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A G Leventhal

Publications and source records attributed to A G Leventhal.

At least 37 records · Page 2Linked to original sources
PubMed1987

Ganglion cell dendritic structure and retinal topography in the rat.

The dendritic field size, the distribution of the dendrites relative to the cell body, and the overall shape of the dendritic field of type I ganglion cells in the rat retina were analyzed. These features of neuronal structure were related to the topography of the rat retina. As in the cat, the cell bodies of type I ganglion cells are arranged in a nonrandom mosaic. Previous work has demonstrated that the density of type I cells in the rat retina does not covary with the density of all ganglion cells. Type I dendritic field size varies over the retina; the increase in dendritic field size is accounted for better by the decrease in type I density than by the decrease in overall ganglion cell density. The center of the dendritic field of most type I cells is displaced in the plane of the retina from the cell body. Unlike in carnivore retina (Schall and Leventhal: J. Comp. Neurol. 257:149-159, '87), the dendritic fields in the rat are not displaced down the ganglion cell density gradient. Rather, there is a tendency for the dendritic trees, especially in temporal retina, to be displaced toward dorsal retina. Most of the dendritic fields are elongated, but the degree of elongation is less than that observed in carnivore or primate retina. Unlike in carnivore and primate retina (Leventhal and Schall: J. Comp. Neurol. 220:465-475, '83; Schall et al.: Brain Res. 368:18-23, '86), there is no relationship between dendritic tree orientation and position relative to any point on the retina in the rat.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1986

Retinal ganglion cell dendritic fields in old-world monkeys are oriented radially.

We analyzed the dendritic field morphology of 297 ganglion cells from peripheral regions of monkey retina. Most of the dendritic fields were elongated, and there was a significant tendency for the dendritic fields to be oriented radially, i.e., like the spokes of a wheel with the fovea at the hub. An overrepresentation of radial orientations in the peripheral retina of primates might explain why humans are best able to detect stimuli which are oriented radially using peripheral vision.

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PubMed1986

Retinal constraints on orientation specificity in cat visual cortex.

Most retinal ganglion cells (Levick and Thibos, 1982) and cortical cells (Leventhal, 1983; Leventhal et al., 1984) subserving peripheral vision respond best to stimuli that are oriented radially, i.e., like the spokes of a wheel with the area centralis at the hub. We have extended this work by comparing directly the distributions of orientations represented in topographically corresponding regions of retina and visual cortex. Both central and peripheral regions were studied. The relations between the orientations of neighboring ganglion cells and the manner in which the overrepresentation of radial orientations is accommodated in the functional architecture of visual cortex were also studied. Our results are based on an analysis of the orientations of the dendritic fields of 1296 ganglion cells throughout the retina and the preferred orientations of 1389 cells located in retinotopically corresponding regions of cortical areas 17, 18, and 19 in the cat. We find that horizontal and vertical orientations are overrepresented in regions of both retina and visual cortex subserving the central 5 degrees of vision. The distributions of the orientations of retinal ganglion cells and cortical cells subserving the horizontal, vertical, and diagonal meridians outside the area centralis differ significantly. The distribution of the preferred orientations of the S (simple) cells in areas 17, 18 and 19 subserving a given part of the retina corresponds to the distribution of the dendritic field orientations of the ganglion cells in that part of retina. The distribution of the preferred orientations of C (complex) cells with narrow receptive fields in area 17 but not C cells with wide receptive fields in areas 17, 18, or 19 subserving a given part of the retina matches the distribution of the orientations of the ganglion cells in that part of retina. The orientations of all of the alpha-cells in 5-9 mm2 patches of retina along the horizontal, vertical, and oblique meridians were determined. A comparison of the orientations of neighboring cells indicates that other than a mutual tendency to be oriented radially, ganglion cells with similar orientations are not clustered in the retina. Reconstructions of electrode penetrations into regions of visual cortex representing peripheral retina indicate that columns subserving radial orientations are wider than those subserving nonradial orientations. Our results provide evidence that the distribution of the preferred orientations of simple cells in visual cortex subserving any region of the visual field matches the distribution of the orientations of the ganglion cells subserving the same region of the visual field.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1985

Morphology, central projections, and dendritic field orientation of retinal ganglion cells in the ferret.

