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Biomedical subjects

R W Guillery

Publications and source records attributed to R W Guillery.

At least 91 records · Page 5Linked to original sources
PubMed1982

The arrangement of axons according to fiber diameter in the optic tract of the cat.

The topographic distribution of axons according to diameter classes in the optic tract of the cat has been studied by light and electron microscopic methods. The subdivision of the tract into a ventral and a dorsal sector, with the former containing the thickest fibers of the tract, has been confirmed. In addition, there is a ventrolateral marginal zone of the tract which contains many of the finest axons and there are gradients of fiber diameters definable for thick and intermediate axons. The gradients show the thinner fibers lying rostral to the thicker fibers. The major points demonstrable by fiber diameter measurements have been confirmed by counts of myelin lamellae. Comparison of fiber distributions in the optic tract with the distributions in the optic nerve on the one hand and with the geniculate terminations on the other shows that, in the region of the optic chiasm, retinofugal axons are sorted not only according to their crossed or uncrossed pathway but also according to their fiber diameter class and thus are presorted in terms of their final destinations.

Animals↗
PubMed1981

The dorsal lateral geniculate nucleus of the normal ferret and its postnatal development.

The anterograde transport of 3H proline and of horseradish peroxidase has been used to study the retinogeniculate pathway in normal adult ferrets and in young ferrets during postnatal development. the lateral geniculate nucleus in adults shows a characteristic "carnivore" pattern, with layers A, A1, C, C1, C2, and C3, and a medial interlaminar nucleus recognizable either cytoarchitectonically or on the basis ofth retinogeniculate innervation. In addition, there is a well-defined, rather large perigeniculate nucleus. At birth the lateral geniculate nucleus is unlaminated and essentially all parts are reached by afferents from both eyes. The crossed component is by far the larger. It extends from the optic tract medially well into the perigeniculate field, in contrast to the uncrossed component which barely reaches the perigeniculate field. During the first 3 postnatal days the uncrossed fibers restrict their arbors to a small posterior and medial region, the precursor of the biocular segment of the nucleus. The crossed fibers gradually retreat from the region within which the uncrossed fibers have concentrated. Between the fourth and eighth postnatal days the field occupied by the ipsilateral component expands again to form a major focus that will define lamina A1 and a minor focus that will define C1. At this stage the crossed and the uncrossed fibers overlap at the borders of lamina A1 and the whole region of lamina C1 is also occupied by arbors of the crossed component. The perigeniculate field becomes clearly distinguishable from the lateral geniculate nucleus and the medial interlaminar nucleus is becoming clearly recognizable between days 3 and 8. Between days 8 and 15 the cytoarchitectonic borders between layers A and A1 become clearly defined, but the retinogeniculate axons from each eye still extend across this border. These axons retreat into their appropriate lamina after the 15th postnatal day an the nucleus reaches its essentially adult structure by about the fourth postnatal week. Segregation of retinofugal axons in the C layers occurs after segregation in the A layers, but many of the cells within the C layers show signs of cytological maturity earlier than those of the A layers. The nucleus undergoes a series of migrations and changes of shape as the ipsilateral and contralateral components become segregated. Whereas in teh newborn the nucleus is roughly comma-shaped and on the lateral aspect of the dorsal thalamus, in the adult it is "L"-shaped and mainly on the posterior aspect of the dorsal thalamus.

Aging↗
PubMed1981

A demonstration of several independent, partially overlapping, retinotopic maps in the optic tract of the cat.

We show here that the retina in the cat's optic tract by several separate, retino-topically organized maps. Fibers in different diameter classes form independent maps, and both hemi-retinae of the opposite side, as well as the temporal retina of the same side, are mapped in the tract. These several maps form rough topographic representations significantly out of register with each other.

Animals↗
PubMed1981

A study of Golgi preparations from the human lateral geniculate nucleus.

