Biomedical subjects

S Howard

Publications and source records attributed to S Howard.

At least 37 records · Page 2Linked to original sources

PubMed1998

Postnatal localization and morphogenesis of cells expressing the dopaminergic D2 receptor gene in rat brain: expression in non-neuronal cells.

The cellular localization of the dopaminergic D2 receptor (D2R) mRNA and protein was determined during postnatal development, from birth to 35 days, in the rat neostriatum by in situ hybridization histochemistry and immunohistochemistry. To localize and identify more precisely the morphology of cells expressing the D2R mRNA, nonradioactive, digoxigenin in situ hybridization was performed. Throughout this period of development, D2R mRNA and protein were widely expressed by neostriatal cells, adjoining forebrain cells and small cellular processes. Within morphologically identifiable neurons, the expression of the D2 receptor appeared to occur after cell division ceased. D2R gene expression appeared during neuronal migration and followed the developmental pattern of neuronal settling within the neostriatum. Both D2R mRNA and protein appeared to colocalize in neostriatal cells and the labeling of both appeared to accumulate within the cells progressively with age. The structural phenotypes of neostriatal neurons bearing D2R mRNA and protein were diverse throughout postnatal development. The most frequently stained cells were a heterogeneous group of medium spiny and aspiny neurons. Large cells corresponding to aspiny neurons were less frequently stained. Both phenotypes exhibited considerable postnatal growth of their cell bodies. In addition to neurons, other cell types were also observed to express the D2R mRNA and protein over the developmental period studied. These other cells included patches of ciliated ependymal cells lining the lateral ventricles and many interfascicular oligodendroglia of forebrain fiber tracts. These results demonstrate the unexpected expression of the dopaminergic D2 receptor in non-neuronal cells within the brain. They provide a novel morphologic suggestion that the dopaminergic D2 receptor may support unrecognized, nonsynaptic functions in specific non-neuronal cell populations in the nervous system.

Animals↗

PubMed1998

Identification of the active site nucleophile in jack bean alpha-mannosidase using 5-fluoro-beta-L-gulosyl fluoride.

Mannosidases play a key role in the processing of glycoproteins and thus are of considerable pharmaceutical interest and indeed have emerged as targets for the development of anti-cancer therapies. Access to useful quantities of the mammalian enzymes has not yet been achieved; therefore, jack bean mannosidase, a readily available enzyme, has become the model system. However, the relevance of this enzyme has not been demonstrated, nor is anything known about the active site structure of this, or any other, mannosidase. Hydrolysis by this enzyme occurs with net retention of sugar anomeric configuration; thus, a double displacement mechanism involving a mannosyl-enzyme intermediate is presumably involved. Two new mechanism-based inhibitors, 5-fluoro-alpha-D-mannosyl fluoride and 5-fluoro-beta-L-gulosyl fluoride, which function by the steady state trapping of such an intermediate, have been synthesized and tested. Both show high affinity for jack bean alpha-mannosidase (Ki' = 71 and 86 microM, respectively), and the latter has been used to label the active site nucleophile. The labeled peptide present in a peptic digest of this trapped glycosyl-enzyme intermediate was identified by neutral loss scans on an electrospray ionization triple quadrupole mass spectrometer. Comparative liquid chromatographic/mass spectrometric analysis of peptic digests of labeled and unlabeled enzyme samples confirmed the unique presence of this peptide of m/z 1180.5 in the labeled sample. The label was cleaved from the peptide by treatment with ammonia, and the resultant unlabeled peptide was purified and sequenced by Edman degradation. The peptide identified contained only one candidate for the catalytic nucleophile, an aspartic acid. This residue was contained within the sequence Gly-Trp-Gln-Ile-Asp-Pro-Phe-Gly-His-Ser, which showed excellent sequence similarity with regions in mammalian lysosomal and Golgi alpha-mannosidase sequences. These mammalian alpha-mannosidases belong to family 38 (or class II alpha-mannosidases) in which the Asp in the above sequence is totally conserved. This finding therefore assigns jack bean alpha-mannosidase to family 38, validating it as a model for other pharmaceutically interesting enzymes and thereby identifying the catalytic nucleophile within this family.

Amino Acid Sequence↗

PubMed1998

Organ pathology following mild hypothermia used as neural rescue therapy in newborn piglets.

