Biomedical subjects

P A Raymond

Publications and source records attributed to P A Raymond.

63 records · Page 4Linked to original sources

PubMed1988

Lighting conditions and retinal development in goldfish: absolute visual sensitivity.

Goldfish (Carassius auratus) were reared from hatching in constant light (340 lux), cyclic light (12 hr 320 lux, 12 hr dark) or constant dark. Absolute visual threshold was determined psychophysically in animals that still responded to visual stimuli after 1-3 years of exposure, by means of a classically conditioned respiration suppression technique wherein animals were presented with different intensities of large diffuse flashes of monochromatic light. Fish reared in constant light and fish reared in cyclic light responded reliably to stimuli above threshold, but fish reared in constant light were on average 0.58 log unit less sensitive at 532 nm, near the peak of the rod action spectrum. Two of the four fish reared in darkness did not respond to the stimuli, and thus could not be conditioned, and another fish reared in darkness responded only occasionally; threshold could not be measured in these three fish. The one fish reared in darkness that responded consistently enough to be conditioned was more than 5 log units less sensitive than normally reared fish on the first day of testing, and became progressively less sensitive over the next 2 days. Rearing under constant dark or constant light had no obvious effect on spectral sensitivity at absolute threshold. The effect of rearing in constant light on absolute threshold correlates with morphological changes in rod density, but the effect of rearing in constant darkness does not.

Animal Husbandry↗

PubMed1987

Germinal cells in the goldfish retina that produce rod photoreceptors.

Dividing cells and their progeny in retinae of young goldfish were labeled with [3H]thymidine, and selected cells were reconstructed from serial sections processed for electron microscopic autoradiography. Our goals were to characterize the cells that were identified as rod precursors in previous light microscopic autoradiographical studies and to determine their origin and fate. (In fish the population of rods increases several-fold postembryonically by proliferation of rod precursor cells scattered across the retina). Over 200 labeled cells taken from 11 retinas were examined, and 20 of these were reconstructed in their entirety. Some retinas were examined at short intervals (1 to 48 hr) after [3H]thymidine injection in order to study mitotically active cells, and others were examined after longer intervals (9 or 14 days) to discover the nature of the progeny of labeled dividing cells. Previous evidence from thymidine studies in larval goldfish suggested that proliferating cells destined to produce rods appear first in the inner nuclear layer and later in the outer nuclear layer, where they continue to divide and generate new rods (P.R. Johns, (1982) J. Neurosci. 2, 179). The present results provide morphological evidence in support of the suggestion that rod precursors migrate from inner to outer nuclear layer and, furthermore, show that the precursors are closely associated with, and perhaps guided by, the radial processes of Müller glial cells. Examination of EM autoradiographs of labeled cells at 9 and 14 days after a pulse label with thymidine confirms that the differentiated progeny of dividing precursor cells are exclusively rods. To our knowledge, rod precursors are the first example of a neuronal germinal cell in the vertebrate central nervous system that under normal conditions produces only one type of neuron.

Animals↗

PubMed1987

Use of osmium tetroxide-potassium ferricyanide in reconstructing cells from serial ultrathin sections.

We describe a technique, modified from Langford and Coggeshall [Anat. Rec., 197 (1980) 297-303; J. Comp. Neurol., 203 (1981) 745-750], for enhancing membrane contrast and defining cellular boundaries, that is useful for reconstructing individual cells from ultrathin sections. The cells of interest in our study were neuronal germinal cells and their differentiated progeny in the retinas of young goldfish. These cells were labeled by pulse injections of [3H]thymidine, and they were subsequently identified in EM autoradiographs by the presence of silver grains overlying their nuclei. In tissue prepared by traditional procedures (fixation in mixed aldehydes, postfixation in osmium tetroxide) it was difficult to follow the processes of these cells through the complex, dense network of cells in the differentiated retina. However, in tissue postfixed with a mixture of osmium tetroxide and potassium ferricyanide, the contrast of the cell membranes was improved and, in favorable preparations, a dense precipitate was formed in the extracellular spaces, serving to outline individual cells. This greatly faciliated the preparation of reconstructions from serial ultrathin sections.

Animals↗

PubMed1986

Movement of retinal terminals in goldfish optic tectum predicted by analysis of neuronal proliferation.

Quantitative, computer-assisted autoradiography was used to assess the relative rate and pattern of growth of retina and tectum in larval and early juvenile goldfish. 3H-thymidine was used to mark the boundary of retina and tectum, and the location of this boundary was charted as the eye and brain grew and added more cells. The pattern of growth is at all times discordant. The original (larval) retina becomes surrounded by annuli of new tissue, whereas the larval tectum remains adjacent to the rostral edge as crescents of new tissue are added to the caudal end. After 2 years of growth, more than 95% of the total surface area of retina and tectum in goldfish derives from cells born after larval stages. Computer-aided reconstructions of 3H-thymidine labeled retina and tecta were used to predict the direction and magnitude of displacement of the retinotopic map. It was estimated that retinal terminals can shift 1.5-1.8 mm caudally at a rate of 5 micron/d during the first 2 years of growth. The terminals that move the farthest are those from temporal retina that project to rostral tectum. The magnitude and direction of the predicted movements matches certain features of HRP-filled retinal axons that others have assumed represented the history of displacements of the terminal arbors.

Animals↗

PubMed1985

Cytodifferentiation of photoreceptors in larval goldfish: delayed maturation of rods.