The Golgi method was used to study nerve cells and their processes in the human lateral geniculate nucleus. Only a few axons were successfully impregnated. These enter the nucleus from the optic radiations and were tentatively identified as corticogeniculate axons. In one brain from a 2-week-old infant these axons showed unusually dense terminal arbors, suggesting that significant developmental changes occur in this fiber system postnatally. Neurons in the magnocellular layers show a great variety of dendritic patterns, and are not readily grouped into well-defined morphological classes. At one extreme are cells with a restricted dendritic arbor, having dendrites that run a sinuous course close to the perikaryon. At the other extreme, cells have a more extended dendritic arbor; their dendrites are long, relatively straight in some cells, markedly tortuous in others. There is a continuous range of intermediate cell types between the "restricted" and the "extended" cells. Many magnocellular dendrites cross freely into adjacent layers; whereas the short dendrites of restricted cells rarely cross from one layer to another, the dendrites of extended cells may either be confined to a single layer (intralaminar) or may have a translaminar distribution across two or even three layers. Small cells, with dendrites entirely confined to an interlaminar region, have been seen in the magnocellular division of the nucleus on either side of layers 2. Parvocellular elements also show a wide range of dendritic patterns, but the extreme forms of restricted and extended cells are not seen. Parvocellular dendrites commonly are oriented perpendicular to the layers and generally show an intralaminar distribution; translaminar dendrites are extremely rare. A minority of parvocellular neurons have most of their dendrites confined to an interlaminar zone. These "interlaminar" cells have large perikarya close to or in the interlaminar zones, and show a predominant dendritic orientation parallel to the layers. A few parvocellular elements with complex axoniform dendrites were seen, and these dendrites, too, tend to run parallel rather than perpendicular to the layers.

Adolescent↗
PubMed1981

Do blue-eyed white cats have normal or abnormal retinofugal pathways?

Three white cats that had blue eyes and no tapetum were studied by behavioral, electrophysiological, and anatomical methods in order to determine whether they showed evidence of abnormal retinofugal pathways comparable to those found in Siamese cats and in other mammalian forms having melanin deficits. The three cats were normal in every respect. However, several other white cats, obtained subsequently, do show an abnormality of the retinogeniculate pathway identical to the abnormality of Siamese cats. Cats of the second type are thought to be homozygous for the Siamese gene and also the express the White gene. Because the characteristics Siamese pigmented "points" fail to develop in the presence of the white gene, cats of the second type are not distinguishable from other white cats on the basis of eye color or coat color. In terms of their central visual pathways and of their patterns, however, they are recognizably Siamese. It is not known how common "crypto-Siamese" cats are in the white cat population, but the possibility of their occurrence suggests that, in general, white cats should not be used for studied of the central visual pathways.

Animals↗
PubMed1981

The distribution of melanin in the developing optic cup and stalk and its relation to cellular degeneration.

The early distribution of melanin in the developing optic cup and stalk and its relationship to cellular degeneration have been studied during intrauterine development in hamsters, mice, ferrets, and humans. The extensive degenerative changes that occur in the region of the optic fissure do not involve any pigment-bearing cells. Melanin is not formed at the site of the fissure until after the processes of fusion and the associated degenerative changes are complete. In contrast to this, there is a small region near the junction of the cup and stalk where melanin is particularly related to degenerative changes. Melanosomes form dense clumps associated with basophilic, apparently degenerate areas of cytoplasm, and these melanosome complexes themselves undergo further degenerative changes. The two types of degenerative changes, pigmented and unpigmented, are limited to the same two regions of the developing eye in all four species. However, the pigment degeneration is more extensive in ferrets and humans than in mice and hamsters. These observations raise the possibility that the lysis of melanosomes plays a significant but undefined local role in ocular development.

Animals↗
PubMed1980

An analysis of the retinal afferents to the cat's medial interlaminar nucleus and to its rostral thalamic extension, the "geniculate wing".

The retinal afferents to the medial interlaminar nucleus and to its rostro-dorsal extension at the edge of the pulvinar have been studied in cats by fiber degeneration and autoradiographic methods. Fiber degeneration following section of one optic nerve shows two distinct retinal inputs: One is coarse-fibered and goes to the medial interlaminar nucleus itself; the second, which is fine-fibered, goes to the rostral and medial borders of the medial interlaminar nucleus and continues into the pulvinar. The regions in receipt of these fine fibers have been called the "geniculate wing". The topography of retinal representations and the degree of binocular overlap within the medial interlaminar nucleus and the wing have been studied by combining intraocular injections of 3H proline with local lesions of the injected eye, or with removal of the non-injected eye. In the medial interlaminar nucleus three distinct laminae are recognizable and are particularly clearly shown in horizontal sections. Rostrally and medially, lamina 1 maps the contralateral nasal retina as a mirror reversal of lamina A. Posterior and lateral to this, lamina 2 maps the ipsilateral temporal retina as a mirror reversal of lamina A1. Lamina 3 lies closest to the optic tract and receives crossed afferents from the temporal retina. In this lamina, which is the smallest, vertical retinal dimensions map as in the other layers, but we were unable to determine the mapping of the horizontal dimensions. In the geniculate wing, as in the other geniculate layers, vertical lines of the visual field are mapped as corresponding vertical diencephalic dimensions; horizontal retinal dimensions are mapped as horizontal lines in the wing, with central retinal areas represented furthest from the optic tract. In the geniculate wing the contralateral nasal and ipsilateral temporal retina are mapped with considerable binocular overlap. The crossed temporal retina has no demonstrable representation in the wing.