The aim of this study was to assess the possible adverse effects of hypothermia, used as neural rescue therapy in a newborn piglet model. Sixteen newborn piglets were subjected to transient cerebral hypoxia-ischaemia by temporary occlusion of the carotid arteries and reduction of the fractional inspired oxygen to 0.12. On resuscitation 11 piglets were maintained normothermic (38.5-39.0 degrees C) and, in order to assess the cerebroprotective effect of hypothermia, 5 piglets were cooled to 35 degrees C for 12 h before normothermia was resumed. At 48 or 64 h following resuscitation the animals were sacrificed and the heart, left kidney, specimens of distal small bowel, lung and liver were removed and histologically sectioned. No microscopic abnormalities of the heart, bowel or lung were observed in hypothermic or normothermic animals. All kidney specimens were normal except one from the normothermic group. Abnormal liver pathology suggestive of hypoperfusion injury was found in 5 normothermic and 3 hypothermic piglets. There was no significant difference in the proportion of piglets with liver abnormality between the two groups. Mild hypothermia following cerebral hypoxia-ischaemia in the newborn piglet was not associated with an increased incidence of non-cerebral organ damage. The hepatic injury observed may be related to umbilical venous catheterisation and has potential relevance to neonatal intensive care.

Animals↗

PubMed1997

Human lysosomal and jack bean alpha-mannosidases are retaining glycosidases.

The stereochemical course of the hydrolyses catalysed by two alpha-mannosidases has been determined directly by 1H NMR. Synthetic substrates were incubated with the enzymes and the anomeric configuration of the initially formed product was ascertained in each case by observation of the chemical shift of the anomeric proton at the hemiacetal centre. Both mannosidases were found to catalyse hydrolysis with retention of stereochemistry at the anomeric position. Human lysosomal alpha-mannosidase (a class II mannosidase) is a member of the glycosidase family 38 and thus has sequence similarity with several alpha-mannosidases responsible for glycoprotein biosynthesis. Jack bean alpha-mannosidase was shown to be mechanistically similar to the lysosomal enzyme and will provide a useful model system in mechanistic studies and inhibitor design.

Fabaceae↗

PubMed1997

Endocrine modulation of the neurotoxicity of gp120: implications for AIDS-related dementia complex.

HIV infection often involves the development of AIDS-related dementia complex, a variety of neurologic, neuropsychologic, and neuropathologic impairments. A possible contributor to AIDS-related dementia complex is the HIV envelope glycoprotein gp120, which damages neurons via a complex glutamate receptor- and calcium-dependent cascade. We demonstrate an endocrine modulation of the deleterious effects of gp120 in primary hippocampal and cortical cultures. Specifically, we observe that gp120-induced calcium mobilization and neurotoxicity are exacerbated by glucocorticoids, the adrenal steroids secreted during stress. Importantly, this deleterious synergy can occur between gp120 and synthetic glucocorticoids (such as prednisone or dexamethasone) that are used clinically in high concentrations to treat severe cases of the Pneumocystis carinii pneumonia typical of HIV infection. Conversely, we also observe that estradiol protects neurons from the deleterious actions of gp120, reducing toxicity and calcium mobilization.

AIDS Dementia Complex↗

PubMed1996

A cost-effectiveness analysis of neonatal ECMO using existing evidence.

A cost-effectiveness analysis is part of the U.K. ECMO Trial. In preparation for this analysis, existing evidence on the costs and effectiveness of neonatal ECMO was evaluated. ECMO appears to be more costly but may be more or less effective than conventional treatment. No case can be made for introducing ECMO before trial results are available.

Cost-Benefit Analysis↗

PubMed1996

Recombinant baculovirus-synthesized African horsesickness virus (AHSV) outer-capsid protein VP2 provides protection against virulent AHSV challenge.

African horsesickness virus serotype 4 (AHSV-4) outer-capsid proteins VP2 or VP2 and VP5, prepared from single or dual recombinant baculovirus expression vectors grown in Sf9 insect cells, were administered in different amounts to horses and the neutralizing antibody responses were measured. Control and vaccinated horses were challenged with virulent AHSV-4 6 months later and monitored post challenge. The results indicated that two inoculations of extracts containing VP2 and VP5, or VP2 alone, in doses of 5 micrograms VP2 or more per horse, were sufficient to elicit protection against African horsesickness (AHS) disease. The recombinant VP2 protein is a potential candidate vaccine for AHS in horses.

African Horse Sickness↗

PubMed1995

The development and reliability of the Mental Health Research Institute Unusual Perceptions Schedule (MUPS): an instrument to record auditory hallucinatory experience.

