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Biomedical subjects

K G Thompson

Publications and source records attributed to K G Thompson.

At least 37 records · Page 2Linked to original sources
PubMed2000

Use of the polymerase chain reaction assay for the detection of Mycobacterium avium subspecies paratuberculosis in blood and liver biopsies from experimentally infected sheep.

OBJECTIVE: To evaluate a polymerase chain reaction-based assay for the detection of Mycobacterium avium subsp paratuberculosis in blood and liver biopsies from subclinically infected sheep. STUDY DESIGN: A direct PCR assay for the detection of M a paratuberculosis was applied to liver biopsy specimens and to samples of blood that were sequentially collected over 53 weeks from 14 sheep infected experimentally with the organism. RESULTS: Of 117 blood samples from the 14 experimentally infected sheep, two tested positive in the PCR assay. Both positive results were obtained in two subclinically infected sheep that had paratuberculosis later confirmed by histological examination at necropsy. However, the assay failed to detect the target DNA in samples of blood from five other sheep with histologically confirmed paratuberculosis. Similarly, the PCR assay on liver biopsy specimens collected 32 weeks after administration of M a paratuberculosis gave only two positive results, both of which were obtained in sheep with histological evidence of paratuberculosis. CONCLUSIONS: The PCR assay on blood and liver biopsies does not provide a useful method for the diagnosis of M a paratuberculosis infection in subclinically infected sheep.

Animals↗
PubMed1999

Daily supplementation with aged garlic extract, but not raw garlic, protects low density lipoprotein against in vitro oxidation.

The oxidation of low density lipoprotein (LDL) is believed to be an important process in the development and progression of atherosclerosis. In this study, human subjects were supplemented daily with one of: 6 g raw garlic; 2.4 g aged garlic extract (AGE); or 0.8 g DL-alpha-tocopherol acetate for 7 days to determine the effect on the susceptibility of LDL particles to Cu2+-mediated oxidation. LDL isolated from subjects given either alpha-tocopherol or AGE, but not raw garlic, was significantly more resistant to oxidation than LDL isolated from subjects receiving no supplements. These results suggest that if antioxidants are proven to be antiatherogenic, AGE may be useful in preventing atherosclerotic disease.

Adult↗
PubMed1999

Dietary conjugated linoleic acids promote fatty streak formation in the C57BL/6 mouse atherosclerosis model.

Conjugated linoleic acids (CLA) are positional isomers of linoleic acid which have been suggested by some to possess antiatherosclerotic properties. To test this hypothesis, three groups of twenty C57BL/6 mice were fed on atherogenic diets containing: 5 g CLA/kg, 2.5 g CLA + 2.5 g linoleic acid/kg or 5 g linoleic acid/kg. All diets were fed for 15 weeks and contained (g/kg): triacylglycerol 145, free fatty acids 5, cholesterol 10 and cholic acid 5. At the completion of the experimental period, when data from both groups fed on CLA were combined, dietary CLA did not produce significant differences in body weight, serum total cholesterol concentration or serum HDL-cholesterol concentration. However, mice receiving CLA developed a significantly higher serum HDL-cholesterol: total cholesterol ratio and a significantly lower serum triacylglycerol concentration than controls. Despite causing a serum lipoprotein profile considered to be less atherogenic, the addition of CLA to the atherogenic diet increased the development of aortic fatty streaks. Considering the increased atherogenesis associated with dietary CLA in the present study, and the failure to demonstrate a significant beneficial effect of CLA in other animal studies, there is currently no conclusive evidence to support the hypothesis that CLA protect against atherogenesis.

Analysis of Variance↗
PubMed1999

The detection of visual signals by macaque frontal eye field during masking.

The neural link between a sensory signal and its behavioral report was investigated in macaques trained to locate an intermittently detectable visual target. Neurons in the frontal eye field, an area involved in converting the outcome of visual processing into motor commands, responded at short latencies to the target stimulus whether or not the monkey reported its presence. Neural activity immediately preceding the visual response to the mask was significantly greater on hits than on misses, and was significantly greater on false alarms than on correct rejections. The results show that visual signals masked by light are not filtered out at early stages of visual processing; furthermore, the magnitude of early visual responses in prefrontal cortex predicts the behavioral report.

Animals↗
PubMed1999

Naturally occurring osteoarthritis in the metacarpophalangeal joints of wild horses.

