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Biomedical subjects

A M Johnson

Publications and source records attributed to A M Johnson.

At least 235 records · Page 13Linked to original sources
PubMed1992

The pharmacologic profile of paroxetine, a new selective serotonin reuptake inhibitor.

Paroxetine is a highly potent and selective inhibitor of serotonin reuptake, being more potent in vitro than fluoxetine, fluvoxamine, and sertraline. In contrast to the tricyclic antidepressants, paroxetine has little affinity for catecholaminergic or histaminergic systems. Paroxetine is well absorbed from the gastrointestinal tract and undergoes first-pass metabolism that is partially saturable. Unlike the metabolites of fluoxetine and sertraline, the metabolites of paroxetine are pharmacologically inactive in vivo. Steady-state paroxetine plasma concentrations are generally achieved within 4 to 14 days of commencing therapy and remain stable thereafter. The pharmacokinetics of paroxetine are also consistent with once-daily dosing. This pharmacologic and pharmacokinetic profile, taken together with extensive clinical data, indicates that paroxetine is a valuable addition to the physician's armamentarium for the treatment of depression.

1-Naphthylamine↗
PubMed1991

HIV and AIDS.

Explore the source record for details and available documents.

Acquired Immunodeficiency Syndrome↗
PubMed1991

Cloning of Toxoplasma gondii gene fragments encoding diagnostic antigens.

Two Toxoplasma gondii gene fragments, which encode polypeptides that can be used as diagnostic antigens in an enzyme-linked immunosorbent assay were cloned and their nucleotide sequence was determined. One of the fragments (derived from the H4 gene) is 682 bp long. The mRNA of the single-copy H4 gene is 1300 nt long. The fragment derived from the other gene, termed H11, is 197 bp long. The mRNA of the single-copy H11 gene is 1900 nt long. The native polypeptides encoded by the H4 and H11 genes are 25 and 41 kDa, respectively. Based on computer analysis of the deduced amino acid sequences of the polypeptides encoded by the gene fragments, both appear to be very hydrophilic and that encoded by the H11 fragment has a high antigenic index profile. These results are consistent with the diagnostic usefulness of the polypeptides encoded by the gene fragments.

Amino Acid Sequence↗
PubMed1991

Targeted disruption of chloroplast genes in Chlamydomonas reinhardtii.

We have developed an efficient procedure for the disruption of Chlamydomonas chloroplast genes. Wild-type C. reinhardtii cells were bombarded with microprojectiles coated with a mixture of two plasmids, one encoding selectable, antibiotic-resistance mutations in the 16S ribosomal RNA gene and the other containing either the atpB or rbcL photosynthetic gene inactivated by an insertion of 0.48 kb of yeast DNA in the coding sequence. Antibiotic-resistant transformants were selected under conditions permissive for growth of non-photosynthetic mutants. Approximately half of these transformants were initially heteroplasmic for copies of the disrupted atpB or rbcL genes integrated into the recipient chloroplast genome but still retained photosynthetic competence. A small fraction of the transformants (1.1% for atpB; 4.3% for rbcL) were nonphotosynthetic and homoplasmic for the disrupted gene at the time they were isolated. Single cell cloning of the initially heteroplasmic transformants also yielded nonphotosynthetic segregants that were homoplasmic for the disrupted gene. Polypeptide products of the disrupted atpB and rbcL genes could not be detected using immunoblotting techniques. We believe that any nonessential Chlamydomonas chloroplast gene, such as those involved in photosynthesis, should be amenable to gene disruption by cotransformation. The method should prove useful for the introduction of site-specific mutations into chloroplast genes and flanking regulatory sequences with a view to elucidating their function.

Animals↗
PubMed1991

Recognition of recombinant Toxoplasma gondii antigens by human sera in an ELISA.

We developed an enzyme-linked immunosorbent assay (ELISA) that uses one of two recombinant polypeptides, termed H4/GST and H11/GST, as diagnostic antigens for the detection of antibodies to Toxoplasma gondii in human sera. A total of 59 sera from humans with acute toxoplasmosis, 194 sera from patients with chronic toxoplasmosis, and 151 sera from subjects who were not infected with T. gondii were examined. In all, 68% of the sera from humans with acute toxoplasmosis reacted positively with one or both recombinant T. gondii antigens. By contrast, only 14% of those from patients with chronic toxoplasmosis recognized H4/GST or H11/GST. None of the sera from humans who were not infected with T. gondii, including patients with echinococcosis, entamoebosis, toxocarosis, trichinellosis, glandular fever, or rheumatoid arthritis, recognized H4/GST or H11/GST.

Animals↗
PubMed1991

Conflicting phylogenetic hypotheses for the parasitic platyhelminths tested by partial sequencing of 18S ribosomal RNA.

