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Biomedical subjects

J K Pearson

Publications and source records attributed to J K Pearson.

At least 19 recordsLinked to original sources
PubMed1994

Toxic axonal degeneration occurs independent of neurofilament accumulation.

Alteration of neurofilament (NF) proteins is considered a critical component and a causative factor for a number of neuropathologies, especially certain neurotoxicities. Correlative observations have supported this hypothesis; the current study tests this relationship by exposure of neurotoxicants to crayfish, a species lacking NFs. Morphological and immunological tests verified the absence of NFs in crayfish peripheral nerve axons. Tail injections of acrylamide (ACR), 2,5-hexanedione (2,5-HD), or 3,4-dimethyl-2,5-HD (3,4-DMHD) produced ataxia and paralysis. Morphological expression of axonal degeneration in a spatial and temporal pattern of progression comparable to mammalian species possessing NFs was observed. With gamma-diketones, time to onset was slower than observed in mammals but relative potency between neurotoxic analogues was maintained. Non-neurotoxic analogues failed to produce any functional signs of neurotoxicity. These data are consistent with the conclusion that NF accumulations are not cause-effect related to axonal degeneration in these models of neurotoxicity and raise questions as to the relationship between accumulation of NF proteins and axonal degeneration in other neuropathological conditions.

Acrylamides↗
PubMed1992

Increasing the effect of photodynamic therapy on the RIF-1 murine sarcoma, using the bioreductive drugs RSU1069 and RB6145.

The effect of combining photodynamic therapy (PDT) and bioreductive drugs has been investigated using the RIF-1 experimental murine tumour. Light was delivered interstially to the tumour at 675 nm using a single optical fibre attached to an argon-ion dye laser. The photosensitizer was disulphonated aluminium phthalocyanine (AlS2Pc) and the bioreductive drugs were the dual function nitroimidazole RSU1069 and its pro-drug RB6145. Varying the time between administration of the photosensitizer and light delivery (TL) from 30 min to 24 h had little influence on the extent of the anti-tumour effect of PDT alone, as measured by the regrowth delay endpoint. When the bioreductive drug was included in the treatment, administered 20 min before light irradiation, regrowth delay was greatly increased. The effectiveness of the combined treatment was optimum for short values of TL (about 1 h). Fluorescence microscopy was used to investigate the distribution of the photosensitizer within the tumours. This showed that the compound was mainly confined to the tumour vasculature over the first few hours post-treatment. The high efficacy of the combined treatment of PDT and bioreductive drugs for short values of TL suggest that photodynamic action, during the period when the photosensitizer AlS2Pc is confined to the vasculature, enhances the severity of tumour hypoxia which is sufficient to induce activation of the bioreductive drugs.

Animals↗
PubMed1987

Enzyme activity changes in rat soleus motoneurons and muscle after synergist ablation.

Quantitative enzyme histochemical methods have been used to determine the effect of ablation of synergists on the oxidative metabolism of the alpha-motoneurons and muscle fibers of the rat soleus. Sixty days postablation, the NADH-tetrazolium reductase (NADH-TR) activity of soleus motoneurons decreased 12.5% from 0.327 +/- 0.005 (mean +/- SE; optical density units) to 0.286 +/- 0.007. In the muscle fibers, the alpha-glycerophosphate dehydrogenase activity (glycolytic enzyme) decreased from 0.114 +/- 0.010 to 0.074 +/- 0.009, a change of 35.1%, and the NADH-TR activity decreased 21.2% from 0.348 +/- 0.018 to 0.274 +/- 0.017. In both the motoneurons and the muscle fibers, the decrease was nonspecific for all cells, although a greater effect on the cells with higher enzyme activity was observed. The decreased NADH-TR activity represents a shift in the oxidative profile of the motoneurons and muscle fibers, indicating a decreased ability to use oxidative metabolism for periods of short-term high-energy demands. Furthermore, the parallel decrease in muscle fibers and motoneurons with high NADH-TR activity (fast-twitch oxidative-glycolytic fibers and presumably also motoneurons) demonstrates the tight correlation of the NADH-TR activity between these parts of the motor unit in both control and synergist-ablated muscles.

Animals↗
PubMed1981

Changes of the marginal periodontium as a result of labial tooth movement in monkeys.

Tooth position has been suggested to be an important factor in gingival recession. Due to conflicting reports in the literature, this study was undertaken to examine the effects of labial tooth movement on changes in the marginal periodontium. Orthodontic tooth movement was performed in five monkeys (Macaca nemistrina). Oral health was established and exploratory surgery was performed to assess the level of the connective tissue attachment and marginal bone. Measurements of the gingival margin and mucogingival junction were taken and orthodontic forces were applied. The central incisors were moved labially a mean distance of 3.05 mm. Posttherapy measurements were performed to assess the change which occurred as a result of tooth movement. Significant recession of the gingival margin, connective tissue level and marginal bone was found.

Animals↗
PubMed1976

Bovine leptospirosis: infection by the Hebdomadis serogroup and mastitis.

An outbreak of mastitis involving approximately 70 out of 140 cows over a two-month period is described. Common mastitis pathogens were not incriminated. Leptospires belonging to the Hebdomadis serogroup were isolated from the milk of three out of five cows and the blood of two of those cows.

Animals↗
PubMed1976

Reproducibility of electronic cell counts in milk; a study of 5 further factors.

This paper is a sequel to a previous one in which a number of factors likely to influence the accuracy of counting somatic cells in milk was assessed; in the present work the effects of 5 other factors are investigated. In a study of storage time and temperature of milk samples fixed in formalin, a significant increase in cell count occurred after 5-7 d when samples were stored at room temperature (17-23 degrees C), compared with those maintained at 4 degrees C. When manual and mechanical mixing of fixed samples were compared only marginal differences in cell counts were observed. An increase in cell counts followed manual dilution of milk samples in comparison with automatic dilution. The temperature of samples prepared for counting was also studied and no significant variations occurred between mean temperatures of 12-7 and 32-9 degrees C. The final factor evaluated was that of holding time before counting; using 4 cell-count levels it was observed that counts were acceptable up to 1 1/2 h.

Animals↗
PubMed1975

Evaluation of an iodophor teat spray in the control of infections and cellular reactions in the udder.

A strictly controlled field trial was designed to assess the value of an iodophorpost-milking teat disinfectant in the prevention of new mastitis infections in a 132 cow herd. The disinfectant was applied by a hand spray, a method acceptable, effective, and less costly than conventional teat dipping methods. Only the left side of the udder was treated, the right quarters acting as controls. Dry-cow therapy and other methods of mastitis control were already practised, and no change in routine was introduced apart from half-udder teat spraying. Fifty-eight new cases of mastitis were found to occur on the teat-sprayed side, compared with 91 in the untreated quarters; 35 and 23, respectively, were clinical. No Group B streptococci existed in the herd, and the principal reductions were in Group C streptococci and coagulase-negative staphylococci, the percentages of which were halved. The percentage of coliform infections on the teat-sprayed side was, in contrast, doubled. The incidence of new clinical and subclinical disease without infection was in reverse ratio to that of infections, being 29-9 per cent higher in the quarters which were teat-sprayed. Analysis of cumulative CMT reactions from regular monthly surveys indicated that exponential cell-count values on each side of the udder were identical. Thus, while new infections were significantly reduced, overall cell counts were not, and there is clearly a need for further research into factors other than bacteria which may initiate teat damage and inflammatory changes in the udder.

Aerosols↗