The Mental Health Research Institute Unusual Perceptions Schedule (MUPS) is a comprehensive instrument developed to record subjects' experiences of auditory hallucinations as completely as possible. The Schedule comprises a semi-structured interview and documents the physical characteristics of auditory hallucinations such as their onset and course, number, volume, tone, location, as well as other phenomena associated with them such as delusions. In addition, other aspects of hallucinations, such as coping strategies, contributing factors and subjects' personal views and reactions are also explored. In a sample of 100 subjects drawn primarily from the in-patient wards at Royal Park Hospital the MUPS was found to be an acceptable instrument to subjects in the field. Interrater reliability assessed in a subsample of 30 subjects was found to be high at the level of the individual items. Whether used in whole or part, the MUPS provides a reliable and acceptable method of assessing patients' experience of auditory hallucinations.

Adaptation, Psychological↗

PubMed1995

Comprehensive allelotyping of human renal cell carcinomas using microsatellite DNA probes.

The von Hippel-Lindau locus on chromosome 3p is a tumor suppressor gene known to be involved in nonpapillary renal cell carcinoma. A previous loss of heterozygosity (LOH) study aimed at determining the allelotype of kidney tumors has indicated that in addition to 3p, chromosome arms 5q, 6q, 10q, 11q, 17p, and 19p may also harbor tumor suppressor genes. However, cytogenetic studies reveal that chromosomes 3p, 6q, 8p, 9pq, and 14q most frequently undergo karyotypic changes in renal tumors. To resolve these differences, a collection of microsatellite DNA probes has been used to scan for LOH so that 90% of individual tumor genomes were rendered informative for allele loss. The assay is capable of detecting quantitative genomic alterations in tumor cells as well. We find that LOH is most frequent for chromosome arm 3p. However, in no tumor is 3p exclusively affected. LOH for 6q, 8p, 9pq, and 14q is also distinctly elevated for both nonpapillary as well as papillary tumors and suggest that many of the tumor suppressor loci involved may be common to the etiology of both forms of kidney cancer.

Alleles↗

PubMed1995

Serum cardiac troponin T levels during treatment of early-stage breast cancer.

PURPOSE: To measure serum troponin T concentrations in patients with early-stage left breast cancer during breast-conserving radiation therapy. Troponin T has been introduced recently as a sensitive and specific marker for acute myocardial injury. PATIENTS AND METHODS: We compared pretreatment and posttreatment serum troponin T values in 50 patients undergoing radiation therapy to the entire left breast following conservative surgery for stage I and II breast cancer. RESULTS: No changes in troponin T concentrations were found after 45 to 46 Gy whole-breast irradiation. All women had undetectable or normal troponin T on the first and last day of treatment. There was no evidence of an upward trend during treatment. CONCLUSION: Radiation therapy to the left breast does not affect serum cardiac troponin T levels, despite the fact that a portion of the myocardium lies within the high-dose region. This suggests that the acute effects of radiation on the myocardium are minor. Long-term evaluation of these patients is necessary to rule out the possibility of late cardiac morbidity due to accelerated atherosclerosis. This study also suggests that an elevated troponin T level during or shortly after left breast irradiation should not be attributed to treatment.

Antineoplastic Combined Chemotherapy Protocols↗

PubMed1995

Using electropalatography to treat severe acquired apraxia of speech.

This paper reports on the use of electropalatography (EPG) in the treatment of a patient with severe acquired apraxia of speech. At 2 years post-onset and after a period of conventional speech and language therapy, the patient, AD, presented with severe speech production problems affecting articulation, phonation and resonance. Treatment using EPG is described and both the patient's progress and his continued limitations are outlined. EPG provided a valuable form of visual feedback for the patient and revealed and clarified aspects of oral movements for speech and non-speech activity which had been difficult to capture via auditory perception.

Apraxias↗

PubMed1994

Organization, sequence, and function of 34.5 kb of genomic DNA encompassing several murine T-cell receptor alpha/delta variable gene segments.