This study identified changes consistent with osteoarthritis; articular cartilage damage, subchondral bone sclerosis and marginal osteophytes, in the metacarpophalangeal joints of wild New Zealand horses. The articular cartilage lesions were identified by Indian ink staining techniques and histology. The lesions occurred on the proximodorsal aspect of the first phalanx (P1) and were more severe on the medial compared to the lateral eminence of the bone, and their severity increased with age. The bone mineral density of the subchondral bone underlying the cartilage lesions, assessed using conventional radiography and dual energy absorptiometry, also increased with age and with severity of the overlying cartilage lesion. Subjective assessment of cabinet radiographs revealed that the subchondral bone sclerosis was greater in horses with severe articular cartilage damage. Ossicles, with a distinct trabecular bone pattern, were identified at the proximo-dorsal margin of P1 in 8 specimens from 5 horses from the older age groups (greater than age 5 years). The results of this study demonstrate age-related changes consistent with osteoarthritis in the metacarpophalangeal joints of wild horses. There appears to be a significant relationship between subchondral bone sclerosis and overlying cartilage degeneration in the proximodorsal aspect of P1. We have identified an age-related osteoarthritic process naturally present in horses; and postulate that the stresses of racing and training may accelerate this ageing process.

Absorptiometry, Photon↗
PubMed1999

Neural selection and control of visually guided eye movements.

We review neural correlates of perceptual and motor decisions, examining whether the time they occupy explains the duration and variability of behavioral reaction times. The location of a salient target is identified through a spatiotemporal evolution of visually evoked activation throughout the visual system. Selection of the target leads to stochastic growth of movement-related activity toward a fixed threshold to generate the gaze shift. For a given image, the neural concomitants of perceptual processing occupy a relatively constant interval so that stochastic variability in response generation introduces additional variability in reaction times.

Animals↗
PubMed1999

The effect of moderate alcohol consumption as either red or white wine in the C57BL/6 mouse atherosclerosis model.

BACKGROUND: Epidemiological studies suggest that the moderate consumption of alcohol, especially red wine, protects against atherosclerosis. This hypothesis was tested using the C57BL/6 mouse atherosclerosis model. DESIGN: Sixty mice were fed an atherogenic diet for 15 weeks. Two groups of 20 mice received drinking water containing 3.1% alcohol, either or white wine, while the control group received plain water. At the conclusion of the experiment, serum lipoprotein cholesterol concentrations were measured and the formation of fatty streaks in the aortic sinus was quantified. RESULTS: When mice receiving red wine were compared with mice receiving white wine, no significant differences in serum lipoprotein profile or fatty streak formation were observed. Surprisingly, when data from mice receiving either red or white wine were combined, mice receiving alcohol developed a lower mean serum high-density lipoprotein cholesterol concentration [2.34 +/- 0.44 mmol/l (mean +/- SD)] and an increased mean area of aortic fatty streaks (0.46 +/- 0.22 mm2) than controls (2.70 +/- 0.59 mmol/l and 0.31 +/- 0.11 mm2). CONCLUSIONS: These results do not support the hypothesis that red wine provides more protection against atherosclerosis than white wine. The mechanisms by which the moderate intake of alcohol increased fatty streak formation in C57BL/6 mice require further investigation.

Alcohol Drinking↗
PubMed1998

Signal timing across the macaque visual system.

The onset latencies of single-unit responses evoked by flashing visual stimuli were measured in the parvocellular (P) and magnocellular (M) layers of the dorsal lateral geniculate nucleus (LGNd) and in cortical visual areas V1, V2, V3, V4, middle temporal area (MT), medial superior temporal area (MST), and in the frontal eye field (FEF) in individual anesthetized monkeys. Identical procedures were carried out to assess latencies in each area, often in the same monkey, thereby permitting direct comparisons of timing across areas. This study presents the visual flash-evoked latencies for cells in areas where such data are common (V1 and V2), and are therefore a good standard, and also in areas where such data are sparse (LGNd M and P layers, MT, V4) or entirely lacking (V3, MST, and FEF in anesthetized preparation). Visual-evoked onset latencies were, on average, 17 ms shorter in the LGNd M layers than in the LGNd P layers. Visual responses occurred in V1 before any other cortical area. The next wave of activation occurred concurrently in areas V3, MT, MST, and FEF. Visual response latencies in areas V2 and V4 were progressively later and more broadly distributed. These differences in the time course of activation across the dorsal and ventral streams provide important temporal constraints on theories of visual processing.

Animals↗
PubMed1998

Dietary antioxidants do not reduce fatty streak formation in the C57BL/6 mouse atherosclerosis model.

