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B B Boycott

Publications and source records attributed to B B Boycott.

At least 19 recordsLinked to original sources
PubMed1995

Synapses between cones and diffuse bipolar cells of a primate retina.

The photoreceptor synapses of three representative cells of the six types of diffuse bipolar cell of the rhesus macaque monkey's retina are described at 3.5-4.0 mm eccentricity. Bipolar cell DB3 was found to be postsynaptic to 11 cones at 155 basal synapses; about 70% of these were triad associated. Bipolar cell DB4 as postsynaptic to eight cones at 52 ribbon synapses; in addition it was found also to make an average of two or three basal (non-ribbon) synapses per cone (total 23). The DB5 bipolar cell type had 57 invaginating synapses with seven cones. It too had basal synapses, but only two with each of three cones. The diffuse invaginating bipolar cell described by Mariani (1981) is identified as a member of the DB5 category. Dendrites of cone bipolar cell types which have axons ending in the a-layer of the inner plexiform layer make only basal synapses with the cone pedicle. Those so far investigated are the flat midget bipolar cell and the DB2 and DB3 flat diffuse bipolar cells. All bipolar cells whose axons terminate in the b-layer of the inner plexiform layer are postsynaptic at the ribbon synapses of the cone pedicles. They now appear to fall into two groups. Those whose dendrites are exclusively postsynaptic at the ribbons; these are the blue cone and invaginating midget bipolar cells. And the diffuse bipolar cell DB4, that has both ribbon and basal synapses in a ratio of about 2.3:1. It is uncertain into which category cell DB5 should be placed; its basal synapses are so few the cell could be anomalous. It now seems that at least one primate bipolar cell type may be like those of other vertebrates in having, as defined ultrastructurally, two different kinds of synaptic connection with its cones. The results are discussed in the context of a brief review of the photoreceptor synapses of other mammalian bipolar cells.

Animals↗
PubMed1995

Expression of neurofilament proteins by horizontal cells in the rabbit retina varies with retinal location.

Classical neurofibrillar staining methods and immunocytochemistry with antibodies to the light, medium and heavy chain subunits of the neurofilament triplet have been used for in situ and in vitro investigation of the organization of neurofilaments in A- and B-type horizontal cells of the adult rabbit retina. Surprisingly, their expression and organization within a cell is dependent on its location along the dorso-ventral axis of the retina. A-type horizontal cells in superior retina consistently stained with a wide variety of neurofibrillar methods to reveal neurofibrillar bundles, which immunocytochemistry showed to contain all three neurofilament subunits. A-type horizontal cells in inferior retina were uniformly refractory to neurofibrillar staining, although they expressed all three subunits. However, there was less of the light and medium subunits; the organization of the filaments into bundles (neurofibrils) is minimal. B-type horizontal cells could not be stained with any neurofibrillar method and were not recognizable by in situ immunocytochemistry. However, B-type cells could be seen to express all three subunits in vitro, but the expression of the light and medium subunits was weak. There was only a slight difference between B-type cells taken from superior and inferior retina. Combined with the results of recent transfection studies, these findings suggest that the amount of the light neurofilament subunit present in a horizontal cell determines its content of neurofibrillar bundles, and that rabbit horizontal cells may contain more neurofilament protein, particularly of the heavy subunit, than is used for neurofilament formation.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1994

Immunocytochemical characterization and spatial distribution of midget bipolar cells in the macaque monkey retina.

Midget bipolar cells form the first distinct step in the parvocellular (P-) pathway of the primate visual system, and are the major determinant of the receptive field properties of colour selective midget ganglion cells. This paper describes the sampling properties of the midget bipolar cell population and relates this to the processing of chromatic information in the P-pathway. Immunocytochemical markers were used to label midget bipolar cells so that their spatial density could be compared with that of cones and ganglion cells. Sections through macaque monkey retinae were immunostained with antibodies against cholecystokinin (CCK), and recoverin. In CCK-labelled sections, in addition to blue cone bipolar cells, numerous thin bipolar cell dendrites, which could be associated with individual cone pedicles are stained. CCK-immunoreactive midget bipolar cells are found throughout the retina. A different population of midget bipolar cells is revealed in recoverin-labelled sections. Based on a comparison with midget bipolar cells in Golgi-stained retinae we propose that ON-midget (invaginating) bipolars are immunoreactive for CCK and confirm that OFF-midget (flat) bipolar cells are immunoreactive for recoverin [Milam, Dacey and Dizhoor (1993) Visual Neuroscience, 10, 1-12]. The density of recoverin labelled midget bipolars matches the cone density to an eccentricity of about 10 mm; from there outwards it drops to 60% of the cone density. This suggests convergence of several cones to individual midget bipolar cells in peripheral retina. We conclude that midget bipolar cells are present throughout the entire primate retina, and could, in peripheral as well as in central retina, provide chromatically specific input to the P-pathway.