Retinal ganglion cells were studied in pigmented ferrets that received small electrophoretic injections of horseradish peroxidase (HRP) into the dorsal lateral geniculate nucleus (LGNd) or optic tract. Ferret retina contains a number of types of retinal ganglion cells of which the relative cell body sizes, dendritic field structures, and central projections correspond closely to those of retinal ganglion cell types in the cat. Ferret retina contains about the same proportion of alphalike cells, a lower proportion of betalike cells, and thus a high proportion of other types of ganglion cells than cat retina. Ferret retina has a visual streak and somewhat weaker area centralis than cat retina. Changes in ganglion cell morphology associated with eccentricity are less pronounced in the ferret than in the cat. The adult ferret retina is about 12.5 mm in diameter, and the nasotemporal division is about 2.7 mm from the temporal margin. Interestingly, virtually all alpha cells in the pigmented ferrets studied projected contralaterally. Studies of infant ferrets indicate that 4 days after birth (P4) the area of ferret retina is 25% that of the adult. The neonatal ferret retina contains numerous small, densely packed cells in the presumptive ganglion cell layer. At P4 these cells appear to be uniformly distributed across the retina. The area centralis and visual streak are not obvious as late as 8 days after birth.

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PubMed1985

Abnormal visual pathways in normally pigmented cats that are heterozygous for albinism.

The various forms of albinism affect about one in 10,000 births in the United States. An additional 1 to 2 percent of the population has normal pigmentation but is heterozygous and carries a recessive allele for albinism. The retinogeniculocortical pathways were studied in normally pigmented cats that carry a recessive allele for albinism. The cats exhibited abnormalities in their visual pathways similar to those present in homozygous albinos. These results imply that visual anomalies like those found in albinos may be present in 1 to 2 percent of the human population.

Albinism↗
PubMed1985

Central projections of cat retinal ganglion cells.

The central projections of different groups of cat retinal ganglion cells were studied following small iontophoretic injections of horseradish peroxidase (HRP) into physiologically characterized sites. Analysis was restricted to labeled cells in the upper periphery of the nasal retina, contralateral to the injection site. Injections were made to the A lamina and C lamina of the dorsal lateral geniculate nucleus (LGNd-A,C), the geniculate wing (LGNd-W), the ventral lateral geniculate nucleus (LGNv), the pretectum (PT), and the superior colliculus (SC). The dendritic fields of alpha, beta, and epsilon cells were well labeled by the procedures we employed. A group, termed "g1," had somal sizes within the range of the smaller beta and epsilon cells, but dendritic morphologies distinct from either class. The g1 group may consist of a number of types, but our material provided no basis for further distinguishing them. Many cells were observed that had smaller somas; all had thin axons, and few had dendritic fields that labeled to any significant extent. We were not able to further distinguish these cells, and refer to this group, which may include a number of types, as "g2" cells. From the peripheral nasal retina, alpha cells project to LGNd-A, LGNd-C, PT, and SC. Beta cells project to LGNd-A, LGNd-C, and PT. Epsilon and g1 cells project to the LGNd-C, LGNd-W, LGNv, PT, and SC. We determined the total spatial density of cells in the region of the retina analyzed, using a Nissl-stained preparation. We then estimated the relative fraction of cells in each of the above groupings by injecting HRP throughout a cross section of the optic tract. Multiplying this relative fraction by the total spatial density gave an estimate of the spatial density of each of these groupings. From the spatial density of cells labeled from the injection site, we were able to estimate the fraction of cells of each retinal grouping that project to each of the zones investigated. By these calculations, almost all alpha cells from the upper nasal retina project to LGNd-A and LGNd-C; most project to SC, and about a third to PT. Beta cells, by contrast, project almost exclusively to LGNd-A, with about 10% going to LGNd-C, and about 1% to the PT. The great majority of epsilon cells, if not all, project to LGNd-W, and up to half of this population also project to the other zones noted above.(ABSTRACT TRUNCATED AT 400 WORDS)

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PubMed1985

Retinal projections and functional architecture of cortical areas 17 and 18 in the tyrosinase-negative albino cat.

