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Biomedical subjects

B Roberts

Publications and source records attributed to B Roberts.

At least 73 records · Page 4Linked to original sources
PubMed1997

DNA fragmentation follows delayed neuronal death in CA1 neurons exposed to transient global ischemia in the rat.

Apoptosis is an active, gene-directed process of cell death in which early fragmentation of nuclear DNA precedes morphological changes in the nucleus and, later, in the cytoplasm. In ischemia, biochemical studies have detected oligonucleosomes of apoptosis whereas sequential morphological studies show changes consistent with necrosis rather than apoptosis. To resolve this apparent discrepancy, we subjected rats to 10 minutes of transient forebrain ischemia followed by 1 to 14 days of reperfusion. Parameters evaluated in the CA1 region of the hippocampus included morphology, in situ end labeling (ISEL) of fragmented DNA, and expression of p53. Neurons were indistinguishable from controls at postischemic day 1 but displayed cytoplasmic basophilia or focal condensations at day 2; some neurons were slightly swollen and a few appeared normal. In situ end labeling was absent. At days 3 and 5, approximately 40 to 60% of CA1 neurons had shrunken eosinophilic cytoplasm and pyknotic nuclei, but only half of these were ISEL. By day 14, many of the necrotic neurons had been removed by phagocytes; those remaining retained mild ISEL. Neither p53 protein nor mRNA were identified in control or postischemic brain by in situ hybridization with riboprobes or by northern blot analysis. These results show that DNA fragmentation occurs after the development of delayed neuronal death in CA1 neurons subjected to 10 minutes of global ischemia. They suggest that mechanisms other than apoptosis may mediate the irreversible changes in the CA1 neurons in this model.

Animals↗
PubMed1997

Diagnostic potential of a serological assay for the diagnosis of ulcerans disease based on the putative Mycobacterium ulcerans toxin.

Mycobacterium ulcerans infection is an important and potentially disfiguring disease of man. A rapid diagnostic assay for detection of this organism is required urgently. Serological assays require a species-specific protein to ensure a high level of specificity and thus reduce the occurrence of false positive results. As M. ulcerans had been reported to produce a unique cytotoxin, it was thought that this would provide an ideal antigen on which to base a serological assay for detection of M. ulcerans during infection. Crude culture filtrates, prepared by previously documented methods, were assayed for toxic activity by in-vitro cytotoxicity assays and in-vivo mouse footpad assays. To evaluate the uniqueness of the cytotoxic factor, other species of mycobacteria were also assayed. Analysis of these assays showed that similar biological activity is present in various other mycobacterial species. Furthermore, it was possible to neutralise this activity in all species tested with a polyclonal antiserum raised against M. ulcerans. As the cytotoxic factor was found not to be specific to M. ulcerans, it is unlikely that a serological assay based on such a molecule will be of use.

Analysis of Variance↗
PubMed1997

Immunomagnetic separation and PCR for detection of Mycobacterium ulcerans.

We have developed a technique based on the use of monodisperse magnetic beads to isolate Mycobacterium ulcerans from heterogenous mixtures, prior to PCR amplification. Using this method, we were able to detect M. ulcerans in water samples taken from Phillip Island, Australia, the site of several outbreaks of M. ulcerans disease in recent times.

Antibodies, Bacterial↗
PubMed1997

Rhesus macaques previously infected with simian/human immunodeficiency virus are protected from vaginal challenge with pathogenic SIVmac239.

