate, L-glutamate depolarizes H1 cells at concentrations nearly 15-fold lower than when it is applied alone. The effects of L-aspartate were not potentiated by either D-aspartate or D-glutamate. 3. Since D-aspartate seems also to enhance the effect of the transmitter released by cone photoreceptors, these results are consistent with the possibility that L-glutamate is a neurotransmitter of cones.

Spatial organization of neurochemically classified interneurons of the goldfish retina-I. Local patterns

Certain interneurons in the goldfish retina are uniquely specifiable by their abilities to take up exogenously supplied [3H]gamma-aminobutyric acid (GABA), [3H]glycine, [3H]dopamine of [3H]serotonin al low micromolar concentrations. Each ligand labels one or two unique populations of interneurons yielding six cell types characterized by soma location, soma size, level and form of dendritic arborization, and local spatial patterning. This report summarizes these qualitative features and provides quantitative evidence on the size and spatial distributions of : (1) GABA-ergic horizontal cells, (2) GABA-ergic amacrine cells, (3) glycinergic amacrine cells; (4) glycinergic interplexiform cells; (5) dopaminergic interplexiform cells; and (6) indoleaminergic amacrine cells.

Ionic mechanisms of two types of on-center bipolar cells in the carp retina. II. The responses to annular illumination

On-center bipolar cells in the dark-adapted carp retina were divided into four types (A, B, C, and D) on the basis of response wave forms, spectral response properties, and electrical membrane properties. Type A and B cells responded to a spot of light with a transient depolarization followed by a plateau, whereas the response of type C and D cells were approximately rectangular in shape. The center and surround responses of type A cells had maximum spectral response of approximately 525 nm in the lower mesopic range; the polarity of both responses was reversed at positive membrane potentials as the membrane was depolarized by extrinsic current. The center and surround responses of type D cells had a maximum spectral response of approximately 625 nm in the mesopic or photopic range; the polarity of both responses was reversed at membrane potentials that were more negative than those at the dark level. The results suggest that the center and surround responses mediated by rods are generated by changes in sodium conductance, but in opposite ways; whereas those mediated by red cones are generated by changes in potassium and/or chloride conductances. In type B and C cells, which probably receive inputs from both rods and/or green cones as well as red cones, the center responses were composed of the two ionic mechanisms described above. The surround responses of many type B and C cells were dominated by only one ionic mechanism with a negative reversal potential, but in some type B cells the surround responses were resulted from two ionic mechanisms similar to those of the center responses.