Animals↗
PubMed1980

Development of the dorsal lateral geniculate nucleus in normal and visually deprived Siamese cats.

Neuronal cell bodies in the lateral geniculate nucleus of normal and of monocularly-deprived Siamese cats have been measured. Seventeen normally reared Siamese cats, ranging in age between 20 and 120 days, were used to determine rates of normal geniculate cell growth. A second group of five adult Siamese cats reared from bith with the lids of one eye closed were used to study the effects of monocular visual deprivation upon geniculate cell size. For each of the normal and visually deprived Siamese cats, the cross-sectional areas of 600 lateral geniculate cells were measured from camera lucida drawings of Nissl preparations. During normal development the geniculate cells rapidly increase in size during the first postnatal month of life and reach their adult size sometime between days 28 and 56. While this course of geniculate cell growth is similar to that seen in normally pigmented cats, the pattern of change seen after monocular deprivation is quite different in Siamese cats from that found in normally pigmented cats. In Siamese cats the regions of the nucleus receiving a contralateral projection from the deprived eye appear to be shielded from the effects of binocular competition. Cells throughout lamina A and in the abnormal, contralaterally innervated segment of lamina A1 show only about a 10% reduction in cell size. There are no noticeable differences between the parts of lamina A in the binocular and monocular segments of the nucleus. Cells in the ipsilaterally innervated segment of lamina A1, in contrast, show deprivation-induced changes that average 27.1%. Two mechanisms are proposed to explain why some geniculate cells in Siamese cats appear to be shielded from binocular competition: one depends on possible interactions between geniculo-cortical cells lying in adjacent parts of the same geniculate lamina, and the other depends on an anatomical segregation of the cell type ("Y-cells") most heavily affected by the binocular competition. Each proposed mechanism is related to earlier observations on monocularly deprived, normally pigmented cats.

Animals↗
PubMed1979

Abnormal retino-geniculate and geniculo-cortical pathways in several genetically distinct color phases of the mink (Mustela vison).

Several genetically distinct color phases of mink, which all show an abnormal reduction of pigment in the retinal pigment epithelium and which also show abnormalities of the retinofugal pathways, have been studied. Autoradiographic methods have been used to demonstrate the retino-geniculate pathways, and retrograde degeneration or the retrograde transport of horseradish peroxidase has been used for the geniculo-cortical pathways. The retino-geniculate abnormality is mild in some of the color phases and extremely severe in others, but within any one color phase the variability is relatively low. Although the severity of the abnormality varies between color phases, a rather specific pattern of abnormal geniculate innervation is recognizable for mink in general and this is distinct from that found in Siamese cats. In the abnormal mink the size of geniculate lamina A1 is reduced and there is an abnormal crossed input going to the intermediate sectors of this reduced layer. Layer C1 also receives an abnormal crossed input, but this is more variable than that going to A1 and there appears to be little correspondence, retinotopically, between the normal inputs to layers A1 and C1. In some of the abnormal mink there are interruptions within the cytoarchitectionically definable layer A1, and opposite these gaps reduplications of layer A are commonly seen, as though there is an intrinsic geniculate mechanism for generating the characteristic multilaminar geniculate structure. However, there are also numerous examples of fusions between layers receiving afferents from the same eye, and these demonstrate that the development of geniculate lamination must also be under the influence of the retinal inputs. The geniculo-cortical pathway shows a normal topography in most of the mink. Abnormal geniculo-cortical projections, comparable to the "Boston" pattern of Siamese cats are extremely rare, and their occurrence could not be correlated with the severity of the retino-geniculate abnormality or with the laminar pattern in the lateral geniculate nucleus. We suggest that the development of one or the other pattern of geniculo-cortical projection may depend upon the relative timing of the two mechanisms that produce the geniculate lamination.

