Biomedical subjects

J Wye-Dvorak

Publications and source records attributed to J Wye-Dvorak.

12 recordsLinked to original sources

PubMed1992

Cytoarchitecture and visual field representation in area 17 of the tammar wallaby (Macropus eugenii).

Tritiated proline was injected into one eye in the tammar wallaby and transported label was studied in the cortex after transneuronal passage through the lateral geniculate nucleus. The autoradiographic label and cytoarchitecture were used to anatomically demarcate the borders of area 17. Electrophysiological recordings from single units were done to obtain a retinotopic map of area 17. Single units in area 17 were found to have orientation sensitivity comparable to those seen in placental mammals such as cat and monkey. They could also be classified as simple, complex, and hypercomplex cells. Changes in the cortical areal magnification factor with eccentricity were found to match the drop off in retinal ganglion cell density only along the vertical meridian representation. Along the horizontal meridian, the cortical magnification falls off significantly with eccentricity, whereas the ganglion cell density shows only a mild reduction. Thus central vision, especially the binocular segment, is heavily represented at the cost of the periphery.

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PubMed1992

GABA-like immunoreactive neurons in the retina of Bufo marinus: evidence for the presence of GABA-containing ganglion cells.

gamma-Aminobutyric acid (GABA)-like immunoreactive (IR) neurons in the retina of the cane toad Bufo marinus were revealed using immunohistochemistry on retinal wholemount preparation and sectioned material. GABA-IR neurons included horizontal, bipolar and amacrine cells in the inner nuclear layer and small to medium sized cells in the ganglion cell layer. A few IR axons were seen in the optic fiber layer of the retina. Following the injection of the carbocyanine dye, DiI into the optic tectum ganglion cells were retrogradely filled. A small population of DiI-filled ganglion cells (2.8%) was found to be GABA-IR. GABA-IR neurons in the ganglion cell layer without DiI label were considered to be displaced amacrine cells of which 45.3% were GABA positive. It is proposed that GABA-containing ganglion cells may form an inhibitory projection to visual centers of the anuran brain.

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PubMed1992

Retinal projections in the cane toad, Bufo marinus.

The location and extent of retinorecipient areas in the cane toad, Bufo marinus, were established by anterograde transport of cobaltic-lysine complex from the cut optic nerve. Most of the labeled optic axons travelled in the marginal optic tract, while others were in the axial optic tract, and/or the basal optic tract. Retinal projections terminated in both contralateral and ipsilateral targets. In addition to the optic tectum, the main visual center, retinorecipient areas included the suprachiasmatic nucleus, rostral visual nucleus, neuropil of Bellonci, corpus geniculatum thalamicum, ventrolateral thalamic nucleus (dorsal part), posterior thalamic neuropil, uncinate neuropil, pretectal nucleus lentiformis mesencephali and basal optic nucleus. While all of these retinorecipient areas receive optic fibers from both eyes, the ipsilateral retinal projections were observed to be generally sparser than those from the contralateral retina. A sparse optic fiber projection covers the surface of the ipsilateral optic tectum and is most prominent rostromedially and caudolaterally. The position and the extent of each of the retinorecipient areas were determined in relation to a three-dimensional coordinate system. Morphometric analysis showed that 85.3% of the retinorecipient area is in the contralateral optic tectum, 10.4% in contralateral non-tectal areas, 1.6% in the ipsilateral optic tectum and 2.7% in ipsilateral non-tectal areas. The presence of an ipsilateral tectal projection and the well defined pretectal visual neuropil complex may be related to the highly developed visual behavior and visual acuity of Bufo marinus.

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PubMed1991

Retinal distribution of ganglion cells which project to the ipsilateral optic tectum in Bufo marinus.

The retinotectal projection in anura is mainly crossed, although a small proportion of optic axons projects to the ipsilateral tectum. Using the fluorescent carbocyanide dye, DiI, we mapped the retinal topography of ganglion cells which project to the ipsilateral tectum in adult Bufo marinus. DiI was injected into particular locations in the right tectum. After 10 days survival both the right and the left retinals were wholemounted and the number and retinal position of retrogradely filled ganglion cells were determined. The contralateral and ipsilateral cells were visuotopically distributed in the retina in the majority of experiments. However, in two cases cells were located in visuotopically disparate parts of the retina. The ipsilateral cells represented 3.7% of contralaterally projecting cells in the temporal retina, 0.1% in the nasal and dorsal retina and 0.6% of the ventral retina. The density of ipsilaterally projecting ganglion cells varied from a top of 25 cells/mm2 in the temporal retina, 9 cells/mm2 in the nasal, 3 cells/mm2 in the dorsal to 11 cells/mm2 in the ventral retina. The diversity of size and shape of retrogradely filled ganglion cells indicated that the ipsilateral population corresponded to a heterogeneous class of ganglion cell types. The functional significance of the direct ipsilateral retinotectal projection of the anuran visual system has yet to be elucidated. However, in light of the involvement of the indirect ipsilateral retinotectal projection in binocular vision, the direct pathway is likely to be associated with a retino-tecto-spinal circuit subserving postural adjustment to visually derived stimulation.

