Biomedical subjects

M M Knight

Publications and source records attributed to M M Knight.

At least 19 recordsLinked to original sources

PubMed2001

Protocol for the determination of selected neutral and acidic semi-volatile organic contaminants in fish tissue.

Progress toward the development of a protocol for the determination of a broad spectrum of organic compounds in fish tissue is reported. Finely ground and homogenized fish tissue samples were Soxhlet extracted. Phenolic compounds in the extracts were acetylated and the derivatized extract containing the acetates and neutral semi-volatiles was cleaned up with silica gel and size-exclusion column chromatography. These semi-volatile organic compounds were determined by gas chromatography-mass spectrometry. The method is evaluated for recovery and precision of selected analytes during the analysis of over 300 fish tissue samples of varying species in support of contaminant determination in fish tissue from the Columbia/Snake River watershed.

Animals↗

PubMed2001

Chondrocyte deformation within mechanically and enzymatically extracted chondrons compressed in agarose.

Within articular cartilage, the chondron microenvironment will influence chondrocyte behaviour and response to loading. Chondrons were extracted from intact cartilage using either mechanical homogenisation (MC) or enzymatic digestion (EC) and cell and matrix morphology in unstrained and compressed agarose constructs was examined. Isolated chondrocytes (IC) were used for comparison. Immunolocalisation of type VI collagen and keratan sulphate revealed differences in the structure of the pericellular microenvironment such that MC most closely resembled chondrons in situ. The unstrained cell diameters of IC and EC were larger than MC at day 1 and increased significantly over a 7 day culture period. In contrast, cell diameters for MC remained constant. Compression of constructs at day 1 resulted in cell deformation for IC and EC but not MC. The two chondron extraction methods yielded chondrons of differing matrix morphology and associated differences in cell size and cellular response to load. The results indicate that the pericellular microenvironment of MC initially possessed a greater mechanical integrity than that of EC. Although these differences may be reduced with time in culture, characterisation of mechanically isolated chondrons suggests that the stiffness of the chondrons in situ may be greater than previous estimates.

Animals↗

PubMed2001

Temporal changes in cytoskeletal organisation within isolated chondrocytes quantified using a novel image analysis technique.

This paper examines temporal changes in the organisation of the cytoskeleton within isolated articular chondrocytes cultured for up to 7 days in agarose constructs. Fluorescent labelling and confocal microscopy were employed to visualise microtubules (MT), vimentin intermediate filaments (VIF) and actin microfilaments (AMF). To quantify the degree of cytoskeletal organisation within populations of cells, a novel image analysis technique has been developed and fully characterised. Organisation was quantified in terms of an Edge Index, which reflects the density of 'edges' present within the confocal images as defined by a Sobel digital filter. This parameter was shown to be independent of image intensity and, for all three cytoskeletal components, was validated statistically against a visual assessment of organisation. Both MT and VIF exhibited fibrous networks extending throughout the cytoplasm, while AMF appeared as punctate units associated with the cell membrane. The use of the Edge Index parameter revealed statistical significant temporal variation, in particular associated with VIF and AMF. These findings indicate the possibility of cytoskeletal mediated temporal variation in many aspects of cell behaviour following isolation from the intact tissue. Furthermore, the image analysis techniques are likely to be useful for future studies aiming to quantify changes in cytoskeletal organisation.

Animals↗

PubMed2001

Compressive deformation and damage of muscle cell subpopulations in a model system.

To study the effects of compressive straining on muscle cell deformation and damage an in vitro model system was developed. Myoblasts were seeded in agarose constructs and cultured in growth medium for 4 days. Subsequently, the cells were allowed to fuse into multinucleated myotubes for 8 days in differentiation medium, resulting in a population of spherical myoblasts (50%), spherical myotubes (35%), and elongated myotubes (15%) with an overall viability of 90%. To evaluate cell deformation upon construct compression half-core shaped constructs were compressed up to 40% strain and the resulting cell shape was assessed from confocal scans through the central plane of spherical cells. The ratio of cell diameters measured parallel and perpendicular to the axis of compression was used as an index of deformation (DI). The average DI of myoblasts decreased with strain level (0.99+/-0.03, 0.70+/-0.04, and 0.56+/-0.10 at 0%, 20%, and 40% strain), whereas for myotubes DI decreased up to 20% strain and then remained fairly constant (0.99+/-0.06, 0.55+/-0.06, 0.50+/-0.11). The discrepancy in DI between spherical myoblasts and myotubes at 20% strain was explained by the relative sensitivity of the cell membrane to buckling, which is more pronounced in the myotubes. Sustained compression up to 24 h at 20% strain resulted in a significant increase in cell damage with time as compared to unstrained controls. Despite differences in membrane buckling no difference in damage between myoblasts and spherical myotubes was observed over time, whereas the elongated myotubes were more susceptible to damage.