This study describes the differentiation of photoreceptors in larval goldfish retina. The earliest photoreceptors to differentiate were cones; 3H-fucose labeled cone but not rod outer segments in larval as well as adult goldfish. All major cone types known to be present in the adult goldfish retina (double cones, long and short single cones) were found in the larval retina by 2 days after hatching. The cones matured rapidly; within a few days they had well-developed outer segments and synaptic pedicles that were smaller, but otherwise similar to those in adults. Rods were slower to mature. Their outer segments were at first short, wide, and misshapen; only as they grew longer and narrower did they become straight and properly aligned. Rod spherules were first seen in fish older than 1 month; immature rods contained perinuclear synaptic ribbons and invaginating processes penetrated the cell body. These results suggest that the influence of rods and cones on visual function in larval goldfish may be quite different from the adult.

Animals↗

PubMed1983

Postembryonic growth of the optic tectum in goldfish. I. Location of germinal cells and numbers of neurons produced.

The growth and morphology of the optic tectum of adult goldfish were studied with light and electron microscopy and with thymidine radioautography. The tectum is roughly hemispheric in shape, with a smaller radius of curvature rostrally than caudally. A narrow region containing proliferating cells (the germinal zone) is found along two-thirds of the rim of the tectal hemisphere but is absent rostrally, adjacent to the tectal region which receives input from the rostral visual field. New cells generated in the germinal zone are added to the tectum appositionally in crescent-shaped increments; these was no evidence of migration of new cells into the rostral region which lacks a germinal zone. Some of the new cells added to the adult tectum were shown to be neurons on the basis of cytological and ultrastructural features. Counts of tectal neurons likewise demonstrated that new cells were added with growth of the tectum; large goldfish (25 cm long) had 27% more tectal neurons than did small fish (4 cm long). Spreading apart of existing cells also contributed to overall growth of the tectum. These results confirm and extend those of R. L. Meyer ((1978) Exp. Neurol. 59: 99-111). The topological dissimilarity of the patterns of growth of retina (which adds cells appositionally around its entire perimeter) and tectum supports the suggestion that retinotectal terminals must continually move (Gaze R. M., M. J. Keating, A. Ostberg, and S. H. Chung (1979) J. Embryol. Exp. Morphol. 53: 103-143). Our estimates of cell numbers and tectal areas lead to predictions about the directions and magnitudes of these displacements.

Aging↗

PubMed1983

Postembryonic growth of the optic tectum in goldfish. II. Modulation of cell proliferation by retinal fiber input.

The proliferation of cells in the germinal zone of the optic tectum of adult goldfish was studied following unilateral optic nerve crush or removal of one eye. Dividing germinal cells were labeled with [3H]thymidine, which was injected at various times (0 to 30 days) following surgery; fish were sacrificed after short (48 hr) survival times. The numbers of labeled nuclei in the tectal germinal zones were compared on the two sides (intact and denervated). We show that permanent removal of optic input (by enucleation) resulted in a sustained depression of [3H]thymidine incorporation in the tectal germinal zone on the denervated compared to the intact side. Temporary denervation (by optic nerve crush) initially had a similar effect; however, upon reinnervation of the tectum by regenerating optic fibers, proliferation was enhanced on the experimental side compared to the intact side. Because cells in the germinal zone are known to produce new tectal cells, neurons as well as glia, in the normal growing adult brain (Raymond, P. A. and S. S. Easter, Jr. (1983) J. Neurosci. 3: 1077-1091), some of the proliferating cells may have been generating neurons. This inference is supported by the observation that in two fish whose right eye had been removed more than 2 years earlier, there were fewer neurons in the denervated tectum than in the intact tectum. Thus, it is likely that the observed decrease in incorporation of [3H]thymidine by cells in the germinal zone of the denervated optic tectum resulted in a slower rate of addition of new tectal cells on the affected side. We conclude that cytogenesis in the germinal zone of the growing optic tectum of adult goldfish is regulated by optic fiber input. This mechanism may be important in matching the rates of growth of retina and tectum in the normal brain of the growing adult fish.

Aging↗

PubMedDate not supplied

PCR-SSO typing for DR4-Dw subtypes: application to unrelated bone marrow transplant donor selection.

Thirty-seven DR4-positive patient-unrelated bone marrow donor pairs previously DR/DQ restriction fragment length polymorphism (RFLP) typed and tested in mixed lymphocyte culture (MLC), have been DR4-Dw subtyped retrospectively using sequence specific oligonucleotide probes. We found that DR4-Dw subtyping substantially increased the accuracy of pre-MLC matching and could potentially accelerate donor searches by avoiding unnecessary MLC tests on Dw-mismatched donors.

Bone Marrow Transplantation↗

PubMedDate not supplied

Differential expression of cadherin-2 and cadherin-4 in the developing and adult zebrafish visual system.

Cadherins are homophilic cell adhesion molecules that control development of a variety of tissues and maintenance of adult structures. Although cadherins have been implicated in the development of the brain, including the visual system, in several vertebrate species, little is known of their role in zebrafish. In this study, we examined distribution of cadherin-2 (Cdh2, N-cadherin) in the visual system of developing and adult zebrafish using both immunocytochemical and in situ hybridization methods, and we compared Cdh2 distribution to that of the previously reported and closely related cadherin-4 (Cdh4, R-cadherin). As in other vertebrates, in zebrafish embryos Cdh2 was widely expressed in the early nervous system, but its expression became more restricted as development proceeded. Cdh4 was not detectable until later in development, at about the time when the first ganglion cells are generated. Cdh2 and Cdh4 were expressed in distinct regions of developing visual structures, including the lens. We hypothesize that the differential expression of these two cadherins in developing zebrafish visual structures reflects functionally different roles in the development of the vertebrate visual system.

Animals↗