The visual field representation and functional architecture of cortical areas 17 and 18 in albino cats were studied. In the same animals the distributions of ipsilaterally and contralaterally projecting retinal ganglion cells were determined by injecting horseradish peroxidase into the dorsal lateral geniculate nucleus or optic tract. All cats were tyrosinase-negative albinos (cc), not deaf white cats (W). The proportion of ipsilaterally projecting ganglion cells in the temporal retina of the albino cat was found to be much smaller than in the normal cat or in the Siamese cat. In the albino cat less than 5% of ganglion cells in temporal retina project ipsilaterally. Recordings from areas 17 and 18 provided evidence of a substantial representation of the ipsilateral hemifield in albino visual cortex; cells representing the contralateral and ipsilateral hemifields were often segregated into alternating zones in area 17 and were always segregated in area 18. Cells recorded at the borders of zones representing the ipsilateral and contralateral hemifields often had abnormal properties. Some border cells had two receptive fields separated by as much as 60 degrees of azimuth; one field subserved the contralateral hemifield (contralateral nasal retina) and the other subserved the mirror-symmetric part of ipsilateral hemifield (contralateral temporal retina). Receptive fields of cells subserving the two hemifields did not differ in size. The preferred orientations, preferred velocities, and other characteristics of the two fields were approximately the same; preferred orientation changed gradually and systematically across the borders of zones representing the two hemifields. Our results indicate that afferents representing nasal and temporal regions of retina of the same eye can segregate and form "hemiretina" domains in albino visual cortex. These afferents can also converge upon individual cortical cells in a fashion reminiscent of convergence of afferents from the two eyes upon binocular cells in the normal cortex. The organization of albino visual cortex is therefore different from the organization of Siamese visual cortex. This may be because, in the albino cat but not the Siamese cat, nearly all cells in temporal retina project contralaterally; afferents representing contralateral temporal retina are not at a significant competitive disadvantage in the albino.

Albinism↗
PubMed1984

Relationship between preferred orientation and receptive field position of neurons in extrastriate cortex (area 19) in the cat.

Orientation sensitivity is a characteristic of most retinal ganglion cells (Levick and Thibos, '82), most relay cells in the dorsal lateral geniculate nucleus (Vidyasagar and Urbas, '82), and most neurons in the visual cortex (Hubel and Wiesel, '62) in the cat. In the retina there is a systematic relationship between receptive field position (polar angle) and preferred orientation. Outside of the area centralis most retinal ganglion cells respond best to stimuli oriented radially, i.e., oriented parallel to the line connecting their receptive fields to the area centralis (Levick and Thibos, '82). This relationship is strongest along the horizontal meridian (the visual streak) and appears to reflect the innate, radial orientation of retinal ganglion cell dendritic fields (Leventhal and Schall, '83). A relationship between preferred orientation and polar angle also exists in cat striate cortex; outside of the area centralis representation most cells respond best to lines oriented radially. This relationship is strongest for S-type cells, the most orientation-selective cells, and cells in regions representing the horizontal meridian (Leventhal, '83). To determine if similar relationships exist in cat extrastriate cortex, the preferred orientations and receptive field positions of 226 neurons in area 19 were studied. We find that, as in area 17, most area 19 cells outside of the representation of the area centralis respond best to lines oriented radially; this relationship is strongest for the cells having the narrowest receptive fields and in regions subserving the horizontal meridian. Unlike in striate cortex, in area 19 the relationship between preferred orientation and polar angle is not dependent upon cell type (S or C) or to the degree of orientation sensitivity exhibited. Also, in area 19, but not in area 17, the relationship between preferred orientation and polar angle fails for the cells having the widest receptive fields.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1983

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.

