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Biomedical subjects

M M Johnson

Publications and source records attributed to M M Johnson.

At least 73 records · Page 4Linked to original sources
PubMed1990

Are gender differences in schizophrenia reflected in brain event-related potentials?

Numerous studies have reported relationships between gender and cerebral event-related potentials (ERPs) recorded from the human scalp. Recent studies have suggested that the influences of gender on ERPs may differ in persons with schizophrenia compared to healthy controls. In a further evaluation of the influences of this critical subject variable on ERP characteristics in schizophrenia, ERPs of age- and gender-matched groups (n = 72 each) of unmedicated schizophrenic patients and healthy controls were compared. ERPs elicited by left and right median nerve stimulation, checkerboard pattern visual flash, and auditory clicks were recorded from 15 scalp leads. The results confirm previous findings showing that: (1) number of comparable gender effects present in the ERP records of these two large study groups and (2) specific Diagnosis x Gender interactions suggesting that schizophrenic illness may modify normal gender influences on ERP characteristics. These data illustrate the point that matching schizophrenic patients and healthy control populations for gender is essential but not sufficient. Even in carefully matched groups, gender confounding can persist as a source of error variance because the influence can vary for different diagnostic groups.

Adolescent↗
PubMed1989

The memory advantages of the generation effect: age and process differences.

This study examined the impact of age on the generation effect using measures of study time, recognition (d prime), cautiousness (beta), and judgment reaction time. Thirty-six younger and 36 older adults studied antonym pairs, half of which were intact and half of which were missing two adjacent interior letters requiring active encoding (generation) to complete the word. In general, older adults studied items longer; both younger and older adults studied items requiring generation longer than intact items. Subsequent recognition testing also revealed age-related memory differences and generation effect-related memory improvements, but no age by task interaction. Cautiousness data showed only differences due to encoding task with no age-related differences to indicate older adults were more cautious than younger adults. Response time data also revealed expected effects due to age-related slowing and generation (not previously demonstrated in the literature).

Adolescent↗
PubMed1989

The generation effect extended: memory enhancement for generation cues.

The generation effect is the greater memorability of a response that is actively produced (e.g., in answering a question from memory) than one that is more passively produced (as in reading the answer). The present three experiments addressed a question that is critical to the theoretical interpretation of the generation effect: Is memory enhanced for the cues that are used to elicit generated responses? Using incidental learning procedures, Experiments 1 and 2 gave an affirmative answer (although the effect was substantially weaker than the generation effect for responses). Enhancement of memory for generation cues was observed both in a within-subject/within-list design (reading and generation items within the same trial blocks; Experiment 1) and in a between-subjects design (reading and generation tasks for different groups of subjects; Experiment 2). In Experiment 3, memory enhancement for generation cues was used to produce a previously unobtained result--a generation effect for nonsense responses under incidental learning conditions. These findings provide critical evidence required by theories that interpret the generation effect in terms of enhanced processing of the cue-response item.

Cues↗
PubMed1987

Identification of glycoprotein Ib beta as one of the major proteins phosphorylated during exposure of intact platelets to agents that activate cyclic AMP-dependent protein kinase.

Platelet function is inhibited by prostaglandin E1, prostaglandin I2, or forskolin, agents that increase the intracellular concentration of cyclic AMP. The inhibition appears to result from cyclic AMP-stimulated phosphorylation of specific intracellular proteins. One of the major increases in phosphorylation occurs in a polypeptide of Mr = 24,000 (P24). In this study, an effort was made to identify P24. Platelets prelabeled with [32P]phosphate were incubated with prostaglandin E1, prostaglandin I2, or forskolin. Proteins that became phosphorylated were detected by autoradiography of sodium dodecyl sulfate-polyacrylamide gels. Several lines of evidence indicated that P24 was the beta-subunit of the plasma membrane glycoprotein (GP) Ib, a glycoprotein that is essential for the adhesion of platelets to damaged subendothelium, for the rapid response of platelets to thrombin, and for the attachment of the membrane skeleton to the cytoplasmic face of the plasma membrane. P24 co-migrated with GP Ib beta on reduced gels (Mr = 24,000) and also on nonreduced gels (when GP Ib beta is disulfide-linked to GP Ib alpha and migrates with Mr = 170,000). Like GP Ib beta, P24 was associated with actin filaments in Triton X-100 lysates. Like GP Ib beta, it was selectively associated with filaments of the membrane skeleton and was released from filaments when the Ca2+-dependent protease was active. Antibodies against GP Ib immunoprecipitated P24 from platelet lysates. Finally, exposure of Bernard-Soulier platelets (which lack GP Ib) to prostaglandin E1 resulted in phosphorylation of other polypeptides, but not of P24. These studies show that P24, one of the major polypeptides phosphorylated when platelets are exposed to agents that inhibit platelet function by increasing the concentration of cyclic AMP, is the beta-subunit of GP Ib.