A cosmid-bearing murine genomic DNA, encompassing several T-cell receptor variable alpha/delta gene segments, has been sequenced using shotgun DNA cloning methodology coupled with fluorescence-based high-through-put DNA sequencing technology. This region, spanning 34.5 kb, contains a pseudogene V alpha gene segment (psi V alpha 16.1), a V delta gene segment (V delta 2), and a variable gene segment that has been reported to be expressed with both C alpha (V alpha 6) and C delta (V delta 3). Therefore, this cosmid is the ideal vehicle for examining the possible control sequences that may be involved in determining whether a V gene segment associates with either C alpha or C delta. Polymerase chain reaction experiments demonstrate that the two functional variable gene segments (V delta and V alpha/delta) are expressed individually with both C alpha and C delta genes as mRNA, indicating a permissiveness in their expression patterns. In addition, a variety of genomic sequence-related features have been identified.

Amino Acid Sequence↗

PubMed1994

The human T-cell receptor TCRAC/TCRDC (C alpha/C delta) region: organization, sequence, and evolution of 97.6 kb of DNA.

We sequenced and analyzed 97.6 kb of new DNA sequence containing the human TCRAC (C alpha) and TCRDC (C delta) genes as well as the TCRDV3 (V delta 3) and 61 different TCRAJ (J alpha) gene segments and compared its organization and structure to the previously described mouse T-cell receptor TCRAC/TCRDC (C alpha/C delta) region. A comprehensive nomenclature, consistent with the IUIS nomenclature committee recommendations, for both human and mouse TCRAJ gene segments is presented. In the human sequence, we identified 20 new TCRAJ gene segments and obtained the germline sequence for 23 additional TCRAJ gene segments known from cDNA clones. Using the sequence data obtained from the human TCRAC/TCRDC region, we have extended a polymerase chain reaction-based assay to test for the expression of the individual TCRAJ gene segments. At least five TCRAJ pseudogene segments were identified by sequence criteria. Like the murine TCRAC/TCRDC sequence, this sequence contains a high level of coding sequence, with over 6.6% of the total sequence being transcribed. Comparison of the human sequence with the previously reported mouse DNA sequence reveals homologous counterparts for the variable and joining (J) gene segments and both constant genes. Eleven new J pseudogene segments have been identified in the mouse TCRAC/TCRDC sequence through the use of human and mouse sequence comparisons. In terms of structure and organization, this region of the human and mouse genome appears to be remarkably conserved.

Amino Acid Sequence↗

PubMed1994

Involvement of immunologic mechanisms in a guinea pig model of western red cedar asthma.

Western red cedar asthma is the most common form of occupational asthma in the Pacific Northwest. Plicatic acid (PA) is the chemical component of Western red cedar that causes asthma. The role of immunologic processes involved in the PA-induced asthmatic reaction has not been established. To characterize the mechanisms of PA-induced asthmatic reaction, guinea pigs were sensitized to PA through biweekly injection of PA-ovalbumin conjugate with aluminum hydroxide as an adjuvant for a period of 6 months. Specific IgG1 antibodies to PA were detected in the blood 3 months after sensitization of animals. The level of specific IgG1 antibodies to ovalbumin after 6 months was about two times the level of specific IgG1 to PA. At 6 months, tracheal tissue from PA-ovalbumin-sensitized guinea pigs contracted after exposure to either PA or ovalbumin in vitro. The degree of contraction induced by PA was two to three times less than the contraction induced by ovalbumin. PA caused histamine, prostaglandin D2, and leukotriene D4 release from both lung mast cells and blood basophils. The amount of histamine and eicosanoids released by PA was also two to three times less than the amount of mediators released by ovalbumin. When the trachea of normal guinea pigs was passively sensitized with serum from PA-ovalbumin-sensitized guinea pigs, it contracted in response to PA or ovalbumin in an organ bath. When the serum of PA-ovalbumin-sensitized guinea pigs was depleted of immunoglobulins and then used for passive sensitization of normal trachea, no contraction was observed when challenged with PA, suggesting that IgG1 antibodies mediate the tracheal reaction to PA.(ABSTRACT TRUNCATED AT 250 WORDS)

Allergens↗

PubMed1993

Labeling of cysteine 231 in acetylcholinesterase from Torpedo nobiliana by the active-site directed reagent, 1-bromo-2-[14C] pinacolone. Effects of 2,2'-dipyridyl disulfide and other sulfhydryl reagents.