Nontraumatic vaginal inoculation of rhesus macaques with a simian/human immunodeficiency virus (SIV/HIV) chimera containing the envelope gene from HIV-1 89.6 (SHIV 89.6) results in systemic infection (Y. Lu, B. Brosio, M. Lafaile, J. Li, R. G. Collman, J. Sodroski, and C. J. Miller, J. Virol. 70:3045-3050, 1996). A total of five rhesus macaques have each been infected by exposure to at least three intravaginal inoculations of SHIV 89.6. The SHIV 89.6 infection is characterized by a transient viremia that evokes humoral and cellular immune responses to HIV and SIV antigens, but disease does not develop in animals infected with SHIV 89.6. To determine if a previous infection with SHIV 89.6 by vaginal inoculation could protect animals from vaginal challenge with pathogenic SIV, all five animals were intravaginally inoculated twice with pathogenic SIV-mac239. After challenge, all of the SHIV-immunized animals had low or undetectable viral RNA levels in plasma compared to control animals. Three of the five of the SHIV-immunized animals remained virus isolation negative for more than 8 months, while two became virus isolation positive. The presence of SIV Gag-specific cytotoxic T lymphocytes in peripheral blood mononuclear cells and SIV-specific antibodies in cervicovaginal secretions at the time of challenge was associated with resistance to pathogenic SIV infection after vaginal challenge. These results suggest that protection from sexual transmission of HIV may be possible by effectively stimulating both humoral and cellular antiviral immunity in the systemic and genital mucosal immune compartments.

Animals↗
PubMed1996

Utility of SHIV for testing HIV-1 vaccine candidates in macaques.

SUMMARY: Intravenous injection of SHIV (simian/human immunodeficiency virus, chimeric virus) into rhesus macaques resulted in a viremia in peripheral blood lymphocytes (PBL) and the generation of anti-HIV-1 (human immunodeficiency virus type 1) envelope immune responses. A challenge stock of a SHIV containing HIV-1 HXBc2 envelope glycoproteins was prepared from infected rhesus monkey peripheral blood mononuclear cells (PBMC). The minimum animal infectious dose of the SHIV stock was determined and used in a challenge experiment to test protection. The vaccination of two rhesus monkeys with whole inactivated HIV-1 plus polydicarboxylatophenoxy phosphazene (PCPP) as the adjuvant protected the animals from becoming infected by a SHIV challenge. This experiment demonstrated for the first time that monkeys immunized with HIV-1 antigens can be protected against an HIV-1 envelope-containing virus. As the challenge virus was prepared from monkey PBMC, human antigens were unlikely to be involved in the protection. Protection of rhesus monkeys from SHIV challenge may help,define protective immune responses stimulated by HIV-1 vaccine candidates.

AIDS Vaccines↗
PubMed1996

Spectral regularity as a factor distinct from harmonic relations in auditory grouping.

When the regular spectral pattern formed by an odd-harmonic complex (the base) is disrupted by an added even harmonic, the added component is judged as more salient than its neighbors. This study considered whether the effects of spectral pattern on perceptual segregation are restricted to harmonic stimuli. Participants either rated the clarity or judged the relative pitch of a cued component in a series of complex tones. The difference in clarity between added and base components found for the harmonic complexes was not reduced when the complexes were made inharmonic either by a frequency shift or by spectral stretch or compression. However, the added-base difference could be abolished for an inharmonic complex when the distribution of components across frequency was made uniform. These findings suggest that spectral regularity is a factor distinct from harmonic relations in auditory grouping.

Attention↗
PubMed1996

Light and electron microscopic identification of Cyclospora species in the small intestine. Evidence of the presence of asexual life cycle in human host.

This is the first case of cyclosporiasis in which the parasite was clearly demonstrated in a duodenal biopsy by light microscopy. Electron microscopy identified the stages of sporozoite, trophozoite, schizont, and merozoite. Although only asexual forms were identified in our case, the sexual cycle must have taken place in the human host, because oocysts were detected in stools of the patients. Therefore, it appears that Cyclospora species require only a single host to complete its entire life cycle. Despite the heavy infection, only enterocytes were invaded. The lamina propria and submucosa were not involved. The morphology of Cyclospora in the intestine is similar to that of Isospora, but differs from that of Cryptosporidium. The morphology of the oocyst of Cyclospora resembles that of Cryptosporidium, but differs from that of Isospora. Thus, a combined study of both stool and intestinal biopsy should readily distinguish Cyclospora from Cryptosporidium and Isospora.

AIDS-Related Opportunistic Infections↗
PubMed1996

Identification and characterisation of a superoxide dismutase and catalase from Mycobacterium ulcerans.

