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Biomedical subjects

G S Tucker

Publications and source records attributed to G S Tucker.

16 recordsLinked to original sources
PubMed1991

Primary amoebic meningoencephalitis in the Western Province.

Six cases of primary amoebic meningoencephalitis were diagnosed and treated at the Balimo Health Centre between December 1986 and September 1988. This disease has not previously been reported in Papua New Guinea although from information derived from other studies it should be occurring in the lowlands of Papua New Guinea from time to time. Although less than optimum treatment was given to the early cases the case fatality rate in the series was only 66%. This compares very favorably with a case fatality rate of nearly 100% from other studies. Early diagnosis and prompt treatment should help to reduce mortality.

Amebiasis↗
PubMed1990

Alterations of the cat's electroretinogram induced by the lesioning of the indoleamine-accumulating amacrine cells.

The neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) was used to destroy the indoleamine-accumulating amacrine cells located in the cat's retina. With 100 micrograms of 5,7-DHT, the alterations in the electroretinogram (ERG) were present in all of the treated eyes and the morphological changes were confined to some of the processes in the inner plexiform layer. The ERGs recorded from treated eyes consisted of negative waves at low intensities and depressed b wave amplitude at higher intensities. The duration of the b wave was not altered but the oscillatory potentials were strongly depressed. The changes were probably permanent. The differences in the ERG changes in cats and rabbits were suggested to arise from the differences in signal processing in the inner retina of rabbits and cats.

5,6-Dihydroxytryptamine↗
PubMed1989

Giant cell tumour of ilium.

Most common tumours of ilium are chondrosarcoma and reticulum cell sarcoma. Giant cell tumour commonly presents at the ends of long bones. It is quite uncommon to find osteoclastoma in flat bones, especially ilium. This is the only case of osteoclastoma of ilium seen during the last 7 years in this institution and is reported for its rarity.

Bone Neoplasms↗
PubMed1988

Incidence of osteomalacia in fractures of the proximal end of femur.

Twenty-six cases of fractures of the proximal end of the femur were studied to assess the role of osteomalacia. Biochemical, radiological and histological investigations were carried out in all the cases. Osteomalacia, commonly subclinical, was found to be the underlying cause in 65 per cent of cases. Histological analysis of iliac crest biopsy was the only reliable way of diagnosing subclinical osteomalacia.

Female↗
PubMed1988

Morphological findings in retinitis pigmentosa with early diffuse rod dysfunction.

The retina from the postmortem donor eye of a 64-year-old man with advanced autosomal dominant retinitis pigmentosa (RP) was studied with light and electron microscopy. Two children of the donor were tested with two-color, dark-adapted static perimetry and found to have Type 1 or D-type RP, the psychophysical subtype with early onset of severe rod dysfunction diffusely affecting the entire retina. In the macula of the donor retina, rods and cones were clustered in irregularly shaped patches, in association with pigmented retinal pigmented epithelial cells. Only cones in the middle of these patches possessed outer segments, and these were poorly organized. Of the few photoreceptors remaining outside of the macula, those in the superior retina had well-formed terminals and appeared to be rods. Rods were also observed superior to the disk and in the temporal mid-periphery. The few photoreceptors remaining in the inferior retina were also rod-like, but had less well-formed terminals. The retinal pigmented epithelium was relatively normal near surviving photoreceptors, but was depigmented, had thinned, or was absent in regions of photoreceptor dropout. These findings represent the first reported morphology of the retina from an eye donor with known psychophysical subtype of RP.

Adult↗
PubMed1986

Intranuclear rodlets in the rabbit retina following treatment with MPTP.

Retinas from pigmented rabbits treated with N-methyl-4-phenyl-1,2,3,6- tetrahydropyridine (MPTP, a chemical inducer of Parkinsonism in man and monkeys) were studied using light- and electron microscopy. The nuclei of many cells in the inner nuclear layer and the ganglion cell layer of the treated retinas contained crystalloids (intranuclear rodlets) of varying length (0.5-8 microns) which were composed of bundles of 12 nm filaments and which were seen only rarely in untreated retinas. The induced rodlets are oval to round cylinders, 15-20 filaments across (although they are smaller in untreated retinas). Similar intranuclear inclusions have been described under varying conditions in neurons and glia in the central nervous system of several animal species. In rabbits injected acutely with MPTP, most of the affected cells are in the inner nuclear layer in the position of bipolar cells, while in the chronically injected animals, clearly identifiable amacrine cells, and the nuclei of some cells in the ganglion cell layer also contained the inclusions. Evidence is presented that the rodlet-containing cells in the ganglion cell layer include both ganglion cells and displaced amacrine cells. These anatomic findings are relevant to understanding the physiological and biochemical effects of the drug on the retina which we reported previously (Wong, Ishibashi, Tucker and Hamasaki, 1985).

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1986

Snailtracks of the corneal endothelium.

An unusual pattern of corneal endothelial cell alterations has been observed at the slitlamp in eyes following intraocular surgery. Because of their appearance, we have called these changes "snailtracks". We have commonly seen these snailtracks following extracapsular cataract extraction. Similar changes have been noted in cadaver corneas stored in McCarey-Kaufman (M-K) medium. This study presents information which suggests that these changes represent corneal endothelial cell damage.

Cataract Extraction↗
PubMed1986

Refractile bodies in the inner segments of cones in the aging human retina.