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PubMed1983

Relationship between preferred orientation and receptive field position of neurons in cat striate cortex.

It has been known for two decades that neurons in mammalian visual cortex respond selectively to stimuli falling on the retina at a particular angular orientation (Hubel and Wiesel, '62). Recent evidence suggests that most cat retinal ganglion cells (Levick and Thibos, '82) and relay cells (Vidyasagar and Urbas, '82) in the cat's dorsal lateral geniculate nucleus are also orientation selective. In the retina there is a systematic relationship between receptive field position (polar angle) and preferred orientation. Outside of the area centralis, most retinal ganglion cells have oriented dendritic fields (Leventhal and Schall, '83) and respond best to stimuli oriented radially, i.e., oriented parallel to the line connecting their receptive fields to the area centralis (Levick an Thibos, '82). This relationship is strongest close to the horizontal meridian (the visual streak) of the retina (Leventhal and Schall, '83). To determine if a relationship between preferred orientation and polar angle exists in visual cortex, the preferred orientations and receptive field positions of 768 striate cortical neurons were studied. As in the retina, a systematic relationship exists between preferred orientation and visual field position in area 17. In parts of striate cortex 15--80 degrees from the area centralis projection there is a strong tendency for cells to respond best to lines oriented radially. In regions 4--15 degrees from the area centralis projection this relationship appears weaker. In regions subserving the central 4 degrees of visual angle no such relationship exists. Throughout area 17 the relationship between preferred orientation and polar angle is strongest in regions subserving the horizontal meridian.(ABSTRACT TRUNCATED AT 250 WORDS)

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PubMed1983

Effects of visual deprivation upon the geniculocortical W-cell pathway in the cat: area 19 and its afferent input.

We studied the receptive field properties of 206 single units in area 19 of normal cats and 228 single units in area 19 of cats deprived of vision for 9-14 months by monocular lid suture. The ocular dominance of a sample of cells in area 17 of normal cats was studied for comparison. In some of these monocularly deprived animals, we also studied the sizes of relay cells in the parvocellular C laminae of the dorsal lateral geniculate nucleus labeled by electrophoretic injections of horseradish peroxidase into area 19. In area 19 of normal cats, the large majority of cells, regardless of their laminar location and the retinal eccentricity of their receptive fields, were binocular. Most responded equally well to the two eyes. In area 17, (see also Leventhal and Hirsch, '78, '80) but not in area 19, the cells which had the narrowest receptive fields tended to be activated unequally by the two eyes. In area 19 of monocularly deprived cats, virtually all cells (97%), regardless of their laminar location and receptive field eccentricity, responded only to stimulation of the normal eye. Thus, the effects of monocular deprivation upon area 19 are apparently more severe than those reported for area 17. In area 17 significant numbers of neurons in layer 4 can be activated by the deprived eye (Shatz and Stryker, '78). Within the limits of our technique, measurements of relay cells in the parvocellular C laminae labeled by injections into area 19 of deprived cats indicated that cell size in the deprived C laminae was unaffected by the deprivation. In contrast, cells in the deprived A laminae of these cats were severely shrunken. These findings suggest that the types of relay found in the parvocellular C laminae (referred to collectively as W-cells) are not affected by visual deprivation as severely as are the X- and Y-cells in the A laminae. Since laminar location and receptive field width are related to binocularity in area 17 but not in area 19 and the sizes of relay cells in the parvocellular C laminae (see also Hickey, '80) are not seriously affected by monocular deprivation, it is suggested that binocular interactions in area 19 are mainly determined by connections among cortical cells.

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PubMed1983

Effects of exposure to lines of one or two orientations on different cell types in striate cortex of cat.