Epidemiological studies and animal trials have suggested that dietary antioxidants protect against atherosclerosis. To test this hypothesis, C57BL/6 mice were fed atherogenic diets supplemented with either vitamin E or butylated hydroxytoluene (BHT). Three groups of 20 mice were fed for 15 weeks on diets containing 1% cholesterol and 0.5% cholic acid. The diet of two groups was supplemented with either 2% vitamin E or 1% BHT. The control group received no antioxidant supplements. The lowest mean serum cholesterol concentration was measured in mice supplemented with vitamin E. Mean serum HDL cholesterol concentrations were highest in the control group, which also had the highest ratio of HDL cholesterol to total cholesterol. Mice fed BHT developed a significantly greater area of aortic fatty streak lesions than the other two groups. However, despite having a more atherogenic lipoprotein profile, mice fed vitamin E developed a level of fatty streak formation similar to the control group. At the end of the trial, mice consuming the vitamin E- and BHT-supplemented diets had higher serum total antioxidant levels than the control mice. Because of changes to lipid metabolism caused by both vitamin E and BHT, the results of this study cannot be used to support the hypothesis that antioxidants confer protection against atherosclerosis. The results do, however, raise the possibility that other studies demonstrating an antiatherogenic action of vitamin E and BHT may have been influenced by their effects on lipid metabolism.

Animals↗
PubMed1998

Pharmacokinetics of multiple-dose administration of eltenac in horses.

OBJECTIVE: To compare pharmacokinetics of eltenac after first and last IV administrations (0.5 mg/kg), using a multiple dosing schedule. ANIMALS: 6 adult mares. PROCEDURE: Eltenac (50 mg/ml) was administered IV at a dosage of 0.5 mg/kg of body weight every 24 hours for days 0 through 4. On days 0 and 4, blood samples were collected before, then periodically for 8 hours after eltanac administration. Concentration of eltenac in plasma samples was determined by use of high-performance liquid chromatography. RESULTS: On day 0, median area under the plasma eltenac concentration versus time curve (AUC) was 6.77 microg.h/ml (range, 5.61 to 8.08 microg.h/ml), median plasma clearance was 1.23 ml/min/kg (range, 1.03 to 1.40 ml/min/kg), and median steady-state volume of distribution was 191 ml/kg (range, 178 to 218 ml/kg). Median terminal half-life of eltenac was 2.36 hours (range, 2.30 to 2.98 hours). On day 4, median eltenac AUC was 6.70 microg.h/ml (range, 5.21 to 7.44 microg.h/ml), median plasma clearance was 1.23 ml/min/kg (range, 1.12 to 1.53 ml/min/kg), and median steady-state volume of distribution was 193 ml/kg (range, 172 to 205 ml/kg). Median terminal half-life of eltenac was 2.40 hours (range, 2.11 to 3.25 hours). Protein binding of eltenac, determined by ultrafiltration, was > 99% at a total plasma concentration of 36 microg/ml. CONCLUSION: Pharmacokinetic variables determined for each horse were not different between days 0 and 4. CLINICAL RELEVANCE: Under conditions of this study, there was no clinically relevant accumulation of eltenac in equine plasma or alteration of pharmacokinetic variables after multiple IV dosing of 0.5 mg/kg of eltenac.

Aniline Compounds↗
PubMed1997

Detection of Mycobacterium avium subsp. paratuberculosis in ovine tissues and blood by the polymerase chain reaction.

A direct polymerase chain reaction (PCR) test was applied to DNA extracted from blood, liver, ileocecal lymph node and ileum from twelve ewes in poor condition with histologically confirmed paratuberculosis and ten clinically normal sheep which had no evidence of paratuberculosis. The assay was compared with four serological tests: complement fixation test (CFT), gel diffusion test (AGID) and two enzyme-linked immunosorbent assays (ELISA). The PCR detection rate of Mycobacterium avium subsp. paratuberculosis, when results of single tests were interpreted in duplicate, was 72% for ileocecal lymph node, 90% for liver, and 100% for ileum in sheep with confirmed paratuberculosis. A single PCR test detected the target DNA in 66% of 0.5 ml blood samples. Sensitivities of serological tests compared with histological diagnosis were: 33% for CFT, 66% for AGID, 75% for the Central Animal Health Laboratory (CAHL) ELISA, and 83% for the 'modified' Commonwealth Serum Laboratories (CSL) ELISA. The PCR assay gave no positive reaction in samples collected from 10 sheep considered to be free of paratuberculosis. Similarly, all four serological tests were also 100% specific. The results raise some hope for the development of a PCR-based test using liver biopsy specimens, or possibly blood, in the diagnosis of paratuberculosis in sheep.

Animals↗
PubMed1997

Hepatogenous photosensitisation in fallow deer (Dama dama) in New Zealand.

An outbreak of hepatogenous photosensitisation occurred in fallow deer and was diagnosed as facial eczema on the basis of liver lesions and plasma enzyme changes over 56 weeks. Clinical signs of photosensitisation were not as obvious as they are in sheep and cattle. The condition occurred over autumn and in the following spring. Six of 23 deer died or were destroyed. Concentrations of plasma total bilirubin, total bile acids and cholesterol increased, as well as the activities of aspartate transaminase, glutamic dehydrogenase, lactic dehydrogenase, alkaline phosphatase and gamma glutamyltransferase. Albumin:globulin ratios declined due to moderate increases in globulin and minor reductions in albumin. Many of the plasma enzyme activities did not return to normal after autumn and increased to even higher values during the spring outbreak of photosensitisation. Minor plasma biochemical changes were also detected in non-photosensitive deer in the same herd.