Partial sequencing of the 18S ribosomal RNA in nine parasitic and one free-living species of platyhelminth was used to test hypotheses on the phylogenetic relationships among the major groups. The eucestodes, amphilinideans, gyrocotylideans and monopisthocotylideans appeared as a monophyletic assemblage in a cladistic analysis of the data, with a very close association between the gyrocotylideans and monopisthocotylideans. The polyopisthocotylidean monogeneans were paraphyletic to the monopisthocotylideans. The digeneans appeared to be a sister group to the monogeneans and eucestodes, while the temnocephalidean was closely related to the free-living polyclad.

Animals↗
PubMed1991

Effect of paroxetine, a selective 5-hydroxytryptamine uptake inhibitor, on beta-adrenoceptors in rat brain: autoradiographic and functional studies.

Quantitative receptor autoradiography was used to investigate the effects of paroxetine (8.3 mg/kg), amitriptyline (26 mg/kg) and desipramine (17 mg/kg), administered daily in the drinking water for 21 days, on the number of beta 1- and beta 2-adrenoceptors in the cortex of the rat. In addition, the effect of these drugs on the function of beta-adrenoceptors was examined by measuring noradrenaline- and isoprenaline-stimulated production of cyclic AMP in slices of cortex. Paroxetine did not alter the number of cortical beta 1 or beta 2-adrenoceptors nor did it induce any functional changes in beta-adrenoceptor-linked adenylyl cyclase. In contrast, desipramine caused a significant reduction in the density of beta 1-adrenoceptors and in the sensitivity of both noradrenaline and isoprenaline-stimulated adenylyl cyclase. Although amitriptyline significantly reduced the number of beta 1-adrenoceptors in cortical membranes, no such changes could be detected by autoradiography. It is apparent from these and other studies, that the ability of antidepressants to down-regulate central beta-adrenoceptors is not a property shared by all antidepressants. In particular, the more potent and selective inhibitors of the uptake of 5-HT, such as paroxetine, appear to be devoid of effects on this receptor system.

Adrenergic beta-Antagonists↗
PubMed1991

Prevalence of HIV, hepatitis B and associated risk behaviours in clients of a needle-exchange in central London.

In order to determine the prevalence of risk behaviour for, and antibodies to HIV and hepatitis B in clients of a needle-exchange scheme in central London we employed an anonymous, self-administered questionnaire along with salivary antibody testing by immunoglobulin (Ig) G antibody capture immunoassay. Two hundred and thirty-two subjects (193 men, 39 women; median age 32) participated; a response rate of 89%. Clients were long-term, frequent injectors. Lending used equipment at any time was reported by 55%, and borrowing by 52%. Of those who had shared needles and syringes during the last year, the majority had lent to, or borrowed from, one person only (53 and 55%, respectively). Younger clients (less than 29 years of age) reported more recent sharing than older clients (greater than 30 years of age). Five out of 211 (2.4%) samples tested for anti-HIV were positive. One hundred and eleven out of 199 (56%) samples were positive for anti-hepatitis B core (HBc). In this population of needle-exchange attenders there is no evidence of further spread of HIV, and a low prevalence of HIV infection appears to have been sustained. However, the high prevalence of anti-HBc provides evidence of previous risk behaviour and so constant vigilance is necessary if further viral spread is to be avoided. This study has established an acceptable method for the anonymous surveillance of current risk behaviour and salivary antibodies to HIV and hepatitis B virus (HBV) in a drug-using population.

Adolescent↗
PubMed1991

An improved method for determining high molecular weights by protein immunoblotting: application to apolipoprotein(a) phenotyping.

The determination of very high molecular weights (greater than 500 kd) by protein immunoblotting is limited by a lack of commercially available molecular weight standards in that range. We have therefore investigated the use of the human haptoglobin 2-2 phenotype polymeric series as a high molecular weight standard curve. Using pre-electrophoresed 3-12% SDS polyacrylamide gradient gels, non-dissociated haptoglobin 2-2 serum was separated, transferred and probed with anti-human haptoglobin. We were able to visualize up to 13 bands, with a theoretical molecular weight range of 171.9-859.5 kd, in non-dissociated haptoglobin 2-2 serum. Molecular weights up to 584 kd were confirmed by comparison with available standards. The method was then applied to the determination of apolipoprotein(a) [apo(a)] phenotype molecular weights. Precision of the method was excellent, with intra-run CVs of less than 2.9% and inter-run CVs of less than 3.2% for apo(a) molecular weight. This method of molecular weight calibration is applicable to the characterization of any high molecular weight protein that can be successfully electrophoresed, transferred and visualized.

Apolipoproteins A↗
PubMed1991

Effect of tryptic or peptic digestion or mechanical isolation on the extraction of proteins, antigens, and ribonucleic acids from Sarcocystis muris bradyzoites.