Animals↗

PubMed2001

Mechanical compression influences intracellular Ca2+ signaling in chondrocytes seeded in agarose constructs.

Ca2+ signaling forms part of a possible mechanotransduction pathway by which chondrocytes may alter their metabolism in response to mechanical loading. In this study, a well-characterized model system utilizing bovine articular chondrocytes embedded in 4% agarose constructs was used to investigate the effect of physiological mechanical compressive strain applied after 1 and 3 days in culture. The intracellular Ca2+ concentration was measured by use of the ratiometric Ca2+ indicator indo 1-AM and confocal microscopy. A positive Ca2+ response was defined as a percent increase in Ca2+ ratio above a preset threshold. A significantly greater percentage of cells exhibited a positive Ca2+ response in strained constructs compared with unstrained controls at both time points. In strained constructs, treatment with either Ga3+ or EGTA significantly reduced the number of positive Ca2+ responders compared with untreated controls. These results represent an important step in understanding the physiological role of intracellular Ca2+ in chondrocytes under mechanical compression.

Algorithms↗

PubMed2000

Beta transition and stress-induced phase separation in the spinning of spider dragline silk.

Spider dragline silk is formed as the result of a remarkable transformation in which an aqueous dope solution is rapidly converted into an insoluble protein filament with outstanding mechanical properties. Microscopy on the spinning duct in Nephila edulis spiders suggests that this transformation involves a stress-induced formation of anti-parallel beta-sheets induced by extensional flow. Measurements of draw stress at different draw rates during silking confirm that a stress-induced phase transition occurs.

Animals↗

PubMed2000

Chondrocyte deformation within compressed agarose constructs at the cellular and sub-cellular levels.

Mechanotransduction events in articular cartilage may be resolved into extracellular components followed by intracellular signalling events, which finally lead to altered cell response. Cell deformation is one of the former components, which has been examined using a model involving bovine chondrocytes seeded in agarose constructs. Viable fluorescent labels and confocal laser scanning microscopy were used to examine cellular and sub-cellular morphology. It was observed that cell size increased up to day 6 in culture, associated with an increase in the contents of proteoglycan and collagen. In addition, the organisation of the cytoskeleton components, described using a simple scoring scale, revealed temporal changes for actin fibres, microtubules and vimentin intermediate filaments. The constructs on day 1 were also subjected to unconfined compressive strains. A series of confocal scans through the centre of individual cells revealed a change from a spherical to an elliptical morphology. This was demonstrated by a change in diameter ratio, from a mean value of 1.00 at 0% strain to 0.60 at 25% strain. Using simple equations, the volume and surface areas were also estimated from the scans. Although the former revealed little change with increasing construct strain, surface area appeared to increase significantly. However further examination, using transmission electron microscopy to reveal fine ultrastructural detail at the cell periphery, suggest that this increase may be due to an unravelling of folds at the cell membrane. Cell deformation was associated with a decrease in the nuclear diameter, in the direction of the applied strain. The resulting nuclear strain in one direction increased in constructs compressed at later time points, although its values at all three assessment times were less than the corresponding values for cell strain. It is suggested that the nuclear behaviour may be a direct result of temporal changes observed in the organisation of the cytoskeleton. The study demonstrated that the chondrocyte-agarose model provides a useful system for the examination of compression events at both cellular and sub-cellular levels.

Animals↗

PubMed2000

Confocal analysis of cytoskeletal organisation within isolated chondrocyte sub-populations cultured in agarose.

This study reports the cytoskeletal organisation within chondrocytes, isolated from the superficial and deep zones of articular cartilage and seeded into agarose constructs. At day 0, marked organisation of actin microfilaments was not observed in cells from both zones. Partial or clearly organised microtubules and vimentin intermediate filaments cytoskeletal components were present, however, in a proportion of cells. Staining for microtubules and vimentin intermediate filaments was less marked after 1 day in culture however than on initial seeding. For all three cytoskeletal components there was a dramatic increase in organisation between days 3 and 14 and, in general, organisation was greater within deep zone cells. Clear organisation for actin microfilaments was characterised by a cortical network and punctate staining around the periphery of the cell, while microtubules and vimentin intermediate filaments formed an extensive fibrous network. Cytoskeletal organisation within chondrocytes in agarose appears, therefore, to be broadly similar to that described in situ. Variations in the organisation of actin microfilaments between chondrocytes cultured in agarose and in monolayer are consistent with a role in phenotypic modulation. Vimentin intermediate filaments and microtubules form a link between the plasma membrane and the nucleus and may play a role in the mechanotransduction process.