Actin Cytoskeleton↗
PubMed1987

Loiasis in an expatriate American child: diagnostic and treatment difficulties.

On the basis of this experience, we recommend the following when faced with possible filariasis in an expatriate from Western Central Africa: (1) Attempt a clinical differentiation between L loa and other filarial infections present in West Africa. It is important to suspect loiasis because this is the only filarial infection that is readily curable; (2) ophthalmologic assessment to diagnose onchocerciasis; (3) if L loa is suspected, thick blood smears should be obtained from midmorning to midafternoon and stained with Giemsa or hematoxylin stains, after a concentration technique is used. Nighttime blood specimens should be obtained if the patient has been in an area where W. bancrofti is prevalent; (4) skin snip biopsies prepared as follows: Bilateral symmetrical skin snips should be taken. In the case of suspected West African filariasis, the pelvic girdle, iliac crest, and back of scapula are thought to have the highest yield. One snip from each of six different sites should be obtained. Each skin snip should be approximately 2 to 3 mm (a cornealoscleral biopsy forceps can be used). Each skin snip is placed in 100 microL (approximately one drop) of normal saline in a flat-bottomed microtiter plate. The plate is incubated at room temperature and checked periodically for 24 hours under a dissecting microscope (X20 to X40). If present, the small worms will be seen wiggling and squirming in the drop of saline; (5) serologic diagnostic methods are most efficient if human filarial antigens are used; (6) if treatment is with diethylcarbamazine, the initial dose should be small.(ABSTRACT TRUNCATED AT 250 WORDS)

Cameroon↗
PubMed1987

Familial bleeding disorder associated with deficiencies in platelet signal processing and glycoproteins.

Aggregation responses to low concentrations of ADP, epinephrine, collagen and cationophore A23187 in platelets from two family members with marked bleeding tendencies were virtually absent, whereas shape change with ADP was normal. The contribution to factor X activation by collagen-treated platelets was markedly decreased. Glycoproteins IIb and III were also significantly reduced. The patients' platelets had normal stores of secretable constituents, but secretion of adenine nucleotides and acid hydrolases in response to low concentrations of thrombin and A23187 was drastically reduced compared to normal platelets; secretion of platelet factor 4 was normal. Agonist concentrations that normally produce maximal responses induced only partial aggregation and secretion in the patients' platelets. After prelabelling with [3H]arachidonate thrombin caused less changes in the [3H]phosphatidylinositol, [3H]phosphatidylcholine and free [3H]arachidonate in platelets from the patients than in platelets from normals. We conclude that the patients' platelets have an impairment in part of the signal processing mechanism that is common for all agonists and responses. This platelet abnormality, which has a superficial resemblance to thrombasthenia, represents a hitherto undescribed qualitative platelet disorder.

Adenosine Diphosphate↗
PubMed1986

Inhibition of virulent Mycobacterium tuberculosis by murine peritoneal macrophages and human alveolar lavage cells: the effects of lymphokines and recombinant gamma interferon.

Both murine peritoneal macrophages and human alveolar lavage cells inhibited growth of M. tuberculosis in a medium containing 10% foetal calf serum. However, whereas addition of recombinant gamma interferon or crude lymphokine reproducibly activated further strong anti-mycobacterial mechanisms in the murine cells, these stimuli had weak and variable effects on human alveolar cells.

Animals↗
PubMed1986

Development of a chemically defined serum- and protein-free medium for growth of human peripheral lymphocytes.

A chemically defined, protein-free medium (designated CFBI 1000, where CFBI = Clayton Foundation Biochemical Institute) that supports human peripheral lymphocyte proliferation has been developed. This medium allows exploration of individual metabolic differences by varying the medium composition as well as providing a base to explore further the mechanisms of lymphocyte activation in a system initially free of added macromolecular species other than mitogen. The peripheral blood lymphocyte is an ideal system for metabolic studies because it is easily obtained, is a primary resting cell that can be activated to proliferate, and presumably reflects both the genetic makeup and biochemical environmental history of the individual at the time the cells were formed. Examination of the role of various factors in lymphocyte activation and subsequent events may be simplified by the utilization of a medium that is protein-free and chemically defined. The CFBI 1000 medium supports the growth response of human peripheral lymphocytes to mitogen as measured by [3H]thymidine incorporation to an extent comparable to other media used widely in assessment of lymphocyte proliferation.

Aphidicolin↗
PubMed1986

Macrophage uptake and retention of radiolabeled glycopeptidolipid antigens associated with the superficial L1 layer of Mycobacterium intracellulare serovar 20.

