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Biomedical subjects

S C Johnson

Publications and source records attributed to S C Johnson.

150 records · Page 9Linked to original sources
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Age and fitness effects on EEG, ERPs, visual sensitivity, and cognition.

Measures of EEG, event-related potentials (ERPs), visual sensitivity, and cognition were obtained from 30 young (20-31 years) and 30 older (50-62 years) healthy men. Age groups were evenly divided between subjects with low and high fitness levels documented by VO2max during a maximal exercise test. Age comparisons revealed that, compared to young adults, the older men had reduced visual sensitivity, delayed ERP latencies, greater homogeneity of EEG activity across recording sites, more positive visual-evoked potential (VEP) amplitude-intensity (A/I) slope, and poorer performance on a battery of neurocognitive tests. The EEG and VEP A/I slope findings are believed to reflect weakened central inhibition for the older men. In general, the measures that differentiated groups on the basis of age were also sensitive to differences in aerobic fitness. Compared to low fit men, the physically active men had shorter ERP latencies, stronger central inhibition, better neurocognitive performance, and better visual sensitivity. We speculate the performance superiority of the physically active men was, at least in part, the result of more oxygen being available for cerebral metabolism.

Adult↗
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Lepeophtheirus salmonis: characterization of prostaglandin E(2) in secretory products of the salmon louse by RP-HPLC and mass spectrometry.

Lepeophtheirus salmonis is an ectoparasitic copepod that causes serious disease outbreaks in both wild and farmed salmonids. As the relationship between L. salmonis and its hosts is not well understood, the current investigation was undertaken to investigate whether any immunomodulatory compounds could be identified from secretions of L. salmonis. By incubating live L. salmonis adults with the neurotransmitter dopamine in seawater, we were able to obtain secretions from the parasite. These were analyzed by RP-HPLC column, as well as LC-MS. L. salmonis secretions contained a compound with the same retention time and mass of PGE(2). The identity of this compound as PGE(2) was confirmed by MS-in source dissociation. The concentrations of PGE(2) in L. salmonis secretions ranged from 0.2 to 12.3 ng/individual and varied with incubation temperature and time kept off the host. Prostaglandin E(2) is a potent vasodilator and thought to aid in parasite evasion from host immune responses. This is the first reported evidence of prostaglandin production in parasitic copepod secretions and its implications for the host-parasite relationship are discussed.

Animals↗
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Peritonitis due to Rhizopus in a patient undergoing continuous ambulatory peritoneal dialysis.

A 61-year-old man who had end-stage renal disease secondary to diabetes mellitus and hypertension developed peritonitis due to infection with Rhizopus as a complication of receiving continuous ambulatory peritoneal dialysis (CAPD). At the onset of infection, the patient was neither acidemic nor hyperglycemic; in addition, deferoxamine had not been administered and Elastoplast dressings had not been applied. The infection occurred after the technique for disinfection of the catheter used for CAPD had been changed. The catheter was removed, and therapy with amphotericin B was initiated. Although the patient died of apparently unrelated causes, an autopsy revealed active fungal infection with multiple abscesses and superficial invasion of the ileal wall.

Abscess↗
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Tuberculous psoas muscle abscess following chemoprophylaxis with isoniazid in a patient with human immunodeficiency virus infection.

A 34-year-old man with human immunodeficiency virus infection and disseminated Mycobacterium avium and Mycobacterium intracellulare infection developed a right psoas muscle abscess due to Mycobacterium tuberculosis. The abscess occurred 18 months after completion of a 12-month course of chemoprophylaxis with isoniazid that was given because of a positive reaction with purified protein derivative of tuberculin. The adjacent vertebrae did not appear to be involved. The abscess was drained with a percutaneously inserted catheter, and he received standard antituberculous chemotherapy. Three weeks into therapy, a second drainage with a catheter was required. The isolation of two mycobacteria in this patient and the apparent failure of chemoprophylaxis with isoniazid are noted.

Abscess↗
PubMedDate not supplied

Dementia, quantitative neuroimaging, and apolipoprotein E genotype.

BACKGROUND AND PURPOSE: Quantitative MR imaging differences in an elderly population of subjects with various clinical disorders (including dementia, particularly Alzheimer's disease and vascular dementia) and disorders of mild cognitive impairment were examined. Potential quantitative MR differences were assessed by presence or absence of the apolipoprotein E (APOE) epsilon4 allele and by level of cognitive deficit. METHODS: One hundred eighty subjects with a diagnosis of dementia or other clinical disorders were identified from an eligible population of 5,677 elderly individuals. Age, duration of disease, and head size (where appropriate) were considered as covariates. APOE genotype was determined by polymerase chain reaction using buccal material. Axial and coronal intermediate- and T2-weighted MR images were quantified using a multispectral segmentation algorithm. Cognitive status was assessed by means of a modified Mini-Mental Status Examination. RESULTS: All types of dementing illness showed significant volume reductions in the majority of structures examined, particularly in the total brain, hippocampus, and white and gray matter, and increased CSF and ventricular volumes. Subjects with mild cognitive impairment showed fewer atrophic changes but were still distinguishable from the 24 control subjects. Presence of an epsilon4 allele was associated with smaller hippocampal volume in subjects with Alzheimer's disease and vascular dementia within just 1 year of disease onset. For other analyses, atrophy related to the presence of the epsilon4 allele disappeared after controlling for age and length of disease. CONCLUSION: The effects of the epsilon4 allele on brain morphology may be subtly expressed early in the development of dementia, but do not specifically affect cerebral atrophy thereafter. Cognitive impairment is associated with atrophy irrespective of diagnosis and presence of epsilon4.

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