We raised cats using goggles to control early visual exposure (stripe-rearing). Four conditions were used: (a), both eyes exposed to 0 degrees lines, (b), both eyes exposed to 90 degree lines, (c), one eye exposed to 45 degree lines, the other to 135 degree lines, (d), one eye exposed to 0 degree lines, the other to 90 degree lines. At the completion of the rearing, we recorded extracellularly from single cells in striate cortex (area 17) of these animals; circular statistics were used to analyse the distribution of the orientation preferences of neurones recorded. Exposure to either one or two stimulus orientations produced a significant bias in the distribution of the orientation preferences of cells recorded. We found no more non-selective cells in cats exposed to one orientation (15%) than in cats exposed to two orientations (14%). We found about the same mean proportion of binocular cells in cats exposed to one orientation (27%) as in cats exposed to two orientations (24%). Cells were comparable in orientation selectivity in cats exposed to one orientation (mean half-width at half-height = 37 degrees) and in cats exposed to two orientations (mean half-width at half-height = 34 degrees). The effects of the rearing depended upon the receptive field properties of the cells. For cells with narrow receptive fields and low cut-off velocities, the rearing produced no bias in the distribution of the orientation preferences; for all other groups of cells the rearing produced a bias toward the exposed orientation. In addition, the cells with narrow receptive fields and low cut-off velocities were more finely tuned for orientation than the remaining cells. We conclude that there are cell types in the striate cortex of the cat which differ in their susceptibility to the effects of stripe-rearing; these cell types can be discriminated on the basis of their physiological characteristics. We can compare these cell types with morphologically identified cell types that also differ in their susceptibility to the effects of stripe-rearing.

Animals↗
PubMed1982

Morphology and distribution of retinal ganglion cells projecting to different layers of the dorsal lateral geniculate nucleus in normal and Siamese cats.

Electrophoretic injections of horseradish peroxidase were made into physiologically characterized sites within the different layers of the dorsal lateral geniculate nuclei (LGNd) of normal and Siamese cats. The histochemical procedures used stained the cell bodies, dendrites, and axons of retrogradely labeled ganglion cells. In both normal and Siamese cats, only alpha and beta ganglion cells are labeled by injections restricted to the A laminae. In normal cats, the alpha/beta ratios (number of labeled alpha cells/number of labeled alpha + beta cells) resulting from injections into lamina A increase from about 0.045 at 0.5 mm from the area centralis to about 0.12 in the far periphery. The alpha/beta ratios observed outside of the area centralis in normal cats following injections into different parts of lamina A1 were lower at each eccentricity than those resulting from injections into corresponding parts of lamina A. Also, the cell bodies and dendritic fields of alpha and beta cells projecting to lamina A1 are somewhat larger than those projecting to corresponding parts of lamina A. Outside of the area centralis, the relative numbers of alpha and beta cells projecting to Siamese lamina A are normal. However, alpha cells comprise an abnormally small proportion of ganglion cells projecting to the normal segments of Siamese lamina A1 and an abnormally large proportion of cells projecting to the abnormal segments of lamina A1. In Siamese cats, alpha and beta cells projecting to lamina A1 are distributed continuously throughout virtually all of the ipsilateral and contralateral temporal retinas. Since large parts of the ipsilateral and contralateral hemifields are not represented in Siamese lamina A1, it seems that some of the retinal afferents to this lamina are being suppressed. Injections into the C laminae of the LGNd show that the same morphological classes of ganglion cells project to these laminae in normal and Siamese cats. The classes projecting to the contralateral as C laminae (laminae C and C2) include alpha, beta, gamma, and epsilon as well as two other groups of cells referred to g1 and g2 cells, gamma, epsilon, g1, and g2 cells project to the ipsilateral C lamina (lamina C1). In siamese, but not in normal cats, examples of all of these types are found far into the contralateral temporal retina following injections involving lamina C1. This indicates that all classes projecting to the ipsilateral C lamina misproject in Siamese cats.

Animals↗
PubMed1982

Retinal projections in tyrosinase-negative albino cats.