Acetylcholinesterase (AcChE, EC 3.1.1.7) was isolated from the electric organ of T. nobiliana and treated with the active-site-directed alkylating agent 1-bromo-2-[14C]pinacolone ([14C]BrPin), or with BrPin, which acts initially as a competitive inhibitor, Ki = 0.18 mM, and then inactivates the enzyme, k2 = 1.8 x 10(-4) s-1. AcChE aliquots were digested with trypsin and fractionated by reversed phase high performance liquid chromatography. Inactivation caused a decrease in one absorption peak and an increase in another, identified as the peptide beginning at Ala-222 and extending to Arg-242. 5-Trimethylammonio-2-pentanone, a competitive inhibitor, isosteric with acetylcholine, retarded the inactivation and decreased the quantity of labeled peptide. On sequencing, the 14C label was found associated with Cys-231. This was confirmed by comparison with synthesized S-pinacolonylcysteine, by study of effects of blocking the sequencing by o-phthalaldehyde, and by inactivation by 2,2'-dipyridyl disulfide (2-PDS), a thiol-specific reagent that acts initially as a competitive inhibitor, Ki = 0.042 mM, and then inactivates the enzyme, k2 = 5.0 x 10(-4) s-1. This is retarded by 5-trimethylammonio-2-pentanone, and prior inactivation by 2-PDS prevents subsequent reaction of [14C]BrPin in the active site. BrPin inactivates AcChEs from Electrophorus electricus and from human erythrocyte, but 2-PDS does not. Neither reagent inactivates butyrylcholinesterases from human and horse serum.

2,2'-Dipyridyl↗

PubMed1993

Accreditation of prior learning: andragogy in action or a 'cut price' approach to education?

The rapid changes in nurse education are proceeding within the wider context of developments in adjacent educational fields, which are themselves subject to external influences, and one such development is the accreditation of prior experiential learning (APEL). In order to be critically aware of the potential involved in embracing this concept, it is necessary to clarify and examine the influencing factors which guide the current andragogical climate of nurse education, and those which predispose to the recognition of APEL. Utilizing a case-study approach, this paper will examine the relevant issues as they relate to experienced students pursuing the learning outcomes of Project 2000, and will address the question of value for all parties concerned.

Accreditation↗

PubMed1993

Effect of phospholipase C inhibitor U-73122 on antigen-induced airway smooth muscle contraction in guinea pigs.

The importance of phospholipase C (PLC) in airway smooth muscle contraction was studied, using an inhibitor of PLC, 1-[6-[[17 beta-3-methoxyestra-1,3,5(10)-trien-17-yl] amino]hexyl]-1H-pyrrole-2,5-dione (U-73122). Tracheas from ovalbumin (OA)-sensitized guinea pigs contracted rapidly after exposure to low concentrations of antigen (OA). However, tracheas treated with U-73122 for 10 min prior to the addition of antigen, demonstrated a 3 log rightward shift in the OA dose-response curve with an IC50 of 7 microM. The analogue of U-73122, 1-[6[[17 beta-3-methoxyestra-1,3,5 trien-17-yl]amino]hexyl]-2,5-pyrrolidine-dione (U-73433), was approximately 5-fold less active in inhibiting smooth muscle contraction. In addition to the inhibition of antigen-induced smooth muscle contraction, U-73122 inhibited carbachol- and leukotriene D4-induced smooth muscle contraction. Furthermore, U-73122 inhibited in a dose-dependent manner antigen-induced histamine release from guinea pig tracheal tissue. The inhibition of smooth muscle contraction by U-73122 correlated well with the inhibition of polyphosphoinositide mediates smooth muscle contractile responses to muscarinic agonists and leukotrienes as well as antigenic-induced contraction.

Animals↗

PubMed1993

Cost effectiveness of surfactant replacement in preterm babies.

Surfactant replacement in preterm babies has been shown in recent years in randomised controlled trials to be an effective treatment for respiratory distress syndrome (RDS). It is expensive and, because it increases survival, it has implications for the costs of neonatal services. We used evidence about resource use obtained from trials of surfactant and other studies on the economics of surfactant to assess the cost effectiveness of different policies for its use. For the smallest babies, surfactant is likely to increase overall costs of neonatal care, but also to reduce the ratio of costs to survival, whether surfactant is given prophylactically or as a treatment for established RDS. It is less clear what the optimal policy should be for babies of more than around 31 weeks' gestation. Comparison of the relative cost effectiveness of policies of early prophylactic surfactant and surfactant for later treatment of RDS, and of different dosage policies, is currently being conducted in the context of 2 large multicentre trials. No policy for surfactant use should be considered in isolation from the availability of effective obstetric interventions which have been shown to reduce the risk of RDS in preterm babies and which will therefore reduce the need for surfactant.

Cost-Benefit Analysis↗