Previous investigations have demonstrated the presence of both superoxide dismutase and catalase enzymes in several intracellular pathogens, including a number of mycobacterial species. These enzymes are believed to be involved in the protection of the pathogen from the bactericidal products of oxidative metabolism. Superoxide dismutase and catalase were identified in crude extracts of Mycobacterium ulcerans by polyacrylamide gel electrophoresis. Inhibition experiments showed that the superoxide dismutase probably contained manganese as the metal cofactor. Other mycobacterial species examined for comparison produced bands of superoxide dismutase activity with a different mobility to that of M. ulcerans, suggesting possible structural differences between the enzymes.

Azides↗
PubMed1996

Assessment of stimulated and spontaneous adrenocorticotropin secretory dynamics identifies distinct components of cortisol feedback inhibition in healthy humans.

Corticosteroids inhibit ACTH secretion through diverse cellular mechanisms, including direct pituitary and indirect suprapituitary effects. Although exogenous CRH provides a useful assessment of corticotroph function, the suprapituitary component of ACTH regulation has been difficult to assess in humans. Naloxone (NAL) has been reported to stimulate ACTH secretion indirectly through the release of endogenous hypothalamic CRH, suggesting its potential application in the examination of suprapituitary regulation of ACTH secretory dynamics. We sought to examine the inhibitory effects of corticosteroids on kinetic parameters of ACTH secretion, assessed by a deconvolution method, in healthy human subjects. We also sought to directly compare the ACTH responses to serial administration of human CRH and NAL as well as spontaneously occurring ACTH pulses to distinguish pituitary and suprapituitary components of hypothalamic-pituitary-adrenal regulation. Normal healthy subjects (n = 11) received hCRH (0.4 microgram/kg) at 1800 h and then NAL (65 micrograms/kg) at 1930 h, respectively, on 3 separate study days: placebo pretreatment plus CRH/NAL stimulation, metyrapone (MET) pretreatment plus CRH/NAL, or MET alone. Plasma ACTH and serum cortisol were assessed at frequent (every 10 min) intervals during CRH/NAL or placebo infusions (1800-2100 h) on all 3 study days, and deconvolution analysis was performed to determine kinetic parameters of endogenous and stimulated ACTH secretion. Suppression of endogenous cortisol secretion with MET significantly increased both continuous (basal secretion rate) and pulsatile CRH- and NAL-stimulated ACTH bursts (P < 0.05). The increase in total ACTH secreted per burst was related to two distinct effects of cortisol regulating the amplitude (maximum secretion rate) and half-duration (P < 0.05) of secretory bursts. The ACTH responses to CRH and NAL for individual subjects were significantly and positively correlated in both placebo pretreatment plus CRH/NAL stimulation and MET pretreatment plus CRH/NAL studies (P < 0.01). MET administration disproportionately increased the ACTH response to NAL, producing a significant increase (P < 0.01) in the slope of the regression relating ACTH responses to CRH and NAL. The following conclusions were made: 1) endogenous cortisol secretion, even at levels associated with relatively low serum cortisol concentrations, exerts a significant negative feedback effect on both continuous and pulsatile ACTH secretion; 2) cortisol inhibits pulsatile ACTH secretion through distinct regulatory mechanisms that independently modulate both the mass and the duration of ACTH secretory bursts; 3) the differential sensitivity of the CRH- and NAL-stimulated ACTH responses to MET administration suggests that both pituitary and suprapituitary components of the hypothalmic-pituitary-adrenal axis are sensitive to negative regulation over a rapid or intermediate temporal domain. Endogenous cortisol modulates multiple components of dynamical ACTH secretion through composite effects that appear to be mediated through structurally and functionally distinct regulatory domains.

Adrenocorticotropic Hormone↗
PubMed1996

Molecular cloning of two novel transmembrane ligands for Eph-related kinases (LERKS) that are related to LERK-2.