Various methods have been used for the isolation of bradyzoites of Sarcocystis species. Using Sarcocystis muris as a model, the effect of 3 methods, trypsin digestion, pepsin digestion, and mechanical isolation, on the subsequent extraction of S. muris proteins, antigens, and RNA was examined. Although some quantitative differences were found among the proteins, antigens, and RNA extracted after the 3 isolation methods, qualitative differences were not evident. The overall isoelectric focusing protein profile showed approximately 30 bands in the pH range of 3-9 and was dominated by 5 bands with pI values of approximately 5.3, 6.3, 6.8, 7.0, and 7.4. In experimentally infected mice, antibodies were recorded from 35 days postinoculation (PI) until the end of examination (130 days PI). The S. muris RNA appeared to consist of at least 10 subunits in the range of 200-4,200 nucleotides. A Toxoplasma gondii DNA fragment specific for small subunit ribosomal RNA (rRNA) hybridized mainly to the S. muris 1,900-nucleotide subunit and a range of smaller subunits, and a probe specific for large subunit rRNA hybridized mainly to the 4,200-nucleotide subunit and a range of smaller subunits. All 3 methods of bradyzoite isolation gave good yields of intact messenger RNAs that showed similar in vitro translation curves.

Animals↗
PubMed1991

Separation of antigens from Sarcocystis species using chromatofocusing.

Crude antigen preparations from bradyzoites of Sarcocystis species exhibit a high degree of cross-reactivity with antisera against heterologous Sarcocystis species, preventing the development of a species-specific immunological test for sarcocystiosis. In this study, we fractionated bradyzoite-derived protein extracts from Sarcocystis tenella, Sarcocystis arieticanis, Sarcocystis gigantea, and Sarcocystis muris by chromatofocusing and obtained distinct protein elution profiles for each species. We then examined the isolated protein fractions for antigenicity with homologous and heterologous reference sera in an enzyme-linked immunosorbent assay. Whereas some antigenic fractions of bradyzoite proteins had equally high reactivity with the homologous and heterologous sera, the reactivity of other fractions was 3-38 times higher with homologous serum than with heterologous sera. Mice immunized with less cross-reactive protein fractions of S. gigantea and S. muris bradyzoites produced a specific immune serum. Thus, it is possible to isolate species-specific antigens from crude mixtures of bradyzoite-derived Sarcocystis antigens for development of species-specific immunological tests for sarcocystiosis.

Animals↗
PubMed1991

Murine immune responses to recombinant Toxoplasma gondii antigens.

Recombinant proteins of the RH strain of Toxoplasma gondii were produced by expression in Escherichia coli as glutathione S-transferase (GST) fusion proteins. Enzyme-linked immunosorbent assays were established using 2 of these fusion proteins termed H4/GST and H11/GST. The assays were able to detect antibodies in the sera of mice orally infected with either the cyst or oocyst stage of a pork isolate of T. gondii. In addition, the sera from mice infected with 1 of 4 different T. gondii isolates were investigated for their binding to these fusion proteins. Antibodies in the sera of all mice bound to H11/GST, but not all sera recognized H4/GST. Delayed-type hypersensitivity (DTH) responses to the fusion proteins were found when the mice were sensitized intradermally with H4/GST and H11/GST and challenged with the homologous fusion protein. However, no DTH response was recorded when mice were challenged with homologous fusion proteins after infection with T. gondii, or after immunization with a sonicate of the RH strain of the parasite. In addition, cellular responses were not stimulated against either of the fusion proteins in in vitro assays. These 2 fusion proteins were recognized by anti-T. gondii antibodies in experimental murine infections, and they are therefore potential candidates as antigens in assays for the diagnosis of human toxoplasmosis.

Animals↗
PubMed1990

Preliminary report: accurate assays for anti-HIV in urine.

Untreated urine specimens from 358 patients (344 attending genito-urinary medicine clinics, 14 haemophiliacs) and 353 blood donors were tested blind by a simple IgG-capture particle-adherence test (GACPAT) and a rapid IgG-capture enzyme-linked immunosorbent assay (GACELISA) for antibody to human immunodeficiency virus (anti-HIV). All 158 urine specimens from seropositive subjects were anti-HIV positive by GACPAT and 157 of them (99.4%) were positive by GACELISA. Tests on 553 urine specimens from seronegative subjects gave two repeatable false-positive reactions by GACPAT (0.4%) and none by GACELISA. By means of a modified procedure anti-gp160 was detected by commercial western blot in the urine of 44 of 45 seropositive subjects examined. IgG-capture assays will detect anti-HIV in unconcentrated urine and so allow a diagnosis in circumstances when blood sampling is impracticable.

Blotting, Western↗