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PubMed1987

Retinotopic organization in the dorsal lateral geniculate nucleus of the tammar wallaby (Macropus eugenii).

Electrophysiological recordings were made from 187 single cells in the tammar wallaby (Macropus eugenii) dorsal lateral geniculate nucleus (LGNd). The results show that it is topographically organized such that the superior visual field is represented dorsally, the inferior field is represented ventrally, the nasal visual field is represented caudally, and the temporal visual field is represented rostrally. The visual field of one eye ranges from -30 degrees nasal to +179 degrees temporal in azimuth and +73 degrees superior to -49 degrees inferior in elevation. Ganglion cells that had receptive field positions between -9 degrees and +179 degrees projected to the contralateral LGNd while the ganglion cells that projected to the ipsilateral LGNd had visual fields from 0 to +30 degrees. The binocular visual field extends 60 degrees in azimuth. This representation in the LGNd is expanded relative to the monocular representation. There is also an increased representation of the horizon in the temporal field corresponding to the visual streak of retinal ganglion cells. The binocular visual field is located where contralateral and ipsilateral laminae are shown to interdigitate by proline autoradiography. There are nine eye-specific laminae in the LGNd. Four receive afferents from the contralateral eye and five receive afferents from the ipsilateral eye. The lines of isoelevation are perpendicular to the coronal plane of section while the lines of isoazimuth are nearly parallel to the coronal plane. The lines of projection representing one visual direction are inferred to be perpendicular to the tangent of curvature of the laminae as in the LGNd of other mammals. The majority of cells (85%) recorded had on- or off-centre responses. On- and off-centre responses were not apparently segregated in the LGNd but segregation may not have been revealed by the single-unit recording technique.

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PubMed1986

Morphology and distribution of neurons in the retinal ganglion cell layer of the adult tammar wallaby--Macropus eugenii.

The morphology of the ganglion cell layer of the adult tammar wallaby has been examined from Nissl-stained retinal flatmounts. From this material, neurons have been classed as ganglion cells or displaced amacrine cells according to the disposition of Nissl substance. A further subdivision of ganglion cells into a separate group of alphalike cells was assisted by determining the range of soma sizes in neurofibrillar-stained flatmounts, a method which, in the cat, has revealed the presence of alpha cells. Isodensity contour maps prepared from the Nissl-stained flatmounts show a well-developed visual streak and an area centralis in the total neuronal population. A similar pattern was also found in the ganglion cells, thus confirming Tancred's (J. Comp. Neurol. 196:585-603, '81) finding, and, as well, in the alphalike ganglion cells and the displaced amacrine cells. The relative proportions of ganglion cells to displaced amacrines (GC:DA) were evaluated from isodensity profiles drawn along and vertical to the visual streak for the two cell types and also from maps showing the variation in the GC:DA ratio throughout the retina. A comparison with results published for other species shows that the visual streak development in the tammar wallaby is consistent with the expectations of the "terrain" theory and that, in its relative proportion of displaced amacrines, the tammar closely resembles the rabbit but contrasts sharply with the cat, which has half as many ganglion cells and three times as many displaced amacrines as the other two species.

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PubMed1984

Postnatal development of primary visual projections in the tammar wallaby (Macropus eugenii).

The time course and pattern of retinal innervation of primary visual areas was traced in pouch-young wallabies. Tritiated proline was injected into one eye of animals ranging in age from 1 to 72 days after birth. These results are compared to the 11 primary visual areas found in the adult wallaby, seven of which receive binocular input while four are monocular. At birth retinal ganglion cell axons have not reached any visual areas. Two to 4 days after birth, all of the axons are crossing to the contralateral optic tract. Nine to 12 days after birth axons begin to invade the contralateral lateral geniculate nucleus, the superior colliculus, and the medial terminal nucleus. Twenty to 21 days after birth, ipsilateral axons invade the lateral geniculate nucleus and superior colliculus. The contralateral projection precedes the ipsilateral projection in all binocular visual areas. By 25 days, ipsilateral and contralateral afferents share common territory in the lateral geniculate nucleus; however, afferents from each eye are initially concentrated in appropriate areas. Between 52 and 72 days, afferents to the dorsal lateral geniculate nucleus are gradually segregated into nine terminal bands. Four are contralateral while five are ipsilateral. By 72 days, the ipsilateral component to the superior colliculus is clustered beneath the contralateral projection a deeper layer. Projections to four monocular visual areas--lateral posterior nucleus, dorsal terminal nucleus, lateral terminal nucleus, and nucleus of the optic tract--are established later than binocular visual areas, except the suprachiasmatic nucleus. The suprachiasmatic nucleus is the last to be bilaterally innervated even though it is situated closest to the optic chiasm. At the light microscope level a mature pattern of visual development is emerging by 72 days, although the eyes do not open until 140 days.

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PubMed1981