A search of the nucleic acid database of expressed sequence tags (ESTs) revealed several partial cDNA sequences that could encode proteins homologous to the ligands for Eph-related kinases (LERKs). Oligonucleotides designed from the ESTs were used to probe a human brain cDNA library and obtain overlapping clones that encoded two different novel LERKS (NLERK-1 and NLERK-2). NLERK-1 and NLERK-2 are most closely related to human LERK-2/Elk-ligand and they form a subclass of LERKs that contain a transmembrane domain and a conserved cytoplasmic domain. Full-length NLERK-1 was expressed as a glycosylated membrane protein in COS cells and was not secreted into the medium. Full-length NLERK-2 was similarly expressed in COS cells but both membrane-bound and a truncated, proteolytically-released form were detected. Engineered forms of both NLERK-1 and NLERK-2 lacking transmembrane and cytoplasmic domains were also expressed in COS cells and each was detected in the extracellular medium.

Amino Acid Sequence↗
PubMed1996

Regularity of spectral pattern and its effects on the perceptual fusion of harmonics.

A single even harmonic added to an odd-harmonic complex may be judged as perceptually more salient than the odd harmonics themselves (Roberts & Bregman, 1991). It is proposed that this effect occurs because the even harmonic is inconsistent with the regular spectral pattern formed by the odd-harmonic complex (the base). Therefore, a reduction in the regularity of the base spectrum should reduce the even-odd difference. Spectral regularity was reduced either by removing base components, or by including components in the base that were inconsistent with its original pattern. Subjects listened to (primarily) harmonic complex tones and rated the clarity of one of the harmonics, cued by a preceding pure tone. Both removing components from the base and including extraneous components in the base reduced the even-odd difference. The results suggest that it is easier to segregate a harmonic from a periodic complex tone when it does not form part of the regular pattern of spectral spacing defined by the other harmonics.

Attention↗
PubMed1996

Murine flt3 ligand protects M1 leukemic cells from LIF-induced differentiation and suppression of self-renewal.

Self-renewing cell divisions are an important characteristic exhibited by both normal hematopoietic stem cells and leukemic cell populations. We have examined the action of flt3/flk2 ligand (FL) on physiologic suppression of self-renewal during growth factor-induced differentiation of M1 leukemic cells. Unstimulated M1 cells expressed high levels of flt3 receptor mRNA and protein, with approximately 20,000 molecules present at the cell surface. Consistent with data obtained from normal macrophage populations, expression of both mRNA and protein for flt3 receptor was suppressed as cells were induced to differentiate into mature macrophages in response to leukemia inhibitory factor (LIF). Although FL alone had no detectable action on unstimulated M1 cells, an effect was revealed during LIF-induced differentiation. FL overcame LIF-induced suppression in clonal cultures of M1 cells, prevented morphologic changes associated with macrophage differentiation and interfered with the LIF-induced responsiveness of M1 cells to macrophage colony-stimulating factor (M-CSF). This action of FL was evident on both parental M1 cells and M1 cells whose differentiation program was perturbed by enforced expression of the transcription factor SCL. The action of FL was most striking in clone transfer experiments in which FL rescued M1 cells from LIF-induced suppression of self-renewal. The ability of FL to maintain self-renewal characteristics satisfies one of the criteria predicted for a stem-cell-active molecule and contrasts with the action of FL in stimulating proliferation and differentiation of normal hematopoietic cells.

Animals↗
PubMed1996

Reducing the use of the target animal batch safety test for veterinary vaccines.

The need to submit each batch of every veterinary vaccine to a target animal safety test is questioned. It is proposed that a risk/benefit analysis should be conducted, on a product by product basis, to determine whether the continued application of this test to each batch of a product is beneficial and justified. For an established product, the analysis should consider: the number of batches manufactured; the length of time for which the product has been manufactured; the testing experience and the incidence of reported adverse reactions; the level of GMP compliance and the standard of QA practised by the manufacturer; the method and conditions of manufacture; the use of animals for other batch tests; the recommendations for the use of the product. For a newly developed product the analysis should take into account: the safety data generated during development; the inherent risks in the product and its manufacture; the use of the other animal tests. It is suggested that the continued use of the test could be reduced on a phased basis e.g. after 10 consecutive satisfactory tests the frequency could be reduced by limiting it to the first batch of each production campaign or to every n th batch. Furthermore, the possibility of discontinuing the test altogether, for the product in question, could be considered. A return to full testing frequency would be required in the event of: a test failure; a batch related adverse reaction; introduction of a new seed; a change of manufacturer; a process of modification; a specification amendment; or an interruption of batch continuity. When a manufacturer has established consistency of production and testing, an alternative approach to the need for batch testing, with a view to avoiding or minimising the use of animals, is both desirable and possible.