Refractile inclusion bodies (approximately 0.80 micron in size) were found in the inner segments of cone photoreceptors in the aging human retina. They were easily resolved with the light microscope. They were never seen in rods, and occurred primarily in retinas from eye donors older than 40 years of age. The incidence of these inclusion bodies is related significantly to age (they occur more frequently with increasing age) and to sex (they are more likely to occur in the aging female than in the aging male). They were often smaller in size and fewer in number in the cones of males compared with females, and in males, fewer cones contained the RB than in females. Electron microscopy revealed that these inclusions are membrane-bound organelles having granular, fibrous, and tubular subcomponents. The occurrence of the RB appears to be unrelated to specific disease processes, medications in use at the time of enucleation, or specimen preparation times.

Adolescent↗
PubMed1982

The photoreceptors of the West Indian manatee.

Using light and electron microscopy we found that the manatee retina has both rodlike and conelike photoreceptors in accord with its diurnal behavior pattern. Outer segment disks in both cell types appear to be enclosed along most of their length within the plasma membrane. The synaptic terminals are simple, with small, superficial postsynaptic contacts. The cones have long inner segments, short, conical outer segments and terminals with numerous synaptic ribons and deeply embedded postsynaptic elements. There are two cone subclasses that may subserve color vision. Morphometry shows that there are more ganglion cells of small size ventrally, and that the thickness of the nerve fiber layer there is reduced, suggesting the presence of a specialized visual area in the retina. However, there were no pronounced differences in cone cell density in any of the regions examined.

Animals↗
PubMed1982

Physiologic and anatomic development of the photoreceptors of normally-reared and dark-reared rabbits.

The postnatal development of the rod photoreceptor of normally-reared and dark-reared pigmented rabbits was studied using physiological and anatomical methods. The late receptor potential (LRP) was recorded in vitro and the threshold and maximum amplitude determined. The same specimens used in the electrophysiological studies were then prepared for microscopy, and rod cell outer and inner segment dimensions and photoreceptor spacing were determined. In the light-reared animals a small LRP was first recorded at 5 days, but only at very high stimulus intensities. Thereafter, there was a rapid decrease in the threshold and an increase in the amplitude of the LRP. The threshold and amplitude of the LRP reached adult values at 14 days. Of the anatomical parameters, maturation of inter-receptor spacing (14 days) is clearly associated with the attainment of the adult LRP amplitude levels. Outer segment length was also adultlike by 14 days of age and thus paralleled physiological maturity of the photoreceptor. Changes over time in the mean diameter and length of rod cell inner segments (adultlike at 21 days) follows the pattern of ontogenetic maturation of the LRP. These findings imply a close relationship during ontogeny between the LRP and development of the outer segment. In dark-reared pups there is a delay in the maturation of the photoreceptor mosaic, but by 4 weeks of age, physiological characteristics of the photoreceptor are adultlike.

Aging↗
PubMed1979

Anatomtic and physiologic development of the photoreceptor of the kitten.

The postnatal development of the photoreceptor of the cat was studied using physiological and anatomical methods. The late receptor potential (LRP) was recorded in vitro and the threshold and maximum amplitude determined. The same specimens used in the electrophysiological studies were then prepared for microscopy, and rod cell outer and inner segment length and diameter, photoreceptor density, and inter-receptor distance were determined. A small LRP was first recorded at 9--10 days, but only at very high stimulus intensities. Thereafter, there was a rapid decrease in the threshold and an increase in the amplitude of the LRP. The threshold reached adult values at 17--18 days, while the amplitude of the LRP was adultlike at 23--26 days. Of the anatomical parameters examined, inter-receptor spacing and rod cell diameters seem to be most clearly associated, respectively, with the attainment of adult LRP threshold and amplitude. Outer segment length was adult-like at 35--43 days of age and thus postdated physiological maturity of the photoreceptor. These observations suggest that the surface area of the rod cell outer segment tips is more critical in the development of the adult LRP than is the number of discs in the outer segment. In addition, changes over time in the mean diameter and length of rod cell inner segments follows the pattern of ontogenetic changes in LRP amplitude. These findings imply a close relationship during ontogeny between the metabolic functions of the inner segment and phototransduction at the outer segment disc.

Age Factors↗
PubMed1978

Light microscopic analysis of the kitten retina: postnatal development in the area centralis.

A method was devised for morphological localization of the area centralis, and the timecourse of its formation as a structural entity was established. Postnatal differentiation of the retina proceeds as follows: the irregularly laminated ganglion cell layer of the newborn becomes unilaminar everywhere but in the presumptive area centralis, a difference which is first discernible at five to six days of age; the outer nuclear layer is always of the same thickness in the area centralis, while in the periphery the layer thins with time; the outer nuclear layer is always thinner in the area centralis than in the periphery; inner nuclear layer thickness is invariant early in postnatal life, but in the adult it is thicker in the area centralis than in the near temporal periphery; plexiform layers form by two weeks of age and rach adult thickness thereafter. Retinal ganglion cells were measured and the percent distributions of three ganglion cell size classes (6-10 micron; 11-20 micron; 21-35 micron) were determined for the area centralis and near temporal periphery; Mean ganglion cell size is constant in center and periphery through five weeks age, is adultlike in the periphery soon thereafter and in the center sometime after eight weeks of age. The percent distribution of ganglion cells by size class in center and periphery is not adultlike even at eight weeks of age. The implications of these observations and others are discussed relative to postnatal growth of the eye and placement of the area centralis in the retinal field and optic axis. The involvement of retinal cell proliferation, cell growth, ganglion cell dendrite formation and cell shape changes in the expansion of the retina are also discussed.

Age Factors↗