Actin Cytoskeleton↗

PubMed2000

Cognitive ability and functional status.

Significant confusion exists in the literature about functional status. Despite its importance, little attention has focused on developing and substantiating frameworks that detail the underpinnings of functional status, which has resulted in lack of agreement about its definition and dimensions. The purpose of this literature review was to examine the development of functional status and to describe the inclusion of its cognitive dimension. Cognition is one key dimension of functional status. One must 'know how' to perform to be successful in an activity. While cognitive capacity is generally considered in relation to functional status, the nature of the cognitive dimension is poorly described and poorly understood. Three databases were selected for review: Citations in Nursing and Allied Health (CINAHL), Psychology Literature (PsychLit), and the Medical data base known as MedLine. Key word searches identified thousands of sources. This analysis includes an extensive sampling of these sources from the 1960s through to 1998. The sources sorted into four primary categories and demonstrate a growing recognition of the cognitive dimension of functional status in the literature. Despite this recognition, the lack of conceptual clarity of both the term functional status and its cognitive dimension limits communication among disciplines and limits comparisons of functional status outcomes across studies. Functional status models are needed that include cognition as a core dimension. Population specific descriptions of the cognitive dimension should be guided by knowledge in the neurosciences.

Activities of Daily Living↗

PubMed1999

Application of polydivinylbenzene liquid chromatography columns to remove lipid material from fish tissue extracts for the analysis of semivolatile organics.

Liquid chromatography columns of 100% polydivinylbenzene (DVB) (packing) were used to remove lipid material from fish extracts before analysis of several semivolatile organic pollutants by gas chromatography-mass spectrometry (GC-MS). This packing material was found to be durable as the columns could be operated to about 900 p.s.i. resulting in high efficiency separation. Recoveries and relative standard deviations for 18 polynuclear aromatic hydrocarbons fortified into a fish extract and cleaned up by multiple DVB columns in series were in the range of 86 to 123% and 4 to 11%, respectively.

Animals↗

PubMed1998

The influence of elaborated pericellular matrix on the deformation of isolated articular chondrocytes cultured in agarose.

This study investigates the mechanical influence of pericellular matrix on the deformation of isolated articular chondrocytes compressed within 3% agarose specimens. After 1 day in culture, the cells were associated with minimal amounts of sulphated glycosaminoglycan (GAG) and hydroxyproline and exhibited substantial deformation from a spherical to an oblate ellipsoid morphology when subjected to 20% gross compressive strain. However, over the 6 day culture period, there was a reduction in cell deformation associated with an increase in matrix content. Treatment with testicular hyaluronidase at days 3 and 6 reduced sulphated GAG content to levels observed in untreated specimens at day 1. At day 3, the resulting cell deformation during 20% compression was equivalent to that in specimens compressed at day 1. However, at day 6 cell deformation was only partially restored, suggesting the presence of additional structural matrix components, other than sulphated GAG, which were not present at day 3. Dual scanning confocal microscopy indicated that the elaborated matrix formed a pericellular shell which did not deform during compression and was therefore stiffer than the 3% agarose substrate. Therefore, the elaboration of a mechanically functional pericellular matrix within 6 days, effectively limits the potential involvement of cell deformation in mechanotransduction within cell seeded systems such as those employed for cartilage repair.

Animals↗

PubMed1998

Response of chondrocyte subpopulations cultured within unloaded and loaded agarose.

Although it is well known that the metabolism of chondrocytes can be altered by the application of mechanical strain, it is unclear whether chondrocytes from the superficial and deep zones of cartilage respond in a similar manner. In this study, chondrocytes from the uppermost 15-20% (superficial cells) and the remaining tissue (deep cells) from bovine articular cartilage were isolated separately and cultured in agarose constructs. Cell deformation on application of a 15% static compressive strain was identical for both subpopulations after 24 and 72 hours in culture. The constructs were incubated under static and dynamic (0.3, 1, and 3 Hz) strains of 15% amplitude. Glycosaminoglycan synthesis by deep cells was unaffected by static strain or 3 Hz dynamic strain, whereas 0.3 Hz produced a significant reduction and 1 Hz induced a highly significant 50% stimulation of glycosaminoglycan synthesis (p < 0.001). Superficial cells exhibited a general inhibition of glycosaminoglycan synthesis. By contrast, proliferation of superficial cells was stimulated by dynamic strain whereas deep cells were not influenced. It has been suggested previously that mechanotransduction-induced controls of glycosaminoglycan synthesis and proliferation in chondrocytes embedded in agarose are uncoupled. Data presented in this study demonstrate that the two processes do, in fact, occur in different subpopulations of chondrocytes within the full-depth cell isolate.