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PubMed1993

Cone synapses of a flat diffuse cone bipolar cell in the primate retina.

A Golgi-stained flat diffuse cone bipolar cell from a vervet monkey's retina (Cercopithecus aethiops), contacting six cones, was serially sectioned for electron microscopy (EM) to determine the types of synapses it made with the cone pedicles. All the synapses were basal (flat) contacts. Their distribution and ultrastructural type were similar at each pedicle. Approximately half the synapses were definable as triad-associated and the rest were elsewhere on the cone pedicle base. Their ultrastructure is the same regardless of those positions. About 25 synapses were made with each cone. Thus this type (DB2 of Boycott & Wässle, 1991) of flat diffuse cone bipolar cell is in contact with six cones through about 150 synapses. At the eccentricity studied each cone pedicle probably makes 90-100 basal synapses with between three and four DB2 bipolar cells. This is between two and three times the number that are made with all the types of invaginating bipolar cells. A brief review of cone photoreceptor synapses with bipolar cells shows that, for those so far examined in the primate retina, the dichotomy into two types of bipolar cell invaginating (ribbon-related), with axons ending in the b-layer of the inner plexiform layer (IPL) (hence presumptive On-bipolars) and flat (basal synapses), with axons ending in the a-layer of the inner plexiform layer (hence presumptive Off-bipolars) is the rule. But other vertebrate retinae, including that of the cat, also have bipolar cells which vary from this pattern.

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PubMed1993

Parasol (P alpha) ganglion-cells of the primate fovea: immunocytochemical staining with antibodies against GABAA-receptors.

Retinae of macaque monkeys were immuno-stained with antibodies against GABAA-receptors. In peripheral retina most ganglion cells were immunoreactive. In central retina, around the fovea, staining in the ganglion cell layer was selective and only 5-8% of all ganglion cells were labelled: these had the largest cell bodies and their dendrites occupied a broad stratum in the middle of the inner plexiform layer. From comparison with Golgi-stained ganglion cells it is concluded that the entire population of parasol (P alpha)-cells at the fovea was labelled. The mosaic and sampling properties of parasol cells were determined by combining dendritic field measurements of Golgi-stained cells with their density when immuno-stained. There is convergence of 30-50 cones onto each foveal parasol ganglion cell. The dendritic fields of both ON- and OFF-parasol cells provide complete retinal coverage. The Nyquist limits of their mosaics are 4 min of arc.

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PubMed1992

Synaptic contacts of a two-cone flat bipolar cell in a primate retina.

The Golgi-stained dendrites of a two-cone bipolar cell of a vervet monkey were serially sectioned for electron microscopy and shown to make basal synapses with two neighboring cones. The synapses were all on the cone pedicle membrane adjacent to the bipolar processes invaginating to form the triads. This is the characteristic position for flat midget bipolar cells. The numbers of triads in nine adjacent cone pedicles were not significantly different from those in the cones contacted by the bipolar. Based on this measure the two-cone bipolar does not contact a special population of cones. The advantages and disadvantages of using vertical or horizontal sections for the determination by electron microscopy of the connectivity of the dendrites of Golgi-stained flat bipolar cells are discussed.

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PubMed1990

Retinal ganglion cell density and cortical magnification factor in the primate.

The question of whether the large area occupied by the primate fovea in the visual cortex (V1) is the result of a selective amplification of the central visual field, or whether it merely reflects the ganglion cell density of the retina, has been a subject of debate for many years. Measurements of the ganglion cell densities are made difficult by lateral displacements of cells around the fovea and the occurrence of amacrine cells in the ganglion cell layer. We have now identified and counted these amacrine cells by GABA immunocytochemistry and by retrograde degeneration of ganglion cells. By reconstructing the fovea from vertical and horizontal serial sections, we were able to measure the densities of cones, cone pedicles and ganglion cells within the same retina. We found 3-4 ganglion cells for every foveal cone. This ratio decreased to one ganglion cell per cone at an eccentricity of 15-20 deg (3-4 mm) and in peripheral retina there are more cones than ganglion cells. The ganglion cell density changes by a factor of 1000-4000 between peripheral and central retina. A comparable gradient has been reported for the representation of the peripheral and central visual field in V1. We suggest that ganglion cell density can fully account for the cortical magnification factor and there is no need to postulate a selective amplification of the foveal representation.

