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S R Robinson

Publications and source records attributed to S R Robinson.

115 records · Page 7Linked to original sources
PubMed1985

Cytogenesis in the developing retina of the cat.

Cytogenesis in the cat retina was studied using tritiated (3H) thymidine autoradiography and nuclear stains. Three zones of cell division were recognized. In the first zone cell cleavage occurs at the outer limiting membrane. The distribution of these mitotic figures is uniform as early as an embryonic age of 29 days (E29) until E50. At about E50 a "cold spot", made apparent by the absence of mitotic figures, is evident at the site of the developing area centralis. This spreads to encompass the whole retina by postnatal day 10 (P10). A second zone of cell division was recognized by the presence in the developing inner nuclear layer of 3H-thymidine labelled nuclei which do not migrate to the outer limiting membrane (ventricular surface) to divide. Some of these labelled nuclei are located in regions of the retina where cytogenesis at the ventricular surface has ceased. A third zone was observed in the optic nerve fibre/ganglion cell layers from about E54 until beyond the first postnatal month. This activity gives rise to vascular endothelial cells in the nerve fibre/ganglion cell layers. Once established, the developing vascular cells invade the inner plexiform and inner nuclear layers to form the deeper capillary net.

Animals↗
PubMed1984

Techniques for observing fetal behavior in utero: a comparison of chemomyelotomy and spinal transection.

Two procedures--chemomyelotomy and spinal transection--have been utilized to chemically block or physically sever the spinal cord of pregnant rats, enabling direct observation of fetal behavior without the use of anesthesia. The effect of each procedure on fetal behavior was studied at four gestational ages (Days 17, 18, 19, and 20). Substantial differences in fetal activity were found between chemomyelotomy and spinal transection groups, including differences in the overall level of activity as well as the pattern of developmental change of behavior. Such differential effects indicate that chemomyelotomy and spinal transection are not equivalent maternal preparations in the study of fetal behavior.

Animals↗
PubMed1982

Interocular transfer in a marsupial: the brush-tailed possum (Trichosurus vulpecula).

The corpus callosum has been implicated as the major commissure mediating the interhemispheric transfer of visual information in placental mammals. As marsupials lack a corpus callosum, they may be incapable of such transfer. This study was undertaken to test this hypothesis. Three brush-tailed possums (Trichosurus vulpecula) underwent midsaggital transection of the optic chiasm to ensure that retinal input was restricted to the ipsilateral side of the brain. Three other possums had sham operations to control for visual or learning impairments that might be caused by any other aspects of the surgery. All six animals were monocularly occluded, and conditioned to respond to the positive of two visual stimuli. When a criterion of greater than or equal to 18/20 correct was attained for two consecutive blocks of 20 trials, the trained eye was occluded, and the stimuli were presented to the untrained eye. Conditioning was continued until the criterion of learning was achieved with this eye. The stimulus contingencies were then reversed, so that the previously negative stimulus became the positive one, and the conditioning procedure was repeated. Black/white and horizontal/vertical visual discriminations were used. Both the experimental and control groups exhibited high levels of interocular transfer on all tasks. It is concluded that T. vulpecula possesses a pathway capable of mediating the interhemispheric transfer of visual information.

Animals↗
PubMedDate not supplied

Shifting relationships between photoreceptors and pigment epithelial cells in monkey retina: implications for the development of retinal topography.

This study examines the spatiotemporal relationships between retinal pigment epithelium (RPE) and photoreceptors (PR) during development of Macaca nemestrina retina. Our aim was to learn more about the developmental dynamics of these two important cell populations, particularly whether development changes in RPE cell densities mimic those of PR at selected retinal points. Twelve eyes ranging in age from 100 fetal days (Fd) to adulthood were flatmounted; the retinal perimeters were traced; and then sample punches were taken of the RPE and neural retina at the fovea, optic disc, mid- and far-nasal periphery, and far temporal, inferior and superior periphery. The two tissues were gently separated and the RPE cells and photoreceptors from the same region of the punch were counted using Nomarski contrast interference optics. We found that the total number of cones remains stable around 4 million between Fd100 and adulthood, but RPE number increases from 1.6 million at Fd100 to 2.56 million in adulthood. At the fovea, the core:RPE ratio increases from 5.4:1 at Fd100 to 28:1 by adulthood. In the temporal periphery by contrast, the cone:RPE ratio declines from 2.2:1 at Fd100-110 to less than 1:1 in the adult. In the vicinity of the optic disc, the ratio of (cones+rods); RPE remains around 35:1 throughout development, but in the retinal periphery it decreases to the adult value of 22:1. These changing ratios indicate that photoreceptors and RPE cells are redistributed independently during development, and that these two cellular sheets slide over one another to achieve their final distribution. This situation suggests that the forces or factors causing foveation are intrinsic to the neural retina.