Retinal projections were examined in two tyrosinase-negative albino cats using autoradiographic techniques. Cats from this colony have pink eyes; their retinal pigment epithelium, ciliary body, and iris epithelium are completely devoid of melanin pigment. Test breeding for five generations indicates that these cats are true albinos (cc). The most striking feature of the albino cats' visual pathways was a reduction in ipsilateral input which was more severe than that reported for Siamese cats. The only evidence of ipsilateral input to the laminated dorsal lateral geniculate nucleus of the albino was a small lateral normal segment and a small projection to the lateral portion of lamina C1. Ipsilateral projections to the medial interlaminar nucleus, retinal recipient zone of the pulvinar complex, ventral lateral geniculate nucleus, superior colliculus, and pretectum also were reduced. Ipsilateral projections to the suprachiasmatic nucleus appeared to be normal in the albino cats studied. Our findings indicate that, compared to the normal cat as well as to the tyrosine-positive Siamese cat, the tyrosinase-negative albino has reduced ipsilateral retinal projections. The albino cat is a model system analogous to tyrosinase-negative albinism found in mammals.

Albinism↗
PubMed1982

Abnormal retinal projections in cats with the Chediak-Higashi syndrome.

The Chediak-Higashi syndrome (CHS) occurs in mammals, including humans and cats. The CHS is characterized by decreased oculocutaneous pigmentation, enlarged cytoplasmic granules, increased susceptibility to infections, and a hemorrhagic tendency. Ocular anomalies include pale irides and albinotic or subalbinotic fundi. Cats with CHS also have photophobia and prolonged postrotatory nystagmus. Since hypopigmentation of the pigment epithelium is correlated with misrouting of retinal ganglion cells in mammals, visual projections of CHS cats were examined by autoradiographic techniques to determine whether they exhibit abnormal retinogeniculate projections. In CHS cats, misrouted optic projections fragment layer A1 of the dorsal lateral geniculate nucleus into several islands, similar to the disruption of this lamina reported in the Siamese cat.

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PubMed1981

Retinal ganglion cell classes in the Old World monkey: morphology and central projections.

Labeled ganglion cells were studied in whole-mount retinas of Old World monkeys after electrophoretic injections of horseradish peroxidase into physiologically characterized sites. A number of different morphological classes have been identified, each of which has a distinctive pattern of central projection. Since different functional classes of primate retinal ganglion cells also have distinctive patterns of central projection, correspondences between functional and morphological cell types have been inferred. There prove to be parallels between morphological types of cat monkey ganglion cells.

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PubMed1980

The afferent ganglion cells and cortical projections of the retinal recipient zone (RRZ) of the cat's pulvinar complex'.

A retino-pulvinar projection in the cat was confirmed using anterograde (autoradiography) and retrograde (horseradish peroxidase (HRP)) tracing techniques. The part of the "pulvinar complex" receiving retinal afferents is referred to as the retinal recipient zone (RRZ). The cortical projections of the RRZ were studied by injecting HRP into different cortical areas. The retrograde labeling of the cell bodies and dendritic fields of the retinal ganglion cells projecting to the RRZ was accomplished by injecting HRP electrophoretically into the RRZ. Our results indicate that the RRZ projects to areas 19 and the lateral suprasylvian area (LS) but not to areas 17 or 18. Virtually all RRZ cells, including those that project to the cortex, are small (10-20 micron in diameter); they are the same size as the relay cells of the parvocellular C laminae of the lateral geniculate nuclear complex (LGNd) that project to areas 19 and LS. The majority of the ganglion cells projecting to the RRZ had medium-sized somas (15-25 micron in diameter), large (up to 800 micron in diameter), diffuse dendritic fields with a characteristic morphology, and appeared different from the alpha, beta, gama, and delta cells of Boycott and Wässle ('74). These cells provide evidence for another morphological class of ganglion cells, termed epsilon cells. Our results suggest that the RRZ relays the activity of specific types of retinal ganglion cells to extrastriate visual cortex and, thus, functions in parallel with the different subdivisions of the LGNd.

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