Glycopeptidolipid (GPL) antigens which are associated with the superficial L1 layer of Mycobacterium intracellulare serovar 20 were labeled with radioisotopes by means of internal labeling techniques and used in macrophage uptake and retention studies. The use of tritiated alanine and phenylalanine allowed the incorporation of label into the GPL invariant fatty acyl peptide core, which is common to all members of the Mycobacterium avium-M. intracellulare complex. Radiolabeled GPL antigens were then purified by a one-step column chromatographic procedure and subsequently used to determine the maximum uptake and retention in peritoneal macrophages isolated from C57BL/6 and CBA/J mice. Maximum uptake for peritoneal macrophages from both strains of mice occurred at a concentration between 200 and 250 micrograms of antigen per ml of medium when 3.4 X 10(5) cells were pulsed. Timed experiments demonstrated that approximately 20% of the antigens remained associated with the macrophages up to 4 days after a pulse of 200 micrograms of GPL, and examination of chloroform-extractable components from both macrophages and spent medium revealed that 98% or more of the radioactivity corresponded to intact GPL components. The ability of the GPL antigens to become associated with macrophages is demonstrated by these results, which strongly suggest that these potentially important mycobacterial antigens are inert to degradation by those cells.

Animals↗
PubMed1985

The influence of positive affect on the unusualness of word associations.

A pilot study and two experiments investigated the influence of positive affect, induced in three differing ways, on the uniqueness of word associations. Persons in the positive-affect conditions gave more unusual first-associates to neutral words, according to the Palermo & Jenkins (1964) norms, than did subjects in the control conditions. In Study 3, where word type (positive, neutral, negative) was a second factor along with affect, in a between-subjects design, associates to positive words were also more unusual and diverse than were those to other words. These results were related to those of studies suggesting that positive affect may facilitate creative problem solving and to other work suggesting an impact of positive feelings on cognitive organization.

Affect↗
PubMed1984

Association of acute respiratory symptoms with onset of acute myocardial infarction: prospective investigation of 150 consecutive patients and matched control patients.

Among 150 prospectively investigated patients with acute myocardial infarction (MI) and 150 control patients matched for age, sex and admission date, acute respiratory symptoms occurred in 42 MI patients and in 23 control patients (p less than 0.02). Matched-pairs analysis gave an odds ratio for a respiratory syndrome of 2.2:1 for MI. The statistically significant association of minor respiratory syndromes and the onset of MI must be further investigated to determine whether there is any pathogenetic relation of respiratory symptoms, presumably virally induced, to the onset of MI.

Acute Disease↗
PubMed1983

Variation in erythrocyte purine metabolism among mouse strains.

Erythrocytes of five strains of mice had ATP concentrations of ca 2.7 mumol/ml packed cells, while those of CBA mice were 23% lower, and those of BALB/C mice were 40% lower. The ratio of the concentrations of ATP and GTP were ca 3.3 in four strains but greater than 27 in three other strains. When erythrocytes from different mouse strains were incubated with radioactive precursors, appreciable strain differences were found in the apparent activities of adenine and hypoxanthine-guanine phosphoribosyltransferase, adenosine kinase, adenosine deaminase, guanine deaminase and xanthine oxidase. The activities of adenosine deaminase and guanine deaminase in sera of mice of different strains also varied.

Adenine Phosphoribosyltransferase↗
PubMed1980

Evaluation of a commercial microdilution system for quantitative susceptibility testing of aminoglycosides against multidrug-resistant, gram-negative bacilli.

Susceptibility of clinical isolates of Pseudomonas aeruginosa (29 isolates), Klebsiella species (54 isolates), Escherichia coli (28 isolates), Serratia marcescens (28 isolates), and Enterobacter species (29 isolates) to gentamicin, tobramycin, and amikacin was determined by the following three methods: commercial broth microdilution trays, standard agar dilution, and disk diffusion susceptibility. A total of 504 tests were performed by each method, and overall susceptibility or resistance determined by the broth microdilution method agreed with that determined by the agar dilution method in 92.7% of the tests, whereas results from the disk diffusion method agreed with those from the agar dilution method in 91.9% of the tests. The broth microdilution and disk diffusion methods agreed with each other 88.7% of the time. The broth microdilution system results varied from the agar dilution method results by more than one dilution in 121 of 504 determinations (24%); however, this altered susceptibility determinations in only 7.3% of the assays. E. coli isolates were found to be quantitatively more resistant to the aminoglycosides with the broth microdilution method than with the agar dilution method. In contrast, the broth microdilution method demonstrated P. aeruginosa to be quantitatively more susceptible to the aminoglycosides than when the results were obtained by the agar dilution method. The Micro-Media Systems method is economical, reliable, rapid, and simple to perform and yields quantitative minimum inhibitory concentrations.

Aminoglycosides↗