Journal Article↗
PubMed1997

Dissociation of visual discrimination from saccade programming in macaque frontal eye field.

To determine whether visual discrimination in macaque frontal eye field (FEF) is contingent on saccade planning, unit activity was recorded in two monkeys during blocked go and no-go visual search trials. The eye movements made by monkeys after correct no-go trials, in addition to an attenuation of the visual responses in no-go trials compared with go trials, indicated that covert saccade planning was effectively discouraged. During no-go search trials, the activity of the majority of neurons evolved to signal the location of the oddball stimulus. The degree and time course of the stimulus discrimination process observed in no-go trials was not different from that observed in go trials. We conclude that the discrimination of a salient visual stimulus reflected by FEF neurons is not contingent on saccade production but rather may reflect the outcome of an automatic visual selection process.

Animals↗
PubMed1996

Visual feature selectivity in frontal eye fields induced by experience in mature macaques.

When examining a complex image, the eye movements of expert observers differ from those of novices; experts have learned to ignore features that are visually salient but are not relevant to the interpretation of the image. We have studied the neural basis of this form of perceptual-motor learning using monkeys that have learned to search for a visual target among distractors. Monkeys trained to search only for, say, a red stimulus among green distractors will ignore green stimuli even if they subsequently appear as targets in a complementary search array, that is, among red distractors. We recorded from neurons in the frontal eye field (FEF), a cortical area that responds to visual stimuli and controls purposive eye movements. Normally, FEF neurons do not exhibit feature selectivity, but their activity evolves to signal the target for an incipient eye movement. In monkeys trained exclusively on targets of one colour, however, FEF neurons show selectivity for stimuli of that colour. Because this selective response occurs so soon after presentation of the stimulus array, and is independent of location within the visual field, we propose that it reflects a form of experience-dependent plasticity that mediates the learning of arbitrary stimulus-response associations.

Animals↗
PubMed1996

Effect of selenium and a-tocopherol supplementation on postpartum reproductive function of dairy heifers at pasture.

The objective of this study was to investigate the effects of selenium (Se) and alpha-tocopherol supplementation on uterine involution and ovarian function in dairy heifers fed a prepartum diet containing low concentrations of Se and alpha-tocopherol. Twenty-four pregnant Friesian heifers were randomly allocated to one of four experimental groups in a 2 x 2 design balanced for age and body weight. Prepartum treatments consisted of supplementation with either 2 intraruminal Se pellets or 3600 mg of alpha-tocopherol p.o. 4 times per wk, or both. Control animals received no supplementation. For 8 wk before calving, the heifers were fed exclusively on pasture hay which contained less than 10 microg/kg of Se and 19 mg/kg of alpha-tocopherol. After calving, the heifers grazed perennial ryegrass and white clover pasture. Concentrations of Se and alpha-tocopherol in serum for the prepartum heifers of the control group were 10 ng/ml and 1.3 microg/ml, respectively, indicating deficiencies of these nutrients. Treatment with Se and alpha-tocopherol increased prepartum serum concentrations of Se and alpha-tocopherol to 74 ng/ml and 5 microg/ml, respectively (P < 0.001). However, treatment with Se, alpha-tocopherol, or both, failed to enhance uterine involution, hasten resumption of postpartum ovarian activity or reduce the incidence of clinical postpartum abnormalities. These findings suggest that postpartum reproductive dysfunction is not a primary feature of moderate Se or vitamin E deficiency of cattle at pasture.

Journal Article↗
PubMed1996

Neutropenia with a probable hereditary basis in Border Collies.

This paper documents a disease of Border Collies characterised by chronic neutropenia which probably resulted in recurrent bacterial infections manifesting as osteomyelitis and sometimes gastroenteritis. The neutropenia occurred despite hyperplasia of the myeloid cells in the bone marrow and a shift to the right in myeloid cell maturation. The underlying defect is currently unknown but may result from the inability of neutrophils to escape from the bone marrow into the peripheral circulation. Necrosis and new bone formation commonly involved the metaphyseal regions of long bones. Other findings included a fasting hypercholesterolaemia and the occasional presence of nucleated red blood cells in circulation, despite a non-regenerative anaemia. An autosomal recessive mode of inheritance is suspected. This condition has some features of a rare human disease called myelokathexis which is also believed to have in autosomal recessive mode of inheritance.

Journal Article↗