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PubMed1989

Cortical magnification factor and the ganglion cell density of the primate retina.

It has long been contentious whether the large representation of the fovea in the primate visual cortex (V1) indicates a selective magnification of this part of the retina, or whether it merely reflects the density of retinal ganglion cells. The measurement of the retinal ganglion-cell density is complicated by lateral displacements of cells around the fovea and the presence of displaced amacrine cells in the ganglion cell layer. We have now identified displaced amacrine cells by GABA immunohistochemistry and by retrograde degeneration of ganglion cells. By reconstructing the fovea from serial sections, we were able to compare the densities of cones, cone pedicles and ganglion cells; in this way we found that there are more than three ganglion cells per foveal cone. Between the central and the peripheral retina, the ganglion cell density changes by a factor of 1,000-2,000, which is within the range of estimates of the cortical magnification factor. There is therefore no need to postulate a selective magnification of the fovea in the geniculate and/or the visual cortex.

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PubMed1988

Neurofibrillar long-range amacrine cells in mammalian retinae.

A distinct population of wide-field, unistratified amacrine cells are shown to be selectively stained by using neurofibrillar methods in rabbit and cat retinae. Their cell bodies may be located in the inner nuclear, inner plexiform or ganglion cell layers and they branch predominantly in stratum 2 of the inner plexiform layer. Characteristically, each cell has two or more long-range distal processes which extend for 2-3 mm beyond a more symmetrical, proximal dendritic field of 0.6-0.8 mm diameter. Although the neurofibrillar long-range amacrines account for less than 1 amacrine in 500, they achieve effective coverage of the retina by both the proximal and distal dendrites.

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PubMed1987

Alpha ganglion cells in the rabbit retina.

In the rabbit retina a distinctive morphological class of large ganglion cells was demonstrated by a combination of intracellular staining with Lucifer Yellow and the quantification of reduced silver-stained preparations. The class is called alpha because of the qualitative and quantitative resemblance to the alpha cells of the cat's retina. Rabbit alpha cells change their size with location on the retina. In the high ganglion cell density region of the visual streak, their somata are about 15 micron in diameter, and their dendritic fields have diameters as small as 180-220 micron. The largest alpha cells in the inferior periphery have soma diameters of 30 micron and dendritic field diameters of 960 micron. There is a considerable scatter of sizes at any retinal location. Alpha cell density changes from about 55/mm2 in the streak to about 3/mm2 in far periphery, and the cells make up 1-1.4% of the ganglion cell population. Dendritic trees stratify in either an inner or an outer sublamina of the inner plexiform layer, suggesting an on/off dichotomy in the response to light. Each of the inner and outer branching subtypes is distributed in a regular mosaic, and the dendritic trees cover the retina completely and economically. The possibility is discussed that the alpha cells are the brisk transient/Y cells of physiology.

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PubMed1987

Alpha ganglion cells in mammalian retinae.

Retinae from species of six orders of mammals (table 1) were processed by an on-the-slide neurofibrillar staining method to establish whether alpha-type ganglion cells are generally present in placental mammals. Alpha cells of the domestic cat, where they were first defined as a type, are used as a standard of reference. Alpha cells were found in all the twenty species examined; characteristically they have the largest somata and large dendritic fields with a typical branching pattern. In keeping with the common morphology there are inner and outer stratifying subpopulations and therefore a presumptive 'on-centre' and 'off-centre' responsiveness to light. Depending on the species, alpha cells form between 1 and 4% of the ganglion-cell population and their dendritic fields cover the retina three to four times. The morphology of alpha ganglion cells, and many of their quantitative features, are conserved in mammals coming from different habitats and having a wide variety of behaviours. Because it is known different habitats and having a wide variety of behaviours. Because it is known from the cat that alpha ganglion cells have brisk-transient or Y receptive fields it is possible that all placental mammals possess this physiological system.

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PubMed1987

Cone connections of the horizontal cells of the rhesus monkey's retina.