Aging↗
PubMedDate not supplied

Relationships between Müller cells and neurons in a primitive tetrapod, the Australian lungfish.

We recently proposed a model of cytogenesis which assumes that primitive ancestral mammals and premammalian vertebrates had a retinal composition that consisted of about seven neurons per Müller cell, comprising 1-2 cone photoreceptors, 1-2 rod photoreceptors, 2-3 bipolar cells, 1-2 amacrine cells, less than 1 ganglion cell, and less than 1 horizontal cell (Reichenbach & Robinson, 1995). The Australian lungfish (Neoceratodus forsteri) closely resembles the lobe-finned ancestors of land vertebrates, and has an extremely plesiomorphic nervous system. The present study, therefore, has examined the relative frequencies of retinal neurons and Müller cells (identified by immunolabelling for glutamine synthetase) in the lungfish retina. It was found that for each Müller cell there is an average of 1.9 cone photoreceptors, 1.7 rod photoreceptors, 3.1 amacrine/bipolar/horizontal cells, and 0.6 ganglion cells; amounting to a ratio of 7.3 neurons per Müller cell. These results support our conjecture that the sequence of cytogenesis in mammals is constrained by a developmental program that predates the evolution of mammals. The study also provides the first detailed morphological descriptions of lungfish Müller cells and their relationship with adjacent neurons. It was found that individual Müller cells in lungfish have a volume (more than 12,000 microns3) that is an order of magnitude higher than in mammals, yet the proportion of total retinal volume occupied by these cells (20%) is very similar.

Animals↗
PubMedDate not supplied

Alzheimer's disease and inflammation: a review of cellular and therapeutic mechanisms.

1. Of the neurodegenerative diseases that cause dementia, Alzheimer's disease (AD) is the most common. Three major pathologies characterize the disease: senile plaques, neurofibrillary tangles and inflammation. We review the literature on events contributing to the inflammation and the treatments thought to target this pathology. 2. The senile plaques of AD consist primarily of complexes of the beta-amyloid protein. This protein is central to the pathogenesis of the disease. 3. Inflammatory microglia are consistently associated with senile plaques in AD, although the classic inflammatory response (immunoglobulin and leucocyte infiltration) is absent. beta-Amyloid fragments appear to mediate such inflammatory mechanisms by activating the complement pathway in a similar fashion to immunoglobulin. 4. Epidemiological studies have identified a reduced risk of AD in patients with arthritis and in leprosy patients treated with anti-inflammatory drugs. Longitudinal studies have shown that the consumption of anti-inflammatory medications reduces the risk of AD only in younger patients (< 75 years). 5. There is a considerable body of in vitro evidence indicating that the inflammatory response of microglial cells is reduced by non-steroidal anti-inflammatory drugs (NSAID). However, no published data are available concerning the effects of these medications on brain pathology in AD. 6. Cyclo-oxygenase 2 enzyme is constitutively expressed in neurons and is up-regulated in degenerative brain regions in AD. Non-steroidal anti-inflammatory drugs may reduce this expression. 7. Platelets are a source of beta-amyloid and increased platelet activation and increased circulating beta-amyloid have been identified in AD. Anti-platelet medication (including NSAID) would prevent such activation and its potentially harmful consequences. 8. Increased levels of luminal beta-amyloid permeabilizes the blood-brain barrier (BBB) and increases vasoconstriction of arterial vessels, paralleling the alterations observed with infection and inflammation. Cerebral amyloidosis is highly prevalent in AD, compromising the BBB and vasoactivity. Anti-inflammatory medications may alleviate these problems.

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