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Biomedical subjects

D G Jones

Publications and source records attributed to D G Jones.

At least 19 recordsLinked to original sources
PubMed1992

The bequest of human bodies for dissection: a case study in the Otago Medical School.

AIMS: To explore why and by whom body bequests to the Otago Medical School have been made since the 1960s. METHODS: We sent out a questionnaire to people who have bequeathed their bodies to the medical school, the people being randomly selected on the basis of the inclusion of the initial J in a forename. The questionnaire sought information on sex, marital status, age, occupation at the time of bequest and bequest information source, as well as reasons for the bequest, expectations of cadaver use and attitudes towards organ donation. RESULTS: The most common reasons for making a bequest were--to aid medical science, and gratitude to the medical profession. There was, however, widespread confusion between cadaver use for medical teaching and for research. CONCLUSIONS: These center around the ethical implications of our findings for organ donation and attitudes towards usage of the dead body.

Adult↗
PubMed1992

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Animals↗
PubMed1992

Perforated synapses are present during synaptogenesis in rat neocortex.

It has been known for some time that perforated synapses increase in number and size with increasing age. Initially, these trends were used to support the concept that nonperforated synapses enlarge until an optimal size is reached, at which point they perforate and may subsequently split. More recent stereological and three-dimensional reconstruction investigations, however, suggest that this may not be the case and that perforated and nonperforated synapses constitute separate synaptic populations. In order to test the separate population hypothesis, synapses have been studied ultrastructurally in the parietal cortex of rats aged 19 and 20 days gestation, and 1 and 4 days postnatal. By examining synapses serially, and also by studying three-dimensional reconstructions, it has been demonstrated that perforated synapses are present at each of these ages. Some are relatively simple in organization, resembling previously described perforated synapses at 14 days of age, although others appear to consist of two or more separate PSD components. These findings demonstrate that perforated synapses are present from early on in synaptogenesis and that developing perforated synapses may have distinct characteristics that cast light on their developmental course.

Animals↗
PubMed1992

A comparison of superoxide dismutase (SOD, EC:1.15.1.1) distribution in gastro-intestinal nematodes.

An examination of the distribution of superoxide dismutase (SOD) activities in whole worm homogenates from six gastro-intestinal nematodes, at different life-cycle stages, demonstrated that the third larval stages of each species contained notably more activity than the corresponding adults. Significant SOD activities were detected in culture fluids following in vitro maintenance of third and fourth larval stage and adult Trichostrongylus vitrinus and Teladorsagia circumcincta (formerly Ostertagia circumcincta). Marked interspecies variation was observed when SOD isoenzyme profiles of adult and third larval stage Nippostrongylus brasiliensis, Trichostrongylus vitrinus, Teladorsagia circumcincta and Haemonchus contortus were compared. In addition, SOD activity and isoenzyme polymorphism were greater in Nippostrongylus brasiliensis harvested from primed rats compared to parasites recovered from naive rats.

Animals↗
PubMed1992

Use of enzyme microassay to detect eosinophil potentiating activity of cytokines in sheep.

Microplate assays for eosinophil peroxidase (EPO) and arylsulphatase (EAS) have been established as indices of eosinophil survival/proliferation in sheep bone marrow cell (SBMC) cultures. Cell specificity was confirmed using density-fractionated and differentially depleted SBMC populations. Several recombinant cytokines including interleukins 3 (IL-3) and 5 (IL-5), and granulocyte macrophage-colony stimulating factor (GM-CSF), but not macrophage-CSF (M-CSF), had demonstrable eosinophil-potentiating activity on the basis of enhanced EPO and EAS activities in treated, compared with untreated, SBMC cultures. Effects of IL-5 were abrogated in the presence of a specific monoclonal anti-IL-5 antibody. The results indicate that measurement of EPO and EAS in cultured SBMC offers a simple and effective method for detecting eosinophil potentiating activity in the ovine.

Animals↗
PubMed1991

Development of an opiate-based anaesthetic technique for use in dogs with cardiomyopathy.

An opiate-based anaesthetic technique has been developed for use in dogs with end-stage heart failure due to dilated cardiomyopathy. It has been used in dogs undergoing translocation of the left latissimus dorsi around the descending thoracic aorta to create an autologous counterpulsation system. Anaesthesia was induced with barbiturate (10 mg/kg thiopentone) and fentanyl (500 micrograms) and maintained by an infusion of fentanyl (0.5 micrograms/kg/minute) [corrected] in addition to halothane (0.1 to 0.5 per cent) and nitrous oxide (20 to 60 per cent). This technique provided safe anaesthesia for major intrathoracic surgery.

Anesthesia, General↗
PubMed1991

Frequency of occurrence of perforated synapses in developing rat neocortex.

The frequency of occurrence of perforated synapses in the molecular layer of rat parietal cortex has been determined using the disector method. Perforated and non-perforated synapses were examined in electron micrographs, all quantitative procedures being carried out on adjacent sections, as required by the disector procedure. The numerical densities of perforated, non-perforated and all synapses were determined at nine ages, ranging from 0.5 to 22 months of age. The frequencies of perforated synapses were subsequently calculated. These ranged from 18.1% at 0.5 months to a peak of 37.2% at 10 months of age, and remained at around 34% up to 19 months. A frequency of 26.7% was found at 22 months of age. The mean projected height of the total perforation increased from 66 nm at 0.5 months to 133 nm at 22 months of age. These results suggest that perforated synapses are present throughout the life-span of the animal, and increase in complexity with increasing age.

Aging↗
PubMed1991

Perforated and non-perforated synapses in rat neocortex: three-dimensional reconstructions.