The presence in the rhesus monkey's retina of a second morphological type of horizontal cell (H2), described by Kolb et al. (1980), is confirmed. Both types of cell are here further described. Their cone connections are quantified and compared with those of mammals and other vertebrates. The dendrites and axons of the H2 type of cell contact only cones as do the dendrites of the H1 cell (originally described by Polyak (1941)) which has an axon contacting only rods. The dendrites of foveal H2 cells contact between 11 and 14 cones; those of H1 contact 7. The number of cones that each type of cell contacts increases with increasing distance from the fovea, so that, by 5-6 mm eccentricity, H2-type cells synapse with between 20 and 30 cones, and the H1 cells with 12-15. The qualitatively estimated coverage factors of each are 3 or 4; every cone synapses with more than one of both types. Neither type of horizontal cell makes chromatically specific connections that are anatomically recognizable, unlike the situation in some teleostean and turtle retinae. Individual horizontal cells, particularly those connected to foveal cones, may have different ratios of chromatic input. At equivalent eccentricities, up to about 6 mm from the fovea, the dendritic fields of H2 horizontal cells are about twice the size of H1 cells and contact about twice the number of cones. These relative differences are closely similar to those of the cat's horizontal cells and it is suggested that they are a basic feature of most placental mammals. The organization of foveal cone fibres within Henle's layer is described. The distribution of primate cone telodendria, gap junctions and synapses in the outer plexiform layer are briefly reviewed and compared with those of other vertebrate retinae.

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PubMed1984

A neurofibrillar method stains solitary (primary) cilia in the mammalian retina: their distribution and age-related changes.

Richardson's reduced silver method, developed for the staining of autonomic nerve fibres in the mammalian intestine, is shown consistently to stain solitary (primary) cilia and diplosomes of the cells of the retinae of cats and rabbits. The cilia comprise a centriole, a basal body and an axoneme with a 9 + 0 complement of microtubules. Probably all retinal cells possess a cilium during their development but, contrary to previous reports, not all retain the axoneme after birth. Axonemes are absent from horizontal, bipolar, microglia, Müllerian, and probably some other glial, cells; all of which showed paired centrioles (diplosomes) after staining. Photoreceptor, amacrine, interplexiform, displaced amacrine and ganglion cells have each one cilium. These differences between cell types persist, without significant change, in the retina of adult rabbits up to the age of 2 years, and in the cat up to 5 years. The alpha-type ganglion cells of the cat are an exception. In 4 to 8-week-old kittens they are all ciliated, like other types of ganglion cells. But by two years about 30% of central area alpha-cells lack an axoneme. Individual cells may have only diplosomes, unusual dispositions of the centrioles in the perikaryal cytoplasm, or even show complete loss of the whole ciliary apparatus. By 5 years of age the proportion of those alpha-cells showing unusual arrangements has increased to approximately 70%, while less than 5% of the other types of ganglion cells are so affected. Cilia of peripheral alpha-cells change at a different rate and by 5 years of age are approximately like the 2-year-old central area population.

Aging↗
PubMed1983

A spatial analysis of on- and off-ganglion cells in the cat retina.

Using reduced silver staining methods it was possible to stain all alpha-ganglion cells of the cat retina. The dendritic trees of alpha-cells are unistratified in either of two laminae within the inner plexiform layer. This stratification difference was shown physiologically to correspond to the on-off dichotomy. For all alpha-cells recorded, the dendritic field was covered by the corresponding receptive field centre. In addition the general shape of the receptive field centre corresponded to the shape of the dendritic field. The size of the dendritic tree was always smaller than the receptive field centre. The topographical distribution of on- and off-alpha cells could be studied. They were found to occur in about equal numbers. Both on- and off-alpha-cell perikarya form a regular lattice and both lattices are superimposed independently. The dendritic branches of neighbouring alpha-cells overlap and each retinal point is covered by the dendritic field of at least one on- and one off-alpha-cell. After horseradish peroxidase (HRP) injection into the lateral geniculate nucleus all beta-cells were labelled. In this way it is shown that about 55% of all ganglion cells are beta-cells. The mosaic of on- and off-beta-cells was studied from the HRP-labelled material. It is commonly assumed that beta-cells are associated with the resolution of fine detail in the cat visual system. The mosaic of beta-cells imposes some constraints and permits some predictions to be made with respect to the cat's visual discrimination.

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