Animal Testing Alternatives↗
PubMed1996

Magnetoencephalographic assessment of spontaneous brain activity in schizophrenia.

Magnetoencephalography (MEG) offers an attractive alternative to electroencephalography (EEG) in the assessment of psychiatric patients. In this study, a whole-head biomagnetometer equipped with 122 super-cooled sensors was used to assess spontaneous neuromagnetic activity in 11 unmedicated schizophrenic patients and 8 schizophrenic patients medicated for more than 8 weeks with novel antipsychotics (5 of whom were initially studied as part of the unmedicated group). Ten normal (nonpsychiatric) controls were also examined. For each subject, 5 minutes of data were collected in an eyes-closed state. Data were visually inspected for gross MEG abnormalities, and average power spectra were calculated for the data at each sensor. No gross abnormalities were identified for control subjects. One unmedicated schizophrenic patient showed epileptiform sharp waves, and 4 showed abnormal slow waves. No gross MEG abnormalities were found for the medicated schizophrenic group (which included 3 patients who had previously shown slow waves in the unmedicated state). Spectral analyses showed that the schizophrenia patients demonstrated lower alpha power and peak frequency than controls. The data are interpreted within the context of previously reported magnetic resonance abnormalities of the thalamus.

Adult↗
PubMed1995

A live attenuated vaccine for the control of avian coccidiosis: trials in broiler breeders and replacement layer flocks in the United Kingdom.

Losses caused by coccidiosis are a significant problem in the rearing of breeder and layer flocks. A live vaccine has been developed that contains attenuated lines of the seven species of Eimeria that infect the chicken. The attenuated lines were derived from virulent strains by selection for earlier development in chickens. In 11 field trials, the performance of vaccinated chicks was compared with that of matched controls receiving conventional drug prophylaxis. The vaccine was given in the drinking water to 116,600 young chickens and provided excellent control of coccidiosis. The occurrence of coccidial oocysts in the litter, coccidial lesions post mortem and overt coccidiosis was markedly lower in the vaccinated birds than in the controls.

Animals↗
PubMed1995

Relation between human T-lymphotropic virus type I and neurologic diseases in Panama: 1985-1990.

Human T-cell lymphotropic virus type I (HTLV-I) is endemic in the Caribbean basin and in Japan. HTLV-II, a closely related virus, is endemic in several groups of native Americans, including Panamanian Guaymi. In Panama, a nationwide HTLV-I/II seroprevalence of 1-2% has been reported. We evaluated the frequency of HTLV-I/II infection in patients with neurologic diseases admitted to state tertiary hospitals in Panama City between 1985 and 1990. Nineteen of 322 patients with eligible diagnoses had antibodies to HTLV-I/II, 17 with HTLV-I and 2 with HTLV-II. HTLV-I was associated with spastic paraparesis (13 of 23, 56.5% versus 4 of 299, 1.3%, p < 0.001) and with cerebellar syndrome (2 of 13, 15.4%) and multiple sclerosis (2 of 54, 3.7%) (p < 0.05 for both diseases compared with subject with none of these diagnoses). The two HTLV-I infected patients with cerebellar syndrome later developed spastic paraparesis. HTLV-II infection was noted in one patient with cerebellar syndrome and one with amyotrophic lateral sclerosis. All patients with other diagnoses were seronegative. Among patients with spastic paraparesis, HTLV-I-infected patients were clinically indistinguishable from seronegative subjects. There is apparently an overlapping clinical spectrum of neurologic diseases associated with HTLV-I and HTLV-II infection.

Adolescent↗