Animals↗

PubMed1991

Parasites of domestic and wild animals in South Africa. XXVIII. Helminth and arthropod parasites of Angora goats and kids in Valley Bushveld.

Two adult Angora goats were slaughtered each month for 24 consecutive months on a farm in Valley Bushveld in the eastern Cape Province. On the same farm 2 Angora goat kids were slaughtered each month for 2 consecutive years from the time they were 1 week old until they reached 12 months of age. All these goats were processed for the recovery of helminth and arthropod parasites. Fourteen nematode species, 2 nematode genera and 1 cestode species were recovered. Worm burdens were generally low in the adult goats. Nematode burdens increased erratically in the kids reaching the greatest numbers when they were 1 year old. The tapeworm, Moniezia expansa, was present in kids at 3 or 4 months of age and had usually disappeared by the time they reached 7 months of age.

Animals↗

PubMed1991

Parasites of South African wildlife. IX. Helminths of kudu, Tragelaphus strepsiceros, in the eastern Cape Province.

The helminths of 25 kudu, Tragelaphus strepsiceros, from 3 localities in the eastern Cape Province were collected, counted and identified. The majority of kudu harboured no worms, and the burdens of those infected were small. A race of Cooperia rotundispiculum, a Dictyocaulus sp., a Haemonchus sp., Nematodirus helvetianus and Ostertagia ostertagi were recovered. Two parasites, Nematodirus helvetianus and Ostertagia ostertagi can be added to the list of helminth parasites of kudu in South Africa.

Animals↗

PubMed1988

The treatment of ticks on tortoises using amitraz.

Amitraz at a concentration of 2 ml litre-1 of water successfully induced detachment of Amblyomma marmoreum and Amblyomma hebraeum ticks from the mountain tortoise, Geochelone pardalis. Detached ticks died without reattaching. At the strength used, amitraz had no apparent adverse effects on the tortoises.

Animals↗

PubMed1986

A comparison of the tick burdens of wild animals in a nature reserve and on an adjacent farm where tick control is practised.

Acaricidal treatment of cattle, sheep and goats on a farm in Valley Bushveld in the Grahamstown district resulted in a reduction in the numbers of certain tick species on kudu (Tragelaphus strepsiceros), scrub hares (Lepus saxatilis) and crowned guinea fowl (Numida meleagris) on the same farm. The tick species most severely affected was Amblyomma hebraeum, while Haemaphysalis silacea, Hyalomma marginatum rufipes and Rhipicephalus appendiculatus were affected to a lesser extent. Rhipicephalus glabroscutatum and Rhipicephalus oculatus appeared to be unaffected.

Agriculture↗

PubMed1986

Parasites of domestic and wild animals in South Africa. XX. Arthropod parasites of the Cape mountain zebra (Equus zebra zebra).

The arthropod parasite burdens of 14 Cape mountain zebra (Equus zebra zebra), shot for survey purposes in the Mountain Zebra National Park in the eastern Cape Province, were determined. Three species of Gasterophilus larvae and 9 ixodid tick species were recovered. Larvae of Gasterophilus pecorum were the most numerous of the fly larvae recovered and Margaropus winthemi was the most abundant tick. Two horses examined in the park were infested with 3 species of Gasterophilus larvae and 7 species of ixodid ticks.

Animals↗

PubMed1986

Parasites of domestic and wild animals in South Africa. XXI. Arthropod parasites of vaal ribbok, bontebok and scrub hares in the western Cape Province.

Vaal ribbok (Pelea capreolus), bontebok (Damaliscus dorcas dorcas) and scrub hares (Lepus saxatilis) were slaughtered in the Bontebok National Park at regular intervals and examined for arthropod parasites. Twelve species of ixodid ticks were recovered; the antelope each harboured 9 species and the hares 11. Rhipicephalus nitens was the most prevalent and most abundant tick. The vaal ribbok also harboured large numbers of Ixodes pilosus and the bontebok fairly large numbers of Rhipicephalus glabroscutatum. The vaal ribbok were infested with 2 lice species and the larvae of 3 oestrid fly species. The bontebok harboured 2 lice species and the larvae of 2 oestrid flies, and the scrub hares were infested with a louse species and a flea species. The host preference and seasonal abundance of some of the parasites were determined.

Animals↗