Animals↗
PubMed1979

Variability of laminar patterns in the human lateral geniculate nucleus.

The structure of the human lateral geniculate nucleus has been studied on serial Nissl stained sections from 57 human brains. Most of the brains were from neurologically normal individuals and were obtained during routine autopsy procedures. The laminar arrangement within the human nucleus is surprisingly variable. It is always possible to recognize a small segment with two layers (the monocular segment), one with four layers and one with six layers. Often an 8-layered segment can also be seen. The posterior half of the nucleus, within which central vision is represented, is made up mainly of six layers, and is the least variable part of the nucleus. Here the layers lie roughly parallel to each other. In the anterior half of the nucleus the laminar arrangement is more variable, and the layers often form complex and irregular interdigitations with each other. The 8-layered segment varies greatly in size and may be absent. It generally lies at the edge of the 4-layered segment not, as might have been expected, within the borders of the 6-layered segment. In many parts of the nucleus nerve cells are organized in short rows that run perpendicular to the layers; also, individual nerve cells are elongated in this direction. This neuronal orientation follows the lines of projection that are defined by the borders of a zone of retrograde degeneration, and also corresponds to the orientation of a cellular discontinuity that probably is the geniculate representation of the blind spot. Thus, we conclude that the neuronal orientation indicates the lines of projection within the nucleus.

Adolescent↗
PubMed1978

Terminal arbors of axons that have formed abnormal connections.

Ther terminal arbors of individual retinogeniculate axons that have been induced to grow into an inappropriate geniculate layer have been revealed for light and electron microscopic study by being filled with horseradish peroxidase. After a unilateral ocular enucleation in kittens, single axons from the surviving eye show terminal arbors not only within their own geniculate layers but also in the denervated layers. The new, abnormal arbors arise from the terminal segments of arbors that lie within the nondenervated layer and make patterns of synaptic contacts that appear normal.

Animals↗
PubMed1978

Differential effects of monocular deprivation seen in different layers of the lateral geniculate nucleus.

Recent investigations have suggested that the morphological effects of monocular deprivation can be explained by a developmental competitive interaction between the pathways from the two eyes. This study presents evidence in the tree shrew for binocular competition and for an unequal effect of such competition on the different layers of the lateral geniculate nucleus. The effects of monocular deprivation were evaluated by comparing cell size changes in the binocular and monocular segments of the lateral geniculate nucleus in three tree shrews raised with one eye sutured. In two of these animals the open eye was injected with 3H proline in order to identify accurately geniculate layers innervated by the non-deprived eye. Cell sizes in three normal animals and one monocularly enucleated animal were measured for comparison. The results show the following main effects: First, that monocular deprivation significantly changes cell size in the binocular but not the monocular segment of the geniculate nucleus. Comparisons with cell size in normal animals indicates that non-deprived cells may grow in response to deprivation. Second, that cell size in geniculate lamina 3 is not affected by monocular deprivation, suggesting that cells in this layer are morphologically or functionally secluded from competitive interactions affecting the other layers. Finally, that monocular enucleation in the adult tree shrew affects all parts of the geniculate nucleus including layer 3 and the monocular segment, demonstrating that these parts of the geniculate nucleus are responsive to lack of retinal innervation.

Animals↗
PubMed1977

Retinotopic organization within the thalamic reticular nucleus demonstrated by a double label autoradiographic technique.

A 'visual receptive zone' of the thalamic reticular nucleus can be defined in rabbits by the transneuronal transport of [3H]proline from the retina through the lateral geniculate nucleus to the reticular nucleus. Small injections of [3H]proline into the striate cortex of rabbits produce localized patches of label within this visual receptive zone, smaller than the zone itself. The sum of these small patches corresponds approximately to the total extent of the visual receptive zone, suggesting that there is a retinotopic map within the corticoreticular pathway. This map has been studied by double injections, using [3H]proline and [35S]methionine to label two different parts of the striate cortex. After axoplasmic transport of the isotopes, the reticular distribution of these two labels can be demonstrated by a double emulsion technique. This allows a distinction to be made between the radiation emitted by each isotope and demonstrates that within the reticular nucleus there is an accurate retinotopic map. In accuracy and in the orientation of the major visual field axes, this map corresponds closely to the map established in the dorsal lateral geniculate nucleus. However, the reticular map shows an elongation in the dorsoventral axis, which corresponds to the orientation of dendritic arbors within the nucleus.

Animals↗