Perforated and non-perforated synapses in the molecular layer of rat parietal cortex have been assessed morphologically and quantitatively using three-dimensional reconstructions of the postsynaptic terminal. Perforated synapses were analyzed at nine ages, ranging from 0.5 to 22 months of age, and non-perforated synapses at three ages--0.5, 12, and 22 months. Examination of the reconstructions shows that perforated synapses increase in size and complexity with increasing age. This increasing complexity is reflected in a break-up of the postsynaptic density, which is punctuated by larger, branched perforations. In the most extreme cases the result is the appearance of isolated islands of postsynaptic density separated by, and also surrounded by, a synaptic contact zone. Spinules are especially prominent at around 12 months of age in perforated synapses, and the overall negative curvature of the young junctions is replaced by positively curved junctions from 4 months onwards. The non-perforated synapses are relatively small and show few changes with increasing age. Using the measurement option in the reconstruction program, the following trends emerged. All parameters of perforated synapses increased in size with increasing age, whereas the corresponding parameters of non-perforated synapses remained relatively unchanged over this age range. In addition, the percentage of the synaptic contact zone surface area occupied by the postsynaptic density decreased with increasing age in perforated synapses, but increased in non-perforated synapses. The total postsynaptic density surface area of non-perforated synapses per unit volume of molecular layer was double that of perforated synapses at 0.5 months, but the situation was reversed at 12 months. This parameter was similar in the 2 populations at 22 months. This suggests that perforated synapses contribute more to the total surface area of the postsynaptic density in mid- to late-adulthood than do non-perforated synapses, despite non-perforated synapses outnumbering perforated by 2-3:1 at these ages. These data provide more specific evidence that perforated and non-perforated synapses constitute separate synaptic populations from early in development, and that perforated synapses are responsible for the maintenance of neuronal postsynaptic density surface area from mid-adulthood onwards.

Animals↗
PubMed1991

Neuronal survival and neurite growth in cultured cerebral explants: assessment of the effect of cytosine arabinoside using improved stereology.

Using improved stereological procedures, based on measurements of the total reference volume, the effect of cytosine arabinoside (AraC) on neurons and non-neuronal cells in rat cerebral explants has been reinvestigated. These analyses revealed that, in the AraC-treated explants, neurons support a significantly increased volume of neurites, while the volume of non-neuronal cells in the outgrowth zone is significantly decreased. The total number of neurons is similar in the control and treated explants. Since AraC primarily affects dividing cells, these data suggest that the increased volume of neurites per neuron may be mediated through a curtailment of non-neuronal cell division in the AraC-treated explants. This volumetric approach represents a major improvement on current morphometric approaches for quantifying cultured explants of nervous tissue, and provides important evidence that the previously postulated effects of AraC are real ones.

Animals↗
PubMed1991

Perforated synapses and plasticity. A developmental overview.

Against a background of existing models relating perforated synapses to synaptic plasticity, the numerical density and frequency of perforated synapses in rat neocortex have been assessed from 1 d to 22 mo of age using the disector procedure, and changes in their morphology were assessed using 3-D computer reconstructions. The data point toward perforated and nonperforated synapses being separate synaptic populations from early in development, and with perforated synapses playing a part in the maintenance of neuronal postsynaptic density surface area from mid-adulthood onwards. This suggests that they play a crucial role in synaptic plasticity, although its nature may be different from that postulated by most recent workers.

Animals↗
PubMed1991

Molecular cloning, characterization and analysis of the regulation of the ARO2 gene, encoding chorismate synthase, of Saccharomyces cerevisiae.

We describe here the cloning, characterization and analysis of the regulation of the ARO2 gene of Saccharomyces cerevisiae, the first reported study of a eukaryotic gene encoding chorismate synthase (E.C. 4.6.1.4). The gene contains an ORF of 1128 bp, encoding a protein with a calculated molecular mass of 40.8 kDa. ARO2 is regulated under the 'general control system' for amino acid biosynthesis by the transcriptional activator GCN4 which binds in vitro at three sites within the ARO2 promoter. The ARO2 gene product is highly similar to its Escherichia coli counterpart, with a 47% identity distributed over the entire length of the peptide. We therefore suggest that the S. cerevisiae chorismate synthase, in contrast to the Neurospora crassa enzyme, but like other chorismate synthases, is a monofunctional peptide, solely possessing chorismate synthase activity.

Amino Acid Sequence↗
PubMed1991

A computational model for the overall pattern of ocular dominance.

In layer IV of the primary visual cortex, in both the macaque monkey and the cat, geniculocortical terminals representing the two eyes are segregated into alternating zones known as ocular dominance bands. Viewed tangentially, in the monkey these bands take the form of a series of branching parallel stripes that run roughly perpendicular to the border of striate cortex. In the cat, the overall ocular dominance pattern consists of irregularly branching, beaded bands that exhibit no predominant orientation. If the striking differences in the appearance of these two patterns reflect important differences in the basic rules governing cortical ocular dominance, then this poses a problem for attempts to formulate general principles of visual cortical organization. However, it has been suggested that the differences in the appearance of the ocular dominance patterns in these two species could result simply from known differences in the boundary conditions of their geniculocortical pathways. This article describes the formulation and testing of a single computational model that accurately predicts the quite dissimilar ocular dominance patterns in cats and monkeys. This model also generalizes to predict the different ocular dominance patterns observed in young and old three-eyed frogs, supporting the notion that the overall pattern of ocular dominance is governed by a common set of rules. The significance of these results is discussed in terms of previous models, which have focused largely on local processes underlying the development of ocular dominance segregation. Although the present model is not a developmental one, it does shed some light on potential mechanisms for establishing retinotopy in striate cortex and on possible developmental relationships between the geniculostriate pathway and intrinsic modularity of the striate cortex.

Animals↗